CA2021573C - Process of oxidizing aliphatic hydrocarbons employing a molybdate catalyst composition - Google Patents

Abstract

A process far the production of olefins and diolefins, such as 1,3-butadiene, comprising contacting an aliphatic hydrocarbon, such as butane, with a heterogeneous catalyst composition containing reactive oxygen under reaction conditions such that a more highly unsaturated aliphatic hydrocarbon is selectively formed in a high productivity. The catalyst is a composition comprising a catalyst component of magnesia, an oxide of molybdenum, a Group IA metal oxide promoter, and optionally vanadium oxide. In a preferred embodiment, the catalyst composition also comprises a support component of magnesium and alumina and/or magnesium aluminate spinel. The present catalyst has high surface area and high attrition resistance.

Description

2~~~~"~
PROCESS OF OXIDIZING
ALIPHATTC HYDROCARBONS EMPLOYING
A MOLYBDATE CATALYST COMPOSITION
This invention pertains to the oxidation of aliphatic hydrocarbons, such as alkanes and monoolefins, to form more highly unsaturated aliphatic hydrocarbons.
Unsaturated aliphatic hydrocarbons, such as monoolefins and diolefins, are useful as monomers and comonomers in the preparation of polyolefin plastics.
U.S. Patent 3,119,111 discloses a process for the oxidative dehydrogenation of a Ct~ to C6 alkane hav-ing a four carbon chain to a 1,3-alkadiene. The reac-tion occurs in the presence of oxygen and a catalyst containing an a:Lkali metal molybdate, such as lithium molybdate. It :is taught that the catalyst can be employed with a carrier material, such as powdered alumina. Disadvantageously, this process requires potentially explosive mixtures of alkanes and oxygen.
More disadvantageously, the catalyst of this process contains a high concentration of alkali metal which lowers catalytic activity.
36,823A-F -1-U.S. Patent 3,180,903 discloses a process for -- the dehydrogenation of aliphatic hydrocarbons containing from two to five carbon atoms. Butanes, for example, can be converted to butenes and butadienes. The cata-lyst is taught to contain chromium oxides or molybdenum oxides supported on a gel-type alumina. Optionally, the catalyst may contain one or more alkali metal oxides.
Disadvantageously this process is limited to a low hydrocarbon conversion and a low ultimate yield of butadiene.
U.S. Patent 3,x+88,402 teaches the dehydrogena-tion of butane to butene and butadiene in. the presence of two catalysts. The first is a dehydrogenation cata-lyst containing alumina, magnesia, or combinations thereof, promoted with an oxide of a metal of Groups IVB, VB or VIB, such as chromic, vanadium oxide or molybdenum oxide. The second catalyst is an oxidation catalyst comprising a Group IVA or VA vanadate, molyb-date, phosphomolybdate, tungstate or phosphotungstate.
Disadvantageously, this process comprises two steps and requires subatmospherie pressures. Even more disadvan-tageously, this process produces low butadiene selec-tivity and yield.
U.S. Patent 3,862,256 discloses a process for the oxidative dehydrogenation of paraffin hydrocarbons, such as butane, over a catalyst containing oxy compounds of molybdenum and magnesium, and optionally, vanadium and/or silicon. When butane is contacted with the cata-lyst, the products include butenes and butadiene; how-ever, the selectivity and space-time yield of butadiene are lower than desired. In addition, the feed contains hydrocarbon and oxygen, which is not desirable for 36,823A-F -2-_3- 2~~~'~'~~
safety reasons. Finally, the magnesium oxide support -- does not possess the toughness and attrition resistance needed for fluid bed or transport reactors.
U.S. Patent 4,229,601 discloses a process For the oxidative deh dro enation of a y g paraffin, such as butane, to unsaturated hydrocarbons, such as butenes and butadiene. The catalyst is an oxide of molybdenum deposited on a carrier. The carrier is selected from the group consisting of granulated porous crystalline silica modified with magnesia, magnesium-titanium oxides, and magnesium-aluminum oxides. It is taught that during the carrier preparation, silicates of the alkali metals or titanates or aluminates of magnesium are formed. It is further taught that on the surface of the catalyst there exists an active magnesium molybdate.
Disadvantageously, the catalyst produces a selectivity and space-time yield of butadiene which are too low for industrial use. The low activity of this catalyst is attributed in part to its low surface area.
U.S. Patent x+,388,223 discloses the oxidizing dehydrogenation of butene-1 to butadiene. The catalyst comprises (a) a crystalline phase (I) consisting of one or more molybdates belonging to the monoclinic system, chosen from ferric, aluminum, cerium, and chromium molybdates, (b) a crystalline phase (II) consisting of one or more molybdates belonging to the monoclinic sys-tem, including magnesium molybdate, and (c) one or more promoter elements including vanadium. It is also taught that the catalyst may comprise alkaline elements such as potassium, lithium, cesium and magnesium and/or acidic elements, such as phosphorus and silicon. This process co-feeds hydrocarbon and oxygen, which is undesirable 36,823A-F -3-_~4-for safety reasons. Moreover, the catalyst does not -- have the toughness and attrition resistance required for fluid bed or transport reactors.
U.S. Patent 3,69,238 teaches a catalyst compo-sition comprising (a) a catalytically-active material containing a divalent metal, such as magnesium, tetrava-lent molybdenum, and oxygen in chemically combined form, and (b) a support comprising deacidified alumina. The support is deacidified with a small amount of a Group IA
metal oxide, such as cesium oxide. The composition of tile catalyst, stated in gram-atoms of metal per 100 moles of alumina, is as follows: divalent metal, 1 to 60 gram-atoms; molybdenum, 1.5 to 90 gram-atoms; Group IA metal, 1 to 5 gram-atoms.
While the oxidation of aliphatic hydrocarbons is well researched in the prior art, the selectivity and space-time yield to particular unsaturated hydrocarbons, such as diolefins, fall short of those which are desired for commercial exploitation. Moreover, the catalysts employed in the prior art do not possess the toughness and attrition resistance required for use in industrial fluid bed or transport reactors. Accordingly, i.t would be desirable to have a selective, direct oxidation of an aliphatic hydrocarbon, such as an alkane or monoolefin, to the corresponding unsaturated aliphatic hydrocarbons, specifically the diolefin. It would be more desirable if such an oxidation produced a high selectivity and high productivity of the diolefin and other olefins, and correspondingly low selectivities to deep oxidation products, such as carbon dioxide. Finally, it would be most desirable if the above-identified process could be accomplished with a catalyst of high attrition 36,823A-F -~-_5_ resistance so as to be useful in a commercial scale -- fluid bed or transport reactor.
In one aspect, this invention is a process of preparing an unsaturated aliphatic hydrocarbon compris-ing contacting an aliphatic hydrocarbon having at least three carbon atoms with a catalyst of this invention, described hereinafter. Under the reaction conditions of the process of this invention more unsaturated aliphatic hydrocarbons, such as diolefins, are formed in a selec-tivity of at least about 40 mole percent.
Advantageously, aliphatic hydrocarbons can be oxidized directly to more highly unsaturated aliphatic hydrocarbons by the process of this invention. Surpris-ingly, the process of this invention produces a high selectivity and high productivity of more highly unsaturated aliphatic hydrocarbons, especially diole-fins. More surprisingly, the process of this invention roduces low selectivities and low p yields of undesirable deep oxidation products, such as carbon monoxide and carbon dioxide. Unexpectedly, butadiene can be produced directly from butane in high selectivity and high productivity by the process of this invention while maintaining low selectivities of deep oxidation products. For the purposes of this invention, the "productivity°' is defined as the grams of desired product produced per gram catalyst per hour.
The unsaturated aliphatic hydrocarbons, such as monoolefins and diolefins, are useful as monomers or comonomers in the formation of polyolefins. Butadiene is also potentially useful as an intermediate in the preparation of styrene.
36,823A-F -5--~- ~~2~~'~~
In another aspect, this invention is a solid --- heterogeneous catalyst composition containing labile oxygen, said catalyst being capable of being employed in the above-identified process of preparing unsaturated aliphatic hydrocarbons. The catalyst consists essen-d ally of an oxide of magnesium, an oxide of molybdenum, and an alkali metal promoter in a concentration from about 0.1 weight percent to ~be~t 5 weight percent calculated as alkali hydroxide and based on the weight of the combined magnesium and molybdenum oxides.
Optionally, the catalyst can contain an oxide of vanadium.
In another aspect, this invention is a molyb-date catalyst composition containing reactive oxygen.
The composition comprises a support component containing magnesium oxide and at least one aluminum oxide selected from the group consisting of alumina (A1203) and magne-sium aluminate (MgA120~). . The support is further char-acterized as having a Mg0/A1203 weight ratio in the range from about 0.30 to about 4.0 and a surface area of at least about 25 m2/g. The catalyst composition also comprises a catalyst component consisting essentially of a molybdenum oxide, a magnesium oxide, and a promoting amount of an alkali metal promoter. Optionally, the catalyst may contain an oxide of vanadium. In preferred embodiments, tYze catalyst of this invention has an attrition number, defined hereinafter, less than 5 weight percent per hour.
The catalyst composition of this invention is useful in the above-identified process of oxidizing aliphatic hydrocarbons to more unsaturated aliphatic hydrocarbons. Advantageously, in its preferred forms 36,823A-F -s-~~~.~'~~
the catalyst composition of this invention has improved -.- attrition resistance when compared to the catalysts of the prior art; thus, the catalyst of this invention is useful in commercial fluid bed and transport reactors, such as riser reactors.
The aliphatic hydrocarbons which can be em-ployed in the process of this invention include alkanes and olefins which have three or more carbon atoms.
The alkanes can be alternatively described as paraffin hydrocarbons. These compounds are known to those skilled in the art as saturated hydrocarbons. As noted hereinbefore, the alkanes contain at least three carbon atoms and, additionally, can have straight-chain or branched structures. Typically, the alkane contains up to about 20 carbon atoms. Examples of suitable al-kanes include n-butane, n-pentane, n-hexane, n-heptane, n-octane, n-nanane, n-decane, n-dodecane, and higher saturated homologues, as well as isobutane, isopentane, neopentane, and likewise branched hexanes, heptanes, oetanes, nonanes, decanes, dodeeanes, and higher branched homologues. Certain alicyclic hydrocarbons are suitable reactants and, therefore, for the purposes of this invention, are included herein, Some examples of alicyelie hydrocarbons include cyclobutane, cyclopen-tane, cyelohexane, eycloheptane, cyclooetane, methyl-cyclopentane, methylcyclohexane and other alkyl-sub-stituted cycloalkanes. Preferably, the alkane is normal or linear.
The olefins can be further described as ali-phatic hydrocarbons containing at least one unsaturated double bond. As noted earlier, the olefins should also 36,823A-F -7--~- ~~2~~~J
contain at least three carbon atoms, and typically up to -- about 20 carbon atoms. The location of the double bond is not critical; therefore, the double bond can occur at a terminal or internal location along the carbon chain.
Preferably, however, the olefin has a normal or linear structure, rather than a branched structure. For exam-ple, 1-butane is preferred over isobutylene. Thus, some examples of suitable olefins include, 1-butane, 2-bu-tene, 1-pentane, 2-pentane, 3-pentane, 1-hexane, 2-hex-ene, 3-hexane, and likewise 1-heptene, 1-octane, 1-no-nene, 1-decene, and isomers thereof wherein the unsatu-ration occurs at any ather position along the carbon chain. Olefins containing more than one double bond, such as 1,3-hexadiene and isoprene, are also acceptable, being converted in the process of this invention to more highly unsaturated hydrocarbons. Certain alicyclic ole-fins, such as cyclohexene and vinyleyclohexane, are also suitable starting materials, and therefore, for the pur-poses of this invention are included herein. Prefer-ZO ab1 , the olefin is a monoolefin. More Y preferably, the olefin is 1- or 2-butane. Alkynes, however, are not suitable reactants for the process of this invention.
The many specific examples of aliphatic hydro-carbons, noted hereinabove, are representative of those which are suitable for the process of this invention, and are not intended to be limiting thereof. Other ali-phatic hydrocarbons rnay be available to one skilled in the art and may also be suitable for the process of the invention.
The preferred alkanes are normal paraffins which can be represented by the general formula:
36,823A-F -8-_g_ CH3-(CH2)n-CH3 ~02~~~3 wherein n is an integer from 1 to 8. More preferably, n is an integer from 2 to 6. Most preferably, n is 2, and the alkane is n-butane.
Optionally, the aliphatic hydrocarbon reactant can be diluted with a non-reactive gas, such as nitro-gen, helium, argon, methane, carbon dioxide or steam.
While the type of diluent is determined by prevailing economic considerations, a preferable diluent is nitro-gen. If a diluent is used, the amount can vary widely depending upon the design of the reactor and the capacity of the solid oxidant. The hydrocarbon content of the hydrocarbon-diluent mixture typically ranges from 1 mole percent to 100 mole percent. Preferably, the hydrocarbon content of the mixture ranges from about 10 mole percent to about 100 mole percent, more preferably, from about ~0 mole percent to about 100 mole percent.
The catalyst composition of this invention, described in detail hereinbelow, is a solid hetero-geneous oxide at least a portion of the oxygen of which is reactive. By this it is meant that a labile farm of oxygen is pr°esent in the catalyst, and that this labile form of oxygen is capable of oxidizing the aliphatic hydrocarbon. Thus, in one aspect the catalyst of this invention is a solid oxidant. After the labile oxygen is removed through reaction, the catalyst is spent.
Moreover, the catalyst may build up over time a carbonaceous residue on its surface. The spent and poisoned catalyst can be regenerated by contact with a source of gaseous oxygen. Thus, in addition to the 36,823A-F -9--1°w 2~2~ ~'~~
aliphatic hydrocarbon, oxygen is required for the --- catalytic process of this invention.
Oxygen is typically supplied from a gaseous source prov.i.ded as a continuous oxygen-containing feed.
An source of ox y ygen is acceptable, such as pure gaseous elemental oxygen, air, or nitrous oxide. The preferred source of oxygen is gaseous air. Optionally, the gase-ous elemental oxygen can be diluted with a non-reactive gas, such as nitrogen, helium, argon, or carbon dioxide.
Preferably, the diluent is nitrogen. If a non-reactive diluent is employed, the oxygen content of the mixture is preferably not greater than about 50 mole percent.
More preferably, the oxygen content of the mixture ranges from 0.5 mole percent to 30 mole percent. Most prefErably, the oxygen content of the mixture ranges from 1 mole percent to 20 mole percent.
The amount of oxygen employed in the catalytic process of this invention is any amount which is (1) sufficient to oxidise fully the solid heterogeneous catalyst, and (2) sufficient to remove carbonaceous residues from the catalyst's surface. Preferably, the regeneration of the catalyst is carried out separately from the oxidation of the aliphatic hydrocarbon.
Alternatively, it is acceptable to co-feed a small amount of gaseous elemental oxygen with the ali-phatic hydrocarbon. The function of the co-feed is to burn off carbonaceous residues on the surface of the catalyst, to replenish to some extent the reactive oxygen of the catalyst, and to burn off any hydrogen which is formed in the process. The concentration of oxygen in the aliphatic hydrocarbon and oxygen feed is 36,823A-F -10-limited by the explosive limits of this mixture.
-- Preferably, the oxygen concentration is maintained outside the lower explosive limit.
The solid heterogeneous catalyst employed in the process of this invention consists essentially of an oxide of magnesium, an oxide of molybdenum, arid an alkali metal promoter. Any source of magnesium oxide is acceptable; however, Mg0 is preferred. Likewise, any source of molybdenum oxide is acceptable, including for example, Mo03, (NH~)6Mo702~~~IH20, and (NH~)2Mo0~. The molybdenum oxide can also be obtained from a precursor molybdenum compound, such as molybdenum carbonyls like Mo(CO)6. Preferably, the source of molybdenum oxide is (NH~)6Mo702~~4H20. The alkali metal promoter is a Group IA metal compound possessing a basicity sufficient to increase the formation of higher unsaturates in the pro-cess of this invention. Small amounts of other elements may be present in the catalyst, provided that these ele-ments do not materiall chan a the y g performance of the catalyst.
The catalyst containing the mixed magnesium--molybdenum oxides and alkali metal promoter can be simply prepared. Generally, the desired quantity of a molybdenum oxide or precursor compound, such as ammonium heptamolybdate or molybdenum carbonyl, is dissolved in a solvent to make a solution. Preferably, the molybdenum compound is ammonium heptamolybdate, and the solvent is water. The solution is poured over magnesium oxide to form a slurry, which is thereafter dried to remove sol-vent. If the solution is aqueous, the drying is con-ducted in an oven at a temperature in the range of from 70°C to 120°C. The dried composition is caleined to form 36,823A-F -11-a12 a catalytically active magnesium oxide-molybdenum oxide -- mixture. The calcination is typically conducted at a temperature ranging from 550°C to 650°C for a time ranging from 1 hour to about 24 hours. Preferably, the calcination is conducted at about 600°C for at least about 2 hours. Alternatively, the dried composition, described hereinabove, can be employed directly with no prior caleination in the catalytic process of this invention. Since the molybdenum compound can be Converted into molybdenum oxide at or about 300°C, and since the catalyst bed is heated to a temperature higher than about 300°C, the dried composition will be converted insituinto a catalytically active magnesium oxide-molybdenum oxide mixture.
The mixed oxide catalyst composition may appear amorphous by X-ray diffraction, or may contain diffrac-tion peaks characteristic of magnesium molybdate. The elemental analysis of the caleined solid reveals a com-position ranging from 6 weight percent Mo03 to 50 weight percent Mo03 and from 94 weight percent Mg0 to 50 weight percent MgO. Preferably, the compasition ranges from 10 weight percent Mo03 to 30 weight percent Mo03 and from 90 weight percent Mg0 to 70 weight percent MgO; more preferably, from 15 weight percent Mo03 to 25 weight percent Mo03 and from 85 weight percent Mg0 to 75 weight percent MgO.
In a preferred embodiment, the molybdate catalyst composition of this invention comprises a support component and a catalyst component. The support contains magnesium oxide and at least one aluminum oxide selected from the group consisting of alumina (A1203) and magnesium aluminate spinal (MgA120~). The support 36,g23A-F -12-~Q~1~'~3 has a Mg0/A1~0~ weight ratio in the range of from 0.30 - to 4.0 and a surface axea of at least about 25 m2/g.
The catalyst component consists essentially of an oxide of molybdenum, an oxide of magnesium, and a promoting amount of an alkali metal promoter. Optionally, the catalyst may contain an oxide of vanadium.
The aluminum oxide primarily imparts hardness and attrition resistance to the catalyst particles, so that they might be more suitable for use in fluid bed or transport reactors. Any source of aluminum oxide is acceptable, including a-, ~i-, and y-aluminas, hydrated alumina, such as boehmite alumina, aqueous colloidal alumina, stoiehiometric A1(OH)3, and aluminum alkoxides, as noted hereinbelow. Magnesium aluminate and magnesium aluminate hydroxides are also suitable sources of aluminum oxide. The magnesium oxide functions in a dual role: first, as a support for the catalyst components, and secondly, as a basic catalyst component which neutralizes the acidity of the alumina and other residual acid sites. It is highly desirable for the catalyst to be basic, because basicity enhances the desorption of olefinic products. Any source of mag-z5 nesium oxide is acceptable; however, Mg0 is preferred.
The molybdenum oxide contributes significantly to the catalyst°s activity, especially as combined with magne-sium oxide in the form of magnesium molybdate. Prefer-ably, the molybdenum is in the +6 oxidation state. Any source of molybdenum oxide is acceptable, including for example, Mo03, (NH~)6Mo702~~~4H20, and (NH~)2Mo0~. The molybdenum oxide can also be obtained from a precursor molybdenum compound, such as molybdenum carbonyls, e.g., Mo(C0)6. Preferably, the source of molybdenum oxide is ammonium heptamolybdate represented by the formula 36,823A-F -13-_»_ ~~21. )'~~
(NH4)6Mo702~~4H20. The alkali metal promoter functions - to increase the basicity a~ the catalyst, thereby increasing the selectivity of higher unsaturates in the process of this invention. The alkali metal promoter is a Group IA metal campound. Small amounts of other ele-ments may be present in the catalyst, provided that these elements do not materially change the performance of the catalyst.
It is noted that the support component may con-tain a spinal (MgA120~) phase. The weight percentage of spinal in the support component may range from 0 percent to about 100 percent.
Typically, the preparation of the catalyst begins with the combination of the magnesium oxide and aluminum oxide components to form a support for the other catalytic components. Any method of combination of these components is suitable; however, there are three preferred methods. The first method comprises impregnating a pre-formed spinal (MgA120~) with a solu-tion containing a soluble magnesium salt, such as mag-nesium nitrate, magnesium chloride, magnesium sulfate, magnesium acetate or the like, provided that the salt can be converted to magnesium oxide on calcination; and thereafter caleining the impregnated spinal. The weight ratio of magnesia to magnesium aluminate can be conve-niently expressed as a weight ratio of magnesia to alu-mina. This ratio is critical to the performance of the catalyst composition and is discussed separately herein-below. The temperature of calcination typically ranges from X400°C to 1200°C, preferably, from X450°C to 900°C, more preferably, from 500°C to 700°C. The caleination is conducted for a time sufficient to form a fused 36,823A-F -14--15- ~~~~ J~J
composite which can function as a support for the - catalytic components, but at least about 0.5 hour.
The second method involves impregnating a pre--formed alumina with a solution of a soluble magnesium salt, such as those identified hereinabove. Pre-formed aluminas are defined herein as anhydrous or hydrated solid aluminas, of which a-, ~-, and y-aluminas and boehmite alumina are typical examples. The weight ratio of magnesia to alumina, Mg0/A1203, is a critical parameter which is discussed in detail hereinbelow. The temperature of calcination typically ranges from 400°C
to 1200°C, preferably, from 450°C to 900°C, more preferably, from 500°C to 700°C. The calcination is conducted for a time sufficient to form a fused and hardened composite which can function as a support for the catalytic components. Typically, the calcination is conducted for at least about 0.5 hour. During caleination a portion of the alumina and magnesia may chemically combine to form a spinet phase, MgA1204, which is intimately mixed between the domains of magnesia and alumina.
The third method of preparing the support comprises adding colloidal alumina to magnesium oxide and drying the resulting mixture under conditions sufficient to prepare a magnesia-alumina support.
Colloidal alumina is an acidified aqueous suspension of hydrated aluminum oxide, wherein the particle surface area is so much greater than its volume that the particles are not settled out by gravity. A quantity of colloidal alumina suspension is added to the magnesia such that the final magnesia to alumina weight ratio falls within the range specified hereinafter. The pH of 36,823A-F -15-the colloidal alumina and magnesia mixture is about 9.
The mixture is dried by any one of a variety of techniques, including aging and evaporating, spray--drying, flash drying, tunnel drying, drum drying and the like. One preferred method involves aging and evaporating the mixture over a hot plate or equivalent heating means to form a thicker gel and eventually a hard solid mass, which is crushed and sieved to the desired particle size. The temperature of the aging and evaporation process is any which is compatible with the solvent system. Since the preferred solvent system is water, the temperature is in the range of from 30°C
to 100°C. Preferably, the temperature is in the range of from 50°C to 90°C, more preferably, in the range of from 60°C to 80°C. The time required for aging will depend on the quantity of gel, and is any time sufficient to obtain the solid, hard mass.
For industrial scale applications the mixture containing magnesia and colloidal alumina, prepared hereinabove, is preferably spray dried rather than aged.
Any spray drying equipment which is conventionally used to produce catalyst particles suitable for use in fluid-ized bed reactors may be employed. For example, a Niro Atomizer S-12.5-R/N spray drying apparatus is accept-able. Such an apparatus has a means for controlling the inlet and outlet temperature. Typically, the powder particles obtained by spray drying are spheroidal in shape, range in diameter from about 10 pm to about 250 um, and exhibit excellent flow properties.
The powder which is obtained on aging or spray drying is caleined to yield a composite support consist-ing essentially of magnesia and alumina, and optionally, 36,823A-F -16-r17 ~fl2~.~'~3 a spinet phase of magnesium aluminate. TY~e calcination - is conducted under conditions sufficient to fuse the alumina and magnesia into a hardened mass. Generally, the calcination is conducted at a temperature in the range of from 400°C to 1200°C. More preferably, the caleination temperature is in the range of from 450°C to 900°C, most preferably in the range of from 500°C to 700°C. Generally, the period of calcination depends upon the amount of material to be calcined, but lasts at least far about 0.5 hour, The support component of this invention con-tains any weight ratio of magnesia to alumina provided that a support of sufficient hardness and basicity is obtained. Note that although the spinet phase exists as a distinct composition of MgA1204, a Mg0/A1203 weight ratio is still calculable. Generally, the Mg0/A1203 weight ratio is maintained in the range of from 0.1 to 9.0, but ratios in the range of from 0.3 to 4.0 are preferred. More preferred are weight ratios in the range of from 0.3 to 2Ø Most preferred are weight ratios in the range of from 0.38 to 0.80. Below the preferred lower ratio there may be too little magnesia and the catalyst may be too acidic. Above the preferred upper ratio there may be toe much magnesia and the catalyst may lack attrition resistance and toughness.
The support component of this invention is fur-ther characterized by its surface area. Typically, the surface area is at least about 25 m2/g. Preferably the surface area is at least about 35 m2/g, more preferably, at least 50 m2/g. Even more preferably, the surface area ranges from 50 m2/g to 250 m2/g, most preferably, from 80 m2/g to 170 m2/g. It is well-known among those 36,823A-F -17-~~21~~3 skilled in the art that low surface area is generally correlated with low catalytic activity; whereas high surface area is generally correlated with high catalytic activity. The catalyst composition of this invention exhibits both high surface area and high catalytic activity.
After the support component is prepared, the catalytic elements of molybdenum oxide, alkali metal promoter and, optionally vanadium oxide, are applied to the support. Provided that the Mg0/A1203 weight ratio is adjusted within the suitable range identified hereinabove, there is no further need to add more magnesium oxide. Generally, the desired quantity of a molybdenum oxide or precursor compound, such as ammonium heptamolybdate or molybdenum carbonyl, is dissolved in a solvent to make a solution. Preferably, the molybdenum compound is ammonium heptamolybdate, and the solvent is water. The solution is brought into contact with the support composite, prepared hereinabove, and the resulting slurry is dried to remove solvent. If the selution is aqueous, the drying is conducted in an oven at a temperature in the range of from 70°C to 120°C. The dried slurry is thereafter calcined to form a catalytically active composition containing an aluminum oxide, magnesium oxide and molybdenum oxide. The calcination is typically conducted at a temperature ranging from 300°C to 900°C for a time ranging from 0.5 hour to 24 hours. Preferably, calcination is conducted at a temperature in the range of from 500°C to 800°C, more preferably, from 550°C to 650°C. Alternatively, the dried slurry, described hereinabove, can be employed directly with no prior calcination in the catalytic process of this invention. Since the molybdenum 36,823A-F -18-_1g_ ~~~~~i~
precursor can be converted into molybdenum oxide at or - about 300°C, and since the catalyst bed is heated to a temperature higher than about 300°C, the dried com-position will be converted insituinto a catalytically active aluminum oxide-magnesium oxide-molybdenum oxide mixture.
The mixed oxide catalyst composition usually shows X-ray diffraction peaks characteristic of one or more of the following: magnesium oxide, magnesium molybdate, magnesium aluminate spinet and alumina. The elemental analysis of the caleined solid reveals a com-position ranging from 3 weight percent Mo03 to 50 weight percent Mo03 and from 90 weight percent Mg0 to 1C weight percent Mg0 with the balance being alumina. Preferably, the composition ranges from 10 weight percent Mo03 to 30 weight percent Mo03 and from 60 weight percent Mg0 to 20 weight percent MgO; more preferably, from 12 weight percent Mo03 to 25 weight percent Mo03 and from u0 wei ht ercent M 0 to 25 wei ht g p g g percent MgO.
It is required to add to the supported catalyst described hereinbefore a promoting amount of at least one alkali metal promoter. the promoter serves to increase the selectivity and productivity of unsaturated products, e.g. diolefins, in the process of this invention. Such a promoter is typically a compound of lithium, sodium, potassium, rubidium, cesium or francium of sufficient basicity to improve the selectivity to higher unsaturates in the process of this invention.
Suitable compounds include the alkali oxides, hydroxides and carbonates. Compounds which decompose on heating to the oxides are also suitable, such as alkali metal acetates and oxalates. Alkali metal salts may be found 36,823A-F -19-which are also suitable, although typically, the alkali metal halides and alkali metal silicates are not preferred due to their lower basicity. Preferably, the alkali metal promoter is an alkali metal oxide, hydroxide, carbonate, acetate, or oxalate. More preferabl the alkali metal y, promoter is an oxide or hydroxide of potassium or cesium. Most preferably, the alkali metal promoter is an oxide or hydroxide of potassium.
The amount of alkali metal promoter is critical to the performance of the catalyst. Generally, any amount of alkali metal promoter is acceptable which is sufficient to increase the selectivity and the space--time yield of unsaturated products, such as diolefins, in the process of this invention. Typically, the amount of alkali metal promoter calculated as the alkali hy-droxide is in the range of from 0.1 weight percent to 5 weight percent based on the total weight of the magnesium and molybdenum oxides. Preferably, the amount of alkali metal promoter calculated as the alkali metal hydroxide is in the range of from 0.2 weight percent to 2 weight percent based on the weight of the magnesium--molybdenum oxides, more preferably, in the range of from 0.5 weight percent to 1.5 weight percent. Below the lower preferred amount of alkali metal promoter the selectivity to diolefin is reduced while the selectivity to deep oxidation products is increased. Above the upper preferred amount of alkali metal promoter the selectivity to diolefin is also reduced.
Typically, the amount of alkali metal promoter calculated as the alkali hydroxide is in the range of from 0.05 weight percent to 5 weight percent based on 36,823A-F -20-the total weight of the aluminum, magnesium and molybdenum oxides. Preferably, the amount of alkali metal promoter calculated as the alkali metal hydroxide is in the range of from 0.1 weight percent to 2 weight percent based on the total weight of the magnesium, aluminum and molybdenum oxides, more preferably, in the range of from 0.3 weight percent to 1.5 weight percent.
Below the lower preferred amount of alkali metal promoter the selectivity to diolefin is reduced while the selectivity to deep oxidation products is increased.
Above the upper preferred amount of alkali metal promoter the selectivity and productivity to diolefin are also reduced.
The alkali metal promoter' can be added to the molybdate catalyst in a variety of ways known to those in the art. For example, the promoter can be applied by the well-known impregnation technique, described for example by Charles N. Satterfield in Heterogeneous Catalysis in Practice, MeGraw-Hill Book Company, New York, 1980, pp.
82-83. In this tech-nique the molybdenum-impregnated support is immersed in a solution of the alkali metal promoter, for example, a methanolic solution of the alkali metal oxide or hydrox ide. The alkali-impregnated support is then drained of excess solution, dried in an oven to remove residual solvent, and calcined at a temperature in the range of from 550°C to 650°C. Alternatively, the alkali metal promoter can be impregnated onto the support by the incipient wetness technique, such that the pores are filled with solution of the alkali metal oxide or hydroxide but essentially no excess solution is used.
The impregnated support thus prepared is also dried in an oven to remove solvent. As a :further alternative the -22- i~
molybdenum compound can be impregnated from the same -- solution as the alkali metal compound.
Optionally, the molybdate catalyst of this invention can contain an activator which functions to increase the activity of the catalyst at any given tem-perature. Preferably, the activator does not decrease significantly the selectivity to diolefins and monoole-fins. Preferably, the activator allows the reaction to be run at a lower temperature, while achieving high selectivity and high productivity of diolefins.
Activators which are suitable for incorporation into the catalyst include the oxides of vanadium, preferably 0205. Any amount of vanadium oxid-a can be added to the catalyst provided that (1) the activity of the catalyst is increased, and (2) the selectivity for alkenes, including mono- and diolefins, is not significantly decreased. Generally, if an activator is used, the concentration ranges from 0.05 weight percent to 10 weight percent based on the total weight of the catalyst. Preferably, the concentration of activator ranges from 0.1 weight percent to 5 weight percent, more preferably, from 0.15 weight percent to 1.5 weight percent. The activator can be incorporated into the support and molybdenum oxide slurry prior to caleination, or can be applied to the calcined aluminum--magnesium-molybdenum oxides by the impregnation technique, described hereinbefore.
The preferred commercial reactor for the pro-cess of this invention is a transport bed reactor, such as a riser reactor. In such reactors the catalyst particles are subjected to constant impact with other catalyst particles and with the walls of the reactor.
36,823A-F -22--23- 2~~~.~'~~
- Sueh forces gradually reduce the size of the catalyst - particles to small fines which are lost in the reaction products; thus, the useful lifetime of the catalyst is greatly limited. Consequently, it is required for the catalyst to be prepared in a form which is able to with-stand high impact and erosion forces. A butane oxida-tion catalyst comprising magnesium molybdate supported on magnesia does not possess the attrition resistance required for commercial use. In contrast, the alkali--promoted magnesium molybdate catalyst of this invention supported on the preferred composites described hereinbefore typically possesses the attrition resist-ance required for commercial use.
It is believed that the weakness of a catalyst comprising magnesium molybdate supported on magnesia is directly related to the high sintering temperature of magnesium oxide and the absence of strong intermolecular linkages. The sintering temperature is so much higher than normal calcination temperatures and normal operating temperatures of the process of this invention that the particles do not have the opportunity to fuse and bind together. One means of strengthening the magnesium molybdate catalyst is to incorporate into the catalyst a support component. Preferably, the component is a high surface area, attrition resistant composite of magnesia and alumina, optionally containing a magnesium aluminate spinel phase, as described hereinabove. It is believed that the alumina imparts hardness to the cata-lyst, while the magnesia and/or magnesium aluminate reduces the natural acidity of the alumina. Such a the-ory, however, should not be binding or limiting of the inventions disclosed herein. Suitable methods of 36,823A-F _23--2f-testing attrition resistance are described in the -- section on Illustrative Embodiments hereinafter.
Another important property of the catalyst of this invention is its particle size. The prior art usually teaches the use of small spheroidal catalyst particles for fixed bed and transport fluid bed reactors. Such particles usually range of from 20 ~m to 200 ~m in diameter, preferably from 80 um to 120 ~m in diameter. Surprisingly, we have found that spheroidal, meaning approximately spherical, particles in the range of from 200 pm to 1700 ~m in diameter exhibit improved performance in transport reactors. Preferably, the particles are in the range of from 500 um to 1200 um, more preferably from 600 um to 1000 pm. The larger particles of our invention exhibit less "caking" and therefore give a smoother low velocity flow. Also, our larger particles exhibit lower pressure drop in the dense phase sections of the reactor, less violent particle-wall collisions, and the ability to better differentiate between the gas residence time and the catalyst residence time.
The process of this invention can be carried out in any suitable reactor, including batch reactors, continuous fixed-bed reactors, slurry reactors, fluid-ized bed reactors, and riser reactors. Preferably, the reactor is a continuous flow reactor, such as a contin-uous fixed-bed reactor or a riser reactor of the type described hereinafter.
Typically, the riser reactor comprises an upright vessel of relatively low ratio of diameter to length. The catalyst is continuously charged into the 36,823A-F -24-_Z5_ ~~~i~~~
bottom of the riser reactor. Likewise, the aliphatic hydrocarbon feedstream is delivered concurrently to the bottom of the riser reactor as a vapor phase feed or as a liquid phase feed. Preferably, the alkane is deliv-ered as a vapor phase feed pre-mixed with an inert, aseous diluent, and o tionall g p y, a small concentration of oxygen. The feed moves upward through the reactor, thereby contacting the catalyst. Upon contacting the catalyst, the feed is converted into a mixture of prod-acts, including monoolefins, diolefins, higher unsatu-rated olefins, cracking products, deep oxidation prod-ucts, such as carbon monoxide and carbon dioxide, and heavies, such as benzene and furan in the case of a butane feed. The product stream exits the riser reactor and is separated by known methods, such as distillation, to recover the desired products, typically the diole-fins. Unreacted alkanes and monoolefin products are recycled to the riser reactor for further oxidation.
Riser reactor technology is advantageous for the process of this invention, because (1) the hazard of using a feedstream containing a mixture of alkane and/or olefin and elemental oxygen is eliminated, and (2) the selectivity for diolefins is enhanced, especially at the high temperatures required for this process. In con-trast, if a feedstream of alkane and oxygen is employed at a high temperature and a high oxygen/alkane mole ratio, there is a tendency to produce more deep oxida-tion products, such as carbon monoxide and carbon diox-ide. In addition, the danger of a run-away reaction is greater.
The operation of a riser reactor can be simu-lated by employing a method of alternating pulses.
36,823A-~ -25-~~~i~~3 Thus, a pulse of the hydrocarbon-containing feed is -- passed through the catalyst bed where it is oxidized to form the desired olefin products. Next, a pulse of inert gas is passed through the catalyst bed to purge the bed of residual alkanes and alkenes. After purging, a pulse of oxygen-containing feed is passed through the catalyst bed to regenerate the catalyst. Finally, a second pulse of inert gas is passed through the catalyst bed to purge the bed of oxygen, after which the cycle is repeated. Such a procedure is employed in the illustra-tive embodiments, described hereinafter.
The aliphatic hydrocarbon reactant is contacted with the catalyst at any operable temperature which pro-motes the oxidation process of this invention and yields the desired unsaturated products. Typically, the tem-perature is in the range of from X100°C to 700°C. Prefer-ably, the temperature is in the range of from 500°C to 650°C. More preferably, the temperature is in the range of from 530°C to 600°C. Below the preferred lower temperature the conversion of reactant may be low.
Above the preferred upper temperature the selectivity and productivity of diolefin products may decrease.
Likewise, the aliphatic hydrocarbon reactant is contacted with the catalyst at any operable pressure which promotes the oxidation process of this invention and yields the desired unsaturated products. Typically, the partial pressure of the reactant is adjusted to maintain the reactant in the vapor state at the operat-ing temperature. Preferably, the partial pressure of the aliphatic hydrocarbon is in the range of from about subatmospherie to about 100 psig (690 kPa gauge). More preferably, the partial pressure is in the range of from 36 , 823A-F -26--1 psig to 30 psig (7 to 207 kPa gauge). Most -- preferably, the partial pressure is in the range of from _ 3 psig to 15 prig (21 to 104 kPa gauge).
When the process of this invention is conducted in a continuous flow reactor, described hereinbefore, the flow rate of the reactants can be varied. General-ly, in the process of this invention the aliphatic hy-drocarbon reactant is fed into the reactor at any oper-able flow rate which promotes the oxidation reaction and yields the desired conversion and selectivity of unsaturated products. The flow rate is expressed as the gas hourly space velocity (GHSU) and is given in units of volume of aliphatic hydrocarbon-containing gaseous feed per total reactor volume per hour or simply hr-1.
Typical values vary from 100 hr-1 to 20,000 hr-1. It should be understood that the space velocity controls the residence time of the reactants. In a riser reactor, for example, a gas residence time less than about 10 seconds is preferred, while times less than 5 seconds are more preferred and less than about 1 second are most preferred.
For the ease of the riser reactor, after con-tacting the catalyst with the aliphatic hydrocarbon reactant the spent catalyst leaves the top of the reac-tor and is transported into a second reactor for regen-eration. Regeneration is effected by contact with oxy-gen. Typically, a preheated oxygen source, like that described hereinbefore, is fed into the bottom of the second reactor. The spent catalyst is contacted with the oxygen source at any operable temperature, pressure, and oxygen-source flow rate which are sufficient to regenerate the catalyst. The process variables should 36,823A-F -27-2$- ~~~1 ~ '~3 be controlled, however, so as to prevent a runaway reac--- tion or the buildup of excessive heat. Preferably, the temperature is in the range of from 500°C to 700°C, more preferably, in the range of from 550°C to 650°C.
Preferably, the pressure is in the range of from subatmospheric to 100 psi (690 kPa g gauge), more preferably, in the range of from 2 psig to 50 psig (14 to 345 kPa gauge). The oxygen-source flow rate required will depend upon the heat transfer properties of the particular reactor. For example, at some high flow rates the temperature may rise dramatically resulting in an uncontrolled reaction.
When the aliphatic hydrocarbon is contacted with the catalyst of this invention, an oxidation of the aliphatic hydrocarbon occurs resulting in the loss of at least two hydrogen atoms from the hydrocarbon reactant with formation of by-product water. The organic prod-ucts which are produced are predominantly unsaturated aliphatic hydrocarbons, such as monoolefins and d.iole-fins. These unsaturated products usually contain the same number of carbon atoms as the reactant aliphatic hydrocarbon. Thus, these products are not products of cracking, which would contain fewer carbon atoms than the starting hydrocarbon. Uenerally, also, the unsatu-rated products possess a higher degree of unsaturation than the reactant hydrocarbon. For example, alkanes, such as butane, can lose two hydrogen atoms to yield monoolefins, such as 1-butane, traps-2-butane, and cis--2-butane. In turn, monoolefins, such as the butanes previously cited, can lose two hydrogen atoms to form 1,3-butadiene.
36,$23A-F -2$-~~~~~7~
The preferred diolefin products can be repre--- rented by the general formula:
CH2=CH-CH=CH-(CH2)m-H
wherein m is an integer of from 0 to 6. Preferably, m is an integer of from 0 to 2. More preferably, m is 0 and the unsaturated product is 1,3-butadiene. Isomers of the formula shown hereinabove can also be formed wherein the unsaturation occurs at any other location along the carbon chain. Preferably, the unsaturation occurs in a conjugated fashion, as exemplified in the product 1,3-butadiene. Even more unsaturated variants of the general formula can be formed wherein further oxidation has occurred to yield more than two ethylenie double bonds. Alkynes, however, are not formed in significant amounts.
In addition to alkenes, the product stream can contain b roducts of various t Y-P ypes. For example, when the saturated alkane is n-butane, small quantities of cracking products, such as propylene and ethylene, can be formed, as well as heavies, such as benzene and furan, and deep oxidation products, such as carbon monoxide and carbon dioxide. Unexpectedly, however, these by-products, especially the deep oxidation prod-ucts, are significantly reduced over the prior art processes.
For the purposes of this invention, "conver-sion" is defined as the mole percentage of aliphatic hydrocarbon reactant lost from the feed stream as a result of reaction. The conversion can vary widely depending upon the reactants, the form of the catalyst, 36,823A-F _29--3°- ~~~1~~~
and the process conditions such as temperature, pres--- sure, flow rate, and catalyst residence time. Within the preferred temperature range, as the temperature increases, the conversion generally increases. Within the preferred gas hourly space velocity range, as the space velocity increases, the conversion generally decreases. Typically, the conversion of the aliphatic hydrocarbon is at least about 10 mole percent. Pref-erably, the conversion is at least about 20 mole per-pent; more preferably, at least about 30 mole percent;
even more preferably, at least about 40 mole percent;
and most preferably, at least about 50 mole percent.
Likewise, for the purposes of this invention ''selectivity" is defined as the mole percentage of con-verted carbon which forms a particular product. Typi-cally, selectivities also vary widely depending upon the reactants, the form of the catalyst, and the process conditions. Typically, the process of this invention achieves high selectivities to diolefins. Within the preferred temperature range, as the temperature increases the selectivity for alkenes generally decreases. Within the preferred space velocity range, as the space velocity increases the selectivity for alkenes generally increases. Preferably, the combined selectivity to all alkenes is at least about 50 mole percent; more preferably, at least about 60 mole per-cent; even more preferably, at least about 70 mole per-cent; most preferably, at least about 80 mole percent.
Typically, the selectivity to diolefins is at least about 40 mole percent. Preferably, the selectivity to diolefins is at least about 50 mole percent, more pref-erably, at least about 60 mole percent, most preferably, at least about 70 mole percent.
36,823A-F -30-3' 202~~°~~
The concept of simultaneous high conversion and -- high selectivity can be conveniently expressed in terms o.f yield. For the purposes of this invention, the term "yield" refers to the numerical product of the single--pass conversion and selectivity. For example, a pro-s cess according to the present invention operating at a . conversion of 0.65, or 65 mole percent, and a selectiv-ity to diolefin of 0.75, or 75 mole percent, would have a diolefin yield of O.~t9, or 49 mole percent. Typical-lye the yield of diolefin achieved in the process of this invention is at least about 8 mole percent. Pref-erably, the yield of diolefin achieved in the process of this invention is at least about 18 mole percent, more preferably at least about 28 mole percent, most pref-erably, at least about 35 mole percent. Typically, in the oxidation of butane the yield of total C~ olefins is at least about 25 mole percent. Preferably, in the oxi-dation of butane the yield of total C~ olefins is at least about 30 mole percent, more preferably, at least about 35 mole percent, most preferabl y, at least about 40 mole percent.
The rate at which a desired product is produced in the process of this invention can be expressed in the concept of space-time yield. For the purposes of this invention the "space-time yield" is defined as the mole percentage yield of a given product per hour (yield hr-1), and it is the numerical product of the single-pass conversion, the selectivity, the gas hourly space velocity, and the concentration of the aliphatic hydrocarbon in the feedstream, wherein the conversion, selectivity and concentration are expressed as decimal fractions. Preferably, the space-time yield of diolefin 36,823A-F -31-in the. process of this invention is at least about 30 -- - percent per hour, more preferably, at least about 120 percent per hour, and most preferably, at least about 200 percent per hour.
Another measure of the rate at which a desired product is produced is the "productivity," defined as the grams desired product formed per gram catalyst per hour (g/g cat-hr). Preferably, the productivity of butadiene in this process is at least about 0.2 g/g cat--hr, mare preferably, at least about 0.4 g/g eat-hr, and most preferably, at least about 0.5 g/g cat-hr.
Preferably, the productivity of combined C4 olefins in this process is at least about 0.3 g/g eat-hr, more preferably, at least about 0.4 g/g eat-hr, most preferably, at least about 0.9 g/g cat-hr.
Testing the attrition resistance of a catalyst requires having on hand a large amount of catalyst sam-plc. It would be desirable to have a simple test proce-dune for small catalyst samples which gives an indica-tion of attrition resistance. A test of crush strength is such a procedure, because increased crush strength indicates better attrition resistance. Crush strength can be tested on any conventional equipment employed for such a purpose, for example, an Instron Model 1125.
Generally, the catalyst is sized into 8-mesh (2.36 mm) granules which are calcined at 600°C for 2 hours, and thereafter the crush strength is determined. Usually the crush strength of the preferred catalysts of this invention is at least about 5 lb (2270 g), preferably, at least about 10 lb (4540 g), more preferably, at least about 15 lb (6810 g).
36,823A-F -32-2~~~.~7~
The actual attrition resistance of the pre--- ferred catalyst of this invention can be tested on any conventional equipment intended for such a purpose. A
suitable testing apparatus is comprised of a stainless steel standpipe of 1l2-inch (13 mm) diameter and about 30 inches (760 mm) len th which is g , joined through a "J"
valve to a riser tube of similar diameter and about 52 inches (1320 mm) length. A 3-inch (76 mm) diameter stainless steel cyclone is attached to the riser tube at the cyclone entrance port and to the standpipe at the cyclone exit port, thereby creating a circulation loop wherein gas-solid separation is effected and the solids are returned to the standpipe. Normally, the material to be tested is charged into the system and is fluid.ized by the introduction of a gas at a flow rate of from 0.1 1 s-1 to 1.0 1 s-1 at the °'J°' valve. The entrained powder moves in the upward gas stream and is recirculated upon separation by gravity in the cyclone recovery system. Typically, samples are taken periodically up to a total test time of about 15 hours.
The amount of fines generated per unit time is determined and an attrition number is calculated by comparison to the initial coarse fraction. Preferably, the attrition number of the catalyst of this invention is less than about 5 weight percent per hr (wt. percent hr-1), preferably, less than about 1 weight percent hr-1, The following examples are illustrative of the process and catalyst of this invention, but are not intended to be limiting thereof. All percentages are given in mole percent carbon, unless noted otherwise.
36,823A-~ -33-Examples 1 (a-b) - Catalyst Preparation (a) Magnesium oxide powder (17 g, Magox*Premium Grade Mg0) was dispersed in deionized water (96 g) using a high shear disperses. To the resulting slurry was gradually added 20 weight percent alumina colloid (200 *
g, Nyacol) to form a viscous mixture comprising 30 weight percent Mg0 and 70 weight percent A1203. An additional 52 g of water was added to provide a manageable rheology. The mixture was aged and gelled by heating on a hot plate with stirring at 70°C for about 2 hours to yield a hard white solid. The white solid was crushed and heated over a 4-hour period to 600°C and calcined at 600°C for 4 additional hours resulting in a spinel composite support having a Mg0/A1203 weight ratio of 0.43 and a surface area of 16~~ m2/g. The X-ray diffraction spectrum of the support displayed reflections which can be attributed to crystalline MgO, as well as spinel and alumina. 'the support was tested on an Instron*Model 1125 and was found to have an average crush strength of 15 pounds (6810 g).
(b) A spinel composite support was prepared according to the procedure of Example 1 with the exception that ~~ g of magnesium oxide powder, 280 g of alumina colloid and 249 g of deionized water were employed. The resulting composite support had a Mg0/A1203 weight ratio of 0.78 and a surface area of 163 m2/g. The X-ray diffraction spe<:trum of the support exhibited reflections which can be attributed to crystalline MgO, as well as spinel and alumina.
The spinel composite support (20 g), prepared in (b) hereinabove, was impregnated to incipient wetness *Trade-mark _ ~5-with 20.44 g of a solution containing ammonium hepta-molybdate (35.25 weight percent) and cesium hydroxide (1.85 weight percent). The impregnated support was dried at 125°C for 2 hours, heated up to 600°C over a period of 4 hours, and calcined at 600°C for an additional 3 hours. The resulting catalyst (E1) contained 22.4 weight percent Mo03 and 1.20 weight percent Cs20 and had a surface area of 122 m2/g.
Example 2 (a-b) - Butane Oxidation The catalyst of Example 1(b) (E1) was employed in the oxidation of butane in the following manner:
approximately 15 ec of catalyst was loaded into a Vycor reactor tube (18 mm OD x 7.6 em length). The tempera-Lure of the reaction was measured from a stainless steel thermowell (1/8 inch (3.2 mm) OD) embedded in the catalyst sample. A feedstream containing butane (10-20 volume percent) and helium (90-80 volume percent) was passed over the catalyst for about 10-30 seconds. The flow of the feedstream was stopped and a purge stream comprising pure helium was passed over the catalyst at the same flow rate for 1 minute. The purge stream was stopped and a stream of oxygen (20 volume percent) in helium was passed over the catalyst at the same flow rate for 1 minute, followed by another purge stream of helium for 1 minute. This cycle was repeated and the combined products were collected in a Saran~
polyvinylidene chloride plastic bag for analysis.
Analysis was performed on a Carle gas ehromatograph designed to analyze for C1-C5 alkanes, alkenes and alkadienes, as well as permanent gases such as N2~ 02, C0, C02, H2, and heavier products including furan, benzene, and C6 compounds. Isobutane was mixed with the 36,823A-F °35-~021 j'~~
feed or -products as a standard. "~lnknowns" were -- obtained from the difference between the carbon balance and 100 percent. The process conditions and results are set forth in Table I.

36,823A-F -36-°

TABLE I°
Example ~ 2a 4a 2b 4b Catalyst: E1 E3 Ei E3 Weight % Cs 1.2 1.4 1.2 1.4 T 9 ~ 570 565 580 580 GHSU, hri 1084 1044 990 990 Conversion 19.58 33.25 27.48 41.79 Selectivities:
1-butane 10.96 6.78 7.80 5.50 tr-2-butane 8.66 5.11 5.86 3.99 cis-2-butane 9.28 5,06 7.23 3.94 butadiene 63.60 66.71 68.46 64.98 Sum C4's 92.50 83.66 89.35 78.41 propylene 0.00 0.68 1.37 0.75 ethylene 3.40 2.99 3.57 4.01 ~ Total _ Cracking 3.40 3.67 4.94 4.76 C02 4.10 9.18 4.86 10.91 CO 0.00 2.16 0.85 3.49 Deep 4.10 11.34 5.71.-14.39 Oxidation furan/benzene 0.00 1.33 0.00 1.95 Unknown 0.00 0.00 0.00 0.48 Total 0,00 1.33 0.00 2.43 Heavies Total C balance103,4 100.0 101.1 99.8 g C /g eat-hr 0.108 0.143 0.128 0.168 96 Yield C4's 18.10 27.82 24.55 32.77 °Catalyst, 16 ec.
36,823A-F -37-_38_ It is seen that the cesium-promoted magnesium molybdate catalyst supported on the magnesia alumina spinal com-posite catalyzes the oxidation of butane to butadiene and butane in high selectivity.
Example 3 - Catalyst Preparation A magnesia alumina spinal composite support was prepared as is Example 1(b). The spinal composite (20 g) was impregnated to incipient wetness with 19.49 g of a solution containing cesium hydroxide (1.66 weight per-cent), ammonium vanadate (1.39 weight percent) and ammo-nium heptamolybdate (27.22 weight percent). The impreg-nated support was dried at 125°C for 2 hours, heated to 600°C over a period of 4 hours, and calcined at 600°C for an additional 3 hours. The resulting catalyst (E3) contains 17.44 weight percent Mo03, 0.85 weight percent V205 and i.43 weight percent Cs20 and had a surface area after calcination of 122 m2/g.
Examples 4 (a-b) - Butane Oxidation The catalyst prepared in Example 3 (E3) was emplpyed in the oxidation of butane as described in Example 2. The process conditions and results are set Fortly in Table I. It is seen that the magnesium molyb-date catalyst promoted with cesium and vanadium oxides and supported on the alumina magnesia spinal composite catalyzed the oxidation of butane to butadiene and butane in high selectivity.
36,823A-F -38--39~
Example 5 - Catalyst Preparation (a) Support preparation:
Magnesium oxide powder (600 g) was dispersed in deionized water (5733 g) using a high shear disperser.
To the resulting slurry was gradually added under low shear colloidal. alumina (7000 g, 20 weight percent).
The mixture, thus obtained, was spray dried using a noz-zle atomizer having a 2-mm diameter orifice under a pressure of 40 psig (276 kPa gauge). The inlet temperature of the nozzle was 300°C and the outlet temperature was 120°C. A white powder with excellent flow properties was obtained from the spray drying. The powder was calcined at 600°C for 2 hours to yield a composite support having a surface area of 184.3 m2/g and a Mg0/A1203 weight ratio of 0.43. The X-ray diffraction spectrum of the support exhibited reflections which can be attributed to crystalline Mg0 as well as spinal and alumina phases. Caleining a portion of the powder for 4 hours longer at 800°C
reduced the surface area only slightly to 143.2 m2/g.
The support, obtained by caleining the powder at 600°C, had an average particle size of about 60 Vim.
Examination of the particles by scanning electron microsco showed the py presence of spheroidal particulates which have excellent flow properties. The support was subjected to an attrition test in a circulating loop, as described hereinbefore and an attrition number of 0.2$ weight percent hr-1 was obtained. This value compared favorably with a commercial fluid catalytic cracker (FCC) alumina useful in transport reactors, which had an attrition number of 0.99 weight percent hr-1.
36,823A-F -3g-~~o-(b-d) Catalyst Examples:
-- Magnesia alumina spinet supports were prepared as described in (a) hereinabove, with the exception that they contained sufficient Mg0 to give compositions of 40, 4t1 and 30 weight percent Mg0 and with the exception that the were not calcined. The su Y pports were pressed at 5 Kpsig (35 mPa gauge) in an isostatie press, crushed to 20 to 80 mesh (850 to 180 um), and calcined at 600°C
for 5 hours. To 50 g of each support was added a solution containing ammonium heptamolybdate (33.23 weight percent), K2C03 (0.62 weight percent) and hydrogen peroxide (2.5 weight percent of a 30 weight percent peroxide solution) neutralized to pH 9 with ammonium hydroxide. The impregnated supports (E-5-b-d) were dried at 110°C for 18 hours and calcined at 600°C
for 3 hours to yield the catalysts. The amount of the solution applied to each support is given in Table II.

36,823A-F -~p-41- 2~~1~~~
__ TALE ~a~
Catalyst E-5b E-5c E-5d Solution (g) 49.9 47.00 46.40 Wt ~ Mg0 30 40 44 Wt % Mo0 21.20 20.23 20.03 Wt % K20 0.33 0.32 0.31 Mg0/A1 0 0.43 0.67 0.79 C Conversion 29.18 30.70 34.05 % Seleotivities:
butanes 19.39 17.84 16.38 butadiene 60.21 66.39 64.68 Sum C 's 79.60 84.23 81.07 ethylene 1.74 2.29 1.91 C02 7.68 6.25 7.29 CO 2.79 2.32 2.80 % Deep Oxidation 10.47 8.58 10.09 furan/benzene 0.00 0.63 2.08 Unknown 8.19 4.28 4.85 ~ Total 8.19 4.91 6.93 Heavies Total C balance97.61 98.69 98.35 g C /g eat-hr 0.136 0.161 0.176 g BD/g cat hr 0.10 0.13 0.14 ~ ~ I

Catalyst, 15 ee; T, 570°C9 GHSU, 844/hr.
~Wt. ~ before addition of Mo03 and K20.
BBD = butadiene 36,823A-~' -41-Example 6 - Butane Oxidation The catalysts prepared in Example 5 (E-5b -E-5d) were employed in the oxidatian of butane as described in Example 2. The process conditions and results are set forth in Table II. It is seen that the potassium-promoted magnesium molybdate catalysts supported on the alumina magnesia spinel composite catalyzed the oxidation of butane to butadiene and butene in high selectivity.
Example 7 - Catalyst Preparation A spinel precursor was prepared by a known method of coprecipitating magnesium and aluminum hydrox-ides at pH 9 from an aqueous solution of magnesium and aluminum salts via the addition of NaOH and Na2C03. The spinel precursor was caleined at 600°C for 3 hours thereby forming a magnesium aluminate spinel (MgA1204).
The pre-formed spinel was impregnated to incipient wetness with a 1.75 Molal aqueous solution of magnesium acetate tetahydrate (37 weight percent). The impregnated spinel was calcined for 3 hours a't 600°C to give a spinel composite containing an additional 17.1 '~~eight percent Mg0 and a Mg0/A1203 weight ratio of 0.69.
Thereafter, the composite (16.3 g) was impregnated to incipient wetness with an aqueous solution (17.53 g) of ammonium heptamolybdate (26.5 weight percent), and then calcined at 600°C for 4 hours. This material was further impregnated with a methanolic solution (8.5 g) of cesium hydroxide hydrate (0.63 weight percent) and recalcined at 600°C for 3 hours. The resulting catalyst (E7) contained 18.8 weight percent Mo03 and 0.25 weight percent Cs20 and had a surface area of 115 m2/g.
36 , 823A-F -~2---~3-~~21~~~
Example 8(a-b) - Butane Oxidation The catalyst of Example 7 (E7) was employed in the oxidation of butane according to the procedure described in Example 2. The results are presented in Table IIT.

36,823A-F -~3-_u4_ ~~21~r13 TABLE III
Example ~~8a . 8b CE CE
1a 1b Catalyst: 7 7 CE CE

Weight ~ Cs20 0.240 0.240 0.00 0.00 GHSV, g/ml hr 150 150 600 600 Temperature 570 550 570 550 (C) ~ Conversion 37.91 25.70 48.08 33.82 Selectivities:
1-butene 4.76 7.04 3.08 4.16 tr-2-butene 11.48 7.15 3.15 5.00 cis-2-butene 4.25 5.95 2.29 4.33 butadiene 62.83 62.74 48.69 56.99 Sum C4's 76.32 82.88 57.21 70.47 ethylene 2.24 1.59 1.94 1.39 Total 2,24 1.59 1.94 1.39 2 Cracking C02 7.83 4.84 17.86 12.56 CO 3.53 2.26 8.8 6.33 ~ Deep 11,37 7.10 _ 18.89 Oxidation _ 26.68 furan/benzene 3.91 0.0 9.08 6.78 Unknown 9.84 12.09 7.94 5.79 Total 13.75 12.09 17.01 12.57 Heavies Total C balance97.66 97.83 97.55 99.19 g C4/g cat-hr 0.045 0.033 0.042 0.037 Yield C4's 28.93 21.30 27.50 23.83 °Catalyst, 15 ec.
36,823A-F -44-It is seen that the cesium-promoted magnesium molybdate -- catalyst supported on the spinel composite catalyzed the oxidation of butane to butadiene and butene in high selectivity.
Comparative Example 1 (CE 1-a and CE 1-b) A composition was prepared according to the procedure described hereinabove in Example 7, with the exception that no cesium hydroxide was impregnated into the catalyst. The composition was employed in the oxi-dation of butane according to the procedure described in Example 2. The results are presented in Table III.
When Example 8 is compared with Comparative Experiment 1, it is seen that the catalyst of this invention con tainin low levels of cesium g promoter achieved a higher selectivity to butadiene and butene and a lower selec-tivity to deep oxidation products than a similar cata-lyst which did not contain cesium promoter.
Examples 9 (a-e) - Catalyst Preparation An aqueous solution (1184 g) containing 71.5 weight percent magnesium nitrate hexahydrate was added to porous alumina spheres (713.3 g; UOP, 700 um ). The resulting slurry was dried for 18 hours at 150°C, arid calcined by heating up to 460°C over a 4-hour period, holding at 460°C for 2 hours, heating further to 540°C
over a 2-hour period, and holding at 540°C for 3 hours in flowing air. More of the magnesium nitrate solution (1186.9 g) was added to the dried alumina spheres, and the drying and caleination procedures were repeated. A
composite support was obtained containing 27.7 weight percent Mg0 having a Mg0/A1203 weight ratio of 0.38 and a surface area of 101 m2/g, 36,823A-F -45-~6- 2~~~ ~~~
Samples (35 g) of the composite were -- impregnated with a solution containing ammonium heptamolybdate and potassium carbonate as set forth in Table IV. The concentration of ammonium heptamolybdate varied in each solution, while the concentration of potassium carbonate was nearly constant. The impregnated composites were ealcined at 600°C for 4 hours to yield potassium-promoted molybdate catalysts (E9 a-e) supported on the magnesia, alumina spinel composite characterized in Table IV.

36,823A-F -46-_47-TABLE IVY
Example 10a 10b 10e 10d 10e Catalyst: 9a 9b 9e 9d 9e Solution:

~AHM~ 34.80 29.0 22.50 15.90 11.60 %K2C0 0.65 0.67 0.66 0.65 0.64 Wt % Mo0 24.30 21.90 16.20 11.40 8.40 Wt ~ K20 0.38 0.42 0.40 0.39 0.39 Mg0/A1 0 0.38 0.38 0,38 0.38 0.38 Conversion 24.67 24.27 29.84 22.34 11.28 Selectivities:
25.30 25.56 20.55 22.27 23.81 Sum butenes Butadiene 63.21 65.89 63.48 61.04 40.18 Sum C 's 88.51 91.45 84.03 83.31 64.00 ethylene 0.00 0.00 0.00 0.00 0.00 CO 6.10 4.60 5.63 6.32 10.68 CO 2.79 0.00 2.14 1.86 2,51 ~ Deep 8.89 4.60 7.77 8.19 13.19 Oxidation benzene/furan 0.18 0.00 0.00 0.00 0.00 Unknown 0.15 1.21 5.89 2.69 8.13 ~ Total 0.33 1.21 5.89 2.69 8.13 Heavies ~ C Balance 99.96 99.71 98.24 99.40 99.08 g C /g eat-hr 0.11 0.11 0.13 0.10 0.04 g BD/g eat-hr 0.09 0.08 0.10 0.08 0.03 °Catalyst, 16 cc; T, 572°C; GHSV, 844 hr-1.
~AHM = ammonium heptamolybdate; BD = butadiene 36,823A-F -47-Example 10 (a-e) - Butane Oxidation The catalysts (E9 a-e) of Example 9 were employed in the oxidation of butane as described in Example 2 with the results shown in Table IV. It is seen that a potassium-promoted molybdate catalyst sup-ported on an alumina, magnesia spinel composite cata-lyzed the oxidation of butane to butenes and butadiene in high selectivity. It is further observed that the seleetivities to C4 olefins decrease as the coneen-tration of mol bdate dro y pped below about 11 weight percent.
Example 11 - Catalyst Preparation Alumina spheres (4.09 g; UOP-SAB16) having a nominal diameter of 1700 um were impregnated three times to incipient wetness with 10 ee each of a solution con-taining 1.15 g of Mg0 as the nitrate hexahydrate.
Between each application of the solution the impregnated alumina was caleined at 600°C for 2 hours thereby yield-ing a composite support having a Mg0/A1203 weight ratio of 0.75. A solution (9.2 ml) containing ammonium hepta-molybdate (11.8 g), K2C03 (0.22$ g) and NH4V03 (0.60 g) per 100 ml of solution was added to a sample (6.42 g) of the support, after which the support was caleined to yield a catalyst (E-11) containing 12.03 weight percent Mo03, 0.58 percent V205 and 0.16 percent K20 and having a surface area of 34 m2/g.
Example 12 - Butane Oxidation The catalyst (5.65 g) of Example 11 (E-11) was loaded into a fixed bed reactor as described in Example 2. The reactor was pulsed at 600°C and a GHSV of 1200 36,823A-r -4g_ -~~- 2~21~~3 hr-1 with a mixture of helium and 20 volume percent -- butane for a 5-second pulse duration followed by 60-second pulses sequentially of helium, air and helium.
The cycle was repeated with the following results: Bu-tane Conversion, 45.2 percent; Selectivities: Butadiene, 58.3 percent; Butenes, 20.6 percent; Sum Butenes, 78.9 percent; Deep Oxidation Products (C02 and CO), 6.4 per-cent; Cracking Products, 8.0 percent; and Unknowns, 6.$
percent. The productivity was 0.34 g C4/g eat-hr and 0'25 g butadiene/g eat-hr. It is seen that the productivity of C4 carbons and butadiene is greater than the value generally considered to be necessary for a commercial process (0.2 g/g cat-hr).
Example 13 - Catalyst Preparation Alumina spheres (713.3 g; UOP-MS-R-27) having particles in the range of from 500 um to 1000 um in diameter were used in preparing an alumina magnesia spinel composite support following the method described in Example 9. A composite support was obtained having a Mg0/A1203 weight ratio of 0.38 and a surface area of 106 m2/g. A sample (686 g) of the composite was impregnated with 728 g of a solution containing ammonium heptamolyb-date (22.5 weight percent) and potassium carbonate (0.66 weight percent). The impregnated composite was calcined at 600°C for 4 hours to yield a catalyst composition (E-13) containing 18.4 weight percent Mo03 and 0.45 weight percent K20.
Example 14 - Butane Oxidation The catalyst prepared in Example 13 was employed in the oxidation of butane in a laboratory scale riser reactor. A fluidized bed catalyst feed tank 36,823A-F -49--5°- ~~~1~'~3 (3500 ml capacity) was connected at its bottom to a long tube called the "catalyst standpipe.°' The standpipe was connected via a "J" valve to a riser tube about 2 m in length and 6 mm in diameter, which was attached to the first of a series of three cyclone separators connected in sequence. The catalyst recovered in the cyclones was recycled to the top of the catalyst feed tank. A gase-ous feedstream comprising 10 volume percent nitrogen, 6.9 volume percent butane and the balance helium was Preheated in a preheat tube only 4 mm in diameter, which minimizes the residence time and therefore the thermal cracking of butane. The preheat tube was connected into the system at the juncture of the standpipe and the "J"
valve, and the gaseous feedstream was fed at 500 ec/min.
The catalyst was heated to a temperature of b50°C in the feed tank and subsequently fed into the riser tube at a rate of 200 ce/min. The riser tube obtained a tempera-ture of about 580°C. The gas residence time was 1.6 seconds. The catalyst was entrained in the gaseous feedstream with the following results: Butane Conversion, 28.3 percent; Selectivities: Butadiene, 61.9 percent; Butenes, 22.1 percent; Deep Oxidation Products (C02 and CO), 5.1 percent; C2-3 Cracking Products, 7.7 percent; Methane, 1.0 percent; and Unknowns, 2.1 per-cent. The productivity was about 0.43 g C4/g cat-hr and 0.32 g butadiene/g cat-hr. It is seen that the productivity of C4 carbons and butadiene is greater than the value generally considered to be necessary for a commercial process (0.2 g/g cat-hr).
Example 15 - Butane Oxidation The catalyst of Example 13 was employed in the riser reactor described in Example 14 with a gaseous feedstream comprising 67 volume percent butane and the 36,823A-F -50-ba.lanee nitrogen and helium. The gas feed rate was 1000 -- ec/min resulting in a gas residence time of about 0.82 see. The catalyst was fed at a rate of about 455 ce/min with a resulting catalyst residence time of about 3.1 sec. The average temperature in the riser was measured as 584°C. The results were as follows: Butane conversion, 17.1 percent; Selectivities to butadiene, 39.1 percent; butenes, 2.4 percent; deep oxidation products (CO and C02), 2.5 percent; cracking products, including C2-C3's, 10.6 percent and methane, 1.6 percent; isobutane, 0.5 percent, and unknowns, 1.8 percent. The productivity of combined butadiene and butene products was 0.94 g C4/g cat-hr, while the productivity of butadiene was 0.49 g butadiene/g eat-hr.
It is seen that the productivity of C4 carbons and butadiene is greater than the value generally considered to be necessary for a commercial process (0.2 g/g cat-hr).
Examples 16-20 (a)Preparation of Cesium-Promoted Catalysts 16-20 A series of cesium-doped, molybdate catalysts was prepared according to the following general proce-dure with the exception that the quantity in grams of cesium hydroxide monohydrate per 40 g methanolie solution was varied as follows: Catalyst 1, 0.16 g;
Catalyst 2, 0.23 g; Catalyst 3, 0.29 g; Catalyst 4, 0.53 g; and Catalyst 5, 0.76 g.
Ammonium heptamolybdate, (NH4)6Mo7024~4H20 (72 g; 0.0583 moles), was dissolved in 175 ml of water. The resulting solution was mixed with magnesium hydroxide (300 g; Alfa Research Chemicals & Materials) to form a 36,823A-F -51-~~2~ ~'~~
slurry. The slurry was dried at 70°C for 1$ hours and -- at 130°C for 2 hours to obtain a solid mixture. The solid was crushed and passed through a sieve to obtain particles having a 20 to 120 mesh ($50 to 122 gm) size.
The sieved particles were calcined by heating slowly over 5 hours to a temperature of 600°C and then holding at 600°C for 2 haurs. The calcined solid was cooled to room temperature to yield magnesium molybdate comprising 22 weight percent Mo03 and 78 weight percent MgO. A
methanolic solution was prepared by adding the appropriate weight of cesium hydroxide, CsOH~H20, as cited hereinabove, to methanol to give ~0 g of methanolic solution. The magnesium molybdate (20.6 g) was immersed for 15 minutes in u0 g of methanolic solution. The resulting mixture was filtered, and the filtered solid was dried in air at room temper~ature (taken as about 22°C) for ~ hours and then in a drying oven at 120°C for 16 hours. The dried solid was calcined by heating over 5 hours to a temperature of 600°C, and then by holding for 2 hours at 600°C to yield a cesium-promoted magnesium molybdate catalyst, fhe weight percentage of cesium in Catalysts 16-20 is set forth in Table U.

36,823A-F -52--53 ~Q~~~~ a ~
__ TABLE f~
Example 16 17 18 19 20 Catalyst: 16 17 18 19 20 Weight ~ Cs 0.55 0.90 0.87 1.88 2.92 Surface Area ~m2~g~ 100.094.2 81.9 86.6 72.8 Conversion 61.8747.7044.7529.91 19.28 Seleetivities:
1-butane 2.26 4.92 5.61 10.34 13.65 tr-2-butane 1.29 1.88 2.37 2.96 4.40 cis-2-butane 1.59 2.82 2.64 4.54 6.60 butadiene 71.3071.0973.8553.37 38.49 ~ Total C4's 76.4480.7184.4671.21 63.13 propylene 0.33 0.50 0.33 3.14 7.80 ethylene 2.56 3.23 3.36 5.83 8.70 Total 2,89 373 3.69 8.98 16.49 Cracking 2o Co2 9.89 4.78 4.70 4.22 7.41 CO 4.17 1.78 2.51 2.69 5.30 % Deep Oxidation 14.066.56 7.21 6.91 12.71 Furan/Benzene 4.80 3.28 1.63 2.65 1.30 Unknown 1.82 5.7 3.00 10.25 6.37 ;6 Total 6,61 _ 4.64 12.90 7.67 Heavies 9.00 xield C4's 47.2938.5037.8021.30 12.17 Total C balance98,8897.2798.6696.93 98.77 'Catalyst, 15 cc; T = 550°C; GHSV = 336 hr-1.
36,823A-F -53-(b) Oxidation of Butane Employing Catalysts 16-20 Catalysts 16-20, prepared hereinabove, were tested in the oxidation of butane according to the following general procedure: The catalyst (15 cc) was loaded into a Vycor~glass tube reactor (7.6 cm length x 18 mm O.D.). The Vycor glass tube was connected at the top to an inlet tube for the feed stream, and at the bottom to an outlet tube for collection of the products.
The temperature of the reactor, as measured from a 1/8 inch (3.2 mm) O.D. stainless steel thermowell embedded in the catalyst bed, was raised to 550°C. A feedstream containing 10 volume percent butane, 50 volume percent nitrogen, and 40 volume percent helium was passed through the catalyst bed at a rate of 84 ml/min (GHSV =
336 hr-1) for 30 seconds. The feed stream was halted, and a purge stream containing helium was passed through the catalyst bed at a rate of 84 ml/min for 1 minute.
The purge stream was halted, and an oxygen stream containing 10 volume percent oxygen in helium was passed through the catalyst bed at a similar flowrate for 1 minute. The oxygen stream was halted, and a final purge stream of helium was passed through the catalyst bed at a similar flowrate for 1 minute. The complete cycle was repeated for a total of 30 minutes, and the combined products were collected in a Saran~ polyvinylidene chloride plastic bag. The products were analyzed by gas phase chromatography using a Carle*multi-column Gas Chromatograph fitted with the following 1/8" (3.2 mm) diameter columns: (1) 2.70 percent Carbowax*15~0 on Porasil*C (21" (530 mm), 80/100 mesh (180/150 Vim), Tmax 175°C); (2) 3.0 percent Carbowax 150 on Porasil C (4' (1220 mm), 60/80 mesh (250/180 Vim), Tmax 150°C);
(3) 27.5 percent BIS 2(XE)A on Chromosorb*PAW (17', *Trade-mark _5p_ _55_ (5180 mm) 45/60_mesh (328/250 lim), Tmax 150°C);
-- (4) Porapak Q (9' (2745 mm), 50/80 mesh (292/180 lam), Tmax 250°C); (5) Molecular Sieve 13X (9° (2745 mm), 45/60 (328/60 um) mesh, Tmax 300°C); (6) Molecular Sieve 5A (3' (914 mm), 80/100 mesh (180/150 lim), Tmax 300°C);
and (7) 28 percent DC 200/500 on Chromosorb PAW (3.5' (1068 mm), 60/80 mesh (250/180 lam), Tmax 175°C). The process results are set forth in Table U. The data show that butane was oxidized predominantly to butadiene and butenes in the presence of the magnesium molybdate catalyst doped with cesium.
Comparative Example 2 A composition was prepared in the manner described for Catalysts 16-20 hereinbefore, except that the steps pertaining to the doping of cesium were elimi-nated. The resulting composition contained 22 weight percent Mo03 and 78 weight percent MgO. There was no cesium in the composition. The composition was employed as a catalyst in the oxidation of butane in the manner described in Examples 16-20 (b) with the results given in Table VI.

36,823A-F -55-~~~~. y~~
TABLE VIA' Comparative Example GHSV GHSV
2 336/hr 600/hr Weight ~ Cs 0.0 0.0 Surface Area (m2/g) 107.9 107.9 % Conversion 67.78 52,78 _ Selectiv.ities: 1.43 2.55 1-butene trans-2-butene 1.40 2.33 cis-2-butene 1.15 2.17 butadiene 46.55 58.50 ~ Total C4's 50.53 65.55 propylene 0.78 0.74 ethylene 2.14 1.74 % Total Cracking 2.93 2.48 C02 27.18 16.17 CO 10.28 6.41 ~ Deep Oxidation 37.46 22.58 Furan/Benzene 9.08 5,96 Unknown 0.00 3.43 ~ Tetal Heavies 9.08 9.39 Yield C4's 34.25 34.60 Total C balance 101.9 98.19 "Catalyst, 15 ee; T = 550°C.
When Comparative Example 2 (GHSV 336 hr-1) is compared with Examples 16-20, it is seen that the pres-ence of cesium in the catalyst significantly improves the selectivities to butadiene and butenes. Simulta-neously, the selectivities to undesirable heavies, such 36,823A-F -56--~7- ~U2~.~'~3 as furan and benzene, and especially deep oxidation _- products, such as carbon oxides, decrease. However, when Comparative Example 2 (GHSU 336 hr-1) is compared with Examples 16-20, it is seen that the presence of cesium in the catalyst leads to a decrease in the butane conversion.
Examples 21-25 (a)Preparation of Alkali-Promoted Catalysts 21-25 A series of alkali-doped magnesium molybdate catalysts was prepared according to the following general procedure, with the exception that the amount of alkali metal hydroxide per 40 g methanolic solution was varied as followss Catalyst 6, KOH, 0.049 g; Catalyst 7, KOH, 0.098 g; Catalyst 8, KOH, 0.133 g; Catalyst 9, KOH, 0.320 g; and Catalyst 10, NaOH, 0.073 g.
Ammonium heptamolybdate, (NH4)6Mo7024~4H20 (72 g; 0.0583 mole), was dissolved in 345 ml of water and the resulting solution was added to magnesia (300 g;
CE Basic Industries, Magox Premium magnesia) to form a slurry. The slurry was dried at 70°C for 18 hours and at 130°C for 2 hours to obtain a solid mixture. The mixture was crushed and passed through a sieve to obtain particles having a 20-120 mesh size (850 to 122 um).
The sieved particles were calcined by heating slowly over 5 hours to a temperature of 600°C and then holding at 600°C for 2 hours. The calcined solid was cooled to room temperature to yield magnesium molybdate containing 22 weight percent Mo03 and 78 weight percent MgO. A
methanolic solution was prepared by adding the appropri-ate weight of alkali metal hydroxide, noted hereinabove, to 40 g of methanolie solution. The magnesium molybdate 36,823A-F -57-_5g_ ~~~~~J~~
immersed for 15 minutes in the methanolic solution. The resulting mixture was filtered, dried in air for 4 hours at room temperature, and then dried in an oven at 120°C
for 16 hours. The dried solid was calcined by heating slowly over 5 hours to a temperature of 600°C and then holdin at 600°C for 2 hours to g yield an alkali-promoted magnesium molybdate catalyst. The weight percentage of alkali metal in Catalysts 21-25 is found in Table UII.

36 , 823A-F -58-TABLE VII#
Exempla ~ 21 22 23 24 25 Catalyst (K*) (K-~)(K+) (K~)(Na+) Weight ~ Alkali 0,15 0.28 0.38 0.850.22 Surface Area (m2/g)94.6099.2091.59 74.192.60 Conversion 63.7850.5242.07 21.053.25 % Selectivitiese 1-butene 1.93 4.39 6.63 14.913.38 traps-2-butene 1.36 1.65 2,12 5.291.84 cis-2-butene 1.78 2.32 3.25 7,872.14 butadiene 68.2472.2773.71 47.4476.21 ~ Total C4's 73.3180.6385.71 75.5183.57 propylene 0.31 0.53 0.88 4.060,39 ethylene 2.21 3.02 4.08 6.242.29 Total Cracking 2.52 3.55 4.97 10.302.68 C02 10.995.28 4.38 4.467.08 Co 4,39 1.89 2.73 1,093.03 Deep Oxidation 15.397.17 7.10 5.5510.17 Furan/Benzene 7.26 1.56 2.22 1.383.64 Unknown 1.52 7.08 0.00 7.270.00 ~ Total Heavies 8.79 8.64 2.22 8.653.64 ~ Yield C4's 46.7640,7336.06 15.8644.50 Total C balance 99.0396.42100.5898.48101.82 Catalyst, 15 cc; T = 550°C; GHSV = 336 hr-1.
(b)Oxidation of Butane Employin~ Catalysts 21-25 The potassium- and sodium-doped Catalysts 21-25, prepared hereinbefore, were employed in the 36,823A-F -59--oxidation of butane according to_the procedure of --- Examples 16-20 (b). The results are set forth in Table VII.
The data show that butane is oxidized predom-inantl to butadiene and butenes in the y presence of the magnesium molybdate catalyst doped with potassium and sodium ions. Moreover, when Examples 21-25 are compared with Comparative Example 2 (GHSV, 336 hr-1), it is seen that the catalysts doped with potassium or sodium ions (Catalysts 21-25) achieve significantly higher seleetivities to butadiene and butenes than the undoped magnesium molybdate material. Simultaneously, the selectivity to deep oxidation products is significantly reduced in the alkali-doped catalysts.
Examples 26 and 27 (a)Preparation of Potassium-Promoted Catalysts 26 and 27 Two solutions were prepared comprising ammonium heptamolybdate, (NH~)6Mo702~~~dH20 (35 g), and potassium carbonate in 125 g of aqueous solution. The first solu-tion contained 0.63 g (Catalyst 26) of potassium carbon-ate, whereas the second solution contained 1.44 g (Cata-lyst 27) of potassium carbonate. Each solution was added to magnesia (100 g; CE Basic Industries, Magox Premium Grade magnesia) with stirring, and the resulting mixtures were dried and caleined as in the preparation of Catalysts 16-20 hereinbefore to yield potassium-doped magnesium molybdate catalysts.
36,823A-F -60-~~2~.~~~
(b)Oxidation of Butane Employing Catal'~sts 26 and 27 Catalysts 26 and 27 were employed in the oxidation of butane (Examples 26 and 27, respectively) according to the procedure of Examples 16-20. The results at a variety of process conditions are set forth in Table VIII.

36,823A-F -61---62- 202~.~'~~
Table VIII
Example ~26(a)26(b) 26(c)27(a) 27(b)27(c) wt ~ rc 0.33 0.33 0.33 0.62 0.62 0.62 Surface Area116.0116.0 116.0124.0 124.0124.0 (m2/~) GHSV (hr-1) 600 600 336 600 600 336 Temp. (C) 550 570 550 550 570 55p Conversion 59.9370.58 75.1246.22 57.2558.47 % Selectivity 1-butene 2.46 1.75 1.02 5.55 3.73 4.12 tr-2-butene i.56 0.96 0.76 2.19 1.50 1.31 eis-2- 2.06 1.17 0.77 2.83 1.86 2.07 butene butadiene 71.5868.53 62.4375.38 74.1673.48 ~ Total 77.6672.41 64.9985.96 81.2580.98 C4s propylene 0.00 0.15 0.00 0.00 0.00 0.00 ethylene i.76 2.99 2.03 2.39 2.91 3.77 methane 0.00 0.00 0.00 0.00 0.00 0.00 ~ Total 1.76 3.14 2.03 2.39 2.91 3.77 Cracking C02 8.28 9.74 14.113.72 4.94 4.94 co 3.28 4.71 6.33 1.75 2.11 2.80 % Deep 11.6514.45 20.445.47 7.05 7.74 Oxidation Furan/Ben- 5.07 5.52 6.05 1,33 0.05 1.92 zene Unknown 3.85 4.48 6.49 4.85 8.73 5.58 ~ Total 8.93 10.00 12.546.18 8.79 7.51 Heavies Total C 97.6996.84 95.1397.76 95.0096.74 Balance 36,823A-F -62-_63_ The data show that butane is oxidized predominantly to -- butanes and butadiene in the presence of a magnesium molybdate catalyst doped with potassium carbonate. The data show further that as the reaction temperature increases from 550°C to 570°C, the butane conversion increases, while the seleetivities to butenes and buta-diene decrease. It is further observed that as the gas hourly space velocity decreases from 600 hr-1 to 336 hr-1, the butane conversion increases, while the selee-tivities to butenes and butadienes decrease. When Exam-ple 26 is compared with Example 27, it is seen that the catalyst containing the higher weight percentage of potassium gives a lower conversion of butane and a higher selectivity to butenes and butadienes. When Examples 27(a) and 27(c) are compared with Comparative Example 2(b) and 2(a), it is observed that the catalyst containing potassium ions gives significantly higher selectivities to butadiene, and lower selectivities to heavies and deep oxidation products than the comparative material with no alkali ions.
Example 28 (a)Preparation of Potassium-Doped Catalyst 28 Ammonium vanadate, NH4U03 (2.55 g; 0.022 mole), was added to 100 ml of water and the mixture was heated to 60°C to promote dissolution. The temperature of the solution was raised to about 97°C and ammonium heptamo-lybdate (NH~)6Mo702~~H20 (18.5 g; 0.015 mole) was added with stirring. The resulting solution was boiled until the volume was reduced to 70 ml, whereupon magnesia (3~
g; 0.85 mole) was added to yield a thick paste. An additional 50 ml of water was added to the thick paste to give a smooth creamy mixture. The cream was poured 36,823A-F -63--6~- ~0~~~~~
into a quartz crucible, air dried overnight, dried at -- 110°C for two hours and caleined at 600°C for two more hours to yield a calcined solid containing 4 weight percent X205, 30 weight percent Mo03, and 65 weight percent ~IgO, Next, 8.2 ml of a methanolic solution containing potassium hydroxide (1 g KOH/100 ml solution) was diluted to a total of 16 ml volume with additional methanol. The diluted solution was added dropwise to the calcined solid (7.8 g), prepared hereinabove. The potassium hydroxide-impregnated solid was air dried for 30 minutes, then oven dried at 100°C for one hour. The resulting solid comprised vanadium oxide, magnesium oxide, molybdenum oxide and about 1 weight percent potassium calculated as the hydroxide.
(b)Oxidation of Butane Employing Catalyst 28 Catalyst 28, prepared hereinabove, was employed in the oxidation of butane according to the procedure described in Examples 16-20 hereinbefore. The results were set forth in Table Tx.

36,823A-F -6u--b5- ~~~~~ ~ 3 TABLE IX'~
Example CE 3 28 Weight % Alkali 0 1 Conversion 50 50 Seleetivitiese butenes 9.1 15.3 butadiene 51.1 58.2 Total C4's 60.3 73.5 CO + C02 32.7 16.9 g C4/g cat hr 0.15 0.15 ~ Feedstream contains 20 vol. percent butane and 80 vol. percent nitrogen; T = 540°C; Flow = 125 ml/min; 20 cycles.
It is observed that butane was oxidized pre-dominantly to butadiene and butenes in the presence of a catalyst containing magnesium molybdate, vanadium oxide and potassium ions.
Comparative Example 3 (CE 3).
A comparative material was prepared as in Exam-ple 28 hereinabove, with the exception that the catalyst was not impregnated with potassium hydroxide. The com-parative material contained 4 weight percent V205, 30 weight percent Mo03, and 66 weight percent MgO. The comparative material was employed in the oxidation of butane according to the procedure described in Examples 16-20 hereinbefore. The results are set forth in Table IX. When Comparative Example 3 is compared with Example 2$, it is seen that the presence of potassium promoter 36,823A-F -65--.66_ in the catalyst significantly increases the selectiv-.__ ities for butadiene and butanes, and decreases the selectivity for deep oxidation products.
Example 29 (a)Preparation of Potassium-Promoted Catalyst 29 Ammonium heptamolybdate, (NH~)6Mo702~~~IH20 (13.5 g; 0.011 moles), was dissolved in 120 ml of water, and the resulting mixture was heated to 60°C to make a solution. Magnesium oxide (39 g) was added to the solu -tion gradually over a period of 5 minutes and with vig-orous stirring to make a smooth slurry. The slurry was dried at 110°C overnight to obtain a cake, which was calcined in air at 600°C for two hours to yield a magnesium oxide-molybdenum oxide mixture. The powdery oxide mixture was densified by pressing with 20,000 pounds force in a Carver press to yield a 1 1/8-inch (28.6 mm) pellet. The pellet was broken into several pieces and impregnated with a methanolie solution of potassium hydroxide containing 1 g KOH per 100 ml methanol. A loading of 0.5 weight percent potassium hydroxide was achieved. The potassium hydroxide--impregnated magnesium molybdate catalyst is air dried for 2 hours, then dried in an oven at 110°C for 2 additional hours.
_(b)Oxidation of Butane Employing Catalyst 29 The potassium hydroxide-impregnated magnesium molybdate catalyst (Catalyst 29, 7.15 g), prepared hereinabove, was loaded into the tubular reactor oper-ating in the pulse mode as in Examples 16-20, described 36,823A-F -66-hereinbefore. sutane was oxidized under reaction con--- ditions and with the results set forth in Table '~.

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36,823A-F -6g-The data show that butane is oxidized in the presence of -- a potassium-doped magnesium molybdate catalyst to buta-diene and butanes, predominantly. Moreover, it is observed that at constant temperature and gas hourly space velocity, the butadiene space-time yield increases significantly with increasing percentage of butane in the feed. Under the same conditions, the conversion of butane and the selectivity to butadiene is maintained at a high level. The same observations are made for the sum of the C4 (butadiene and butanes) space-time yield and selectivity.

36,823A-F -69-

Claims (36)

1. A process of preparing an unsaturated aliphatic hydrocarbon comprising contacting an aliphatic hydrocarbon having at least three carbon atoms with a solid heterogeneous catalyst having labile oxygen under conditions such that an unsaturated aliphatic hydrocarbon is produced in a selectivity of at least about 50 mole percent, the catalyst consisting essentially of an oxide of magnesium, an oxide of molybdenum, and a Group IA alkali metal promoter in a concentration of from 0.1 weight percent to 5 weight percent calculated as the alkali hydroxide and based on the combined weight of the magnesium and molybdenum oxides, and optionally containing an oxide of vanadium.

2. A process of preparing an unsaturated aliphatic hydrocarbon comprising contacting an aliphatic hydrocarbon having at least three carbon atoms with a solid heterogeneous catalyst composition having reactive oxygen under conditions such that an unsaturated aliphatic hydrocarbon is produced in a selectivity of at least about 40 mole percent, the catalyst composition comprising (a) a support component containing magnesia and at least one aluminum oxide selected from the group consisting of Al2O3 and MgAl2O4, the support having a MgO/Al2O3 weight ratio in the range of from 0.30 to 4.0, and a surface area of at least 25 m2/g; and (b) a catalyst component consisting essentially of an oxide of magnesium, an oxide of molybdenum, and a promoting amount of an alkali metal promoter in a concentration of 0.05 weight percent to 5 weight percent, calculated as alkali hydroxide and based on the total weight of the aluminum, magnesium, and molybdenum oxides.

3. The process of Claim 1 or 2 wherein the aliphatic hydrocarbon is an alkane represented by the general formula:
CH3-(CH2)n-CH3 wherein n is an integer from 1 to 8.

4. The process of Claim 1 or 2 wherein the aliphatic hydrocarbon is diluted with a non-reactive gas.

5. The process of Claim 1 or 2 wherein the hydrocarbon concentration ranges from 40 mole percent to 100 mole percent.

6. The process of Claim 1 or 2 wherein the oxide of magnesium and the oxide of molybdenum are partially combined in the form of magnesium molybdate.

7. The process of Claim 1 or 2 wherein the alkali metal promoter is an alkali metal oxide, hydroxide, carbonate, acetate, or oxalate.

8. The process of Claim 1 or 2 wherein the alkali metal promoter is an oxide, hydroxide, carbonate, acetate, or oxalate of cesium or potassium.

9. The process of Claim 2 wherein the weight ratio of magnesia to alumina is in the range of from 0.30 to 2Ø

10. The process of Claim 1 or 2 wherein the temperature is in the range of from 400oC to 700oC.

11. The process of Claim 1 or 2 wherein the aliphatic hydrocarbon partial pressure is in the range of from subatmospheric to 100 psig (690 kPa gauge).

12. The process of Claim 1 or 2 wherein the gas hourly space velocity of the feedst:ream is in the range of from 100 hr-1 to 20,000 hr-1.

13. The process of Claim 1 or 2 wherein the unsaturated aliphatic hydrocarbon i.s a diolefin and wherein the diolefin is represented by the general formula:
CH2=CH-CH=CH- ( C:H2 ) m-H
wherein m is an integer from 0 to 6.

14. The process of Claim 1 or 2 wherein the catalyst composition has an attrition number less than 5 weight percent hr-1.

15. A process of preparing an unsaturated aliphatic hydrocarbon comprising contacting an aliphatic hydrocarbon having at least three carbon atoms with a solid heterogeneous catalyst composition containing reactive oxygen under conditions such that an unsaturated aliphatic hydrocarbon is produced in a selectivity of at least 40 mole percent, the catalyst composition comprising (a) a support component containing magnesia and at least one aluminum oxide selected from the group consisting of Al2O3 and MgAl2O4, the support having a MgO/Al2O3 weight ratio in the range of from 0.30 to 4.0, and a surface area of at least 25 m2/g; and (b) a catalyst component consisting essentially of an oxide of magnesium, an oxide of molybdenum, an oxide of vanadium and a promoting amount of an alkali metal promoter in a concentration of 0.05 weight percent to 5 weight percent, calculated as alkali hydroxide and based on the total weight of the aluminum, magnesium, and molybdenum oxides.

16. A process of preparing 1,3-butadiene comprising contacting n-butane with a solid heterogeneous catalyst composition containing reactive oxygen at a temperature in the range of from 500°C to 650°C, and a pressure in the range of from 1 psig to 30 psig (7 to 207 kPa gauge) and under such other reaction conditions that a mixture of products is formed containing 1,3-butadiene in a selectivity of at least 40 mole percent, said catalyst comprising (a) a support component containing magnesia and at least one aluminum oxide selected from alumina and magnesium aluminate spinet, the support having a MgO/Al2O3 weight ratio in the range of from 0.3 to 4.0, and a surface area of at least 25 m2/g, and (b) a catalytic component consisting essentially of magnesia, molybdenum oxide, and an alkali metal promoter in a concentration of from 0.05 weight percent to 5 weight percent calculated as the alkali hydroxide and based on the total weight of the aluminum, magnesium and molybdenum oxides.

17. A process of preparing 1,3-butadiene comprising contacting n-butane with a solid heterogeneous catalyst containing labile oxygen at a temperature in the range of from 500°C to 650°C, and a pressure in the range of from 1.5 psia (10.5 kPa) to 30 psia (207 kPa), and a gas hourly space velocity in the range of from 400 hr-1 to 4,000 hr-1, and under such other reaction conditions that a mixture of products is formed containing 1,3-butadiene in a selectivity of at least 50 mole percent, said catalyst consisting essentially of a magnesium oxide, a molybdenum oxide, a Group IA alkali metal promoter in a concentration of from 0.1 weight percent to 5 weight percent calculated as the alkali hydroxide and based on the weight of the magnesium-molybdenum oxides, and optionally, an oxide of vanadium.

18. The process of Claim 15, 16 or 17 wherein the selectivity to butadiene is at least 60 mole percent.

19. The process of Claim 15, 16 or 17 wherein the selectivity to butadiene is at least 70 mole percent.

20. The process of Claim 15, 16 or 17 wherein the productivity of butadiene is at least 0.4 g/g cat-hr.

21. The process of Claim 15, 16 or 17 wherein the productivity of butadiene is at least 0.9 g/g cat-hr.

22. A solid heterogeneous catalyst composition capable of providing a reactive form of oxygen comprising (a) a support component of magnesia and at least one aluminum oxide selected form alumina (Al2O3) and magnesium aluminate (MgAl2O4), the support having a MgO/Al2O3 weight ratio in the range of from 0.3 to 4.0 and a surface area of at least 25 m2/g; an (b) a catalyst component consisting essentially of an oxide of magnesium an oxide of molybdenum, and a promoting amount of a Group IA alkali metal promoter in a concentration of 0.05 weight percent to 5 weight percent, calculated as alkali hydroxide and based on the total weight of the aluminum, magnesium, and molybdenum oxides.

23. A solid heterogeneous catalyst composition consisting essentially of an oxide of magnesium, an oxide of molybdenum, and a Group IA alkali metal promoter in a concentration of from 0.1 weight percent to 5 weight percent calculated as alkali hydroxide and based on the weight of the combined magnesium and molybdenum oxides, and optionally containing an oxide of vanadium, said composition being capable of providing a labile form of oxygen.

24. The catalyst of Claim 22 or 23 wherein the molybdenum oxide concentration ranges from 3 weight percent Mo03 to 50 weight percent Mo03 based on the total weight of the aluminum, magnesium and molybdenum oxides.

25. The catalyst of Claim 22 or 23 wherein the molybdenum oxide concentration ranges from 10 weight percent Mo03 to 30 weight percent Mo03 based on the total weight of the aluminum, magnesium and molybdenum oxides.

26. The catalyst of Claim 22 wherein the Mg0/Al203 weight ratio ranges from 0.3 to 2Ø

27. The catalyst of Claim 22 or 23 wherein the alkali metal promoter concentration ranges from 0.1 weight percent to 2 weight percent.

28. The catalyst of Claim 22 or 23 wherein the alkali metal promoter concentration ranges from 0.3 weight percent to 1.5 weight percent.

29. The catalyst of Claim 22 or 23 wherein the alkali metal promoter is an alkali metal oxide, hydroxide, carbonate, acetate, or oxalate.

30. The catalyst of Claim 22 or 23 wherein the alkali metal promoter is an oxide or hydroxide of potassium or cesium.

31. The catalyst of Claim 22 having an attrition number less than 5 weight percent hr-1.

32. The catalyst of Claim 22 having a crush strength of at least 5 lb (2270 g).

33. The catalyst of Claim 22 or 23 having a particle size in the range of from 500 µm to 1200 µm.

34. A solid heterogeneous catalyst composition capable of providing a reactive form of oxygen comprising (a) a support component of magnesia and at least one aluminum oxide selected from alumina (Al2O3) and magnesium aluminate (MgAl2O4), the support having a MgO/Al2O3 weight ratio in the range of from 0.3 to 4.0 and a surface areas of at least 25 m2/g; and (b) a catalyst component consisting essentially of an oxide of magnesium, an oxide of molybdenum, an oxide of vanadium and a promoting amount of a Group IA alkali metal promoter in a concentration of 0.05 weight percent to 5 weight percent, calculated as alkali hydroxide and based on the total weight of the aluminum, magnesium, and molybdenum oxides.

35. The process of preparing the catalyst of Claim 22 comprising (a) forming a gel from a mixture of colloidal alumina and magnesia, (b) drying the gel to form a powder, (c) calcining the powder to form a support, and (d) impregnating the support with a solution of a molybdenum salt and a Group IA alkali metal promoter.

36. A process of preparing a solid heterogeneous catalyst composition consisting essentially of an oxide of magnesium, an oxide of molybdenum, and a Group IA alkali metal promoter in a concentration from 0.1 weight percent to 5 weight percent calculated as alkali hydroxide and based on the weight of the combined magnesium and molybdenum oxides, said composition being capable of providing a labile form of oxygen, the process comprising (a) preparing a solution of an oxide of molybdenum or a precursor thereof, (b) pouring said solution over magnesium oxide to form a slurry, (c) calcining said slurry at a temperature sufficient to form a magnesium oxide and molybdenum oxide mixture having a composition in the range of from 6 weight percent to 50 weight percent MoO3, and from 94 weight percent to 50 weight percent MgO, and (d) impregnating said oxide mixture with a solution of a Group IA alkali metal promoter such that the concentration of alkali is in the range of from 0.1 weight percent to 5 weight percent calculated as the alkali metal hydroxide and based on the weight of the magnesium-molybdenum oxide mixture.