CATALYST COMPOSITION WITHOUT ANTIMONY OR MOLYBDENUM FOR AMMOXIDATION OF ALKANES, A PROCESS OF MAKING AND A

PROCESS OF USING THEREOF

SPECIFICATION

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION: The invention relates to a catalyst for the catalytic ammoxidation of alkanes, more specifically C ₃ to C ₅ paraffins, such as propane or

isobutane, to the corresponding α,β-unsaturated mononitriles, e.g. acrylonitrile and

methacrylonitrile. The disclosed catalyst can be utilized also for the ammoxidation of olefins, such as propylene and isobutylene, to the same nitriles. In addition, the catalyst may be used in the ammoxidation of xylenes and methylpyridines to the corresponding mono- and dinitriles.

The invention is directed also to making the catalyst by precipitating, drying and calcining the catalyst precursor to produce active phases with the right proportion. The invention is directed also to using the catalyst in a process for catalytic ammoxidation of alkanes.

DESCRIPTION OF THE PRIOR ART: Nitriles, such as acrylonitrile and methacrylonitrile, are useful as intermediates for the preparation of fibers, synthetic resins, synthetic rubbers, and the like. One method for producing such nitriles is a gas phase reaction at a high temperature of an olefin, such as propene or isobutene, with ammonia and oxygen in the presence of a catalyst. Known catalysts for conducting this reaction include Mo-based and Sb-based oxides. However, in view of the price difference between propane and propene or between isobutane and isobutene, there are advantages

for ^' dlvilϋφfcfeήt ^" δf'^'rfϊέtMbd for producing acrylonitrile or methacrylonitrile by an ammoxidation reaction with a lower alkane, such as propane or isobutane, as a starting material, which is catalytically reacted with ammonia and oxygen in a gaseous phase in the presence of a catalyst. The majority of effective catalysts reported for propane ammoxidation generally contain vanadium oxides in combination with oxides of antimony and/or molybdenum.

A number of patents assigned to the Standard Oil Company disclose V-Sb oxide catalysts promoted with different elements and various procedures for preparation of those. For instance, U.S. Patent nos. 4,746,641 and 4,797,381 disclose paraffin ammoxidation catalysts that contain tungsten in addition to vanadium and antimony. U.S. Patent nos. 4,871,706 and 4,873,215 disclose V-Sb oxide catalysts with tungsten and phosphorus. U.S. Patent no. 5,079,207 discloses a catalyst with tellurium or bismuth in addition to vanadium-antimony. Bismuth is also optionally present in the vanadium- antimony based catalyst claimed in the U.S. Patent no. 6,162,760. U.S. Patent no. 5,336,804 discloses vanadium-antimony based catalysts in which bismuth is always present and iron, gallium, indium and mixtures thereof are optionally present.

A molybdenum-based catalyst for propane ammoxidation is the Mo-V-Nb-Te oxide system is disclosed in the U.S. Patent no. 5,281,745. This catalyst may optionally contain tungsten, bismuth and other elements. U.S. Patent no. 4,978,764 discloses Bi-Fe- Mo based oxide catalysts in which bismuth must be present and tungsten is optionally present. U.S. Patent no. 5,470,815 describes In-Ga-Bi-Mo based oxide catalysts that contain always bismuth and optionally tungsten. U.S. Patent no. 4,760,159 discloses a propane ammoxidation catalyst having the formula Bi _a V _b LiM _m T _t O _x , in which Bi, V, M

(selected Worn among Mo, W, Cr, Ge and Sb) and oxygen are necessarily present. From a number of examples set forth in this patent, it comes that best selectivities to acrylonitrile are obtained on catalysts containing vanadium, bismuth and molybdenum and, optionally, another metal such as chromium, potassium, zinc, cesium or antimony. One example uses a catalyst based on vanadium, bismuth and tungsten of the formula Bi ₁ V ₀ . ₇ W ₀ . ₅ Ox and deposited onto a silica/alumina mixture in an amount of 50% by weight. This catalyst, however, produces acrylonitrile with the selectivity considerably lower than that attained on catalysts containing molybdenum.

U.S. Patent nos. 4,111,983 and 4,289,654 claim an improved process for acrolein oxidation to acrylic acid using Mo-V based oxide catalysts, which necessary contain tungsten. Bismuth is not mentioned even to be an optional element. U.S. Patent no. 6,693,059 describes a method for preparing catalyst for propane oxidation to acrylic acid having the formula W ₃ VbX _x YyO _n , wherein X is at least one element selected from the group consisting of Te, Bi, Sb and Se. The examples listed in this patent use catalysts that contain tellurium along with tungsten and vanadium. None of them contains bismuth. Also, there is no mention of the usefulness of these catalysts for ammoxidation reactions.

U.S. Patent no. 6,514,902 discloses a process for producing acrylonitrile or methacrylonitrile from propane or isobutane with a catalyst containing at least molybdenum, vanadium and antimony and optionally niobium, tungsten, chromium, titanium, tantalum, zirconium, hafnium, manganese, rhenium, iron, ruthenium, cobalt, rhodium, nickel, palladium, platinum, copper, silver, zinc, boron, gallium, indium, germanium, tin, tellurium, phosphorus, lead, bismuth, rare earth elements and alkaline

''"' ekth'tøeffls'^brMrFtKS iatSlyst is made by subjecting a raw material mixtures solution or slurry to an oxidation treatment.

U. S. Patent no. 4,883,895 discloses a process of catalytic ammoxidation of propane and isobutane to acrylonitrile and methacrylonitrile with a first catalyst composition containing vanadium, phosphorus, tungsten, one or more of iron, cobalt, nickel, chromium, lead, manganese, zinc, selenium, tellurium, gallium, zirconium, indium or arsenic, one or more of an alkali metal or thallium, optionally, one or more of tin, molybdenum, boron, germanium and, optionally, one or more of calcium, strontium, magnesium, and barium, and a second composition containing bismuth, iron, molybdenum, optionally one or more of an alkali metal, samarium or silver, optionally one or more of manganese, chromium, copper, vanadium, zinc, cadmium or lanthanum, optionally one or more of phosphorus, arsenic, antimony, tellurium, tungsten, boron, tin, lead or selenium and optionally, one or more of cobalt, nickel or alkaline earth metal. In the first catalyst composition, molybdenum is present at no more than 2 atoms per atom of vanadium, bismuth is present at no more than 0.2 atoms per atom of vanadium, antimony is present at no more than 0.01 atom per atom of vanadium and the first catalyst composition is essentially uranium free.

All the above patent documents describe selective oxidation catalysts containing vanadium in combination with antimony or/and molybdenum as major constituents. Among numerous complementary elements, tungsten and bismuth are mentioned. The present invention discloses ammoxidation catalysts in which tungsten and bismuth along with vanadium are basic elements. The claimed catalysts do not contain antimony and

mόlyb ^" denύπϊ "M aH"be"ca'us"e the presence of these elements deteriorates catalyst behavior in the ammoxidation of propane to acrylonitrile.

SUMMARY OF THE INVENTION

The present invention provides mixed metal oxide catalysts containing vanadium, tungsten and bismuth for the ammoxidation of paraffins to unsaturated mononitriles, in particular the ammoxidation of propane and isobutane to acrylonitrile and methacrylonitrile, respectively.

The present invention provides a method for preparing mixed vanadium-tungsten- bismuth oxides having a phase composition catalytically active in propane ammoxidation to acrylonitrile.

The present invention provides an ammoxidation process for making unsaturated mononitriles from lower paraffins, in particular for producing acrylonitrile and methacrylonitrile from propane and isobutane, using mixed metal oxide catalysts based on vanadium, tungsten and bismuth.

Embodiments, aspects, features and advantages of the present invention will become apparent from the study of the accompanying disclosure and appended claims.

According to one aspect of the invention, there is provided a catalyst system comprising the elements in proportions indicated by the following empirical formula:

VW _a Bi _b M _c 0χ where M is at least one element selected from sodium, cesium, magnesium, calcium, barium, boron, yttrium, indium, aluminum, gallium, tin, titanium, silicon, zirconium, germanium, niobium and tantalum;

0.5 < b < 5

O ≤ c ≤ lO and

x is determined by the valence requirements of the elements present.

In another aspect of the present invention, there is a method of preparing a catalyst having the following empirical formula:

VW _a Bi _b M _c 0χ where M, a, b, c and x are as defined above. The method comprises precipitating catalyst precursor from a solution or suspension of vanadium, tungsten, bismuth and M compounds as desired to obtain a particular catalyst composition, removing solvent from the precipitate to form a dried catalyst precursor, and calcining the resultant dried

precursor at a final temperature in the range of 500 to 900°C to form the catalyst with a

certain phase composition.

The present invention provides also a process for making α,β-unsaturated

mononitriles by gas phase reaction of propane or isobutane, oxygen and ammonia in the presence of a catalyst having the elements and proportions indicated by the empirical formula:

VW _a Bi _b M _c O _x where M, a, b, c and x are as defined above.

The catalyst may also be used in the ammoxidation of propylene and isobutylene to acrylonitrile and methacrylonitrile, and in the ammoxidation of xylenes and methylpyridines to the corresponding mono- and/or dinitriles.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:

Figure 1 : Effect of the presence of antimony in a vanadium-tungsten-bismuth catalyst on propane conversion and acrylonitrile selectivity at 500 ⁰ C

Figure 2: Effect of the presence of molybdenum in a vanadium-tungsten-bismuth catalyst on propane conversion and acrylonitrile selectivity at 500° C

Figure 3: XRD patterns of catalysts prepared in Examples 3 and 6

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention is for a catalyst comprising the elements in proportions indicated by the following empirical formula:

VW _a Bi _b M _c O _x where M is at least one element selected from sodium, cesium, magnesium, calcium, barium, boron, yttrium, indium, aluminum, gallium, tin, titanium, silicon, zirconium,

germanium, niobium and tantalum; 0.2 < a < 10; 0.5 < b < 5; 0 ≤ c < 10 and x is

determined by the valence requirements of the elements present. In one embodiment of the invention, M is one element selected from the group consisting of sodium, magnesium, gallium, yttrium, boron, titanium, tin, silicon, zirconium, germanium, aluminum and niobium. In another embodiment of the invention, M are two elements, one selected from aluminum and niobium and one selected from gallium, indium, sodium,

t'kiklutøϊ' with the two elements being different. The catalyst composition of the present invention can contain oxides of elements other than those set forth as long as they do not have a material detrimental effect on the catalyst performance. The M elements or any additional elements may become part of the catalyst composition by co-precipitation with vanadium, tungsten and bismuth or by impregnation by any means known in the art, including incipient wetness, before or after calcination of the catalyst precursor to form the catalyst.

In the method of making the present invention, firstly a catalyst precursor is prepared by precipitation from a solution of compounds of vanadium, tungsten, bismuth and, optionally, M with no compounds of antimony or molybdenum present. In this description, "solution" includes not only a solution wherein a solute is completely dissolved but also a solution in a slurry state wherein a part of the solute is present as undissolved.

The vanadium, tungsten, bismuth and M compounds are preferably to be soluble in water. When material is insoluble in water, an acid or alkali may be added to the solution or the solution may be heated to facilitate dissolution. An example of an acid added to the solution to facilitate dissolution is nitric acid. The solution may be heated to

a temperature of from 40 to 90 ⁰ C to facilitate the dissolution. Generally, a solution can

be prepared by dissolving two and more compounds and then adding the remaining compounds, for instance by adding the vanadium compound to the mixed solution of the tungsten, bismuth and optional M compounds. In the alternative, solutions of each of the vanadium, tungsten, bismuth or M compounds can be prepared separately and the separate solutions mixed.

Exemplar^ YaiikffiuTfti compounds soluble in water include, without limitation, ammonium metavanadate, vanadyl acetylacetonate, vanadyl chloride, vanadium pentafluoride and other vanadium halides. Exemplary tungsten compounds soluble in water include, without limitation, ammonium tungstates and tungstic acids. Exemplary bismuth compounds include, without limitation, bismuth nitrate, bismuth halides and oxyhalides, bismuth sulfate, bismuth acetate and other bismuth organic salts. The compounds containing an element represented by M include, without limitation, nitrate, chloride, carbonate, oxalate, hydroxide and other preferably soluble compounds.

Separate solutions of these compounds may be admixed or the compounds may be commonly dissolved in a solution to precipitate a catalyst precursor to form a suspension. The precipitation can be carried also with addition, for example, of aqueous ammonia or hydrochloric acid during or at the end of mixing of the salts. This procedure may include obtaining and maintaining, if needed, a given pH. The pH may be adjusted to be within a range of 5 to 10, preferably about 8. It is preferable to heat the suspension to a temperature from 30 to 90°C to drive the precipitation of the precursor to completion.

In the next step, the precipitate is separated from the solvent liquid by any conventional technique known in the art. Examples for the present invention are filtration and evaporation. To evaporate the solvent, the suspension is heated to a temperature ranging from 30 to 100°C until a viscous paste is obtained, which is then dried at atmospheric pressure at a temperature ranging from 30 to 200°C, preferably from 100 to 150°C. The dried catalyst precursor is calcined with final temperature ranging from 500 to 900 ⁰ C, most preferably from 550 to 650°C, in different atmospheres, preferably in air.

ωie*§ompσsϊte' ^~ όxid:©s of vanadium, tungsten and bismuth thus obtained can comprise different individual and mixed oxide phases. The presence of particular mixed oxides of bismuth and vanadium or of bismuth and tungsten, such as BiVO ₄ and Bi ₂ WO ₆ , positively affects catalyst behavior in terms of its selectivity, while individual oxides, such as V ₂ O ₅ , WO ₃ and Bi ₂ O ₃ , affect negatively by making the catalyst less selective. Provided the appropriate ratios of vanadium, tungsten and bismuth are present and provided a preparation procedure which includes precipitating vanadium, tungsten and bismuth into a mixed metal oxide catalyst precursor and drying and calcining the catalyst precursor as described in the present patent application, catalysts in which mixed oxides, e.g., BiVO ₄ and Bi ₂ WO ₆ , predominate over individual oxides, e.g., V ₂ O ₅ , WO ₃ and Bi ₂ O ₃ , can be produced. To produce mixed oxides of bismuth and vanadium or of bismuth and tungsten, such as BiVO ₄ and Bi ₂ WO ₆ , the molar ratio of bismuth: vanadium:molybdenum from the compounds in solution should be at least 3:1:1. Catalysts containing M elements may comprise, in addition to the above-listed oxides, tricomponent oxide phases. For instance, a niobium-containing catalyst may have the Bi ₃ W ₁ Nb ₉ O _3O phase which may contribute to enhanced selectivity.

The catalyst can be employed in the powder form or be shaped, for example, as beads, spheres, pellets, extrudes or crushed particles, according to various known techniques. For the examples below, freshly prepared catalysts were ground to fine powder, tabletted at 20 Kpsi, crushed, sieved to 18-30 mesh and loaded to the reactor.

In an ammoxidation process, the reaction is run in the gas phase by contacting a mixture containing paraffin, ammonia and molecular oxygen, and diluent, if any, with the catalyst of the present invention. The catalyst may be in a fixed bed, or a fluidized bed or

a άiøviigωtøed- ^1' (iM&'Wimibr). There may be one or more catalyst used in the ammoxidation process, but preferably one catalyst. The mole ratio of paraffin to ammonia is usually in the range from 0.5 to 10, preferably from 1 to 2.5, and the mole ratio of paraffin to oxygen is usually from 0.1 to 10, preferably from 0.5 to 2. The mole ratio of gaseous diluent, e.g., N ₂ , He ₅ Ar, CO ₂ and H ₂ O, to paraffin usually ranges from 0 to 20, preferably from 0 to 10. Higher molar ratios can be used but are usually uneconomical.

In the present process, the paraffin as the starting material is not particularly limited, and it may be any lower alkane having from 2 to 8 carbon atoms. However, from the viewpoint of industrial application of the obtainable nitriles, it is preferred to employ propane or isobutane. Low-weight olefins, such as propylene and isobutylene, can also be employed for production of acrylonitrile and methacrylonitrile, respectively. The process according to the invention is more particularly suitable for the ammoxidation of propane.

The reaction temperature can vary from 350 to 550°C, preferably from 425 to

500°C. The latter temperature range is especially useful in the case of propane

ammoxidation to acrylonitrile.

The pressure of the reaction can be greater than or equal to atmospheric pressure. It advantageously ranges from 1 to 40 psig. Preferably, pressure is 1 to 20 psig.

The effective contact time is in the range from 0.01 to 10 seconds, but is preferably from 0.05 to 8 seconds, more preferably from 0.1 to 5 seconds.

The most advantageous combination of temperature, pressure and contact time for a given desired result from a given feed can be determined by routine experimentation.

'ϊlffiipresrøtSiSθiδioin is described in further detail in the following Examples. However, it should be understood that the present invention is by no means restricted to such specific Examples.

EXAMPLE 1

In a 800 ml beaker, a solution of bismuth nitrate was prepared by dissolving at 40°C 12.1 g of Bi(NOs) ₃ ^H ₂ O in the diluted nitric acid prepared by mixing concentrated acid and de-ionized water in the proportion of 1:8. After 5 minutes of stirring, 0.77 g of solid (NH ₄ ) ₆ W ₁₂ θ ₃₉ was added to the bismuth nitrate solution to obtain white slurry. To this slurry, 1.81 g of solid NH ₄ VO ₃ was added in small portions at 8O ⁰ C and stirred for five minutes to obtain yellow-green slurry. In the next step, water was evaporated by heating the slurry on a hot plate under continuous stirring until the orange-brown paste formed. The paste was transferred to a porcelain dish and dried for 6 hours at 12O ⁰ C in the air flow of 250 niL/min. After drying was over, the temperature in the oven was raised to 32O ⁰ C at 20°C/min and catalyst precursor was pre-calcined at this temperature for 4 hours. Then the temperature was raised to 520 ⁰ C at 20°C/min and the solid was calcined at this final temperature for 6 hours. The product thus prepared had yellow color and nominal composition VW _0-2 Bi _L6 O _x . For testing in propane ammoxidation to acrylonitrile, it was ground to fine powder, pressed and sieved to 16-30 mesh.

EXAMPLES 2-7

The catalysts were prepared in the same manner as described in Example 1 except for the following:

1. The amount of ammonium metavanadate was doubled to be 3.62 g.

2. The amounts of ammonium paratungstate and bismuth nitrate are listed in Table 1

3. The resultant compositions were different from Example 1.

4. The physical appearance of the catalyst precursor (paste) and of the finished catalyst and the nominal composition of the catalyst are shown in Table 1.

TABLE l

EXAMPLE 8

In a 800 ml beaker, 12.1 g of Bi(NO ₃ ) ₃ -5H ₂ O was dissolved at 42°C in 45 ml of the diluted nitric acid prepared by mixing 1 part concentrated acid and 8 parts of de- ionized water. After five minutes of stirring, 3 g of solid (NH ₄ ) ₆ W ₁₂ O ₃₉ was added to the above solution at 60°C to obtain white slurry. To this slurry, a solution of 0.13 g of NaNO ₃ in 30 ml of de-ionized water was added and stirred to increase the temperature to 75°C. At this temperature, 1.81 g of solid NH ₄ VO ₃ was added in small portions and stirred five minutes to obtain light yellow-green slurry. Then the slurry was heated on a

lαt ^' ffeli ^! if6ueva|xbϊaf@fiie3water until orange-brown paste formed. This paste was transferred to a porcelain dish and placed into the oven for drying and calcination in the air flow of 250 mL/min under the following thermal conditions. The temperature in the oven was raised to 12O ⁰ C at 20°C/min and held for 6 hours. Then it was increased to 320 ⁰ C at 20°C/min and held for 4 hours. And finally, the temperature was ramped up to 600 ⁰ C at 20°C/min and held for 6 hours. The catalyst material calcined in this way and cooled to room temperature had yellow color and nominal composition of VWo. ₈ Bi ₁ . ₆ Nao. ₀₅ O _x . For testing in the ammoxidation of propane to acrylonitrile, it was ground to a fine powder, pressed and sieved to 18-30 mesh.

EXAMPLES 9-20

The catalysts in these examples were prepared using the procedure similar to that described in Example 8 including the amounts of ammonium metavanadate, ammonium paratungstate and bismuth nitrate used in preparations. The difference was that instead of sodium nitrate different compounds had been used to prepare catalysts containing other optional M elements in different proportions. The chemical formulae and amounts of utilized M compounds are listed in Table 2 along with the color of catalyst precursor and appearance and composition of finished catalysts.

TABLE 2

EXAMPLE 21

Using 800 ml beaker, a solution of bismuth nitrate was prepared by dissolving at room temperature 12.1 g of Bi(NO ₃ ) ₃ -5H ₂ O in 45 ml of the diluted nitric acid prepared by mixing concentrated acid and de-ionized water in the proportion of 1:8. After stirring this solution for five minutes, 3 g of solid (NH ₄ ) ₆ W ₁₂ O ₃₉ was added to obtain white slurry. To this slurry, 0.78 g of solid Ga(NO ₃ ) ₃ was added, and the mixture was heated to increase the temperature to 45°C. Once this temperature was attained, 2 g of solid NbCl ₅ were added in small portions. An exothermic reaction took place that increased the temperature to 62°C and changed the color of the slurry to light yellow. Then a solution of 1.82 g OfNH ₄ VO ₃ in 50 ml of de-ionized water was added to this slurry at 95°C and stirred five minutes to obtain orange precipitate. To separate the precipitate by evaporation of water, the mixture was heated to 95°C and maintained at this temperature until brown paste formed. The residue was dried at 12O ⁰ C for 6 hours, pre-calcined at

¥Iθ^U-M^liEm:s M[i ^~ M'My ^z Mcm.ed at 600°C for 6 hours in the air flow of 250 ml/min. The temperature ramp in each step was 20°C/min. Catalyst thus prepared had yellow- grey color and empirical formula VWo _-8 Bi _1-6 Ga _O aNb _O-S O _x . For testing in propane ammoxidation, it was ground to a fine powder, pressed and sieved to 18-30 mesh.

EXAMPLE 22

In a 800 ml beaker, a solution of bismuth nitrate was prepared by dissolving at 40°C 12.1 g of Bi(NO ₃ ) ₃ -5H ₂ O in 45 ml of the diluted nitric acid prepared by mixing one part of concentrated acid and eight parts of de-ionized water. Under stirring, the temperature of solution was raised to 6O ⁰ C and 3 g of solid (NH ₄ ) _O W ₁₂ O ₃₉ was added to obtain white slurry. The temperature of this slurry was increased to 70°C to add 5.84 g of solid A1(NO ₃ ) ₃ -9H ₂ O and then to 8O ⁰ C to add 2.48 g of solid In(NO ₃ ) ₃ η ₂ O. The resultant mixture was heated to 95°C and a solution of 1.82 g Of NH ₄ VOs in 50 ml of de-ionized water was added under stirring to precipitate catalyst precursor of orange color. The water was evaporated by heating the slurry at 95 ⁰ C until yellow paste formed. The paste was then transferred to a porcelain dish and dried at 120 ⁰ C for 6 hours in the air flow of 250 rnL/min. Dried precursor was pre-calcined at 32O ⁰ C for 4 hours and finally calcined at 600 ⁰ C for 6 hours. In both procedures the temperature was increased at 20°C/min. The catalyst thus prepared had yellow color and nominal composition VWo _-8 Bi _I-6 Al _11O In _0-5 O _x . For testing in propane ammoxidation reaction, it was ground to a fine powder, pressed and sieved to 18-30 mesh.

EXAMPLES 23-26

The catalysts were prepared in the same manner as described in Example 22 including the used amounts of ammonium metavanadate, ammonium paratungstate, bismuth nitrate and aluminum nitrate which were respectively 1.82, 3.0, 12.1 and 5.84 g. The difference was that instead of indium nitrate the salts of gallium, sodium, niobium or tantalum were utilized to prepare catalysts containing these metals as one more optional M element. Formulae and amounts of used M compounds are listed in Table 3 along with the color of catalyst precursor and appearance and composition of finished catalysts.

TABLE 3

Catalysts in Examples 1-26 were tested for propane ammoxidation to acrylonitrile in a ¹ A inch LD. silica-coated stainless steel, fixed bed reactor at atmospheric pressure, 500 ⁰ C and flow rate 50 mL/min. The feed consisted of 18% C ₃ H ₈ , 8% NH ₃ , 15% O ₂ and balance He. Contact time was varied by changing catalyst amount loaded to the reactor in the range from 1 to 2.5 cc. Catalyst was mixed with quartz chips to have total volume 5 cc. All reactants and reaction products were analyzed on line by gas chromatography. The results of testing catalysts under these conditions assumed to be standard are

presented in Table 4.

TABLE 4

Exam. Catalyst _C (2) Selectivity (%)

No. composition (S) (%) C ₃ H ₆ AN ^(j) AcN ^w HCN CO _x

1 VWo. ₂ Bii. ₆ O _x 2.4 1.9 6.5 2.1 _ _ 91.4

2 VW _0-5 Bi _1-6 O _x ^■ 2.4 9.3 1.9 56.0 - 5.7 37.8

3 VWc ₈ BiL ₆ O _x 2.4 10.9 1.4 55.0 0.7 8.4 34.6

4 VW ₂ Bi _L6 O _x 2.4 13.6 1.0 46.7 0.9 11.7 39.8

5 VWo. ₈ Bio. ₅ O _x 1.2 14.4 8.4 7.5 2.1 9.0 73.1

6 VWc ₈ Bi ₁ O _x 1.8 11.5 11.3 29.8 0.9 12.6 45.4

7 VWo. ₈ Bi ₂ O _x 3.0 8.7 1.3 39.1 1.8 1.5 56.3

8 VW _0-8 BiL ₆ Na _0-05 O _x 1.5 1.4 11.1 66.7 - 3.2 19.0

9 VW _0-8 BiL ₆ Mg _C o ₅ O _x 3.0 10.0 1.8 53.7 - 8.7 35.9

10 VW _0-8 Bi _1-6 Ga _C5 O _x 1.5 13.0 10.2 56.3 2.1 8.7 22.8

11 VWo _-8 Bi _1-6 Yc ₅ O _x 3.0 5.9 2.2 53.7 0.8 3.7 39.6

12 VW _0-8 BiL ₆ B _0-5 O _x 3.0 7.2 1.0 55.5 - 15.1 28.4

13 VW _0-8 Bi _1-6 Ti _C5 O _x 3.0 17.4 1.3 43.7 1.2 14.9 38.9

14 VW _0-8 Bi _1-6 Sn _0-5 O _x 1.5 8.7 11.7 52.1 1.2 8.8 26.3

15 VW _0-8 Bi _1-6 Si ₁ O _x 1.5 7.4 16.6 51.3 2.0 12.7 17.6

16 VW _0-8 Bi _1-6 Zr ₂ O _x 1.8 12.2 5.1 56.3 1.3 8.3 29.0

17 VW _0-8 Bi _{1 6} Ge _0-5 O _x 3.0 7.3 7.1 57.4 1.1 8.4 26.1

18 VW _0-8 Bi _1-6 Al ₁ O _x 1.8 10.8 4.3 65.1 1.7 8.3 20.7

19 VWo _-8 Bi _1-6 Nb _0-5 O _x 0.9 10.8 4.1 63.8 1.6 12.9 17.7

20 VW _0-8 Bi _1-6 Nb _1-5 O _x 2.1 9.0 5.0 64.6 1.7 12.2 16.5

21 VW _0-8 Bi _1-6 Nb _O-5 Ga _0-2 O _x 1.2 10.8 9.0 60.5 2.0 12.3 16.3

22 VW _0-8 Bi _I-6 Al ₁ In _0-5 O _x 2.4 11.0 9.4 50.7 2.4 4.5 31.5

23 VWc ₈ Bi _1-6 Al ₁ Ga _0-1 O _x 1.8 11.8 9.2 54.4 1.7 11.9 22.8

24 VWo _-8 Bi _1-6 Al ₁ Na _0-05 O _x 2.4 10.0 10.9 55.2 0.9 7.8 25.3 -

25 VWo _-8 Bi _1-6 Al ₁ Nb _0-5 O _x 1.2 14.5 6.0 53.3 1.9 15.4 23.5

26 VW _0-8 Bi _1-6 Al ₁ Ta ₁ O _x 1.2 9.5 10.1 63.8 2.3 10.6 12.9

⁽¹⁾ CT is contact time, seconds ⁽²⁾ C is propane conversion, percent ^AN is acrylonitrile ⁽⁴⁾ AcN is acetonitrile

The catalyst of the present invention does not contain any significant amount of antimony or molybdenum. The essential absence of the antimony and molybdenum is a critical feature of the present invention. The presence of antimony or molybdenum

hegaϊiv5øly.Jιaffecfstt Gataϊyβt-pertormance especially in the ammoxidation of propane to acrylonitrile.

COMPARATIVE EXAMPLE 1

Five antimony-containing catalysts VWo.sBii.βSbyOx where y was 0.25, 0.5, 1, 2, 4, 7 and 10, were prepared by the method described above in Example 8. The only difference was that instead of sodium nitrate we used the antimony trichloride which was added in different amounts to the reference VWo _-S Bi _1-6 O _x catalyst.

In a 800 ml beaker, a solution of bismuth nitrate was prepared by dissolving at 40°C 12.1 g of Bi(NO ₃ ) ₃ .5H ₂ θ in the 38 ml of diluted nitric acid prepared by mixing concentrated acid and de-ionized water in the proportion of 1:8. After 5 minutes of stirring, a solution of 3 g of (NHO ₆ W ₁₂ O ₃₉ in 30 ml of de-ionized water was added at 60°C to the bismuth nitrate solution to obtain white slurry. To this slurry, solid SbCl ₃ .xH ₂ O was added to in small portions via spatula at ~70°C (the amount of added antimony trichloride varied from 1.7 to 68 g to prepare catalysts with different content of antimony). An exothermic reaction occurred and brown fumes of NO ₂ were given off. After 10 minutes of reaction, the color of slurry became white. To this slurry, 1.81 g of solid NH ₄ VO ₃ was added in small portions at 80°C and stirred for 10 minutes to obtain yellow-green slurry which in 15 minutes changed color to red-brown. In the next step, water was evaporated by heating the slurry on a hot plate under continuous stirring until an orange-brown paste was formed. The paste was transferred to a porcelain dish and dried for 6 hours at 12O ⁰ C in an air flow of 250 ml/min. After drying was over, the temperature in the oven was raised to 32O ⁰ C at 20°C/min and catalyst precursor was pre-

for 4 hours. Then the temperature was raised to 600 ⁰ C at 20°C/min and the solid was calcined at this final temperature for 6 hours. After calcinations, yellow-green material was obtained (high antimony catalysts had beige-gray color). For testing in propane ammoxidation to acrylonitrile, it was ground to fine powder, pressed and sieved to 18-30 mesh.

COMPARATIVE EXAMPLE 2

Three molybdenum-containing catalysts VWo _-S Bi _1-6 MOyO _x , where y was 0.5, 1 and 2, were prepared by the method described above in Example 8. The only difference was that instead of sodium nitrate we used the ammonium heptamolybdate which was added in different amounts to the reference VWo. ₈ Bii. ₆ O _x catalyst.

In a 800 ml beaker, a solution of bismuth nitrate was prepared by dissolving at 40°C 12.1 g of Bi(NO ₃ ) ₃ .5H ₂ θ in the 38 ml of diluted nitric acid prepared by mixing concentrated acid and de-ionized water in the proportion of 1:8. After 5 minutes of stirring, a solution of 3 g of (NKU) ₆ W ₁₂ O ₃₉ in 30 ml of de-ionized water was added at 60°C to the bismuth nitrate solution to obtain white slurry. To this slurry, solid (NH ₄ ) _ό Mo ₇ O ₂₄ was added in small portions via spatula at -60° C (the amounts of ammonium heptamolybdate added were 1.4, 2.8 and 5.6 g to prepare catalysts with different content of molybdenum). An exothermic reaction occurred and brown fumes of NO ₂ were given off. After 10 minutes of reaction, the color of slurry became white. To this slurry, 1.81 g of solid NH ₄ VO ₃ was added in small portions at 8O ⁰ C and stirred for 10 minutes to obtain yellow-green slurry which in 20 minutes changed color to orange. In the next step, water was evaporated by heating the slurry on a hot plate under continuous

stirMg lttMTE&tϊ '6τMge^βst& formed. The paste was transferred to a porcelain dish and dried for 6 hours at 120°C in an air flow of 250 ml/min. After drying was over, the temperature in the oven was raised to 320 ⁰ C at 20°C/min and catalyst precursor was pre- calcined at this temperature for 4 hours. Then the temperature was raised to 600 ⁰ C at 20°C/min and the solid was calcined at this final temperature for 6 hours. After calcinations, yellow-gray material was obtained. For testing in propane ammoxidation to acrylonitrile, it was ground to fine powder, pressed and sieved to 18-30 mesh.

Catalysts in the Comparative Examples were tested for propane ammoxidation to acrylonitrile in a ¹ A inch LD. silica-coated stainless steel, fixed bed reactor at atmospheric pressure, 500°C and flow rate 50 mL/min. The feed consisted of 18% C ₃ H ₈ , 8% NH ₃ , 15% O ₂ and balance He. Contact time was varied by changing catalyst amount loaded to the reactor in the range from 0.5 to 2.5 cc. Catalyst was mixed with quartz chips to have total volume 5 cc. All reactants and reaction products were analyzed on line by gas chromatography. The results of testing catalysts under these conditions assumed to be standard are presented in Figures 1 and 2. ^'

Figure 1 shows the propane conversion and the acrylonitrile selectivity for catalysts containing antimony. As the amount of antimony increases over a Sb: V molar ratio of 4:1, the propane conversion decreases. As the amount of antimony increases over a Sb:V molar ratio of 0:1, the acrylonitrile selectivity decreases. Figure 2 shows the propane conversion and the acrylonitrile selectivity for catalysts containing molybdenum. As the amount of molybdenum increases over a Mo: V molar ratio of 0:1, the propane conversion decreases.

^■ AS th6^amcnmt»ol molybiaemiih increases over a Mo:V molar ratio of 0:1, the acrylonitrile selectivity decreases.

As noted above, the presence of particular mixed oxides of bismuth and vanadium or of bismuth and tungsten, such as BiVO ₄ and Bi ₂ WO ₆ , positively affects catalyst behavior in terms of its selectivity, while individual oxides, such as V ₂ O ₅ , WO ₃ and Bi ₂ O ₃ , have a negative effect by making the catalyst less selective. As shown in Figure 3, the XRD pattern for the catalyst prepared in Example 6 which has low selectivity to acrylonitrile shows both BiVO ₄ and WO ₃ phases while the XRD pattern for the catalyst prepared in Example 3 which has high selectivity to acrylonitrile shows primarily BiVO ₄ and Bi ₂ WO ₆ phases with only a trace OfWO ₃ detected.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.