Molybdenum based complex oxide catalyst, its preparation method and use

Abstract

Disclosed are a molybdenum based composite oxide catalyst, its preparation method and use. The catalyst has the following general formula: BiMo.sub.xM.sub.yN.sub.zO.sub.a; wherein M is one of V, Cr, Mn, Fe, Co, Ni and Cu, or a mixture of two or more of V, Cr, Mn, Fe, Co, Ni and Cu in any ratio; N is one of Na, K, Cs, Ca and Ba, or a mixture of two or more of Na, K, Cs, Ca and Ba in any ratio; x=0.5˜20; y=0.05˜20; z=0.01˜5; a is a number satisfying the valance of each atom. The catalyst is prepared by the following method: firstly mixing a certain amount of the lead metal oxides according to the chemical proportion and then grinding the mixture with high-energy ball milling for a period of time to obtain the molybdenum based composite oxide catalyst. The catalyst exhibits excellent performance when using for preparation of butadiene by oxidative dehydrogenation of butene, and the preparation process is simple, controllable, and repeatable. Waste water or waste gas that is difficult to be treated is not produced during preparation.

Claims

1. A molybdenum based composite oxide catalyst having the following formula:
BiMoxMyNzOa wherein M is one of V, Cr, Mn, Fe, Co, Ni or Cu; N is one of Na, K, Cs, Ca and Ba, or a mixture of two or more thereof in any ratio; x=0.5-20; y=0.05-20; z=0.01-5; a is a number satisfying the valance of each atom; wherein the catalyst is prepared by the method comprising the steps of: (1) weighing bismuth molybdate and oxide precursors of other metal elements according to the proportions of ingredients in the above formula, grinding and sieving to obtain a mixture; (2) transferring the mixture to a ball mill jar, ball milling same to produce the molybdenum based composite oxide catalyst.

2. The molybdenum based composite oxide catalyst according to claim 1, wherein M is one of V, Fe, Co or Ni; and N is K or Cs.

3. The molybdenum based composite oxide catalyst according to claim 1, wherein X is 0.8-18; y is 0.08-15; and z is 0.02-4.0.

4. The catalyst according to claim 1, wherein the frequency of ball milling is 15-35 Hz, the time of ball milling is 10-1,000 minutes, the mass ratio between the milling ball and the mixture of oxides is 50-5:1.

5. The catalyst according to claim 4, wherein the mass ratio between the milling ball and the mixture of oxides is 30-10:1.

6. The catalyst according to claim 4, wherein the oscillation frequency of ball milling of the ball mill is 20-30 Hz, the time of milling is 180-820 minutes.

7. A method for forming a molybdenum based composite oxide catalyst having the following formula:
BiMoxMyNzOa wherein M is one of V, Cr, Mn, Fe, Co, Ni and Cu; N is one of Na, K, Cs, Ca and Ba, or a mixture of two or more thereof in any ratio; x=0.5-20; y=0.05-20; z=0.01-5; a is a number satisfying the valance of each atom; said method comprising the steps of: (1) weighing bismuth molybdate and oxide precursors of other metal elements according to the proportions of ingredients in the above formula, grinding and sieving to obtain a mixture; (2) transferring the mixture to a ball mill jar, ball milling same to produce the desired molybdenum based composite oxide catalyst.

8. The method according to claim 7, wherein M is one of V, Fe, Co and Ni; and N is K or Cs.

9. The method according to claim 7, wherein X is 0.8-18; y is 0.08-15; and z is 0.02-4.0.

10. The method according to claim 7, wherein the frequency of ball milling is 15-35 Hz, the time of ball milling is 10-1,000 minutes, the mass ratio between the milling ball and the mixture of oxides is 50-5:1.

Description

DETAILED DESCRIPTION OF THE INVENTION

Specific Mode for Carrying Out the Invention

(1) 1. Molybdenum Based Composite Oxide Catalyst

(2) The present invention relates to a molybdenum based composite oxide catalyst, which exhibits excellent activity and selectivity for product in the reaction for producing butadiene by the oxidative dehydrogenation of butene.

(3) The molybdenum based composite oxide catalyst of the present invention has the following structural formula:
BiMo.sub.xMo.sub.yN.sub.zO.sub.a

(4) wherein M is one of V, Cr, Mn, Fe, Co, Ni and Cu, or a mixture of two or more thereof in any ratio; preferably is Fe, Co or Ni;

(5) N is one of Na, K, Cs, Ca and Ba, or a mixture of two or more thereof in any ratio; preferably is K or Cs.

(6) x in the above composite oxide catalyst is a range formed by any two, as end points, selected from the group consisting of 0.5, 20, 0.8, 18, 1.0, 15, 1.2 and 12. In one embodiment of the present invention, x is 0.5˜20, preferably 0.8-18, more preferably 1.0-15, and most preferably 1.2-12.

(7) y in the above composite oxide catalyst is a range formed by any two, as end points, selected from the group consisting of 0.05, 20, 0.08, 15, 0.10, 12, 0.12, 8, 0.15 and 5. In one embodiment of the present invention, y is 0.05˜20, preferably 0.08-15, more preferably 0.10-12, even more preferably 0.12-8, and most preferably 0.15-5.

(8) z in the above composite oxide catalyst is a range formed by any two, as end points, selected from the group consisting of 0.01, 5.0, 0.02, 4.0, 0.03, 2.0, 0.05, 1.0, 0.08 and 0.50. In one embodiment of the present invention, z is 0.01˜5.0, preferably 0.02˜4.0, more preferably 0.03˜2.0, even more preferably 0.05˜1.0, and most preferably 0.08˜0.50.

(9) a is a number satisfying the valance of each atom.

(10) In one preferred embodiment of the present invention, the composite oxide catalyst of the present invention is selected from the group consisting of Bi.sub.1.0Mo.sub.1.0Fe.sub.0.2K.sub.0.05O.sub.c, Bi.sub.1.0Mo.sub.1.5Ni.sub.0.6K.sub.0.1O.sub.c, Bi.sub.1.0Mo.sub.1.5Co.sub.0.2Ca.sub.0.2O.sub.c, or Bi.sub.1.0Mo.sub.1.5Ni.sub.0.8Ba.sub.0.2O.sub.c, or a mixture of two or more thereof in any ratio.

(11) 2. Method for Preparing the Molybdenum Based Composite Oxide Catalyst

(12) The molybdenum based composite oxide catalyst of the present invention can be prepared by the following steps.

(13) (1) Weighing bismuth molybdate and oxide precursors of other metal elements according to the desired proportions of ingredients, grounding and sieving.

(14) The oxide precursor may be a single oxide, or a mixture of metal oxides, depending on the steps of the method. Compounds that can be decomposed to form the oxide upon grinding can also be used. In one embodiment of the present invention, the metal oxide may be prepared by a precipitation method, a hydrothermal method, a thermal decomposition method or the like, or can be a commercially available one.

(15) It is known that ball milling itself functions as mixing and grinding. Therefore, the steps of grinding and sieving before ball milling in the present invention are for shortening the duration of ball milling, because small particle size of the oxide can facilitate to shorten such duration. In one preferred embodiment of the present invention, after grinding and mixing, the metal oxides are sieved to 0.001-0.1 millimeters, preferably 0.01-0.09 millimeters, and more preferably 0.03-0.07 millimeters.

(16) (2) Transferring the Sieved Mixture to a Ball Milling Jar and Ball Milling.

(17) The material constituting the milling ball used in the present method is not specifically limited, as long as the milling ball will not un-advantageously affect the performance of the catalyst. In one embodiment of the present invention, a stainless steel ball is used as the milling ball. Generally, the mass ratio between the milling ball and the mixture to be ball milled (or between the milling ball and the mixture of the sieved oxides) in each pass is 50˜5:1, preferably 40˜10:1, and more preferably 30-20:1. If the mass ratio is too low, the duration for ball milling in each pass will be prolonged, resulting in reduced production efficiency of the catalyst. On the contrary, if the mass ratio is higher than the most preferred mass ratio, the yield of the catalyst and, in turn, the production efficiency, will be decreased.

(18) In the present invention, the oscillation frequency of the ball mill is associated with the milling time. If the oscillation frequency of the ball mill is too low, a long milling time is required and the efficiency of preparing the catalyst will be very low. If the oscillation frequency of the ball mill is too high, the ball mill cannot be continuously operated due to un-timely heat emission. On the other hand, if the milling time is too short, the solid phase reaction among the metal oxides will be insufficient, resulting in low catalytic activity. On the contrary, if the milling time is extended beyond the most preferred milling time, the performance of the catalyst will not be further enhanced, sometimes the performance may even be decreased.

(19) In one embodiment of the present invention, the oscillation frequency is 15-35 Hz, the milling time is 10-1,000 minutes; preferably, the oscillation frequency is 18-32 Hz, and the milling time is 100-900 minutes; more preferably the oscillation frequency is 20-30 Hz, and the milling time is 180-820 minutes; and most preferably, the oscillation frequency is 22-28 Hz and the milling time is 220-750 minutes.

(20) Upon ball milling for a period of time, the active ingredients of the molybdenum based composite oxide catalyst can be directly obtained.

(21) Atmosphere used during ball milling in the present invention is not specifically limited, which may be air, nitrogen gas or other inert gases.

(22) In one embodiment of the present invention, the present method may further comprise steps of mixing the resultant active ingredients of the catalyst with graphite and molding to prepare the final catalyst. In one embodiment of the present invention, the addition amount of graphite comprises 2%˜10%, preferably 5%˜8%, and more preferably 6%˜7%, of the total mass of the catalyst.

(23) 3. Use of the Molybdenum Based Composite Oxide Catalyst

(24) The molybdenum based composite oxide catalyst of the present invention is useful in the preparation of butadiene by the oxidative dehydrogenation of butene, especially in a reaction condition that no water vapor is used as diluent gas. A suitable reaction may comprise the following steps: firstly, homogeneously mixing the butane (or a mixed hydrocarbons comprising butene), as starting material, and water vapor, air and a diluent gas; secondly, pre-heating same, and then passing the pre-heated mixed gases to a catalyst bed to perform dehydrogenation under the following reaction conditions: reaction temperature being 250-450° C., space velocity (with respect to butene as starting material) being 50˜500 h.sup.−1, molar concentration of butane being 1˜20%, and molar ratio of butane, oxygen, water vapor, and diluent gas being 1:0.2˜5:0˜20:0˜20; wherein the diluent gas is one of nitrogen gas, argon gas and helium gas.

(25) In one embodiment of the present invention, the reaction for preparing butadiene by the oxidative dehydrogenation of butene comprises the following steps: preheating a mixture of butene as staring material and water vapor, air and a diluent gas, passing the mixture to a catalyst bed for the oxidative dehydrogenation under the following reaction conditions: reaction temperature being 300-420° C., space velocity (with respect to butene as the starting material) being 100˜300 h.sup.−1, molar concentration of butene being 4˜12%, and molar ratio of butane, oxygen, water vapor, and diluent gas being 1:0.5˜2.0:1˜4:0˜12, wherein the diluent gas is nitrogen gas.

(26) In the present reaction for preparing butadiene by the oxidative dehydrogenation of butene, the molybdenum based composite oxide catalyst of the present invention is used in the catalyst bed.

(27) The butene starting material may be one of 1-butene, trans-2-butene and cis-2-butene, or a mixture of any two or three of them.

(28) In the present reaction for preparing butadiene by the oxidative dehydrogenation of butene, the conversion rate of butene and the selectivity for butadiene are calculated according to the following formulae, in which the amounts of butene and butadiene are weight amounts:
Conversion rate of butene (%)={[(the amount of butene before reaction)−(the amount of butene after reaction)]/(the amount of butene before reaction)}×100%
Selectivity of butadiene(%)=(the amount of butadiene produced)/(the amount of butene reacted)×100%

(29) The molybdenum based composite oxide catalyst prepared by the method of the present invention exhibits high conversion rate of butene and high selectivity for butadiene. As demonstrated by the following examples, the conversion rate of butene by the molybdenum based composite oxide catalyst prepared by the present method is 80-98%, and the selectivity for butadiene is 90-97%, both of which are higher than those of the catalyst produced by the conventional co-precipitation method. In addition, when preparing the molybdenum based composite oxide catalyst, the present method has the advantages of simple, readily to be repeated, no metallic ion lose, and no metallic ion-containing waste water and exhaust gas.

(30) The advantages of the present invention will be further demonstrated in view of the following examples.

EXAMPLE 1

(31) 1. Preparation of Catalyst

(32) 3.77 g β-Mo.sub.2.0Bi.sub.2.0O.sub.9 and 1.6 g ferric oxide (containing 1.08 wt % potassium) were weighed and placed in a grinding bowl to manually grind for 5 minutes to homogenously mix same. The mixture was sieved to 0.001-0.1 millimeters and transferred to a 50 ml stainless steel ball milling jar. 100 g stainless steel balls were added and the mixture was milled for 4 hours under a ball mill rate of 25 Hz, obtaining a powder of molybdenum based composite oxide catalyst.

(33) Upon analyzing by ICP, it was found that the composition of the catalyst was Mo.sub.1.0Bi.sub.1.0Fe.sub.0.2K.sub.0.05O.sub.x. The molar ratio of Mo, Bi, Fe and K was identical to that in the starting material initially added, indicating no metal ion loss during preparation.

(34) 2. Evaluation of Performance of the Catalyst By the Dehydrogenation of Butane

(35) The resultant catalyst powder was mixed with graphite by adding 3 wt % of graphite based on the total mass of the mixture. The mixed powder was molded to form particles having a size of 20-40 meshes and then loaded into a stainless steel tubular reactor to test the catalytic performance. Evaluation of the catalytic performance was conducted in the stainless steel tubular reactor having an inner diameter of 10 mm and a length of 350 mm. The volume of the catalyst was 12 ml.

(36) The 1-butene, as starting material, was mixed with water vapor and air. The mixed gases was pre-heated to 300° C. and passed through the catalyst bed. The space velocity of 1-butene was 200 h.sup.−1, the reaction temperature was 320° C., the molar ratio between air and butene was 5.7, the molar ratio between water vapor and butene was 2, the diluent gas was nitrogen gas and the concentration of butene was 8%.

(37) 20 hours after reaction (at that time the reaction was stable), the exhaust gas was subjected to online analysis by gas chromatograph (Agilent 7890).

(38) According to the above equations, the conversion rate of 1-butene was 88% and the selectivity for butadiene was 94.8%.

COMPARATIVE EXAMPLE 1

(39) 1. Preparation of Catalyst by Calcination Rather Than Ball Milling

(40) A molybdenum based composite oxide catalyst was prepared by a solid state reaction at high temperature. 3.77 g β-Mo.sub.2.0Bi.sub.2.0O.sub.9 and 1.6 g ferric oxide (containing 1.08 wt % potassium) were weighed, placed in a grinding bowl, and manually grinded for 5 minutes to homogenously mix same. The mixture was sieved to 0.001-0.1 millimeters and transferred to a crucible. The crucible was placed in a muffle furnace for calcination. The atmosphere used for calcination was air, the calcination temperature was 550° C., and the calcination time was 4 hours.

(41) Upon analysis by ICP, it was found that the composition of the catalyst was Mo.sub.1.0Bi.sub.1.0Fe.sub.0.2K.sub.0.05O.sub.x. The molar ratio of Mo, Bi, Fe and K was identical to that in the starting material initially added.

(42) 2. Evaluation of Performance of the Catalyst by the Dehydrogenation of Butane

(43) The performance of the catalyst was evaluated by the same experimental apparatus and method as those in Example 1. The space velocity of 1-butene was 200 h.sup.−1, the reaction temperature was 320° C., the molar ratio between air and butene was 5.7, the molar ratio between water vapor and butene was 2, the diluent gas was nitrogen gas and the concentration of butene was 8%.

(44) 20 hours after reaction, the composition of the resultant gas was analyzed and calculated. The conversion rate of 1-butene was 38% and the selectivity for butadiene was 84.8%. As compared to the catalyst of Example 1, the catalyst prepared by solid state reaction at high temperature has poor activity and selectivity.

COMPARATIVE EXAMPLE 2

(45) 1. Preparation of Catalyst by Co-Precipitation

(46) A molybdenum based composite oxide catalyst was prepared by a co-precipitation method. 80.8 g ferric nitrate and 485.10 g bismuth nitrate were dissolved in 1000 g distilled water acidified by nitric acid, forming solution A. 176.6 g ammonium metamolybdate was dissolved in 2,000 g distilled water and 5.05 g solid potassium nitrate was added thereinto, forming solution B. The molar ratio of Mo, Bi, Fe and K was 1:1:0.2:0.05. Solution A was added dropwise into solution B while stirring. PH of the mixture was adjusted by strong ammonia to 4.0, and the mixed solution was subjected to aging under ambient temperature for 2 hours. The solution was filtered and washed with distilled water until the filtrate has a neutral pH. The filter cake was dried at 110° C. to produce a loose solid. The resultant solid was ground and sieved. 2 wt % graphite was added into and mixed with the sieved solid. The mixture was pressed, broken up, and sieved to obtain particles having particle size of 10-20 meshes. The particles were calcined in a tubular furnace in a flowing air atmosphere under 520° C. for 3 hours, obtaining a molybdenum based composite oxide catalyst.

(47) Upon analyzing the catalyst powder by ICP, it was found that the molar ratio of Mo, Bi, Fe and K in the catalyst was 0.8:1:0.2:0.02. Upon analyzing the filtrate by ICP, it was found relative larger amount of Mo ion, small amount of K ion and few or no Fe or Bi ions in the filtrate. The results showed that Mo, Bi, Fe and K were hardly precipitated completely when preparing the molybdenum based composite oxide by the co-precipitation method, and showed the element Mo ion loss seriously.

(48) 2. Evaluation of Performance of the Catalyst

(49) The performance of the catalyst was evaluated by the same experimental apparatus and method as those in Example 1. The space velocity of 1-butene was 200 h.sup.−1, the reaction temperature was 320° C., the molar ratio between air and butene was 5.7, the molar ratio between water vapor and butene was 2, the diluent gas was nitrogen gas and the concentration of butene was 8%. 20 hours after reaction, the composition of the resultant gas was analyzed and calculated. The conversion rate of 1-butene was 82% and the selectivity for butadiene was 84.8%. The activity of the catalyst prepared by the co-precipitation method almost similar to that of the catalyst in Example 1, but the former has poor selectivity, which was caused by loss of Mo and K.

COMPARATIVE EXAMPLE 3

(50) 1. Preparation of Catalyst by Co-Precipitation

(51) A molybdenum based composite oxide catalyst was prepared by the co-precipitation method. 80.8 g ferric nitrate and 485.10 g bismuth nitrate were dissolved in 1000 g distilled water acidified with nitric acid, forming solution A. 220.75 g ammonium metamolybdate was dissolved in 2000 g distilled water, and 12.12 g solid potassium nitrate was added thereinto, forming solution B. The molar ratio of Mo, Bi, Fe and K was 1.25:1:0.2:0.12. Solution A was added dropwise into solution B while stirring. PH of the mixture was adjusted by strong ammonia to 4.0, and the mixed solution was subjected to aging under ambient temperature for 2 hours. The solution was filtered and washed with distilled water until the filtrate has a neutral pH. The filter cake was dried at 110° C. to produce a loose solid. The resultant solid was ground and sieved. 2 wt % graphite was added into and mixed with the sieved solids. The mixture was pressed, broken up, and sieved to obtain particles having particle size of 10-20 meshes. The particles were calcined in a tubular furnace in a flowing air atmosphere under 520° C. for 3 hours, obtaining a molybdenum based composite oxide catalyst.

(52) Upon analyzing the catalyst powder by ICP, it was found that the molar ratio of Mo, Bi, Fe and K in the catalyst was 1:1:0.2:0.05. Upon analyzing the filtrate by ICP, it was found relative larger amount of Mo ion, small amount of K ion and few or no Fe or Bi ions. The results showed that Mo and K seriously lost. This Comparative Example produced such a solid catalyst that had the same element composition as that of the catalyst of Example 1 by increasing the addition amounts of ammonium metamolybdate and potassium nitrate as compared with Example 1 and Comparative Example 2.

(53) 2. Evaluation of Performance of the Catalyst

(54) The performance of the catalyst was evaluated by the same experimental apparatus and method as those in Example 1. The space velocity of 1-butene was 200 h.sup.−1, the reaction temperature was 320° C., the molar ratio between air and butene was 5.7, the molar ratio between water vapor and butene was 2, the diluent gas was nitrogen gas and the concentration of butene was 8%. 20 hours after reaction, the composition of the resultant gas was analyzed and calculated. The conversion rate of 1-butene was 85% and the selectivity for butadiene was 92.8%. Although the activity and selectivity of the catalyst in this Comparative Example were improved as compared with those in Comparative Example 2 by increasing the addition amount of ammonium metamolybdate and potassium nitrate, they were still inferior to the performance of the catalyst of Example 1.

EXAMPLE 2

(55) 1. Preparation of Catalyst

(56) 4.48 g α-Mo.sub.2.0Bi.sub.3.0O.sub.12.0 and 0.45 g nickel oxide (containing 0.98 wt % potassium) were weighed and placed in a grinding bowl to manually grind for 5 minutes. The mixture was sieved to 0.001-0.1 millimeters and transferred to a 50 ml stainless steel ball milling jar. 70 g stainless steel balls were added and the mixture was milled for 2 hours under a ball mill rate of 28 Hz, obtaining a molybdenum based composite oxide catalyst.

(57) Upon analyzing by ICP, it was found that the composition of the catalyst was Mo.sub.1.0Bi.sub.1.5Ni.sub.0.6K.sub.0.1O.sub.x. The molar ratio of Mo, Bi, Fe and K was identical to that in the starting material initially added, indicating no metal ions loss during preparation.

(58) 2. Evaluation of Performance of the Catalyst by Dehydrogenation of Butane

(59) The resultant catalyst powder was mixed with graphite by adding thereinto 3% by weight of graphite based on the total mass of the mixture. The mixed powder was molded to form particles having particle size of 20-40 meshes. The particle was loaded to a stainless steel tubular reactor to test the catalytic performance. Evaluation of the catalytic performance was conducted in the stainless steel tubular reactor having an inner diameter of 10 mm and a length of 350 mm. The volume of the catalyst was 12 ml.

(60) The 1-butene starting material was mixed with water vapor and air. The mixed gas was pre-heated to 300° C. and passed through the catalyst bed. The space velocity of 1-butene was 200 h.sup.−1, the reaction temperature was 380° C., the molar ratio between air and butene was 8, the molar ratio between water vapor and butene was 1, the diluent gas was nitrogen gas and the concentration of butene was 6%.

(61) 20 hours after reaction (at that time the reaction was stable), the exhaust gas was subjected to online analysis by gas chromatograph (Agilent 7890).

(62) According to the above equations, the conversion rate of 1-butene was 80% and the selectivity for butadiene was 95.8%.

EXAMPLE 3

(63) 1. Preparation of Catalyst

(64) 4.48 g α-Mo.sub.2.0Bi.sub.3.0O.sub.12.0, 0.16 g Co.sub.3O.sub.4 and 0.112 g CaO were weighed and placed in a grinding bowl to manually grind for 5 minutes, obtaining a homogenous mixture. The mixture was sieved to 0.001-0.1 millimeters and transferred to a 50 ml stainless steel ball milling jar. 100 g stainless steel balls were added and the mixture was milled for 4 hours under a ball mill rate of 25 Hz, obtaining a molybdenum based composite oxide catalyst.

(65) Upon analyzing by ICP, it was found that the composition of the catalyst was Mo.sub.1.0Bi.sub.1.0Co.sub.0.2Ca.sub.0.2O.sub.x. The molar ratio of Mo, Bi, Co and Ca was identical to that of the starting material initially added, indicating no metal ions loss.

(66) 2. Evaluation of Performance of the Catalyst by Dehydrogenation of Butane

(67) The resultant catalyst powder was mixed with graphite by adding thereinto 3% by weight of graphite based on the total mass of the mixture. The mixed powder was molded to form particles having particle size of 20-40 meshes. The particle was loaded to a stainless steel tubular reactor to test the catalytic performance. Evaluation of the catalytic performance was conducted in the stainless steel tubular reactor having an inner diameter of 10 mm and a length of 350 mm. The volume of the catalyst was 12 ml.

(68) The 1-butene starting material was mixed with water vapor and air. The mixed gas was pre-heated to 300° C. and passed through the catalyst bed. The space velocity of 1-butene was 300 h.sup.−1, the reaction temperature was 380° C., the molar ratio between air and butene was 6, the molar ratio between water vapor and butene was 1, the diluent gas was nitrogen gas and the concentration of butene was 10%.

(69) 20 hours after reaction (at that time the reaction was stable), the exhaust gas was subjected to online analysis by gas chromatograph (Agilent 7890).

(70) According to the above equations, the conversion rate of 1-butene was 82% and the selectivity for butadiene was 96.8%.

COMPARATIVE EXAMPLE 4

(71) 1. Preparation of Catalyst by Co-Precipitation

(72) 26.48 g ammonium heptamolybdate was weighed and dissolved in distilled water, forming solution A. 48.51 g bismuth nitrate, 5.86 g cobalt nitrate and 3.28 g calcium nitrate were weighed and dissolved in 200 ml distilled water acidified with nitric acid, forming solution B. Solution B was slowly added dropwise into solution A while stirring and, at the same time, ammonia was added dropwise to adjust the final pH of the solution to be 3.0. After addition, the resultant slurry was subjected to aging at 60° C. for 1 hour and then dried in an oven at 110° C. for 8 hours.

(73) The resultant solid was broken up and sieved. 2 wt % of graphite was added. After mixing, the resultant mixture was pressed, broken up and sieved, obtaining particles having particle size of 10-20 meshes. The particles were calcined in a tubular furnace in a flowing air atmosphere under 510° C. for 10 hours, obtaining a composite oxide catalyst.

(74) Upon analyzing by ICP, it was found that the composition of the catalyst was Mo.sub.1.5Bi.sub.1.0Co.sub.0.2Ca.sub.0.2O.sub.x. No metal ion lost as compared with the element ratio initially added. However, during calcination, a great amount of pungent exhaust gases containing NOx were produced. Device for treating the exhaust gas must be equipped when industrially producing the catalyst by this method and the exhaust gas must be treated before discharge.

(75) 2. Evaluation of Performance of the Catalyst by Dehydrogenation of Butane

(76) Evaluation of the catalytic performance was conducted in the stainless steel tubular reactor. The volume of the catalyst was 12 ml.

(77) The starting material 1-butene was mixed with water vapor and air. The mixed gas was pre-heated to 300° C. and passed through the catalyst bed. The space velocity of 1-butene was 300 h.sup.−1, the reaction temperature was 380° C., the molar ratio between air and butene was 6, the molar ratio between water vapor and butene was 1, the diluent gas was nitrogen gas and the concentration of butene was 10%. 20 hours after reaction (at that time the reaction was stable), the conversion rate of 1-butene produced by the catalyst was 84% and the selectivity for butadiene was 95.0%.

EXAMPLE 4

(78) 1. Preparation of Catalyst

(79) 4.48 g α-Mo.sub.2.0Bi.sub.3.0O.sub.12.0, 0.6 g nickel oxide and 0.3068 g barium oxide were weighed and placed in a grinding bowl to manually grind for 5 minutes, obtaining a homogenous mixture. The mixture was sieved to 0.001-0.1 millimeters and transferred to a 50 ml stainless steel ball milling jar. 100 g stainless steel balls were added and the mixture was milled for 10 hours under a ball mill rate of 25 Hz, obtaining a molybdenum based composite oxide catalyst.

(80) Upon analyzing by ICP, it was found that the composition of the catalyst was Mo.sub.1.0Bi.sub.1.0Ni.sub.0.6Ba.sub.0.2O.sub.x. The molar ratio of Mo, Bi, Ni and Ba was identical to that in the starting material initially added, indicating no metal ions loss during preparation.

(81) 2. Evaluation of Performance of the Catalyst by Dehydrogenation of Butane

(82) The resultant catalyst powder was mixed with graphite by adding 3% graphite based on the total mass of the mixture. The mixed powder was molded to form particles having particle size of 20-40 meshes. The particle was loaded to a stainless steel tubular reactor to test the catalytic performance. Evaluation of the catalytic performance was conducted in the stainless steel tubular reactor having an inner diameter of 10 mm and a length of 350 mm. The volume of the catalyst was 12 ml.

(83) The 1-butene starting material was mixed with water vapor and air. The mixed gas was pre-heated to 300° C. and passed through the catalyst bed. The space velocity of 1-butene was 150 h.sup.−1, the reaction temperature was 320° C., the molar ratio between air and butene was 5.7, the molar ratio between water vapor and butene was 2, the diluent gas was nitrogen gas and the concentration of butene was 8%.

(84) 20 hours after reaction (at that time the reaction was stable), the exhaust gas was subjected to online analysis by gas chromatograph (Agilent 7890).

(85) According to the above equations, the conversion rate of 1-butene was 92% and the selectivity for butadiene was 93.8%.

(86) By comparing the experimental results of the above examples with those of the comparative examples, it can be found that the process of the present method is simple, repeated readily, no metallic ions lost, and no metallic ion-containing waste water. Additionally, the catalyst prepared by the present method exhibits excellent performance when using for dehydrogenation of butene, i.e., exhibiting higher activity and selectivity for butadiene than those of the same catalyst prepared by a co-precipitation method.