Oxidative dehydrogenation catalyst
Oxidative dehydrogenation catalysts comprising MoVNbTeO having improved consistency of composition and a 25% conversion of ethylene at less than 420° C. and a selectivity to ethylene above 95% are prepared by treating the catalyst precursor with H 2 O 2 in an amount equivalent to 0.30-2.8 mL H 2 O 2 of a 30% solution per gram of catalyst precursor prior to calcining.
1. A method to improve the consistency of an oxidative dehydrogenation catalyst of the empirical formula (measured by PIXE);
Mo 1.0 V 0.22-0.33 Te 0.10-0.16 Nb 0.15-0.19 O d
where d is a number to satisfy the valence of the oxide
comprising treating a catalyst precursor prior to calcining with H 2 O 2 in an amount equivalent to 0.30-2.8 mL H 2 O 2 of a 30% solution per gram of catalyst precursor.
2. The method according to claim 1 , wherein the precursor is prepared by a method comprising:
i) forming an aqueous solution of ammonium heptamolybdate (tetrahydrate) and telluric acid at a temperature from 30° C. to 85° C. and adjusting the pH of the solution to 6.5 to 8.5 with a nitrogen containing base to form soluble salts of the metals;
ii) preparing a aqueous solution of vanadyl sulphate at a temperature from room temperature to 80° C.;
iii) mixing the solutions from steps i) and ii) together;
iv) slowly adding a solution of niobium monoxide oxalate (NbO(C 2 O 4 H) 3 ) to the solution of step iii) to form a slurry;
v) heating the resulting slurry in an autoclave under an inert atmosphere at a temperature from 150° C. to 190° C. for not less than 10 hours.
3. The method according to claim 2 , the resulting solid from step v) is filtered and washed with deionized water, and drying the washed solid for a time from 4 to 10 hours at a temperature from 70 to 100° C.
4. The method according to claim 3 , further comprising calcining the catalyst in an inert atmosphere at a temperature from 200° C. to 600° C. for a time from 1 to 20 hours.
5. The method according to claim 4 , wherein the precursor is treated with the equivalent of from 0.3-2.8 mL of a 30% w/w aqueous solution of H 2 O 2 per gram of catalyst precursor for a time from 5 minutes to 10 hours at a temperature from 20 to 80° C.
6. The method according to claim 5 , wherein in the calcined catalyst the molar ratio of Mo:V is from 1:0.22 to 1:0.29.
7. The method according to claim 6 , wherein in the calcined catalyst the molar ratio of Mo:Te is greater than 1:0.11 and less than 1:0.15.
8. The method according to claim 7 , wherein the calcined catalyst has a bulk density from 1.20 to 1.53 g/cc.
9. The method according to claim 8 , wherein in the crystalline phase of the catalyst the amount of the phase having the formula (TeO) 0.39 (Mo 3.52 V 1.06 Nb 0.42 )O 14 is above 75 wt. % of the measured crystalline phase as determined by XRD.
10. The method according to claim 9 , wherein in the crystalline phase of the catalyst the amount of the phase having the formula (TeO) 0.39 (Mo 3.52 V 1.06 Nb 0.42 )O 14 is above 85 wt. % of measured crystalline phase as determined by XRD.