Structure, activity and selectivity relationships in propane ammoxidation to acrylonitrile on V–Sb oxides Part 3Modifications during the catalytic reaction and effect of feed composition

Abstract

The change in surface reactivity up until steady-state behavior is reached in propane ammoxidation of a series of V–Sb-oxide catalysts with Sb:V ratios in the range 1–10 and prepared either by calcination or heat treatment in vacuum at 600°C is reported and analyzed in terms of the change in the structural features of the catalyst determined as a function of the time on stream by IR spectroscopy, X-ray diffraction and chemical analysis data. The results indicate that during the catalytic reaction, V⁵⁺ oxide when present, quickly reduces forming a V⁴⁺O₂/VSbO₄ solid solution with an increase in the selectivity to propene, but not to acrylonitrile. An increase in the selectivity and productivity to acrylonitrile occurs when an Sb-rich approximate VSbO₄ phase forms (‘VSbO₄’). This phase, however, is partially metastable, decomposing to ‘VSbO₄’+Sb₂O₄ when Sb⁵⁺ ions are reduced and not rapidly reoxidized. V⁵⁺ ions on the surface of the rutile phase stabilize the Sb-rich ‘VSbO₄’ phase, and catalyze the reoxidation of Sb³⁺. This side oxidation of ammonia to nitrogen competes for the reduction of these V⁵⁺ ions and influences the above redox and solid-state reactions. Therefore, a considerable dependence of the surface reactivity on the feed was observed. The optimal catalytic behavior determined for the series of catalysts studied was found to depend on the feed composition indicating that in the analysis of the structure, activity and selectivity relationships in propane ammoxidation the concentration of reactants in the feed plays a specific important role.

References

1. G. Centi, in Elementary Reaction Steps in Heterogeneous Catalysis(NATO Symp. Ser.), ed. R. W. Joyner and R. A. Van Santen, Kluwer Academic Press, Dordrecht, 1993, p. 93.
2. Y. Moro-oka and W. Ueda, in Catalysis, The Royal Society of Chemistry, Cambridge, UK, 1994, vol. 11 p. 223.
3. G. Centi, R. K. Grasselli and F. Trifirò, Catal. Today, 1992, 13, 661.
4. V. D. Sokolovskii, A. A. Davydov and O. Yu. Ovsitser, Catal. Rev.-Sci. Eng., 1995, 37, 425.
5. A. T. Guttmann, R. K. Grasselli and J. F. Brazdil, US Pat., 4 746 641 and 4 788 317, 1988.
6. L. C. Glaser, J. F. Brazdil, D. D. Suresh, D. A. Orndoff and R. K. Grasselli, US Pat., 4 767 739 and 4 788 173, 1988.
7. M. A. Toft, J. F. Brazdil and L. C. Glaser, US Pat., 4 784 979, 1988.
8. M. A. Toft, J. J. Brazdil and L. C. Glaser, US Pat., 4 879 264, 1989.
9. C. S. Lynch, L. C. Glaser, J. F. Brazdil and M. A. Toft, US Pat., 5 094 898, 1992.
10. R. Catani, G. Centi, F. Trifirò and R. K. Grasselli, Ind. Eng. Chem. Res., 1992, 31, 107.
11. A. Andersson, S. L. T. Andersson, G. Centi, R. K. Grasselli, M. Sanati and F. Trifirò, in New Frontiers in Catalysis, ed. L. Guczi, F. Solymos and P. Tétényi, Elsevier, Amsterdam 1993, p. 691.
12. G. Centi and S. Perathoner, in Preparation of Catalysts VI, ed. G. Poncelet, J. Mertens, B. Delmon, P. A. Jacobs and P. Grange, Elsevier Science, Amsterdam, 1995, p. 59.
13. G. Centi, E. Foresti and F. Guarneri, in New Developments in Selective Oxidation II, ed. V. Cortes Corberan and S. Vic Bellon, Elsevier, Amsterdam 1994, p. 281.
14. G. Centi and P. Mazzoli, Catal. Today, 1996, 28, 351.
15. G. Centi, F. Guarneri and S. Perathoner, Appl. Catal. A, 1997, in press.
16. T. Birchall and A. E. Sleight, Inorg. Chem., 1976, 15, 868.
17. F. J. Berry, M. E. Brett and W. R. Patterson, J. Chem. Soc., Dalton Trans., 1983, 9.
18. S. Hansen, K. Ståhl, R. Nilsson and A. Andersson, J. Solid State Chem., 1993, 102, 340.
19. A. Landa-Canovas, J. Nilsson, S. Hansen, K. Ståhl and A. Andersson, J. Solid State Chem., 1995, 116, 369.
20. C. Rocchiccioli-Deltcheff, T. Dupuis, R. Frank and M. Harmelin, J. Chim. Phys. Phys.-chim. Biol., 1970, 67, 2037.
21. C. A. Cody, L. DiCarlo and R. K. Darlington, Inorg. Chem., 1979, 18, 1572.
22. B. Darriet, J. Bovin and T. Galy, J. Solid State Chem., 1976, 19, 205.
23. D. B. Rogers, R. D. Shannon, A. W. Sleight and J. L. Gillson, Inorg. Chem., 1969, 8, 841.
24. R. G. Teller, M. R. Antonio, J. F. Brazdil and R. K. Grasselli, J. Solid State Chem., 1986, 64, 249.
25. J. K. Burdett, Inorg. Chem., 1985, 24, 2244.
26. W. H. Baur and A. A. Khan, Acta Crystallogr., Sect. B, 1971, 27, 2133.
27. A. Andersson, S. L. T. Andersson, G. Centi, R. K. Grasselli, M. Sanati and F. Trifirò, Appl. Catal. A, 1994, 113, 43.
28. G. Centi and F. Trifirò, Catal. Rev.-Sci. Eng., 1986, 28, 165 and references therein.
29. G. Centi, S. Perathoner, F. Trifirò, Appl. Catal. A, 1997, in press.
30. G. Centi, F. Marchi and S. Perathoner, J. Chem. Soc., Faraday Trans., 1996, 92, 5141; 5151.