The influence of the valence state of vanadium and of the P:V ratio on the activity and selectivity in maleic anhydride in the oxidation of 1-butene on vanadium-phosphorus oxides was investigated. Chemical and spectroscopic analyses indicated that two redox couples are mainly involved in the mechanism of C4 fraction oxidation to maleic anhydride: (1) Viv reduction to V111 for the dehydrogenation of 1-butene to butadiene and (2) Vv reduction for the formation of maleic anhydride from adsorbed butadiene. A slight excess of phosphorus strongly stabilizes vanadium(IV), avoiding excessive formation of surface Vv ions, which influence the ratio between rates of maleic anhydride formation and decomposition; on the other hand, a greater excess of phosphorus has a negative effect on the overall rate of butene oxidation, Inhibiting the reduction of Viv to V111. It is suggested that the nonstoichiometry of the catalyst structure (B phase), which is able to maintain high contents (up to approximately 20%) of both Vv and V111 as well as an excess of phosphorus without the formation of new crystalline phases, plays an important role in the catalyst activity.

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Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 565-570 565 Oil Company for aging the catalyst on an engine dynamometer.Registry NO. Pd, 7440-05-3; Pt, 7440-06-4; Rh, CO, 630-08-0; NO,, 11104-93-1. Literature CitedEngh, 0. T.; Wallman, S. SA€ (Society of Automotive Engineers) 1977, Falk, C. D.; Mooney. J. J. SA€ 1980, 800462. Fed. Regist. 1977, 42(124), 32906. Gandhl, H. S.; Steplen, H. K.; Shelef, M. Meter. Res. Bull. 1975, IO, 837. Gandhl, H. S.; Plken, A. G.; Shelef, M.; Delosh, R. G. SA€ Trans. 1978, 85, 770295. 901; SA€ 1978, 760201. Gandhi, H. S.; Plken, A. G.; Shelef, M.; Delosh, R. G.; Steplen, H. K.; Heyde, M. E. SA€ 1977, 770196. Patent 4 172047, 1979. Gandhi, H. S.; Shelef, M.; Yao, H. C.; Kummer, J. T.; Steplen, H. K. US. Gandhl, H. S.; Yao, H. C.; Steplen, H. K. ACS Symp. Ser. 1982, 178. 143. Hammerle, R. H.; Wu, C. H. Submitted to SAE International Congress, 1984. Hammerle, R. H.; Wu, C. H. SA€ 1981, 810275. Hegedus, L. L. Am. Chem. SOC. Div. fat. Chem. frepr. 1973, 18, 487. Jones, J. H.; Kummer, J. T.; Otto, K.; Shelef, M.; Weaver, E. E. Envfron. Sci. Technol. 1971, 5 , 790. Kummer, J. T.; Yao, Y.. McKee, D. SA€ 1978, 760143. Lachman, I. M.; McNelly. R. N. Preprints of Papers, 83rd Annual Meeting of American Ceramic Society, Washington, DC, 1981. Lester, G. R.; Marlnangell, R. E. SA€ 1980, 800844. Mooney. J. J.; Thompson, C. E.; Dettllng, J. C. SA€ 1977, 770365. National Fuel Survey, Motor Vehlcle Manufacturers Assoc., Detroit, 1982. Oda, I.; Matsuhlsa. T. Preprints of Papers, 83rd Annual Meeting of American Ceramic Society, Washington, DC, 1981. Oser, P. SA€ 1979, 790306. Seler, R. E.; Clark. R. J. SA€ 1978, 780203. Shelef, M.; Koester, D. W.; Mlchel, M. M., Jr., Adv. Chem. Ser. 1975, No. Steplen, H. K.; Wllllamson, W. B.; Gandhi. H. S. SA€ 1980, 800843. Weaver, E. E.; Shlller, J.; Plken. A. 0. AIChE Symp. Ser. 1976, 72(156), Yao, H. C.; Shelef, M. J . Catal. 1978, 43, 393. Yao, H. C.; Japar, S.; Shelef, M. J . M a l . 1977, 5 0 , 407. Yao, H. C.; Wynblatt, P.; Sleg, M.; Plummer, B. K., Jr. In "Sintering Processes"; Kuczynskl, G. C., Ed.; Plenum: New York, 1980; p 561.The oxidation of 1-butene and butadiene to maleic anhydride was tested with an integral reactor with vanadiumphosphorus mixed oxides prepared by different methods and presenting different activities and selectivities. The data were analyzed by utilizing a Langmuir-Hinshelwood type rate expression derived under differential conditions. At high partial pressure, competition between 1-butene and butadiene for the same active centers leads to a decrease in the rate of formatlon of maleic anhydride. This competitlon does not affect the rates of formation of methyl vinyl ketone, acetaldehyde, and carbon oxides. Emphasis is made on the necessity of operating with oxygen-nriched air in order to avoid the negative effect of the reactant on the rate of maleic anhydride formation.

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