III International Conference

PP-III-801) C 6 H 5 CH 3 + 2 [YO] → 2 [Y] + C 6 H 5 CHO + H 2 O,2) 2 C 6 H 5 CHO + 3 [YO] → 2 [YC 6 H 5 COO] + [Y] + H 2 O,3) C 6 H 5 CH 3 + 18 [ZO] → 18 [Z] + 7 CO 2 + 4 H 2 O,4) C 6 H 5 CH 3 + [ZO] → [ZOC 7 H 8 ],5) [ZOC 7 H 8 ] + 17 [ZO] → 18 [Z] + 7 CO 2 + 4 H 2 O.The kinetic equations corresponding to steps 1–5 are as follows:mYOr1 = k1C T θ , r2 = k2C BA θYO, nr3 = k3C T θ , ZO r4 = k4C T θ ZO , r5 = k5θTθZO ,where C T and C BA are the concentrations of toluene and benzaldehyde in the gas phase (molefractions); θ YO , θ ZO , θ YB , θ ZT are the fractions of adsorbed species, benzoate and toluene on thecatalyst surface, correspondingly; θ Y , θ Z are the fractions of not occupied sites of themonolayer; k j are the rate constants of the corresponding steps (s -1 ); m, n are the reactionOn the base kinetic model the modeling of the interaction of toluene with the preoxidizedvanadia/titania catalyst has been performed. It was shown, that under periodicoperation it is possible to increase selectivity towards to BA essentially with comparisonsteady state ones. This was due to presence a different surface oxygen species: nucleophiliclattice species and electrophilic surface species participating in the parallel routes of thetoluene oxidation. The latter species could be formed easier in the presence of gaseousoxygen providing the decrease of BA selectivity.The benzaldehyde formation is probably determined by nucleophilic-lattice oxygen,involved in the monolayer vanadia species. Electrophilic oxygen, formed at a higherconcentration of vanadia, is responsible for the formation of carbon oxides and main part ofsurface carbon containing species. The proposed kinetic model was used to estimate the rateconstants, reaction orders, activation energies and relative amount of active oxygen sites. Itsatisfactorily describes the transient behaviour of benzaldehyde, CO 2 and toluene for the submonolayercatalysts in the temperature range 523-633 K. The model demands a modificationto simulate kinetics of the toluene interaction with the 3.7 ML V/TiO 2 catalyst explained bythe presence of V 2 O 5 in excess. This V 2 O 5 provides oxygen participating in the interactionwith toluene.Acknowledgment. The authors acknowledge to RFBR (Grant № 06-03-32473-а) for thefinancial support.References1. R. M. Contractor, A.E. Sleight. Catal. Today. 1, 587 (1987).2. S.I. Reshetnikov, N.M. Ostrovsky: React. Kinet. Catal. Lett., 71, 129 (2000).3. R. M. Contractor, A.E. Sleight. Catal. Today. 1, 587 (1987).4. G.K. Boreskov, Yu.Sh. Matros: Catal. Rev.-Sci. Eng., 25, 551 (1983).5. Silveston, P.; Hudgins, R. R.; Renken, A. Catal. Today, 25, 91 (1995).6. Bulushev, D. A.; Kiwi-Minsker, L.; Renken, A. Catal.Today, 61, 271 (2000).7. Bulushev, D. A.; Kiwi-Minsker, L.; Zaikovskii, V. I.; Lapina, O. B.; Ivanov, A. A.; Reshetnikov,S. I.; Renken, A. Appl. Catal. A: General, 202, 243 (2000).621