Reaction kinetic analysis of the gas-phase epoxidation of propylene over Au/TS-1

The superior activity and stability of Au/TS-1 catalysts has allowed the first comprehensive kinetic analysis of the propylene epoxidation system in the absence of significant deactivation. A unique design of experiments combining the best features of factorial experiments with one-at-a-time experimentation over the nonflammable range was used to collect kinetic information, from which a power rate law was extracted using the statistical software package JMP. Explaining the resultant fractional reactant orders (O-2 = 0.31 +/- 0.04, Hz = 0.60 +/- 0.03, and C3H6 = 0.18 +/- 0.04) requires a sequence of elementary kinetic steps having a minimum of two active sites participating in the rate-determining step. A reaction sequence is proposed that accounts for the experimentally determined reaction orders and is consistent with DFT calculations and other results from the literature. This mechanism suggests that titanium and gold sites must generate and use the epoxidation oxidant simultaneously rather than sequentially, as previously suggested in the literature. (c) 2006 Elsevier Inc. All rights reserved.