AUTONOMOUS KINETIC OSCILLATIONS DURING NO+C2H4+O-2 REACTION OVER PT-ZSM-5 UNDER HIGHLY OXIDIZING CONDITIONS

This work has investigated, using a packed-bed laboratory reactor, the steady-state behavior of a Pt-ZSM-5 catalyst for the NO + C2H4 + O-2 reaction under highly oxidizing conditions, typical of lean-burn gasoline engine exhaust. Results have revealed very unusual kinetic behavior near the reaction lightoff temperature. For the first time, we have observed sustained kinetic oscillations, induced by the presence of NO, in the steady-state rate of the NO + C2H4 + O-2 reaction. The pattern of the oscillation was found to be very sensitive to catalyst temperature and feed composition. The steady-state rate of the NO + C2H4 + O-2 reaction is inhibited by NO and exhibits a strong kinetic isotope effect; the inhibition effect of 15NO is much greater than that of 14NO. Possible mechanisms of the observed kinetic oscillations are discussed on the basis of both the kinetic inhibition effect of NO on the catalytic surface and the surface phase transition of Pt induced by adsorbed NO. (C) 1995 Academic Press, Inc.