Kinetics and mechanism of the reduction of NO by C3H8 over Pt/Al2O3 under lean-burn conditions

The effect of temperature, contact time, and reactant concentration on the kinetics of NO reduction by C3H8 under lean burn conditions over Pt/Al2O3 has been investigated and a kinetic model which satisfactorily fits the data has been developed. Under reaction conditions adsorbed atomic oxygen is the dominant species on the metal surface, resulting in C3H8 oxidation being inhibited by O-2 and in the facile oxidation of NO to NO2. The rate determining step in C3H8 oxidation by O-2 is believed to be dissociative chemisorption of C3H8 involving the breaking of a C-H bond. Possible mechanisms for the reduction of NO to N-2 and N2O are discussed and the kinetics predicted for each mechanism, compared with the empirical data. It is concluded that NO dissociation on the Pt surface is not a major route. Instead, the reduction of NO appears to occur by spillover of NO2 from the Pt metal onto the Al2O3 support where it reacts with C3H8-derived species to form N-2 and N2O. (C) 1997 Academic Press.