Kinetics of NO Reduction by NH3 over Supported Pt and the Effect of SO2

Abstract

Kinetics of the catalytic reduction of NO by NH3 over supported Pt were determined in a steady-state flow microreactor. The rate of reaction is satisfactorily described by a single-site Langmuir-Hinshelwood kinetic model involving associative NO adsorption and dissociative NH3 adsorption, with reaction between adsorbed NO and an adsorbed nitrogen fragment appearing to be rate limiting. O2 markedly enhances the rate of reaction. Auger studies indicate that H2S and SO2 form different compounds upon reacting with Pt, Pd and Ni, and the susceptibility of attack by H2S and SO2 increases with Pt 〈 Pd 〈〈 Ni. The rate of NO reduction by NH3 is markedly reduced by very low concentrations of SO2. Pt, Pd, Ru and Ni which show the following activity sequence Pt 〉 Pd 〉〉 Ru 〉 Ni, in the absence of SO2, decrease in activity according to Ru 〉〉 (Pt, Pd, Ni) in the presence of SO2. O2 markedly enhances the rate of NO reduction over Pt in the presence of SO2.