NO dissociation and N 2 production in the presence of co-adsorbed S 18O 2 and D 2 on Pt(3 3 2)

Abstract

NO dissociation and subsequent N 2 production in the presence of co-adsorbed S 18O 2 and D 2 on the surface of stepped Pt(3 3 2) were studied using Fourier transform infra red reflection–absorption spectroscopy (FTIR-RAS) combined with thermal desorption spectroscopy (TDS). Reduction of NO by D (D 2 is adsorbed dissociatively on Pt surfaces) proceeds to a limited extent, because this reaction is rate-controlled by NO dissociation and the supply of D atoms at the higher surface temperatures at which NO dissociation becomes significant (350 K and higher). NO–D reaction is suppressed in the presence of S 18O 2, depending significantly on the S 18O 2 coverage and the competition between the reactions NO–D and S 18O 2–D. When the supply of D 2 is limited, e.g., 0.1 L in this study, the presence of S 18O 2 suppresses the NO–D reaction. With a sufficient supply of D 2, e.g., 0.4 L and higher, D-atom competing reactions do not play a role any more because the reactions of both NO and S 18O 2 with D proceed only to a very limited extent. As such, generation of O atoms from S 18O 2 dissociation is the main reaction that leads to the suppression in NO dissociation and consequently, N 2 production. It is also concluded that the presence of S 18O 2 does not seriously poison the active sites on the Pt surface, providing that there is a sufficient D supply to remove O atoms from both NO dissociation and S 18O 2 dissociation.