Investigation of the role of oxygen in NO reduction by C 2H 4 on the surface of stepped Pt(3 3 2)

Abstract

The influence of pre-dosed oxygen on NO–C 2H 4 interactions on the surface of stepped Pt(3 3 2) has been investigated using Fourier transform infrared reflection–absorption spectroscopy (FTIR-RAS) and thermal desorption spectroscopy (TDS). The presence of oxygen significantly suppresses the adsorption of NO on the steps of Pt(3 3 2), leading to a very specific adsorption state for NO molecules when oxygen–NO co-adlayers are annealed to 350 K (assigned as atop NO on step edges). An oxygen-exchange reaction also takes place between these two kinds of adsorbed molecules, but there appears to be no other chemical reaction, which can result in the formation of higher-valence NOx. C 2H 4 molecules which are post-dosed at 250 K to adlayers consisting of 18O and NO do not have strong interactions with either the NO or the 18O atoms. In particular, interactions which may result in the formation of new surface species that are intermediates for N 2 production appear to be absent. However, C 2H 4 is oxidized to C 18O 2 by 18O atoms at higher annealing temperature. This reaction scavenges surface 18O atoms quickly, and the adsorption of NO molecules on step sites is therefore quickly restored. As a consequence, NO dissociation on steps proceeds very effectively, giving rise to N 2 desorption which closely resembles that following only NO exposure on a clean Pt(3 3 2), both in peak intensity and desorption temperature. It is concluded that the presence of 18O 2 in the selective catalytic reduction (SCR) of NO with C 2H 4 on the surface of Pt(3 3 2) does not play a role of activating reactants.