Investigation Of The Role Of Oxygen In No Reduction By C_2h_4 On The Surface Of Stepped Pt(332)

摘要

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 ~(18)O and NO do not have strong interactions with either the NO or the ~(18)O 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~(18)O_2 by ~(18)O atoms at higher annealing temperature. This reaction scavenges surface ~(18)O 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 ~(18)O_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.