Catalytic reduction of NO in the presence of benzene on a Pt(3 3 2) surface

Abstract

The catalytic reduction of NO in the presence of benzene on the surface of Pt(3 3 2) has been studied using Fourier transform infra red reflection-absorption spectroscopy (FTIR-RAS) and thermal desorption spectroscopy (TDS). IR spectra show that while the presence of benzene molecules at low coverage (e.g., following an exposure of just 0.25 L) promotes NO–Pt interaction, the adsorption of NO on Pt(3 3 2) at higher benzene coverages is suppressed. It is also shown that there are no strong interactions between the adsorbed NO molecules and the benzene itself or benzene-derived hydrocarbons, which can lead to the formation of intermediate species that are essential for N 2 production. TDS results show that the adsorbed benzene molecules undergo dehydrogenation accompanied by hydrogen desorption starting at 300 K and achieving a maximum at 394 K. Subsequent dehydrogenation of the benzene-derived hydrocarbons then begins with hydrogen desorption starting at 500 K. N 2 desorption from NO adlayers on clean Pt(3 3 2) surface becomes significant at temperatures higher than 400 K, giving rise to a peak at 465 K. This peak corresponds to N 2 desorption from NO dissociation on step sites. The presence of benzene promotes N 2 desorption, depending on the benzene coverage. When the benzene exposure is 0.25 L, the N 2 desorption peak at 459 K is dramatically increased. Increasing benzene coverage also results in the intensification of N 2 desorption at ∼410 K. At benzene exposures of 2.4 L, N 2 desorption develops as a broad peak with a maximum at ∼439 K. It is concluded that the catalytic reduction of NO by platinum in the presence of benzene proceeds by NO decomposition and subsequent oxygen removal at temperatures lower than 500 K, and NO dissociation is a rate-limiting step. The contribution of benzene to N 2 desorption is mainly attributed to providing a source of H, which quickly reacts with NO-derived atomic O, leaving the surface with more vacant sites for further NO dissociation.