Study on the selective catalytic reduction of NO with toluene over CuO/CeZrO2. A confirmation for the three-function model of HC-SCR using the temperature programmed methods and in situ DRIFTS

Abstract

This paper deals with the selective catalytic reduction of NO with the use of toluene as a reducer and in the presence of excess oxygen. The three-function model of HC-SCR of NO has been studied over ceria-zirconia supported copper oxide (CuO/CeZrO2). The particular functions of CuO/CeZrO2 catalyst have been proved by the catalytic runs carried out in temperature-programmed conditions (TPSR) and in situ DRIFTS. On the basis of obtained results it was observed that NO is oxidized by O2 to NO2, which is subsequently used for toluene activation. Obtained oxygenates (CxHyOz) clean the active sites from oxygen, which was left during NO reduction to N2. The DRIFTS studies have shown that NO adsorbs on the surface of ceria-zirconia forming (i) the bridging nitrate when the adsorption of NO is carried out in the absence of gaseous O2 and (ii) both nitrite and nitrate species when the adsorption is carried out in the presence of O2. Formation of these surface species can be due to the presence of surface peroxide species (O22−) or superoxide species (O2−). The presence of the latter enhances NO adsorption and influences the evolution of surfaces species during temperature programmed reaction.