In situ FT/IR study of selective catalytic reduction of NO over alumina-based catalysts

The selective catalytic reduction of NO by hydrocarbons (HC-SCR) is a promising method for the removal of nitrogen oxides (NOx) from various types of oxygen rich exhaust gases. For the elucidation of reaction mechanism of the HC-SCR, in situ FT/IR spectroscopy is a powerful method. Here, studies of dynamics of surface adsorbed species on the HC-SCR over alumina-based catalysts (Al2O3, Cu-Al2O3 and Ag-Al2O3) by means of in situ FT/IR spectroscopy are reviewed. On alumina-based catalysts, nitrates and oxygenates were observed as major surface adsorbed species under the SCR conditions. Kinetic analysis of these surface species revealed that the selective reaction of NO to N-2 initially proceeds by the oxidation of NO to surface nitrates and of hydrocarbon to surface oxygenates, followed by the selective reaction between these surface species. This surface reaction forms NCO and CN species, and finally results in the formation of N-2. On the-basis of the reaction mechanism thus proposed, improvement of the HC-SCR system should be possible. For example, the HC-SCR activity of Ag-Al2O3 was significantly enhanced by decrease of the surface nitrate coverage when using higher hydrocarbons as reductants. Kinetic analysis of surface adsorbed species by in situ FT/IR provides a key to control the HC-SCR activity. (C) 2003 Elsevier Science Ltd. All rights reserved.