NO Reduction with CO on Copper and Ceria Oxides Supported on Alumina

Abstract

The problem about decreasing the harmful emissions of nitrogen oxides in industrial gases or in motor vehicles is an important contemporary task in relation to the environmental protection and people health. Recently, the investigations on this topic increase because of the growing concern about ecological standards. One of the ways of neutralizing nitrogen oxides proposed by modern chemistry is their catalytic conversion to nitrogen. Transition metal oxides have shown very good achievements with respect to NO reduction with CO [1]. The use of spinel catalysts, which are not sensitive to catalytic poisons, is also very helpful. In addition, the spinel formation affects favorably the reduction of oxides. Nhe CuxCo(3-x)O4 spinel catalysts and those promoted with noble metals Pt-Rh/CuCo2O4/c-Al2O3 are found to possess a high activity toward NO reduction with CO [2–6]. Jiang et al. [7] have established TiO2supported and CuOpromoted cerium to demonstrate a high activity in the NO + CO reaction, 100% conversion of NO being achieved at 300 C. The high activity has been ascribed to the presence of four sites of NO adsorption NO (Cu, Cu(I), Cu(II) b Ce) and Cu(I)–Cu b Ce–Ce containing active sites for the NO + CO reaction. Studying the same reaction on preliminary reduced or re-oxidized CuO/TiO2, Jiang et al. [8] observed an activity rising during the reduction of the catalyst surface. This was attributed to reduction-provoked appearance of ‘‘oxygen caves’’ on the catalyst surface, increasing Cu species dispersion and Cu(II) formation. Park et al. [9] investigated the same catalyst type applied on Al2O3 and found the promotion of a cerium catalyst with copper to lead to an enhanced activity towards CO oxidation, the effect on methane oxidation being weaker. Larsson et al. [10] have established that the modification of alumina support with ceria before the copper oxide deposition gives well dispersed copper oxide species and enhances the activity towards CO oxidation. Zou et al. [11] has determined that the interfacial CuO and CeO2 interaction and synergistic effect enhances the red–ox properties of CuO/CeO2 catalyst and the highly dispersed copper species have been proposed as active sites for the selective CO oxidation. The purpose of the present work is to investigate how the way and the sequence of copper and cerium oxide deposition on alumina influence on the activity of the prepared catalysts in the reduction of NO with CO.