Low-temperature H2-SCR of NO on a novel Pt/MgO-CeO2 catalyst

The selective catalytic reduction of NO by H-2 under strongly oxidizing conditions (H-2-SCR) in the low-temperature range of 100-200 degrees C has been studied over Pt supported on a series of metal oxides (e.g., La2O3, MgO, Y2O3, CaO, CeO2, TiO2, SiO2 and MgO-CeO2). The Pt/MgO and Pt/ CeO2 solids showed the best catalytic behavior with respect to N-2 yield and the widest temperature window of operation compared with the other single metal oxide-supported Pt solids. An optimum 50 wt% MuO-50wt% CeO2 support composition and 0.3 wt% Pt loading (in the 0.1-2.0 wt% range) were found in terms of specific reaction rate of N-2 production (mols N-2/g(cat) s). High NO conversions (70-95%) and N-2 selectivities (80-85%) were also obtained in the 100-200 degrees C range at a GHSV of 80,000 h(-1) with the lowest 0.1 wt% Pt loading and using a feed stream of 0.25 vol% NO, 1 vol% H-2, 5 vol% O-2 and He as balance gas. Addition of 5 vol% H2O in the latter feed stream had a positive influence on the catalytic performance and practically no effect on the stability of the 0.1 wt% Pt/MgO-CeO2 during 24 h on reaction stream. Moreover, the latter catalytic system exhibited a high stability in the presence of 25-40 ppm SO2 in the feed stream following a given support pretreatment. N-2 selectivity values in the 80-85% range were obtained over the 0.1 wt% Pt/MgO-CeO2 catalyst in the 100-200 degrees C range in the presence of water and SO2 in the feed stream. The above-mentioned results led to the obtainment of patents for the commercial exploitation of Pt/MgO-CeO2 catalyst towards a new NOx control technology in the low-temperature range of 100-200 degrees C using H-2 as reducing agent. Temperature-programmed desorption (TPD) of NOx and transient titration of the adsorbed surface intermediate NOx species with H-2 experiments, following reaction, have revealed important information towards the understanding of basic mechanistic issues of the present catalytic system (e.g., surface coverage, number and location of active NOx intermediate species, NOx spillover). (c) 2006 Elsevier B.V. All rights reserved.