NO SCR reduction by hydrogen generated in line on perovskite-type catalysts for automotive diesel exhaust gas treatment

This paper deals with the preparation (by solution combustion synthesis, SCS), characterization (by XRD, BET, FESEM and TPD/R analyses), catalytic activity evaluation (in a temperature-programmed reaction TPRe apparatus), and the assessment of the reaction mechanism of NO reduction by H-2 in the presence of oxygen on a series of perovskite-type catalysts belonging to the LaFeO3 family (LaFeO3, La0.8Sr0.2FeO3, Pd/La0.8Sr0.2FeO3. La0.8Sr0.2Fe0.9Pd0.1O3, La0.7Sr0.2Ce0.1FeO3, Pd/La0.7Sr0.2Ce0.1FeO3, La0.7Sr0.2Ce0.1Fe0.9Pd0.1O3). The catalysts have been studied in the 25-350 degrees C temperature range. Significant catalytic activities were measured at 150-250 degrees C. Among the catalysts screened, La0.8Sr0.2Fe0.9Pd0.1O3, showed the best performance. Hence, it was deposited directly over a ceramic honeycomb monolith by in situ SCS and then tested in a lab-scale test rig. A mechanistic analysis is presented concerning the relationship between the observed activity and the reducibility of the B site, determined from TPR experiments, as well as the correlation between the observed oxygen inhibition and the proposed NOx reduction mechanism. Some final conclusions are drawn on the perspective of the practical application of the investigated after-treatment route for diesel exhaust gases. (C) 2009 Elsevier Ltd. All rights reserved.