Investigation of anodic alumina supported silver catalyst for the selective reduction of NO by propene: Promotional effect of hydrogen and effect of electrical heating

A series of anodic-alumina-supported silver catalysts (Ag/Al₂O₃) were synthesized to investigate the promotional effect of H₂ and electrical heating possibility on the selective catalytic reduction (SCR) of NO by C₃H₆. It was observed that the SCR activity of Ag/Al₂O₃ catalyst was greatly improved at low temperatures in the presence of H₂. Moreover, this promotional effect became more significant with increasing H₂ concentration. According to the results of the reaction without C₃H₆, H₂ did not significantly improve the activity; this indicates that the H₂ acted as a promoter but did not directly participate in NO_x reduction. The results of NO_x-TPD (Temperature Programmed Desorption) and NO_x-H₂-TPR (Temperature Programmed Reduction) showed that the NO_x adsorbed on the catalyst surface was quickly desorbed in the presence of H₂, while NO_x desorption became faster by increasing the concentration of H₂ added to the flow as well as the Ag loadings. In the case of catalysts with low Ag loadings, nitrate poisoning was considered to be the main reason for low NO_x conversion at low temperatures. On the other hand, in the case of the high Ag loadings, the scarcity of Ag_n ^δ+ clusters was inferred to result in unfavorable SCR activity. Additionally, electrical heating tests on the SCR by C₃H₆ in the presence of Ag/Al₂O₃ catalysts showed excellent denitration activity and rapid reaction rate. On the basis of the electrical heating pattern, a new strategy for controlling NOx emission from diesel engines was formulated.