Silica modulated palladium catalyst with superior activity for the selective catalytic reduction of nitrogen oxides with hydrogen

Abstract

A significant promotion effect of colloidal SiO2 on Pd/TiO2 catalyst for improving the activity and N2 selectivity in the selective catalytic reduction of NO with H2 (H2-SCR) was reported, both before and after hydrothermal aging. The SiO2 addition not only benefited the formation of more oxygen vacancies but also increased Pd dispersion and created rich Pd-SiO2 interfaces on Pd-SiO2/TiO2 catalyst. The H2-SCR of NO on both Pd/TiO2 and Pd-SiO2/TiO2 followed a Langmuir-Hinshelwood mechanism, in which the adsorbed bridging bidentate nitrates on TiO2 could react with dissociated H2 species on Pd sites at Pd-TiO2 interface. Particularly, on the promoted Pd-SiO2/TiO2, the Pd-TiO2 interface could facilitate NO adsorption and activation, and the created Pd-SiO2 interface could benefit H2 adsorption and dissociation, thus contributing to its significantly improved H2-SCR activity. Furthermore, the active Pd species (which should be Pd0 under reaction condition with higher surface concentration) within Pd-SiO2/TiO2 could be well stabilized during long-term hydrothermal aging process through the formation of rich Pd-SiO2 interfaces.