Selective catalytic reduction of nitric oxide by hydrogen over Zn-ZSM-5 and Pd and Pd/Ru based catalysts

Abstract

The catalytic reduction of NOx with hydrogen (H2-SCR) in excess oxygen over a non-noble metal catalyst, Zn-ZSM-5, was studied for the first time. The results showed that Zn-ZSM-5 had considerable activity for H2-SCR, with a single NOx conversion peak at 250°C, and high N2 product selectivity. Two noble metal based catalysts, Pd/Zn-ZSM-5 and Pd/Ru/W/(ZrO2–SiO2)SO4, were also synthesized and their H2-SCR activities were evaluated and compared with Zn-ZSM-5 under identical laboratory experimental conditions. The effects of CO concentration, water vapor and SO2 added to the feed gas (NO, H2, balance He) on H2-SCR over these three catalysts were also studied and compared. hydrogen temperature programmed desorption (H2-TPD) experiments were performed on Zn-ZSM-5: the results showed strong chemisorption of hydrogen, while both the amount and the binding strength of the chemisorbed hydrogen increased with the hydrogen dosing temperature. The role of Zn cations in the chemisorption is also discussed.