SCR of Nitric Oxide by Hydrogen over Pd and Ir Based Catalysts with Different Supports

Selective catalytic reduction of NO x with hydrogen (H 2 -SCR) in excess oxygen over Pd and Ir based catalysts with various silica supports was studied. The Pd/V 2 O 5 /TiO 2 /SBA-15 and Ir/SBA-15 catalysts showed the highest activities. The effects of noble metal, various silica supports, CO and SO 2 on H 2 -SCR over these catalysts were also studied and compared, and possible underlying mechanisms discussed. A comparison of 1 % Ir-doped on silicas with a wide range of pore sizes showed that the peak temperature (where the NO conversion maximum was located) was directly related to the pore size: larger pores of the support resulted in higher peak temperatures. This result indicates that pore diffusion limitation played a role in determining the peak temperature. In addition, a non-noble metal catalyst, Nb 2 O 5 /SiO 2 , was found to have considerable activity. Graphical Abstract Larger pores of the support resulted in higher peak temperatures, which indicated that pore diffusion limitation played a direct role.