Reduction of nitric oxide with methane on Pd/Co/H-ZSM-5 catalysts: Cooperative effects of Pd and Co

Reduction of low concentration of nitric oxide (NO) with methane as a reductant under wet conditions has been investigated using Pd/Co/H-ZSM-5 catalysts and the effects brought about by coexistence of Pd and Co are discussed. The role of Co is attributed to the acceleration of oxidation of NO to NO2, which is the necessary species for reduction of NO with CH4 on Pd sites. A Pd/H-ZSM-5 loading of 1 wt% Co shows a maximum activity for NO reduction as well as for NO oxidation. Excess loading of Co led to a decrease in activity for NO reduction. An XPS study shows that Pd and Co are well dispersed inside the zeolite when the concentrations of Pd and Co are less than 1 wt%. Loading of excess Co, however, causes aggregation of Pd on the surface of ZSM-5.