Selective catalytic reduction of NO over M–Ag/ZSM-5 bimetallic nanocatalysts (M = Mn, Fe and Ni). Physicochemical properties and catalytic performance

Selective catalytic reduction of NO by ammonia in the presence of excess oxygen has been studied over monometallic Ag/ZSM-5 and bimetallic M–Ag/ZSM-5 (M = Mn, Fe and Ni) nanocatalysts. Ag/ZSM-5 shows a good activity but low selectivity to N2 and produces N2O in considerable amounts. To improve selectivity for N2 the Ag/ZSM-5 catalyst was modified by adding different transition metals (Mn, Fe and Ni). The Fe–Ag/ZSM-5 bimetallic nanocatalyst showed the highest activity (95% NO conversion and 73% selectivity to N2 at 300°C). X-ray diffraction, transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), ammonia temperature-programmed desorption (NH3-TPD), and X-ray photoelectron spectroscopy were applied to characterize Ag/ZSM5 and M–Ag/ZSM-5 nanocatalysts. TEM results revealed the presence of nano-sized Ag/metal oxide species on the H-ZSM-5 support in M–Ag/ZSM-5 catalysts and highly dispersed Ag/metal oxide species in the Fe–Ag/ZSM-5 catalyst. The NH3-TPD measurements confirmed that compared to other catalysts the Fe–Ag/ZSM-5 catalyst has an increased amount of strong acid sites and a higher NH3 storage capacity.