Promoting effect of multi-transition metals on the NO reduction by NH3 over TiO2 catalyst studied with in situ DRIFTS

Abstract

NOx is one of the most detrimental pollutants to the atmospheric and ecological environment. Currently, selective catalytic reduction (SCR) of NOx by NH3 was conducted by transition metals-doped (Mo, Ce, Cu, Fe, W, and Zr, including P) TiO2 catalysts through orthogonal experimental design. It was found that Mo, Cu, Fe, and Zr significantly affected the catalytic activity, while Mo showed the highest impact. The optimum amounts of Mo, Ce, Cu, Fe, W, P, and Zr were 1.5 wt%, 2 wt%, 6 wt%, 4 wt%, 0 wt%, 0.9 wt%, and 4 wt%, respectively. The catalysts’ redox properties and adsorption capacity for NO were key factors affecting the catalytic activity. Proper amounts of adsorbed oxygen, together with appropriate adsorption capacity for NO and acidity distribution, were beneficial for the formation of intermediates. The mechanistic cause of the promoting effect of metal oxides for NH3-SCR was studied using in situ DRIFTS. These results revealed that the addition of metal oxides is to promote the adsorption and activation of NH3 on the catalyst surface, which is beneficial for the promotion of SCR activity. Promoting effect of multi-transition metals was confirmed for the selective catalytic reduction of NO by NH3 over TiO2 following the order of Mo > Fe ≈ Zr > Cu > W>P > Ce.