An in-depth revelation of a novel facilitation mechanism of H2O on the NH3-SCR reaction of Mn-Ce/TiO2 catalyst with exposed anatase {001} facets

H2O typically has a detrimental impact on the NH3-SCR reaction, exacerbating the sulfur poisoning of the catalysts. This study thoroughly explores the unusual facilitating mechanism of H2O (gas) (g) at low concentrations (volume fraction less than 3.5 vol%) on the NH3-SCR reaction of a Mn-Ce/TiO2 (M−C/Ti) catalyst with preferential exposure of the anatase {001} facets (M−C/Ti-001) through comprehensive experimental characterization and DFT (Density functional theory) calculations. The optimum water vapor promotion concentration of 2.5 vol% was experimentally determined. It generated new Brønsted acid sites after H2O adsorption on the anatase {001} facets, increasing the activity of the Lewis acid sites and the NH3 adsorption capacity on Brønsted acid sites (B-NH4+). B-NH4+ species can react with NO2 in a fast SCR reaction, significantly enhancing the overall reaction rate. The low content of H2O (g) contributes to the inert linear nitrite involved in the NH3-SCR reaction, which is favourable for the NH3-SCR reaction. In addition, the Brønsted acid sites effectively inhibited the adsorption of SO2 onto the surface of the M−C/Ti-001 catalyst, enhancing its sulfur resistance. This study provides new insights into the promotion mechanism of M−C/Ti-001 catalysts by low concentration of water vapor.