Mechanistic Aspects of Highly Efficient Fe a S b TiO x Catalysts for the NH3‑SCR Reaction: Insight into the Synergistic Effect of Fe and S Species

A series of highly efficient, environmentally friendly, and low-cost Fe a S b TiO x catalysts were prepared by a simple thermal hydrolysis method for the NH3-selective catalytic reduction (SCR) reaction. The Fe a S b TiO x catalysts had a crystalline structure typical of anatase TiO2, with Fe3+ ions well dispersed and probably incorporated into anatase TiO2 through Fe–O–Ti bonds. Sulfur species, present in the form of SO4 2–, significantly increased the stability and amount of both Brønsted and Lewis acidic sites, which greatly enhanced NH3 adsorption. The catalytic activity was dominated by the iron species, whereas the sulfur species improved the high-temperature activity by suppressing the side reaction of NH3 oxidation, and the similar effect of sulfate was also found over the typical Ce-based, V-based, and Mn-based catalysts. In situ diffuse reflectance infrared Fourier transform spectroscopy results indicated that strongly adsorbed NH3 attributed to sulfate could participate in the NH3-SCR reaction with Fe3+ activation instead of the NH3 oxidation reaction. Consequently, the synergistic effect of Fe and S species resulted in the catalyst Fe0.07S0.1TiO x , exhibiting high activity with >90% NO x conversion and N2 selectivity within a broad operating temperature window of 300–500 °C.