Systematic effects of S-doping on the activity of V2O5/TiO2 catalyst for low-temperature NH3-SCR

S-doped V2O5/TiO2 catalyst for low-temperature selective catalytic reduction (SCR) of NO with NH3 was synthesized using the sol-gel and impregnation methods with (NH4)2TiF6 as a precursor, and characterized by X-ray powder diffraction (XRD), Brunauer-Emmett-Teller surface area (BET), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence spectra (PL), UV-vis diffuse reflectance spectroscopy (UV-vis), temperature-programmed reduction of H2 (H2-TPR), temperature-programmed desorption of NH3 (NH3-TPD)and electron paramagnetic resonance techniques (EPR). It has been found that S-doping could prevent the phase transformation of anatase to rutile, create crystal defects, and decrease the band gap. BET experiments indicated that S-doping could inhibit particle-to-particle sintering, resulting in an increase in the surface area due to the decreased particle size. XPS results suggested that the presence of sulfur was in the form of hexavalent (S6+), tetravalent (S4+) and sulfide (S2−) in titania. EPR studies proved the fact that the formation of more superoxide radicals on the surface of the catalyst by S-doping. The addition of sulfur could bring more NH3 adsorption species, and simultaneously enhance the catalytic activity for NH3-SCR of NO. The observed influence of oxygen vacancies on the SCR activity might lead to new routes toward the design of highly selective catalysts.