SO2-induced dual active sites formation over VOx/Fe2O3 for accelerating NH3 selective catalytic reduction of NOx

Abstract

The construction of plausible alternatives of V2O5-WO3/TiO2 for effectual NOx purification is becoming a research hotspot. Herein, a robust VOx/Fe2O3-S catalyst with SO2 tailored surface acid sites and active VOx sites was engineered for boosting the NOx reduction performance. The VOx/Fe2O3-S catalyst afforded above 90% NOx conversion and 90 % N2 selectivity at 275–425 °C, coupled with the exceptional long-term SO2 + H2O resistance. Py-IR and in situ DRIFTS disclosed that the formation of Fe2(SO4)3 endowed Fe2O3-S and VOx/Fe2O3-S with abundant medium-strong Lewis and Brønsted acid sites rather than covering the active sites, strengthening the NH3 adsorption and suppressing the overoxidation of NH3 on the reducible Fe2O3 support. Raman analysis revealed the generation of new species of polymeric vanadyl species on VOx/Fe2O3-S induced by the SO2. In-depth mechanistic understanding through DFT analyses indicated that the NOx reduction reaction over the Fe2O3-S and VOx/Fe2O3-S obeyed the Langmuir-Hinshelwood and Eley-Rideal mechanism simultaneously. Moreover, the presence of polymeric vanadyl species dramatically lower the overall energy barrier for NOx reduction, thus speeding up the SCR reaction of VOx/Fe2O3-S. This study can shed light on the more rational design of VOx-based catalysts for highly efficient NOx reduction in industry.