Modification of FeOx–VOx mixed oxide catalysts with WO3 for the selective catalytic reduction of NOx with NH3

Abstract

Developing a strategy to broaden the operational temperature window of the catalysts at a high gas hourly space velocity (GHSV) can effectively minimize catalyst usage and reduce the operation cost while maintaining a satisfactory deNO_x efficiency. In this study, the effect of WO₃ on the physicochemical properties and catalytic performance of FeO_x–VO_x mixed oxide catalysts for selective catalytic reduction (SCR) was systematically investigated. The introduction of WO₃ significantly enhanced SCR activity at various temperature ranges. The catalyst prepared with a W/V molar ratio of 3:1 achieved optimal NO_x conversion efficiency (>89 %) within the temperature range of 250–400 °C at a GHSV of 200,000 mL g⁻¹ h⁻¹. The WO₃ modification significantly altered the characteristics of the catalyst, thus enhancing surface acidity while simultaneously reducing oxidative capacity and specific surface area. This trade-off effectively suppressed undesirable NH₃ over-oxidation to NO_x, thereby improving high-temperature performance. At lower and intermediate temperatures, the enhanced NH₃ adsorption capacity—attributable to increased surface acidity—outweighed the negative effects of reduced reactant activation and weakened catalyst-reactant interactions caused by decreased oxidative capability and surface area. This synergistic effect broadened the operational temperature range. Mechanistic studies revealed that both pristine and WO₃-modified FeO_x–VO_x catalysts mainly followed the Eley-Rideal mechanism, with the dehydrogenation of adsorbed NH₃ species being the critical step. Furthermore, the FeO_x–VO_x–WO₃ ternary system exhibited strong sulfur tolerance, making it a promising material for industrial emission control.