Active sites of NO selective catalytic reduction over V₂O₅-WO₃/TiO₂

Selective catalytic reduction (SCR) is the most effective technology to control NO emission using commercial V2O5-WO3/TiO2 catalysts, but the nature of active catalytic sites remains under debate. Here we provide evidence demonstrating that dinuclear vanadium-tungsten sites are the most active catalytic sites of conventional V2O5-WO3/TiO2 catalysts, inconsistent with a prevailing view that dimeric vanadium sites are the active sites. The dinuclear vanadium-tungsten sites have inherently stronger acidity than the dimeric vanadium sites, favoring NH3 adsorption. Meanwhile, the vanadium 3d electrons of the dinuclear vanadium-tungsten sites are richer than those of the dimeric vanadium sites, facilitating O-2 activation in SCR. Hence, the dinuclear vanadium-tungsten sites have higher SCR activity than the dimeric vanadium sites under identical reaction conditions. This work settles a long dispute on the identification of active sites of conventional V2O5-WO3/TiO2 SCR catalysts, thus having implications for a unified explanation of disparate SCR reaction mechanisms and rational design of improved SCR catalysts.