Nature of Active Sites and Surface Intermediates during SCR of NO with NH₃ by Supported V₂O₅-WO₃/TiO₂ Catalysts

Time-resolved in situ IR was performed during selective catalytic reduction of NO with NH₃ on supported V₂O₅-WO₃/TiO₂ catalysts to examine the distribution and reactivity of surface ammonia species on Lewis and Brønsted acid sites. While both species were found to participate in the SCR reaction, their relative population depends on the coverage of the surface vanadia and tungsta sites, temperature, and moisture. Although the more abundant surface NH₄⁺_,ads intermediates dominate the overall SCR reaction, especially for hydrothermally aged catalysts, the minority surface NH_3,ads intermediates exhibit a higher specific SCR activity (TOF). The current study serves to resolve the long-standing controversy about the active sites for SCR of NO with NH₃ by supported V₂O₅-WO₃/TiO₂ catalysts.