The selective catalytic reduction (SCR) of NO x with NH 3 to harmless N 2 and H 2 O plays a crucial role in reducing highly undesirable NO x acid gas emissions from large utility boilers, industrial boilers, municipal waste plants, and incinerators. The supported V 2 O 5 −WO 3 /TiO 2 catalysts have become the most widely used industrial catalysts for these SCR applications since introduction of this technology in the early 1970s. This Perspective examines the current fundamental understanding and recent advances of the supported V 2 O 5 −WO 3 / TiO 2 catalyst system: (i) catalyst synthesis, (ii) molecular structures of titaniasupported vanadium and tungsten oxide species, (iii) surface acidity, (iv) catalytic active sites, (v) surface reaction intermediates, (vi) reaction mechanism, (vii) ratedetermining-step, and (viii) reaction kinetics.

Time-resolved in situ IR was performed during selective catalytic reduction of NO with NH on supported VO-WO/TiO 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 NH intermediates dominate the overall SCR reaction, especially for hydrothermally aged catalysts, the minority surface NH 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 NH by supported VO-WO/TiO catalysts.

Selective catalytic reduction (SCR) of NO x with NH3 by supported vanadium oxide catalysts is an important technology for reducing acidic NO x emissions from stationary sources and mobile diesel vehicles. However, rational design of improved catalysts is still hampered by a lack of consensus about reaction pathways and kinetics of this critical technology. The SCR fundamentals were resolved by applying multiple time-resolved in situ spectroscopies (ultraviolet–visible light (UV-vis), Raman and temperature-programmed surface reaction (TPSR)) and isotopically labeled molecules (18O2, H2 18O, 15N18O, ND3). This series of experiments directly revealed that the SCR reaction occurs at surface V5+O4 sites that are maintained in the oxidized state by O2 and the rate-determining step involves the reduction of V5+O4 sites by NO and NH3, specifically the breaking of N–H bonds during the course of formation or decomposition of the NO–NH3 intermediate.

The selective catalytic reduction (SCR) of NOx with NH3 to N2 with supported V2O5(‐WO3)/TiO2 catalysts is an industrial technology used to mitigate toxic emissions. Long‐standing uncertainties in the molecular structures of surface vanadia are clarified, whereby progressive addition of vanadia to TiO2 forms oligomeric vanadia structures and reveals a proportional relationship of SCR reaction rate to [surface VOx concentration]2, implying a 2‐site mechanism. Unreactive surface tungsta (WO3) also promote the formation of oligomeric vanadia (V2O5) sites, showing that promoter incorporation enhances the SCR reaction by a structural effect generating adjacent surface sites and not from electronic effects as previously proposed. The findings outline a method to assess structural effects of promoter incorporation on catalysts and reveal both the dual‐site requirement for the SCR reaction and the important structural promotional effect that tungsten oxide offers for the SCR reaction by V2O5/TiO2 catalysts.

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