Reaction Pathways and Kinetics for Selective Catalytic Reduction (SCR) of Acidic NOx Emissions from Power Plants with NH3

Selective catalytic reduction (SCR) of NOx with NH3 by supported vanadium oxide catalysts is an important technology for reducing acidic NOx 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, H218O, 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.