Promoter rather than Inhibitor: Phosphorus Incorporation Accelerates the Activity of V2O5–WO3/TiO2 Catalyst for Selective Catalytic Reduction of NOx by NH3

The selective catalytic reduction of NOx by NH3 (NH3–SCR) over the V2O5–WO3/TiO2 catalyst is the state-of-the-art technology for NOx removal from both stationary and mobile sources. Phosphorus can be presented in the fuel gas or as a pelletizing additive to increase the mechanical strength of the industrial extruded monolithic V2O5–WO3/TiO2 catalyst. Herein, we demonstrated that a 2-fold increase in the intrinsic activity without detriments to N2 selectivity and anti-H2O/SO2 stability can be achieved by incorporating V2O5–WO3/TiO2 with a certain amount of phosphorus, which was generally considered as an inhibitor for such type of catalyst. Phosphorus incorporation enhanced both Brønsted and Lewis acid sites on V2O5–WO3/TiO2, and NH3 bound to both sites are involved in the SCR reaction but with different rates. The molecular structure of surface vanadyl species was modulated to be more polymeric (dimer and oligomer content increases from 77% to 90%) by phosphorus incorporation through a spatial effect, during which an interaction between phosphorus and tungsten was observed. This study reveals the promotional effect of phosphorus to V2O5–WO3/TiO2 catalyst, which is important for the fundamental understanding and design of vanadium-based catalyst.