Revisiting the Impact of Tungsten on the Catalytic Properties of Ammonia-SCR V2O5-WO3/TiO2 Catalysts: Geometric vs. Electronic Effects

Abstract

The SCR performance of V2O5-WO3/TiO2 SCR-catalysts characterized by different surface W density (2.1W/nm2 and 9.5W/nm2) and different surface V density varying in the range 1–8V/nm2 has been investigated in order to clarify existing controversies on the preferential involvement of electronic and geometric effects in the catalytic properties. It was found that tungsten has a weak effect on the VOx cluster size distribution through contraction of dilution effect. In contrast, the optimal interaction between W and V, when both reach their highest composition, appears to be a relevant parameter that can enhance their acidic properties and improve the catalytic efficiency in dry conditions. On the other hand, an absence of significant interaction leads to discontinuity due to deactivation. In the presence of steam, acidic properties are averaged, lowering the impact of the V to W ratio. Finally, the critical importance of acidic properties which outperform redox properties in the definition of active site is pointed out in the light of this study.

Theoretical insight into H2O impact on V2O5/TiO2 catalysts for selective catalytic reduction of NOx

“…There is long argument about the nature of the active sites, Marberger et al 34 observed that the Lewis acid site is the primary site for the SCR reaction, while Brønsted acid sites served as a storage of NH 3 , and this theory is also supported by others. [72][73][74][75] To represent the reactivity of SCR catalysts more accurately, the adsorption of NH 3 is modeled with a similar approach as H 2 O. The adsorption configuration is determined by surface scans of adsorption energy over the Lewis acid sites, for each configuration with different level water coverage.…”