Cation synergies affect ammonia adsorption over VOX and (V,W)OX dispersed on α-Al2O3 (0001) and α-Fe2O3 (0001).

The catalytic behavior of oxide-supported metal oxide species depends on the nature of the support and the presence of co-catalysts. We use density functional theory (DFT) to explore the relationship between the structure and chemical behavior of vanadium oxide in light of its industrial use for the selective catalytic reduction of nitric oxide with ammonia (NO-SCR). The relative stabilities of dispersed VOX monomers, dimers, and long-chain oligomers on two model oxide support surfaces with similar structure but drastically different chemical behavior, α-Al2O3 (0001) and α-Fe2O3 (0001), are determined. The effect of added tungsten, known to promote NO-SCR, is also investigated on the relatively inert α-Al2O3 (0001) support. We find that the adsorption behavior of NH3, representing the first step of the NO-SCR reaction, depends strongly on the VOX local structure. Protonation of NH3 to NH4+ over surface hydroxyls is energetically favorable over VOX-WOX dimers and VOX oligomers, which are stabilized by the reducible α-Fe2O3 (0001) support. Graphical abstractImage 1Highlights· Surface structures were calculated for V atop α-Al2O3 (0001) and α-Fe2O3 (0001). · Adding W to V creates stronger Brønsted acid sites that convert NH3 to NH4+.· α-Fe2O3 (0001) stabilizes oligomeric VOX species needed for NO-SCR. · Cation synergies mediated by O ligands explain behavior of NO-SCR catalysts. [ABSTRACT FROM AUTHOR]