Chemisorption of NH₃ on Monomeric Vanadium Oxide Supported on Anatase TiO₂: A Combined DRIFT and DFT Study

Abstract

V/TiO2 catalysts are used in various reactions, including oxidative dehydrogenation, partial oxidation of ethanol, and selective catalytic reduction of NO x with NH3. In this work, we investigated the effect of supported monomeric vanadium oxide (VO3) on the acidity of anatase TiO2(101) surface by using density functional theory calculations combined with in situ diffuse reflectance infrared Fourier transform (DRIFT) experiments. The hydrogenation of TiO2 to form hydroxyl groups on the surface was energetically more favorable in the presence of the supported monomeric vanadium oxide. Charge transfer between TiO2 support and VO3 was considered as an origin of −OH stabilization, which made Brønsted acid sites more abundant on the V/TiO2 surface than on TiO2. Moreover, it was observed that the cationic vanadium center in VO3 can act as much weaker Lewis acid sites than the titanium center in TiO2. Such weakened acidity of Lewis acid sites in the presence of monomeric vanadium oxide was consistently observed in in situ DRIFT results, which could explain the higher reactivity of NH3 adsorbed on Lewis acid sites of V/TiO2 than those of TiO2 in the NH3-selective catalytic reduction reaction.

Chemisorption of NO2 on V-Based SCR Catalysts: A Fundamental Study toward the Mechanism of “Fast SCR” Reaction

“…The (001) surface of the TiO 2 crystals was the most commonly used surface in previous studies because it is the most active surface in anatase-phase TiO 2 crystals. ,, However, the (101) surface of the TiO 2 crystals was reported as the most thermodynamically stable surface and occupies about 94% in the construction of the anatase TiO 2 crystal. , In this study, both (001) and (101) surfaces were used to model the TiO 2 and V/Ti catalysts, which ensures that the calculated results can cover different possible features. As shown in Figure a,b, the top layer of Ti(001) and (101) surfaces have three kinds of atoms including O 2C (two-fold coordinated O), O 3C (three-fold coordinate O), and T 5C (five-fold coordinate).…”

“…30,31 The parameters of the optimized TiO 2 anatase were calculated to be a = b = 0.38 nm and c = 0.97 nm, which are identical to those reported in previous literatures. 32,33 Both (001) and (101) surfaces were cut from the optimized (3 × 2) TiO 2 supercell. A vacuum slab of 15 Å in the z-direction was used.…”

Ca-Poisoning Effect on V2O5-WO3/TiO2 and V2O5-WO3-CeO2/TiO2 Catalysts with Different Vanadium Loading

“…For 1.5VWT catalyst, the negative band at 3660 cm −1 is ascribed to doubly coordinated and bridging O-H stretching modes [30][31][32], the broad bands in the range of 3100-3400 cm −1 , 1100-1300 cm −1 , and peaks at 1600 cm −1 belong to NH 3 adsorption on the Lewis acid sites, whereas peaks at 3060 cm −1 , 1669 cm −1 and 1429 cm −1 can be assigned to the NH 4 + on the Brønsted acid sites [27,33,34]. The region between 1900 cm −1 and 2150 cm −1 , centering at around 2000 cm −1 is typical V 5+ =O [35].…”

In Search of the Active Sites for the Selective Catalytic Reduction on Tungsten-Doped Vanadia Monolayer Catalysts supported by TiO2

“…Numerous experiments studying the catalytic activity of surface vanadium oxides [29][30][31] stressed the specific role of dangling oxygen atoms on the active VO x surfaces. However, to the best of our knowledge, most theoretical studies addressing the SCR have modeled the active catalyst as a VO 3 H monomer supported on TiO 2 [32][33][34][35][36][37] or as clean unsupported V 2 O 5 . [38][39][40] In addition, V 2 O 7 clusters have also been employed as model catalysts to represent polymeric vanadyl species.…”