Migration and oxidation of vanadium atom and dimer supported on anatase TiO2(1 0 1) surface

The Conundrum of “Pair Sites” in Langmuir–Hinshelwood Reaction Kinetics in Heterogeneous Catalysis

“…Furthermore, supported metal oxide catalysts contain mobile surface adsorbates and metal oxide sites that diffuse on the support surface during reaction. As noted above, the surface diffusion barrier of supported metal oxides, especially supported VO x , is merely ∼40 kJ mol –1 at circa room temperature, , and the Tammann temperature of V 2 O 5 is ∼200–210 °C. ,− On the other hand, activation barriers for the slow reaction step(s) are often two to four times larger in magnitude than the diffusion barrier of surface VO x sites, and the reaction temperatures are in the range of 200–500 °C (e.g., reaction temperature ≥ Tammann temperature), indicating that under reaction conditions the surface VO x sites will easily diffuse. Involvement of mobile sites and mobile adsorbates can lead to nonlinear correlations between reaction rate and [*] o , since the probability (and frequency) of effective collisions between two adsorbates/sites scales nonlinearly with [*] o .…”

Understanding the prototype catalyst TiO2 surface with the help of density functional theory calculation

“…52 Besides, many other studies also support the adsorption and migration of precious metal atoms on the surfaces. 37,[53][54][55] Furthermore, Kalantari et al discovered that Ni's adsorption energies decrease as the number of adsorbed atoms increases, implying that Ni prefers to form larger clusters than Cu, Fe, and Co. 53 In addition to single atoms, the doping of metal clusters on TiO 2 surfaces has also been studied extensively. The structures of Cu n (n = 2-10) clusters supported on anatase (101) surface were studied by Huang et al 56 They found that the atomic structures exhibit an obvious hereditary feature, that is, most of the low-energy structures of larger clusters can be obtained by adding additional Cu atoms to those of smaller clusters.…”

“…44 Notably, one site each on the pristine and reduced surfaces was located that consists of a near-linear O Pt O geometry. The O v will be more stable in the subsurface of the anatase (101) surface, but once the surface adsorbs the single V atom, it will move to the surface to form BBO v -M. 37 A detailed study on the surface doping of the Pt atom was performed by Wang et al 45 Pt can adsorb on a stoichiometric surface at two O 2c sites (Pt ads ) and at the BBO V site if O v exists (Pt 2c ). Under oxygenrich conditions, Pt can replace Ti to form the Pt 5c and Pt 6c motifs.…”

“…Han et al reported that the (001) surface is more feasible for the preparation of noble metal single‐atom catalysts due to the “soft” structural character caused by incompletely saturated surface atoms 52 . Besides, many other studies also support the adsorption and migration of precious metal atoms on the surfaces 37,53–55 . Furthermore, Kalantari et al discovered that Ni's adsorption energies decrease as the number of adsorbed atoms increases, implying that Ni prefers to form larger clusters than Cu, Fe, and Co 53 …”

“…With the DFT + U method, a new surface O v site related to electron localization at surface and subsurface Ti atoms state is found. In addition, substrate adsorption and surface doping could induce the diffusion of the O v from the subsurface to the surface 36,37 . Using DFT and GW (G is the Green's function, W is the screened coulomb interaction) calculations, Hao et al 38 stated that the localized deep defect state on the anatase TiO 2 (101) surface, as observed in experiments, originates from the two under‐coordinated Ti atoms at bridging‐bonded oxygen vacancies (BBO v ) forming a σ‐bond arising from coupling between their 3d orbitals.…”