Adsorption, Dissociation, and Spillover of Hydrogen over Au/TiO₂ Catalysts: The Effects of Cluster Size and Metal–Support Interaction from DFT

Abstract

The effects of cluster size and metal–support interaction on the catalytic activity of Au nanoparticles supported on anatase TiO2(101) and (001) surfaces for H2 adsorption, activation and dissociation were investigated by periodic density functional theory (DFT) calculations. On the stoichiometric TiO2 surfaces, it was found that the adsorptions of both Au clusters and H2 molecules are sensitive to the cluster size of gold, and the (001) facet with “soft” lattice and coordination unsaturated atoms on the surface is superior for Au adsorption stability, but H2 adsorption does not show apparent distinction on the two catalysts. The Au atoms active for H2 activation should be neutral in charge and located at the edge or corner of the Au nanoparticles in lower coordination. The metal–support interaction plays an important role for H2 activation and dissociation, and the O2––H+–H––Au structure was identified in the transition state through which H2 dissociation occurred via a heterolytic dissociation process at the Au–TiO2 interface for both facets. H* spillover from the Au site to the bridging −O2cH site can generate H2O molecules on the two facets, and O-vacancy formation is energetically more favorable on (101) than (001). The presence of O-vacancy defects significantly impacts the adsorption stability of Au clusters and H2 molecule but has small effect on the energy barrier for H2 dissociation, which proceeds fast on both the stoichiometric and reduced anatase TiO2(101) and (001) surfaces.

Origin of the synergistic effect between TiO2 crystalline phases in the Ni/TiO2-catalyzed CO2 methanation reaction

“…The results, presented on Table S13, clearly show that the conversion improvement linked to the Ni on Ni/TiO2-anatase is much higher than the one linked to the TiO2anatase support itself. The precise role of the H species is still unclear, but it is worth mentioning that TiO2 reduction by hydrogen spillover has been reported [94][95][96]. Additionally, it was reported that on Rh catalyst supported on CeO2 (another reducible support), the fraction of CO that undergoes dissociation increases significantly as the CeO2 surface is reduced [97].…”

Water adsorption and dissociation on gold catalysts supported on anatase-TiO2(101)

“…We choose such small size in order to keep the simulation cell as small as possible. Besides, many experimental studies have shown that such small clusters with various sizes can be easily deposited on the TiO 2 surface, being highly active catalysts for a broad class of reactions [25][26][27]. For supported Au 4 , we use a 1×4 anatase unit cell.…”

Distance Effect of Ni-Pt Dual Sites for Active Hydrogen Transfer in Tandem Reaction

“…The hydrogen transfer can be well coupled with the spillover of active hydrogen at the metal-oxide interface with the -Ti-OH surface intermediate. 40 Therefore, we propose a plausible mechanism for active hydrogen transfer on the five-layer catalyst as shown in Figure 5 . The active hydrogen atoms from the decomposition of N 2 H 4 ·H 2 O (H-Ni) transfer from the Ni layer to the TiO 2 interlayer and further to the Pt interlayer for hydrogenation.…”