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Sub-nanometer-sized Cu 6 and Au 6 clusters are stably anchored on the oxygen-deficient anatase TiO 2 surface, where Cu 6 -(V O)-TiO 2 shows high catalytic activity and satisfactory selectivity toward MG. [Display omitted] • The size and structure of stable Cu and Au clusters on TiO 2 are determined. • Oxygen vacancies can stabilize sub-nanometer-sized metal clusters. • Ti 5c and Cuδ+/Auδ- ions are coordinated to reaction intermediates. • The activity of Cu 6 -(V O)-TiO 2 (1 0 1) shows strong temperature sensitivity. • Cu-TiO 2 has good catalytic performance for DMO hydrogenation and MG production. The electronic structures of Cu-TiO 2 and Au-TiO 2 and their catalytic behaviors in the hydrogenation of dimethyl oxalate (DMO) have been studied by the stochastic surface walking-global neural network potential method, density functional theory calculation, and microkinetic analysis. Calculated results indicate that metal clusters on the pristine and oxygen-deficient TiO 2 are mostly coordinated to O 2c ions, and the defective surface may provide additional oxygen vacancies for Cu 6 and Au 6 cluster anchoring. It turns out that the interfacial Ti 5c and Cuδ+/Auδ- ions provide adsorption and hydrogenation sites for the reaction intermediates with unsaturated O and C atoms, respectively. The turnover frequency for DMO consumption is much higher on Cu-TiO 2 than on Au-TiO 2 , Cu(1 1 1), and Cu(2 1 1) at 443.15 K and 20 bar of total pressure. Given the satisfactory methyl glycolate (MG) selectivity, the Cu-TiO 2 catalyst has the potential to act as an excellent catalyst for the selective MG production. [ABSTRACT FROM AUTHOR]

The finding that the MG selectivity increases and the DMO hydrogenation activity decreases with increasing the Ag nanoparticle size reveals the structure sensitivity of DMO partial hydrogenation. [Display omitted] • The structural sensitivity of DMO partial hydrogenation over Ag catalysts. • Ag stepped surfaces dominate the kinetics of the hydrogenation reaction. • The DMO consumption rate decreases with increasing the nanoparticle size. • The MG selectivity rises as the particle size changes from 5 nm to 10 nm. • A new strategy to ensure thermodynamic consistency of the reaction. Silver nanoparticles of different sizes have been synthesized to study their catalytic performance in dimethyl oxalate (DMO) partial hydrogenation to methyl glycolate (MG). Then, a detailed microkinetic analysis based on the results of DFT calculations has been performed to elucidate the origin of the observed size-dependent kinetics, where tabulated thermodynamic properties of gas-phase species are used to ensure the thermodynamic consistency of the reaction. Calculated results show that the turnover frequency for DMO consumption is much higher on Ag(2 1 1) than on Ag(1 1 1), suggesting the stepped surface dominates the kinetics. The hydrogenation of DMO on the two surfaces occurs along the same dominant reaction pathway, and the rate-determining step for the partial and deep hydrogenation of DMO is DMO and MG dissociation, respectively. The finding that the MG selectivity increases while the DMO hydrogenation activity decreases with the Ag nanoparticle size reveals the structure sensitivity of DMO partial hydrogenation. [ABSTRACT FROM AUTHOR]