Local Bonding Effects in the Oxidation of CO on Oxygen-Covered Au(111) from Ab Initio Molecular Dynamics Simulations

C-H oxidation enhancement on a gold nanoisland by atomic-undercoordination induced polarization

C-H activation is of great significance in the chemical industry while an effective solvent-free catalyst is highly desired. This work shows that a gold nanoisland which was inert in the bulk is effective for C-H activation reactions. We investigated the C-H activation of toluene on an Au nanoisland (58 atoms) using relativistic density functional theory (DFT). We found that (i) the bonds between under-coordinated gold atoms (corner site) shrink spontaneously and become stronger; (ii) the valence charges of corner atoms are polarized to the upper edge of the valence band (near the Fermi level), indicating the electron donation ability in the catalytic process; (iii) during C-H oxidation, the indirect path (O2 dissociation and O-H bonding) and direct path (O2-H bonding) were considered. The Au-O2 complex is active enough to abstract a hydrogen atom directly from toluene, with a barrier that is 6.8 kcal mol-1 lower than that of the indirect path; and (iv) a transfer of up to ∼0.8 electrons from gold to O2 occurs. Moreover, hybridization between delocalized gold orbitals and oxygen p-orbitals leads to the stabilization of the singlet spin state of Au58O. Our results suggest that undercoordination-charge-polarization are key factors for the C-H oxidation catalyzed by an Au nanoisland.

Catalytic mechanisms of Au₁₁ and Au₁₁-nPt n (n=1-2) clusters: a DFT investigation on the oxidation of CO by O₂

The oxidation of CO catalyzed by clusters of Au11, Au10Pt and Au9Pt2 was investigated using the M06 functional suite of the density functional theory. Au and Pt atoms were described with the double-ζ valence basis set Los Alamos National Laboratory 2-double-z (LanL2DZ), whereas the standard 6-311++G(d,p) basis set was employed for the C and O atoms. Our theoretical model showed that (1) after coordination to Au and Au-Pt cluster, O2 and CO are apparently activated, and Mulliken charges show that the gold atoms in the active sites of Au11 are negatively charged; (2) Au-Pt clusters with 11 atoms can effectively catalyze the oxidation of CO by O2; (3) Au11 exhibits good catalytic performance for the oxidation of CO; (4) oxidation of CO occurs preferably on the Au-Pt active sites in Pt-doped clusters, and the single-center mechanisms are more favorable energetically than the two-center mechanisms; (5) after adsorption, an O2 molecule oxidates two CO molecules via stepwise mechanisms; and (6) the catalytic processes are highly exothermic.