Surface functionalization: an efficient alternative for promoting the catalytic activity of closed shell gold clusters

Abstract

Surface functionalization through adsorption of ligands or non-metal atoms is considered to be an interesting and viable approach for tuning the physicochemical properties of gold clusters. Highly stable and magic numbered electronic configurations of thiolate protected gold clusters such as Au₂₅(SR)₁₈, Au₃₈(SR)₂₄etc. with intriguing properties are the direct manifestation of the rich chemistry of the Au–S interface. The present investigation discerns the CO oxidation activity of structurally well characterized sulphur functionalized gold cluster anions Au_mS₄⁻, m = 6–10. To establish an in-depth understanding, their activities are analyzed and compared with the corresponding pristine gold clusters. It is seen that sulphur functionalization irrespective of a closed or open shell nature leads to a significant decrease in the O₂ adsorption energies on the anionic gold clusters. However, in sharp contrast to O₂ adsorption, surface functionalization gives rise to multifarious catalytic behavior in Au_mS₄⁻ clusters with catalytic activity ranging from low (for Au₆S₄⁻, Au₈S₄⁻) to moderate (for Au₉S₄⁻, Au₁₀S₄⁻) to very high (for Au₇S₄⁻) for CO oxidation. It is interesting to note that the closed shell Au₇S₄⁻ and Au₉S₄⁻ clusters with poor O₂ adsorption show remarkably low activation barriers and enhanced catalytic activity as compared to the open shell Au_mS₄⁻ clusters with an odd number of electrons. In particular, in the case of Au₇S₄⁻ the lowest activation energy barriers of 0.01 and 0.21 eV are obtained, making the CO oxidation reaction facile. Moreover, ab initio molecular dynamics are performed to confirm the enhanced catalytic behaviour of Au₇S₄⁻ and its dynamical stability during the desorption of CO₂ molecule from its surface.