Two techniques to study the surface chemistry of supported gold nanoparticles were developed. First, phenylethyl mercaptan (PEM) adsorption from hexane solution was followed with UV-vis spectroscopy to evaluate the total amount of surface Au available. Two catalysts, Au/Al2O3 and Au/TiO2, were found to have Au:S surface stoichiometries of ∼2:1, whereas a Au/SiO2 catalyst had a Au:S surface stoichiometry of ∼1:1. The room temperature equilibrium binding constants for PEM adsorption on the Au/Al2O3 and Au/TiO2 catalysts were similar (∼3 × 105 M-1; ΔG ≈ -31 kJ/mol); the PEM-Au/SiO2 binding constant was somewhat larger (∼2 × 106 M-1; ΔG ≈ -36 kJ/mol). XPS data for all of the catalysts showed no observable changes in the Au oxidation state upon adsorption of the thiol. Implications of these experiments regarding self-assembled monolayers and thiol-stabilized Au nanoparticles are discussed. Second, kinetic titrations (i.e., controlled thiol-poisoning experiments) were developed as a method for evaluating the number of active sites for selective 4-methoxybenzyl alcohol oxidation. These experiments suggested only a fraction of the surface Au (∼10-15% of the total Au) was active for the reaction. When thiol was added with the 4-methoxybenzyl alcohol substrate, more thiol was required to poison the catalyst, suggesting that the thiol and substrate compete for initial adsorption sites, possibly at the metal-support interface. These two methods were combined to evaluate the magnitude of the support effect on selective 4-methoxybenzyl alcohol oxidation. Correcting the catalytic activity of the catalysts to the number of sites determined by thiol titration provided clear evidence that the support has a strong influence on the catalytic activity of Au in benzyl alcohol oxidation. (Chemical Presented).
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