Understanding and quantifying how the active sites in supported metal catalysts can be modified are critical for rationally designing catalysts. This problem is particularly complex for reactions that occur at the metal−support interface (MSI) because of the multiple chemistries associated with the metal and the support. In this study, we used the oxidation of substituted benzyl alcohol over Au/TiO 2 and Au/Al 2 O 3 to probe MSI chemistry. Substituents impacted substrate binding, deprotonation, and the rate-limiting transfer of a hydride from benzyl alcohol to Au, as shown by a combination of Michaelis−Menten (M−M) saturation kinetics and kinetic isotope effects. Hammett studies performed with a single substrate versus those done with two substrates together in competition experiments showed significant differences, which were attributable to stronger competitive adsorption on the support by more electron-rich alcohols. The M−M analysis showed that alcohol substitution impacts substrate binding and deprotonation equilibria, which in turn affect the number of active alkoxides adsorbed at the MSI. Hammett slopes should therefore be measured under saturating conditions using one substrate at a time. The Hammett slopes measured for heterogeneous systems in this manner agree well with the KIE−Hammett slope relationship determined in homogeneous systems, which provide information on the early or late nature of the transition state. Our results show that the combination of Michaelis−Menten and Hammett techniques for benzyl alcohol oxidation provides mechanistic information associated with the MSI chemistry of supported Au catalysts as well as information on active site electronics.

Au nanoparticles (NP) on TiO 2 have been shown to be effective catalysts for selective oxidation reactions by using molecular oxygen. In this work, we have studied the influence of support morphology on the catalytic activity of Au/TiO 2 catalysts. Two TiO 2 anatase supports, a nanoplatelet-shaped material with predominantly the {001} facet exposed and a truncated bipyramidal-shaped nanoparticle with predominantly the {101} facet exposed, were prepared by using a nonaqueous solvothermal method and characterized by using DRIFTS, XPS, and TEM. Au nanoparticles were deposited on the supports by using the deposition−precipitation method, and particle sizes were determined by using STEM. Au nanoparticles were smaller on the support with the majority of the {101} facet exposed. The resulting materials were used to catalyze the aerobic oxidation of benzyl alcohol and trifluoromethylbenzyl alcohol. Support morphology impacts the catalytic activity of Au/TiO 2 ; reaction rates for reactions catalyzed by the predominantly {101} material were higher. Much of the increased reactivity can be explained by the presence of smaller Au particles on the predominantly {101} material, providing more Au/TiO 2 interface area, which is where catalysis occurs. The remaining modest differences between the two catalysts are likely due to geometric effects as Hammett slopes show no evidence for electronic differences between the Au particles on the different materials.

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