Evaluating differences in the active-site electronics of supported Au nanoparticle catalysts using Hammett and DFT studies

Supported metal catalysts, which are composed of metal nanoparticles dispersed on metal oxides or other high-surface-area materials, are ubiquitous in industrially catalysed reactions. Identifying and characterizing the catalytic active sites on these materials still remains a substantial challenge, even though it is required to guide rational design of practical heterogeneous catalysts. Metal–support interactions have an enormous impact on the chemistry of the catalytic active site and can determine the optimum support for a reaction; however, few direct probes of these interactions are available. Here we show how benzyl alcohol oxidation Hammett studies can be used to characterize differences in the catalytic activity of Au nanoparticles hosted on various metal-oxide supports. We combine reactivity analysis with density functional theory calculations to demonstrate that the slope of experimental Hammett plots is affected by electron donation from the underlying oxide support to the Au particles. Understanding how a supporting material can change the surface chemistry of the nanoparticle catalysts that it hosts is critical to tuning catalytic properties. Experimental Hammett studies and density functional theory calculations show that differences in reactivity can be attributed to differences in the electron density at metal active sites, which arises from differences in electron donation from the support.