Unravelling the Nature of Gold Surface Sites by Combining IR Spectroscopy and DFT Calculations. Implications in Catalysis

A combination of XPS, IR spectroscopy of adsorbed CO, and DFT calculations has allowed us to identify different gold sites on Au/TiO2 catalysts, and to analyze the electronic and structural changes induced on the supported gold nanoparticles when adsorbing CO. The characteristics of low coordinated neutral Au0, slightly positively charged Auδ+, and cationic AuIII species have been studied, and the IR bands associated with CO adsorbed on these species have been determined. The shift in the νCO frequency not only depends on the charge on the particle or on the particular gold atom to which CO binds but also on the degree of coordination of gold atoms, that is, particle shape, and the capability of CO to modify this particle shape. It has been unequivocally shown by combining IR/DFT results and H/D isotopic exchange experiments that, among the different gold species identified, only the low coordinated neutral gold atoms not involved in Au−O−Ti linkages are responsible for H2 dissociation on Au/TiO2 catalysts.