Heterolytic and heterotopic dissociation of hydrogen on ceria-supported gold nanoparticles. Combined inelastic neutron scattering and FT-IR spectroscopic study on the nature and reactivity of surface hydrogen species

Inelastic neutron scattering of gold nanoparticles (3–4 nm, 0.48 wt%) supported on nanoparticulate ceria (5 nm) (Au/CeO2) shows that hydrogen treatment of Au/CeO2 gives rise to the appearance of a new band (400–600 cm−1) corresponding to bridging hydroxyl groups. This band disappears (without observing the appearance of any new band) when the sample is exposed to CO2 or O2. FT-IR spectroscopy on the same samples shows the formation of Au–H after hydrogen chemisorption. The Au–H band also disappears when the sample is subsequently treated with CO2 or O2. In the last case formation of hydroperoxide is observed. The band assignments were supported by isotopic labelling with D2 and 18O2. The above data clearly establish that upon treatment of Au/CeO2 with hydrogen at 150 °C, heterolytic bond cleavage of dihydrogen occurs leading to a proton bonded to a ceria oxygen and a hydride bonded to gold.