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

Abstract

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.