FT-IR study of CO adsorption on Pt/CeO2: characterisation and structural rearrangement of small Pt particles

CO adsorption has been followed by IR spectroscopy on a Pt/CeO2 sample (Pt loading = 0.5%) treated under oxygen and vacuum or reduced by H-2 and then evacuated at various temperatures. The sample contains highly dispersed Pt. Attention is paid to the presence of an unusual nu((CO)) band at 1937 cm(-1) on the reduced sample. Such a band is in particular not observed when the support is fully covered by CO ( CO adsorption at liquid nitrogen temperature) or by methanol, allowing one to assign it to CO bridged species bound to both Pt very lowly coordinated and to the support, e. g. to sites at the periphery of very small Pt particules. Experiments performed after sample reduction at 423 K followed by increasing evacuation temperature between 423 and 673 K showed that the increase of the latter provokes a sintering of the Pt particles, due to ceria surface O2- mobility.