Use of methanol as an IR molecular probe to study the surface chlorination of ceria

Ceria has been chlorinated either by CCl 4 treatment at 473 K or by impregnation with an aqueous HCl solution and the surface studied by IR spectroscopy using methanol as a probe. It was shown that methanol was molecularly adsorbed on the CCl 4 -treated ceria, being H bonded to Cl - surface species and O bonded to reduced Ce 3+ surface cations. This assumes the reductive surface substitution of O 2- species by Cl - ions during the CCl 4 treatment with the formation of CeOCl species (Ce III ). With the HCl-impregnated ceria sample, methanol was either molecularly adsorbed or dissociated into methoxy species, indicating a mainly unreduced (Ce IV ) surface that is homogeneously chlorinated by HCl-chemisorption. The importance of CeOCl surface species was further evidenced when methanol was adsorbed on a reduced Pd/CeO 2 catalyst prepared from the PdCl 2 precursor.