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

Ceria has been chlorinated either by CCl4 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 CCl4-treated ceria, being H bonded to Cl- surface species and O bonded to reduced Ce3+ surface cations. This assumes the reductive surface substitution of O2- species by Cl- ions during the CCl4 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/CeO2 catalyst prepared from the PdCl2 precursor.