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

Abstract

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.