Abstract: Mo-Bi-Ce/SiO₂ has been investigated by XPStechnique before and after reduction with mathanol. The result shows that the catalyst consists of Bi1₂(MoO₄)₃ and CeO₂ before reduction, and after reduction with mathanol Ce⁴⁺ reduces to Ce⁰ with a small amount of Ce₂O₃ and Bi, Mo reduces to lower valence state. The sequence of reduction is Ce, Bi, Mo. Before reduction Bi resides at the external layer in the catalyst and then diffuses into internal layer during reduction. The reduced catalyst re-oxidized with oxygen in pulse experiment shows that all of active components are reoxidized and the sequence of oxidation is Mo, Bi, Ce. Bi migrates back to surface during reoxidation.

Key words: XPS, Mo-Bi-Ce/SiO₂ catalyst, Reduction of methanol