Thermal evolution of the adsorbed methoxy species on CexZr1-xO2 solid solution samples: a FT-IR study

Thermal reduction of a series of CexZr1-xO2 solid solution samples by metha nol adsorbed at room temperature was investigated using infrared spectrosco py (IR), Methoxy species resulting from methanol dissociation and adsorbed as on-top or bridging species, either on Zr4+ or Ce4+ ions, are well differ entiated. Upon the thermal treatment, Ce4+ sites appear to be exclusively t he reactive ones through their reduction into Ce3+. First, on-top methoxy s pecies adsorbed on Ce4+ sites are oxidised to mobile formate species in the 423-473 K temperature range, with the subsequent partial cerium reduction. Second, bridging methoxy species and formate ones decomposed in the 473-52 3 K temperature range through processes involving CO, CO2, H-2, H2O gaseous evolution. The reduction of surface cerium ions is then complete, The prod uction of H-2 molecules was established by a complementary temperature prog rammed desorption study. The different temperature range at which mixed oxide reduction and hydrogen evolution take place demonstrates that the catalysts are nor reduced by H- 2 uptake, but by framework oxygen consumption, due to methoxys oxidation in to formate species, (C) 1999 Elsevier Science B.V. All rights reserved.