XPS and XRD investigation of Co/Pd/TiO2 catalysts by different preparation methods

In the article, the Co/Pd/TiO2, Co/TiO2 and Pd/TiO2 catalysts prepared by the impregnation and sol-gel method are studied by using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The result shows that Co2+ and metal I'd may act as the active center for the direct synthesis of acetic acid from CH4 and CO2 by a two-step reaction sequence. When the catalysts are prepared by the sol-gel, Co2+ can enter the crystal lattice of the TiO2, causing the phase transition from anatase to rutile at lower temperature, but existence of Pd2+ can prevent from the phase transition. When the catalysts are prepared by the impregnation, the phase transition is inhibited not only Co2+ but also Pd2+. (c) 2009 Elsevier B.V. All rights reserved.