Mobility of gold, copper and cerium species in Au, Cu/Ce, Zr-oxides and its impact on total oxidation of methanol

CeO2, ZrO2 and mixed CeZrOx (Ce:Zr = 1:1 assumed) mesoporous oxides were synthesized and used as supports for gold (nominal 1.5 wt%) and copper (nominal 2 wt%). The materials obtained were characterized by UV–vis, XPS and TEM techniques, which allowed monitoring of the oxidation state of metals and surface properties of the catalysts, in particular the concentration of the components on the surface of the solid and in the bulk of the material. The metal-support and metal–metal (in bimetallic Cu-Au samples) interactions were considered. The aim of this work was to investigate the changes in chemical composition of catalyst surfaces and the oxidation states of metals upon the activation of the samples at different temperatures (423 and 573 K) in the argon flow and evaluation of the influence of these changes on the catalytic activity and selectivity in the low temperature oxidation of methanol. It was evidenced that the electronic state of gold and the mobility of metals towards and oxygen from the support play an important role in the low temperature total combustion of methanol. The activation temperature strongly affects the mobility of surface oxygen and the oxidation states of the cationic components playing the role of Lewis acid sites (it causes an increase in Cu+ and Ce3+ species concentration and a decrease in that of cationic gold on the surface after thermal treatment), and therefore strongly affects the activity and selectivity in the oxidation of methanol. The catalysts effective in low temperature total combustion of methanol are proposed.