SURFACE CHARACTERIZATION OF CuO-ZnO-Al2O3 METHANOL-SYNTHESIS CATALYSTS BY XPS

ln recent years great efforts have been devoted to understand the ZnO-CuO-Al2O3 catalysts structure and its relation to the catalvtic behaviour in hydrogen involving rections. mainlv methanol svnthesis and water-shift reaction. However. although copper based catalvsts are activated by reduction before use, several aspects related to the nature and oxidation state of surface Cu-species as well as their catalytic behaviour are not completely understood. In fact, whereas some authors bv bulk techniques claimed Cu+1 dissolved in ZnO lattice others proposed the formation of Cu2O upon reduction of CuO-ZnO catalysts: apart from that only a few surface studies have been published on these systems. The present communication is concerned with an XPS study of CuO -ZnO-Al2O3 well defined system of varying copper-zinc ratios (mainly 2 or I ) and alumina content (0<Al2O3<20%). The aim was: (a) to analvse in situ the reduction process related to the copper component estahlishing the oxidation states of copper as function of extent of reduction and showing how it is possible to provide a chemical picture of surface states by the analvsis of Cu 2p3/2 photoemission and Cu L3VV Auger peaks; (b) to assess the mutual interacticln between the different and so closelv associated phases as ZnO-CuO or ZnO-Cu: (c) to investigate the role of alumina on the sintering phenomena.