IMPROVEMENTS TO RANEY COPPER METHANOL SYNTHESIS CATALYSTS THROUGH ZINC IMPREGNATION .1. ELECTRON-MICROPROBE ANALYSIS

The specific activity of a Raney Cu-ZnO-Al2O3 catalyst for methanol synthesis from carbon monoxide and carbon dioxide has been found to be related to the mass of zinc per unit total area of Raney catalyst surface. This correlation has been found to be independent of the conditions used to leach the material, although the level of zinc was found to be strongly dependent on the leaching conditions. The mass of zinc oxide in the catalytic material produced by leaching a Cu-Al-Zn alloy pellet in sodium hydroxide has been found to decrease continuously from the highest level close to the alloy/catalyst interface to the lowest level at the outer edge of the leached pellet. By leaching the alloy in a zincate rich solution the ZnO concentration profile in the leached material Cu-Al-Zn alloys can be improved. The resulting catalysts have significantly higher specific activity which shows a strong correlation to the mass of zinc per unit total surface area. The zincate leached materials were found to have total amounts of zinc similar to the hydroxide leached materials. However, the aluminium levels were significantly lower. The high specific activity was attributed to improved contact between the copper and the ZnO which is precipitated onto the copper surface. On the basis of these results it is suggested that the active sites for methanol synthesis are at the interface between the copper and the ZnO crystallites.