Localization of copper atoms in the structure of the ZnO catalyst for methanol synthesis

The microstructure of a copper-zinc oxide catalyst for methanol synthesis has been studied using high resolution electron microscopy. Two alternatives for the arrangement of copper atoms in the zinc oxide crystallite were suggested and discussed. The high concentration of copper atoms in the sample (up to 10 atom%) against the known solubility of Cu2+ ions in ZnO (not more than 2 atom%), as well as the high density of dislocations seen in micrographs of the catalyst, may be accounted for by the occurrence of octahedral copper atom clusters of 0.25 nm radius built up into the host oxide lattice. These clusters lie at the dislocation wall along the (001) plane of ZnO. Copper atoms were also shown to be involved in isolated square planar CuO clusters not more than 0.5-1 nm in size.