The catalytic activity of CuZn catalysts in the synthesis of methanol is related to those reduced Cu species, which originate from the CuxZn1-xO solid solution of wurtzite-like structure. Copper cations in the CuxZn1-xO solid solution are localized in the extended stacking faults of the ZnO lattice. Copper sites could be supposedly described as the product of introducing (OH)center dot center dot center dot Cu center dot center dot center dot(OH) to the planar defects of zinc oxide structure. Hydroxyl groups stabilize the planar defects of ZnO. The process of the samples reduction leads to the formation of flat Cu-0 particles over the surface of zinc oxide. The planar defects of ZnO structure are preserved in the reduced state. During the reoxidation, copper atoms return back to the extended stacking faults of ZnO as the tape-like clusters of flat-square coordinated copper cations. (c) 2005 Elsevier B.V. All rights reserved.