Mechanochemical reactions in Cu/ZnO catalysts induced by mechanical milling

Preparation of Cu/ZnO catalysts is discussed in which mechanochemical react ions are involved. These reactions include oxidation of copper and copper o xides during milling in the presence of oxygen, reduction under vacuum, and formation of carbonates in CO2. Oxidation and reduction are promoted by th e presence of ZnO. Formation Of Cu2O-like intermediates is suggested in oxi dic mixtures, which are not observed when milling occurs without ZnO. This effect may be partly due to defect formation. The various resulting copper species reduce at different temperatures in H-2 atmosphere and this gives a n indication for the intimacy of the Cu-Zn interaction. When milling is car ried out in the presence Of CO2, mixed carbonates are formed. Intimate mixt ures of Cu and Zn are thus obtained, exhibiting high surface areas after re duction that can be explained by evolved porosity. A linear relation betwee n Cu-0 surface area and activity for methanol synthesis at 2 bar is observe d. Irreversible deactivation is explained by over-reduction and sintering. Both Cu-0 specific surfaces and BET surfaces (determined after reduction in hydrogen) are substantially increased for all milled Cu/ZnO samples, but e specially for samples that undergo mechanochemical reactions. This method t hus allows investigation of mixed oxide catalyst precursors and provides an interesting alternative for the preparation of promoted heterogeneous cata lysts.