Oxidation and reduction in copper/zinc oxides by mechanical milling

When zinc oxide is milled under vacuum or in the presence of oxygen, creation of various types of defects results in an increased amorphous fraction, as well as higher surface area. Mechanochemical reactions occur when copper and copper oxides are milled together with zinc oxide: oxidation of copper and copper oxides takes place in the presence of oxygen, whereas reduction takes place under vacuum. These reactions are promoted by the presence of ZnO. Formation of a Cu2O-like intermediate is suggested, which is not observed when milled without ZnO. The various resulting copper species reduce at different temperatures in H2 atmosphere. Both Cu0 specific surfaces and BET surfaces are substantially increased for all milled Cu/ZnO samples, making this method an interesting alternative for the preparation of promoted heterogeneous catalysts.