Reaction of CuO with hydrogen studied by using synchrotron-based x-ray diffraction

CuO and Cu2O powders were reacted by hydrogen to study the reduction mechanism and the ionic states of Cu (Cu2+, Cu1+ and Cu-0). The reduction behaviour and the existence of an intermediate state were investigated by using synchrotron-based high-resolution in situ x-ray diffraction (S-XRD) techniques. The results revealed that CuO directly reduces to metallic Cu (Cu2+ --> Cu-0), under a normal flow of hydrogen. There was no hint of an intermediate state (Cu1+) during the reduction. In certain conditions, however, an intermediate phase (Cu2O) appears under either very small flow of hydrogen (<1 cm(3) min(-1)) or very fast temperature ramping (>20 degreesC min(-1)), suggesting that the reduction kinetics strongly depends on reduction conditions.