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 Cu⁰). 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⁺ → Cu⁰), under a normal flow of hydrogen. There was no hint of an intermediate state (Cu ¹⁺) during the reduction. In certain conditions, however, an intermediate phase (Cu₂O) appears under either very small flow of hydrogen (<1 cm³ min^-1) or very fast temperature ramping (>20°C min^-1), suggesting that the reduction kinetics strongly depends on reduction conditions.