From Oxide to Metal: A Kinetic Perspective on CuO Reduction by Hydrogen

This study investigates the reduction kinetics and mechanisms of copper oxide by hydrogen gas. A horizontal tube furnace was used for the reduction experiments at 500–1000 °C and 5–30 min reaction times. Material characterization was performed using X-ray diffraction, and scanning electron microscopy-energy dispersive X-ray spectroscopy were used to analyze the phase evolution, microstructure changes, and the overall reduction behavior. The scanning electron microscopy (SEM) results show that after 5 min of hydrogen reduction of pellets (2 g CuO) at 500–700 °C, both Cu2O and metallic Cu start to form, while some CuO particles remain unreduced. In contrast, at higher temperatures (800–1000 °C), all CuO particles on the pellet surface are fully reduced to Cu2O and Cu. The degree of reduction varies with hydrogen flow rate and pelletizing pressure. It was demonstrated that a hydrogen flow rate of 300 mL/min is sufficient to avoid a gas-phase mass transfer limitation. Kinetic analysis reveals a two-stage reduction process: a rapid interface reaction followed by a diffusion-controlled stage. The apparent activation energies are 11.2 kJ/mol for the interface reaction stage and 8.8 kJ/mol for the diffusion-controlled stage. Graphical Abstract