Inverse ZnO/Cu catalysts for methanol synthesis from CO2 hydrogenation

A series of inverse ZnO/Cu catalysts were prepared with varied Zn/Cu ratios using a microemulsion method. The catalysts were tested for CO2 hydrogenation to methanol and the structure was characterized by nitrogen physisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Transmission electron microscopy (TEM), Scanning electron microscope (SEM), H2 temperature-programmed reduction (H2-TPR) and H2 temperature-programmed desorption (H2-TPD). On the inverse samples, less amount of highly dispersed Cu was observed than that of the conventional Cu/ZnO catalysts. Thus, the inverse ZnO/Cu catalysts showed a lower CO selectivity and a higher methanol selectivity. CuZn alloy was formed in the samples, in which ZnO/Cu(4:6) had the most amount of the CuZn alloy. A linear relationship between the methanol yield and the CuZn alloy content can be found for the ZnO/Cu catalysts. Among all the catalysts, ZnO/Cu(4:6) exhibited the highest CH3OH yield (2.8 mmol g−1 h−1) at 2.0 MPa and 250 °C, much higher than the conventional Cu/ZnO catalyst with the same composition. Moreover, microemulsion method is a very effective method to tune particle size of the catalysts.