Liquid-phase preparation of catalysts used in slurry reactors to synthesize dimethyl ether from syngas: Effect of heat-treatment atmosphere

A CuZnAl slurry catalyst was prepared directly from a solution of metal salts by an entirely liquid-phase method. The influence of heat-treatment atmospheres with different proportions of CO2 on the single-step synthesis of dimethyl ether (DME) from syngas was investigated and the catalysts were characterized by powder X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), temperature-programmed desorption of ammonia (NH3-TPD), X-ray photoelectron spectrometry (XPS) and thermogravimetry-mass spectrometry (TG-MS). Results showed that the introduction of CO2 into the heat-treatment atmosphere made it easier to reduce the catalyst. It also adjusted the Cu0/Cu+ ratio on the catalyst surface, the CO2 reacting with the metallic carbide there to form CO, which then reduced part of the Cu2O to Cu. Moreover, it was concluded that the final phase structure of the catalyst and the Cu/Zn ratio on its surface depended mainly on its composition and the reaction environment and less so on the heat-treatment atmosphere. In the DME synthesis reaction, it was found that the introduction of CO2 into the heat-treatment atmosphere restrained the water–gas shift reaction and raised the DME selectivity. An optimal amount of CO2 in the heat-treatment atmosphere favored the increase of the DME space–time yield. The catalysts performed best when the heat-treatment atmosphere contained 50% CO2.