Enhancement of stability and activity of Cu/ZnO/Al2O3 catalysts by microwave irradiation for liquid phase methanol synthesis

The stability and activity of Cu/ZnO/Al2O3 catalysts in liquid phase methanol synthesis have been enhanced by using microwave irradiation in precipitation and aging processes. The phase composition of precursors and the microstructure of calcined CuO/ZnO/Al2O3 catalysts were characterized by XRD, FT-IR, DTG, HR-TEM, H2-TPR and XPS, and the catalytic performances were tested in liquid phase reactor for methanol synthesis from syngas (CO + H2). The results showed that the microwave irradiation during precipitation process leaded to a slight improvement of activity of Cu/ZnO/Al2O3 catalysts. In the aging process, microwave irradiation promoted the substitution of Zn2+ in Zn5(CO3)2(OH)6 compound by Cu2+, leading to enhancement of the content of (Cu, Zn)5(CO3)2(OH)6 phase in precursors and the stability and activity of Cu/ZnO/Al2O3 catalysts. When microwave irradiation was used in both precipitation and aging processes, the stability and activity of Cu/ZnO/Al2O3 catalysts were further enhanced. The optimum preparation conditions for the Cu/ZnO/Al2O3 catalyst were precipitated at 60 °C and aged at 80 °C under microwave irradiation, the average methanol space time yield (STY) and deactivation rate (R) of the optimum catalyst were 312 mg/(g h) and 0.05%/d, respectively.