A study on the catalytic performance of Pd/γ-Al_(2)O_(3),prepared by microwave calcination,in the direct synthesis of dimethylether

A series of Pd/γ-Al_(2)O_(3) hybrid catalysts were prepared by impregnation and subsequent calcination under microwave irradiation.The catalysts were used for direct synthesis of dimethylether(DME)from syngas.The results show that calcination under microwave irradiation improved both the activity and selectivity of the catalysts for DME synthesis.The optimum power of the microwave was determined to be 420 W.Under such optimum conditions,CO conversion,DME selectivity and time space yield of DME were 60.1%,67.0%,and 21.5 mmol$mL-1$h^(-1),respectively.Based on various characterizations such as nitrogen physisorption,X-ray diffraction,COtemperature-programmed desorption,and Fourier transform infrared spectral analysis,the promotional effect of the microwave irradiation on the catalytic property was mainly attributed to both the higher dispersion of Pd and the significant increase in the adsorption on the CO-bridge of Pd.Microwave irradiation with very high power led to the increase in CO-bridge adsorption and thereby decreased the catalytic activity,whereas the coverage by metallic Pd of the active sites on acidicγ-Al_(2)O_(3) significantly occurred under microwave irradiation with very low power,resulting in a decrease in the selectivity to DME.