A series of Pd/γ-Al2O3 catalysts with different additons of Pd were prepared by impregnation. The effect of calcination condition and Pd loading on catalytic performance of catalysts for one-step dimethyl ether synthesis has been investigated. The physic-chemical performance and structure of Pd/γ-Al2O3 catalysts were characterized by CO-TPD, TGA and nitrogen physisorption. The results show that the dispersion of Pd and the amount of adsorbration on the CO-bridge of Pd could be increased to by the moderate microwave heating on the catalysts, and the catalyst performance can be improved. But a large number of surface acidic sites of Pd/γ-Al2O3 are covered by highly fragmented Pd-grain, it causes DME selectivity reduced. And the excessive Pd can reduce the samples’ surface acid, decrease the dispersion of the metal Pd and block up the pore of γ-Al2O3. The CO conversion rate and DME space-time yield could reach 60.1% and 28.76 mmol·g-1·h-1 respectively at 2% Pd loading, at this time Pd/γ-Al2O3 has a high Pd activity surface and ideal acid sites.
A series of Pd-CeO2/γ-Al2O3 catalysts which have a different CeO2 loading were prepared by impregnation under microwave irradiation. Based on various characterizations, such as XRD, H2-TPR and CO-TPD, the effect of CeO2 loading on catalytic performance and stability of Pd/γ-Al2O3 were examined for one-step dimethyl ether synthesis from syngas. The results show that there are two completely opposite effect on the CO conversation rate of Pd/γ-Al2O3 catalysts after adding CeO2, namely that it can improve Pd dispersion at a suitable loading, hence the CO conversation rate will increase too. However, the surface area and total pore volume of Pd/γ-Al2O3 catalysts decrease by adding excessive CeO2 and CO conversation rate will also reduce. When the CeO2 loading achieve to 2%, catalysts can have relatively high catalytic stability and activity that the CO conversation rate and DME space-time yield can reach 64.7% and 27.82 mmol·ml-1·h-1, respectively.
A series of Pd/γ-Al 2 O 3 catalysts with different types of compound additives were prepared by impregnation under microwave calcination; the physicochemical properties and catalytic performance of catalysts for one-step synthesis of dimethylether from sulfur-containing syngas were investigated. The results show that the catalysts added CeO 2 -ZrO 2 showed much better catalytic performance and sulfur tolerance than those added CeO 2 -ZnO or CeO 2 -CaO in terms of CO conversion, methanol, and dimethylether selectivities and time space yield of dimethylether, which are closely related to higher pore volume and Pd dispersity, moderate CO adsorption, and moderate surface acidity of the catalyst. The optimum compound additive content was determined to be 2%CeO 2 -1%ZrO 2 . Under such optimum conditions, CO conversion, dimethylether selectivity, and time space yield of dimethylether are 63.2%, 68.5%, and 30.92 mmol·(ml·h) −1 , respectively.
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