The direct synthesis of dimethyl ether from syngas over hybrid catalysts with sulfate-modified γ-alumina as methanol dehydration components

A series of γ-Al2O3 samples modified with various contents of sulfate (0–15 wt.%) and calcined at different temperatures (350–750 °C) were prepared by an impregnation method and physically admixed with CuO–ZnO–Al2O3 methanol synthesis catalyst to form hybrid catalysts. The direct synthesis of dimethyl ether (DME) from syngas was carried out over the prepared hybrid catalysts under pressurized fixed-bed continuous flow conditions. The results revealed that the catalytic activity of SO42−/γ-Al2O3 for methanol dehydration increased significantly when the content of sulfate increased to 10 wt.%, resulting in the increase in both DME selectivity and CO conversion. However, when the content of sulfate of SO42−/γ-Al2O3 was further increased to 15 wt.%, the activity for methanol dehydration was increased, and the selectivity for DME decreased slightly as reflected in the increased formation of byproducts like hydrocarbons and CO2. On the other hand, when the calcination temperature of SO42−/γ-Al2O3 increased from 350 °C to 550 °C, both the CO conversion and the DME selectivity increased gradually, accompanied with the decreased formation of CO2. Nevertheless, a further increase in calcination temperature to 750 °C remarkably decreased the catalytic activity of SO42−/γ-Al2O3 for methanol dehydration, resulting in the significant decline in both DME selectivity and CO conversion. The hybrid catalyst containing the SO42−/γ-Al2O3 with 10 wt.% sulfate and calcined at 550 °C exhibited the highest selectivity and yield for the synthesis of DME.

The hybrid catalyst containing the SO42−/γ-Al2O3 with 10 wt.% sulfate content and calcined at 550 °C as dehydrating component exhibited high activity, selectivity and stability for the direct synthesis of dimethyl ether from syngas. Figure optionsDownload as PowerPoint slide