Dimethyl Ether Synthesis from Carbon Dioxide by Catalytic Hydrogenation (Part 2) Hybrid Catalyst Consisting of Methanol Synthesis and Methanol Dehydration Catalysts

Direct DME synthesis from CO2 and H2 was carried out using hybrid catalysts consisting of a methanol synthesis catalyst (CuO-ZnO-Al2O3-Ga2O3-MgO) and a methanol dehydration catalyst (γ-Al2O3 or ZrO2·Al2O3). The effects of the compositions of the two catalysts on methanol + DME yield, DME selectivity and durability of the hybrid catalysts were investigated. The optimum mixing ratio of the methanol synthesis catalyst to the methanol dehydration catalyst in a hybrid catalyst was 50 : 50 wt%. In the DME direct synthesis from CO2 and H2, the methanol + DME yield and the DME selectivity increased with higher temperature. However, after the methanol yield reached the equilibrium, the methanol + DME yield declined with higher temperature. ZrO2·Al2O3 as a methanol dehydration catalyst had a higher DME synthesis activity than γ-Al2O3. A two-layer structure consisting of an upper layer of methanol synthesis catalyst and a lower layer of a mixture of the methanol synthesis catalyst and the methanol dehydration catalyst was the most effective. The hybrid catalyst with the two-layer structure also showed better durability than catalysts with other structures.