Direct conversion of Co₂ into dimethyl ether over Al₂o₃/Cu/ZnO catalysts prepared by sequential precipitation

Bifunctional Al₂O₃/Cu/ZnO catalysts with Al composition of between 30 mol% and 80 mol% were prepared by sequential precipitation (SP) for the conversion of CO₂ into dimethyl ether (DME). In the SP synthesis, the concentration of a precipitation agent managed to be high enough to induce the complete precipitation of Al³⁺. The prepared precipitates were composed of zincian malachite and amorphous AlO(OH). Furthermore, the calcined mixed metal oxide materials of 60% and 80% Al exhibited a higher acidity than commercial Al₂O₃ and the H₂‐reduced catalysts showed the similar Cu dispersion of 6%–7% at all Cu loadings. In the activity test at 573 K and 50 bar, the SP‐derived catalyst of 80% Al (SP‐80) displayed the best performance corresponding to CO₂ conversion of 25% and DME selectivity of 75% that are close to equilibrium values. In order to overcome the thermodynamic limitation, a dual‐bed catalyst system was made up of SP‐80 in the first layer and zeolite ferrierite in the next. This approach enabled DME selectivity to be enhanced to 90% while CO₂ conversion increased a little. Consequently, the studied catalyst system based on the SP‐derived catalysts can contribute greatly to selective DME production from CO₂.