Direct synthesis of dimethyl ether from syngas over Cu-based catalysts: Enhanced selectivity in the presence of MgO

• Synthesized bifunctional hybrid catalysts of malachite crystalline structure.
• Malachite structured materials effectively catalyzed direct conversion of syngas to dimethyl ether (DME).
• MgO promoted DME yield and minimized CO2 and lower hydrocarbon by-products.
• As-synthesized recyclable catalysts have the potential to improve the economy of DME production technology.

Direct synthesis of dimethyl ether (DME) from syngas was investigated over a series of hybrid catalytic systems containing a Cu-based methanol synthesis component with varying amounts of ZnO and MgO, and γ-Al2O3 as a methanol dehydration component. Methanol synthesis and methanol dehydration components were homogeneously mixed in a 2:1 weight ratio to prepare the hybrid catalysts, which were characterized by transmission electron microscopy, scanning electron microscopy, BET surface area analysis, powder X-ray diffraction, NH3 temperature-programmed desorption, and H2 temperature-programmed reduction methods. The syngas-to-DME (STD) reaction was studied in an isothermal fixed bed reactor at 30 bar and 260 °C. The catalysis results revealed improved effectiveness of the catalyst in the presence of 20 mol% MgO, enabling a significant enhancement in CO conversion from 19% to 37% and in DME selectivity from 36% to 83%, as compared with the activity of a catalyst without MgO. By-product CO2 and C1 and C2 hydrocarbon selectivity was also decreased from 48% to 14% for CO2 and from 8% to 2.5% for hydrocarbons. Catalyst performance, CO conversions and DME selectivity were evaluated by varying the reaction temperature, pressure, space velocity and H2/CO ratio in syngas. XRD data revealed the formation of a good crystalline malachite structure for the catalysts containing up to 20 mol% MgO, but the crystallinity in the structure was lost when 30% MgO was added, resulting in decreased catalytic activity.

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