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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-Al 2 O 3 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, NH 3 temperature-programmed desorption, and H 2 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 CO 2 and C 1 and C 2 hydrocarbon selectivity was also decreased from 48% to 14% for CO 2 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 H 2 /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. [ABSTRACT FROM AUTHOR]

-Highlights: [•] TiO2-supported HPAs are very active for low-temperature DME production. [•] H2O molecules between Keggin units on HPA/TiO2 are weakly bonded leading higher reaction rates. [•] The acidity of HPAs and HPA/TiO2 is very strong. [•] The Keggin structure is stable upon deposition on TiO2 until ca. 723K. [ABSTRACT FROM AUTHOR]