Synthesis of dimethyl ether from syngas over core–shell structure catalyst CuO–ZnO–Al2O3@SiO2–Al2O3

• Dimethyl ether synthesis from syngas directly over a core–shell catalyst.
• The core is methanol catalyst CuO–ZnO–Al2O3 and the shell is amorphous SiO2–Al2O3.
• The shell thickness and acidity could be altered by a facile hydrothermal treatment.
• High CO conversion and dimethyl ether selectivity under mild reaction condition.

A core–shell structure catalyst, CuO–ZnO–Al2O3@SiO2–Al2O3, with commercial methanol synthesis catalyst CuO–ZnO–Al2O3 as the core and amorphous SiO2–Al2O3 as the shell, was prepared by facile hydrothermal treatment. In the synthesis procedure, the core–shell catalyst was synthesized using tetraethylorthosilicate, silica sol, or water glass as the silica source, aluminum nitrate as the aluminum source, and without using any aid, alkali or amine template to avoid etching of core material, CuO–ZnO–Al2O3. The core–shell structure and acidic property of the catalyst materials were characterized by XRD, SEM and NH3-TPD. The results indicated that an amorphous SiO2–Al2O3 shell coated the surface of the core materials. The thickness of shell and acidity of the catalysts could be altered by adjusting the quantity of silicon source added. The core–shell structure catalysts were utilized as bifunctional catalysts in the syngas to dimethyl ether reaction (STD). The acidity and the thickness of the shell affect the catalytic performance in the STD reaction. The conversion of CO and the selectivity of dimethyl ether on the core–shell catalyst, with moderate acidity and suitable shell thickness, are 71.1% and 61.9%, respectively.