The influence of composition on the functionality of hybrid CuO–ZnO–Al2O3/HZSM-5 for the synthesis of DME from CO2 hydrogenation

Abstract

A series of CuO–ZnO–Al₂O₃/HZSM-5 hybrid catalysts with different Cu/Zn ratios and disparate Al₂O₃ doping were prepared and characterized by XRD, BET, H₂-TPR, NH₃-TPD and XPS techniques. The optimal Cu/Zn ratio is 7 : 3, and the introduction of a suitable amount of Al₂O₃ to form hybrid catalysts increased the BET specific area and micropore volume, facilitated the CuO dispersion, decreased the CuO crystallite size, increased the interaction between CuO and ZnO, enhanced the number of weak acid sites, altered the copper chemical state and improved the catalytic performance consequently. The highest CO₂ conversion, DME selectivity and DME yield of 27.3%, 67.1% and 18.3%, respectively, were observed over the CZA₇H catalyst. The suitable temperature of 260 °C and the appropriate space velocity of 1500 h⁻¹ for one-step synthesis of dimethyl ether (DME) from carbon dioxide (CO₂) hydrogenation were also investigated. The 50 h stability of the CZA₇H catalyst was also tested.