One-step synthesis of dimethyl ether from biomass-derived syngas on CuO-ZnO-Al2O3/HZSM-5 hybrid catalyst: Combination method, synergistic effect, water-gas shift reaction and catalytic performance

Abstract

The hybrid systems of CuO-ZnO-Al2O3/HZSM-5 for the one-step synthesis of DME from biomass-derived syngas were prepared by four different combination methods (granule-mixing, powder-mixing, physical coating and dual-bed fixing) and characterized by N2 adsorption, XRD, N2O titration, H2-TPR, NH3-TPD and TG techniques. The influences of combination method on the physicochemical properties and catalytic performances of hybrid catalyst were investigated, and the relationship among the combination method, the synergistic effect and the WGS reaction was discussed based on the composition features of the biomass-derived syngas (CO2-rich and H2-deficient). A maximum of CO conversion and DME yield was obtained over the hybrid catalyst prepared by granule-mixing method. There is a synergistic effect, which remarkably promotes the formation of DME, between the methanol synthesis and the methanol dehydration over the hybrid catalysts except for the hybrid system configured using the dual-bed fixing method. The WGS reaction, playing a pivotal role in the direct DME synthesis because of the in-situ produced hydrogen, relates to the combination method closely. An interaction between the two catalyst components arising in the combination process affects the properties of active sites and further the catalytic performances. The deactivation of the hybrid catalyst is ascribed mainly to the increase in the particle size of Cu in CuO-ZnO-Al2O3.