Effect of Modification of HZSM-5 in Hybrid Catalyst on Direct Synthesis of Dimethyl Ether from Syngas

A series of Mg-ZSM-5 zeolite catalysts were prepared by using solid-state reaction. The structure and surface acidity of thus prepared zeolite catalysts were studied using XRD and NH_3-TPD methods. The results indicate that the structure and crystallinity were not changed in comparison with the parent HZSM-5. However, weak acid sites increased, strong acid sites decreased, and acid distribution was more concentrative. The hybrid catalysts with Mg-ZSM-5 as methanol dehydration components were used for direct synthesis of DME from syngas. The experimental results show that the Mg modification of HZSM-5 improved the catalytic dehydration properties significantly: the selectivity of DME increased from 53.62% to 68.31%, while the selectivities of the undesired side products of CO_2 and hydrocarbons decreased from 41.75% and 0.23% to 27.67% and 0.02%, respectively.