Cu/ZnO Catalysts Derived from Bimetallic Metal-Organic Framework for Dimethyl Ether Synthesis from Syngas with Enhanced Selectivity and Stability

摘要

Direct conversion of syngas to dimethyl ether (DME) through the intermediate of methanol allows more efficient DME production in a simpler reactor design relative to the conventional indirect route. Although Cu/ZnObased multicomponent catalysts are highly active for methanol synthesis in this process, the sintering issue of Cu during the prolonged reaction generally deteriorates their performance. In this work, Cu/ZnO catalysts in a novel octahedron structure are prepared by a two-step pyrolysis of Zn-doped Cu-BTC metal-organic framework (MOF) in N2 and air. The catalyst CZ-350/A, hybrid of MOF-derived Cu/ZnO sample CZ-350 and γ-Al_2O_3 for methanol dehydration, displays the best activity for DME formation (7.74% CO conversion and 70.05% DME selectivity) with the lowest deterioration rate over 40 h continuous reaction. Such performance is superior to its counterpart CZ-CP/A made via the conventional coprecipitation method. This is mainly due to the confinement of Cu nanoparticles within the octahedron matrix hindering their migration and aggregation. Besides, partial reduction of ZnO in the activated CZ-350 prompts the formation of Cu~+-O-Zn, further facilitating the DME production with the highest selectivity compared to literature results. The results clearly indicate that Cu and ZnO distribution in the catalyst architecture plays an important role in DME formation.