Abstract:

The hydrogenation of CO₂ to dimethyl ether (DME) is a potential method for the efficient utilization of CO₂ as a renewable resource. In comparison with the photocatalytic and electrocatalytic routes, the thermal conversion of CO₂ over a solid catalyst exhibits a higher efficiency. However, the reported catalysts for the one-step hydrogenation of CO₂ to DME commonly suffer from a lower activity and a poorer stability. In this perspective, progresses on the structure of active sites and the reaction mechanism of the one-step hydrogenation of CO₂ to DME are summarized for the Cu-based bifunctional catalyst and the recently reported GaN catalyst. In the case of the Cu-based bifunctional catalyst, DME is formed via the CO₂ hydrogenation to methanol and the dehydration of the intermediate methanol to DME. Moreover, copper at reduced state (Cu⁰, Cu⁺ or Cu ^δ+, 0<δ<2) is the active site for the CO₂ hydrogenation, and the DME yield and the stability of the bifunctional catalyst are mainly determined by the dispersion and the stability of reduced Cu, the strength and distribution of acid sites, and the synergetic effect between reduced Cu and the acid sites. In contrast, the GaN catalyzed DME synthesis proceeds via the direct hydrogenation of CO₂ to the primary product of DME, which is totally different from that over the Cu-based bifunctional catalysts. Based on these analyses, the challenges and the further researches on the one-step hydrogenation of CO₂ to DME are provided, and the benefit of the DME economy is remarked.

Key words: CO₂ hydrogenation, dimethyl ether, gallium nitride, copper, bifunctional catalyst

摘要：

CO₂加氢制二甲醚（DME）是有潜力实现CO₂资源化利用的重要途径之一。与光、电催化相比，CO₂的非均相催化转化具有转化效率高等优点，但目前CO₂加氢一步制备DME催化剂的反应活性较低、稳定性较差。本文在简要介绍CO₂加氢一步制DME的铜基双功能催化剂、复合氧化物和氮化镓催化剂的基础上，重点总结了活性中心结构和反应机理的研究进展。对于铜基双功能催化剂，CO₂加氢经甲醇中间体合成DME，其中还原态铜（Cu⁰、Cu⁺及Cu ^δ+，0<δ<2）是其催化活性中心，且还原态铜的分散度及稳定性、固体酸的性质和酸性位分布以及两类活性中心的耦合效应是决定DME收率和催化剂稳定性的关键因素。与此相反，DME是氮化镓催化CO₂加氢的初级产物。这与铜基双功能催化剂有着本质区别，属新催化剂体系。在此基础上，文章对CO₂加氢制DME的可能研究方向进行了展望，认为“二甲醚经济”更具发展潜力。

关键词: 二氧化碳加氢, 二甲醚, 氮化镓, 铜, 双功能催化剂