Oxidative Dehydrogenation of Ethane with CO2 over Mo/LDO Catalyst: The Active Species of Mo Controlled by LDO

A series of the layered double oxides supported molybdenum oxide catalysts were synthesized and evaluated in the oxidative dehydrogenation of ethane with CO2 (CO2-ODHE). The 22.3 wt% Mo/LDO catalyst delivered a 92.3%selectivity to ethylene and a 7.9% ethane conversion at relatively low temperatures. The molybdenum oxide catalysts were fully characterized by XRD, BET, SEM, TEM, UV-vis, Raman TG, and XPS. Isolated [MoO4](2-) dominated on the surface of the fresh 12.5 wt% Mo/LDO catalyst. With the increase of the Mo content, the Mo species transformed from [MoO4](2-) to [Mo7O24](6-) and [Mo8O26](4)(-) on the 22.3 wt% and 30.1 wt% Mo/LDO catalysts, respectively. The redox mechanism was proposed and three Mo species including [MoO4](2-), [Mo7O24](6-), and [Mo8O26](4-) showed quite different functions in the CO2-ODHE reaction: [MoO4](2-), with tetrahedral structure, preferred the non-selective pathway; [Mo7O24](6)(-), with an octahedral construction, promoted the selective pathway; and the existence of [Mo8O26](4-) reduced the ability to activate ethane. This work provides detailed insights to further understand the relationship between structure-activity and the role of surface Mo species as well as their aggregation state in CO2-ODHE.