Hydrogenation of Magnesite to Methane and Magnesium Oxide with a Ferromagnetic Catalyst toward CO2 Direct Utilization

The calcination of carbonate rocks in mineral processing produces CO 2, and hydrogenation of carbonate rocks opens a window for CO 2 direct use, meanwhile producing valuable-added hydrocarbons. However, the process faces challenges of hydrocarbon selectivity and reacted solid separation in case of multisolids in the process. The direct hydrogenation of magnesite for CH 4 and MgO production using a Ni/Fe/ZrO 2 catalyst with ferromagnetic activity is first proposed. Thermodynamic analysis and experiments were performed with key issues to be identified as influence of H 2 on the thermal decomposition behavior of magnesite, effect of the catalyst on CH 4 production, and separation of the catalyst and solid product. The solids before and after reaction were characterized by X-ray diffraction (XRD), in situ XRD, and SEM–EDS. In comparison to the decomposition of magnesite in an inert atmosphere, the process lowered the initial magnesite’s decomposition temperature at least 40 °C and enhanced its conversion. High temperature favored CO formation, and low temperature was beneficial for CH 4 formation. Without catalyst, CO was the hydrogenation product, and its production occurred when the temperature was higher than 500 °C. With the catalyst, almost 100% CH 4 selectivity was achieved at 350 and 400 °C. Magnetic separation was applied and validated to well separate the solid product and reacted catalyst. 60 h operation results suggested a relatively stable reactivity of the catalyst during the process.