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 CO2, and hydrogenation of carbonate rocks opens a window for CO2 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 CH4 and MgO production using a Ni/Fe/ZrO2 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 CH4 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 degrees C and enhanced its conversion. High temperature favored CO formation, and low temperature was beneficial for CH4 formation. Without catalyst, CO was the hydrogenation product, and its production occurred when the temperature was higher than 500 degrees C. With the catalyst, almost 100% CH4 selectivity was achieved at 350 and 400 degrees 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.