Evaluation of Temperature-Programmed and Isothermal Hydrogenation Behaviors of Magnesite in Fluidized Bed

Magnesite calcination is a crucial step for MgO production, but it releases substantial CO2. Direct hydrogenation of magnesite offers a promising route to simultaneously produce MgO and convert carbonate-derived carbon into valuable C1 products (CO and CH4), thereby reducing CO2 emissions at the source. In this study, the direct hydrogenation of natural magnesite was systematically investigated in a fluidized-bed reactor under both isothermal and temperature-programmed conditions, aiming to achieve simultaneous MgO production and in situ carbon utilization. The effects of the temperature, H2 concentration, and heating mode on gas evolution, carbon conversion, and apparent reaction kinetics were comprehensively evaluated. Results reveal that the presence of H2 markedly lowers the initial decomposition temperature, enhances carbon conversion, and shifts the reaction equilibrium forward through in situ CO2 consumption, thereby accelerating MgCO3 decomposition. Elevated temperatures strongly promote MgCO3 decomposition and increase the CO2 yield and selectivity, though the CO yield decreases at higher temperatures due to insufficient time for CO2 conversion via the reverse water–gas shift reaction. In contrast, increasing H2 concentration enhances CO and CH4 yields, shifts CO2 evolution to earlier stages, and shortens the overall reaction time. Isothermal hydrogenation proceeds at a markedly faster rate than temperature-programmed hydrogenation. Kinetic analysis further shows that H2 reduces the apparent activation energy from 201.96 to 180.53 kJ mol–1, confirming its role in lowering the reaction barrier. X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM)-EDS characterizations verify the complete conversion of MgCO3 to MgO in a H2 atmosphere and the formation of significant cracks favorable for mass transfer. These findings provide fundamental insights and practical guidance for developing energy-efficient, low-carbon magnesite processing technologies.