Microstructural evolution and reaction characteristics of limestone during hydrogenation

• Limestone hydrogenation under fluidized conditions is feasible and efficient. • The high CO selectivity (∼93%) of limestone hydrogenation is achieved at 650 °C. • Decline in temperature and raise in H 2 concentration leads to higher CO selectivity. • The solid product CaO accelerates the limestone hydrogenation reaction. • Carbonate hydrogenation is a promising technology for reducing CO 2 emissions. Hydrogen (H 2 ) reduction of limestone offers a promising strategy for the cement industry, as it not only mitigates process-related CO 2 emissions but also valorizes the greenhouse gas by transforming it into valuable chemical products such as carbon monoxide (CO) or syngas. This study systematically explores the hydrogenation behavior of limestone in a fluidized bed reactor, providing quantitative insights into metrics such as CO yield and selectivity. The influences of reaction temperature, H 2 concentration, and pre-addition of calcium oxide (CaO) on the hydrogenation performance are evaluated. The in-situ XRD results provide crystallographic evidence that H 2 not only reduces the initial decomposition temperature of limestone but also alleviates the sintering of CaCO 3 from the perspective of grain evolution. The experimental results show that in a pure H 2 reducing atmosphere, the decomposition temperature of limestone decreases from ∼ 850 °C (under an inert atmosphere) to ∼ 650 °C. Within the temperature range of 650 ∼ 700 °C, the hydrogenation of limestone proceeds with nearly complete CaCO 3 conversion (∼ 100%), delivering a high CO yield (∼ 91%) that also reflects the high selectivity of the CO formation pathway. Consistent with expectations, higher H 2 concentrations further improve CO yield and selectivity. Additionally, the pre-addition of CaO indicates that the resulting solid product, CaO, serves as a catalyst in the hydrogenation reaction, significantly accelerating the reaction rate in the early stage and markedly shortening the overall reaction process while enhancing CO selectivity. This catalytic effect provides important insights for the low-carbon improvement of future cement clinker production processes based on carbonate hydrogenation.