CaO is promising to be widely used to capture CO2. The produced CaCO3 can be considered as solid CO2, which is also a plentiful, convenient, and useful carbon resource. Here, for the first time, we report that an alkaline earth metal can selectively induce the hydrogenation of the CaO-captured CO2 (namely, the produced CaCO3) to CH4 under room-temperature ball-milling conditions. The effects of ball-milling conditions and different catalysts on the methanation performance were studied. The results show that the CH4 yield can reach 56.1%, and the CH4 selectivity is 100%. When adding metal Ni, the CH4 yield can be further increased. The experimental and density functional theory calculation results indicate that the in situ formed metal hydride plays a key role in the process of methanation. This work provides a novel and energy-saving method to convert the metal oxide-captured CO2/carbonate to CH4 at room temperature.

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In this study, we investigated the reduction of CO2 using magnesium and calcium hydride (AeH2, Ae = Mg or Ca), in the process of which clean H2‐mixed CH4 fuel is produced. The result of this investigation shows that the particle size of AeH2 and AeH2/CO2 molar ratio can greatly affect the molar percentage value and reaction yield of methane. In general, the magnesium or calcium hydride as‐milled for 2 hr is enough active for reduction of CO2 to CH4. When the molar ratio of AeH2/CO2 is set to 2:1, the methanation effect is optimal for both reaction systems. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd.