Direct Reduction of Magnesium Carbonate to Methane

Carbonate hydrogenation under active catalysts is a promising method to produce valuable hydrocarbons. Our thermodynamic feasibility studies indicate that several products could be expected, and our experimental results showed that the exclusive product is methane. Current scenarios indicate synthetic methane production as of greater value in a less fossil fuel-dependent economy, accepting methane could come from sources such as direct air capture and sustainable production routes. Mineral carbonation (mineralization), which mimics the natural process of carbon weathering is a promising method for CO 2 storage. High-volume CO 2 mitigation based on magnesium silicate minerals is considered feasible as these minerals are one of the best minerals for carbonation. Here, we envision scenarios for direct air capture with mineralization of magnesium oxide/magnesium silicate into carbonates. We describe the direct conversion of MgCO 3 with renewable hydrogen in the presence of a solid catalyst. Our results indicate that with proper optimization of the conditions (pressure, temperature, gas- and solid-phase residence time, ratio of the catalyst and carbonate), the reaction leads to the higher selectivity and yield of methane, when compared to other metal carbonate sources. We started this work analyzing hypothetical scenarios of direct air capture with mineralization. We present compelling numbers that may inspire new opportunities to be explored for mitigating the excess of CO 2 in the environment. These results demonstrated that we could recover the CO 2 from magnesium carbonate, and in a direct conversion in the presence of commercially available nickel catalyst with renewable H 2, we could produce renewable methane at 100% selectivity (no CO detected) at temperatures <360 °C. Our method consisted of mixing the solid magnesium carbonate with nickel and Co-syngas catalysts. The results showed that in the presence of high proportion of the Ni catalyst, at temperatures <360 °C, no CO 2 was detected, which confirmed the effect of the catalyst on carbonate reduction and product formation. At elevated pressure, we also produced predominantly methane and no other valuable hydrocarbons than methane could be obtained using the Co-based syngas catalyst.