Improvements in the pre-combustion carbon dioxide sorption capacity of a magnesium oxide-cesium carbonate sorbent

Cesium-carbonate-doped magnesium oxide has been shown to be a prospective candidate for pre-combustion CO₂ capture at temperatures between 300 and 410°C. Materials were synthesized by wet mixing commercially available materials as well as a solvothermal approach using a magnesium methoxide in methanol solution. The materials were activated by heat treatment at 600-610°C to yield the active CO₂ sorbent. The sorbents showed working capacities of around 4 wt % in up to 25 partial pressure swing (12 min of sorption and 24 min of desorption) cycles. If the cesium carbonate was dissolved in the magnesium methoxide solution before solvothermal synthesis, multi-cyclic working capacities were increased to 5 wt %. Brunauer-Emmett-Teller surface area measurements of the activated materials showed that the solvothermal method led to materials with higher surface areas of ∼13 m ²/g, as compared to 3.4 m²/g if made from commercial MgO. Transmission electron microscopy showed the morphology of the activated solvothermally mixed materials to consist of spheres of approximately 50 nm diameter, with crystallinity increasing during heat treatment. Powder X-ray diffraction results confirmed this result and also proposed a similar chemistry during CO₂ sorption of the solvothermally synthesized materials compared to the materials made from commercial precursors. Fourier transform infrared spectroscopy shows shifts in the carbonate ion spectra between the cesium carbonate precursor and the CO₂-saturated mixed sorbent, indicating different carbonates in both of these materials. Elemental mapping using scanning transmission electron microscopy showed a uniform distribution of cesium and magnesium in the sample, with occasional clustering of cesium being visible in some particles. It appears that cesium carbonate addition into the solvothermal process created a better mixture of Cs and Mg in the particle than wet mixing onto dispersed particles. This led to the creation of a higher number of active sorption sites and, thus, a higher capacity for CO₂ sorption.