Nanoscale structural investigation of Cs₂CO₃-doped MgO sorbent for CO₂ capture at moderate temperature

MgO sorbents doped with alkali-metal carbonates have been shown to exhibit improved sorption capacities at both low and moderate operating temperatures, compared to pure MgO sorbents. However, the mechanism of how alkali-metal carbonates enhance the CO₂ sorption is not well understood. Using in situ X-ray diffraction, TEM, and thermogravimetric analysis, we have shown that the cesium dopants in the Cs₂CO₃-doped MgO nanoparticle system do not simply act as a promoter in sorption of CO₂, but rather as a reagent alongside MgO. A new mixed magnesium-cesium carbonate phase has been found to be responsible for the improved sorption capacity of the doped-MgO-based sorbents. On the basis of our findings, it is suggested that a higher sorption capacity may be achieved if cesium is uniformly dispersed throughout the MgO particles.