Intermediate Temperature CO 2 Capture by Porous MgO–CaO Nanostructures: Enhanced Sorption and Cycle Stability

Porous MgO–CaO nanostructure foams synthesized by a rapid self-sustained combustion reaction were probed as CO2 sorbents at SEWGS operating temperature, 400 °C. Porous MgO–CaO hetero-oxides of varying ratios (1:1), (2:1), and (3:1) exhibit CO2 sorption capacities of 6.0, 5.5, and 4.0 mmol g–1 with capture efficiency retention of 39, 40, and 60% after 100 cycles, respectively. The augmented sorption capacity and cycle stability are proposed to be due to self-sustained chain reaction at the MgO–CaO interfaces propagating the formation and diffusion of CO32– and O2– ions across the oxide interfaces. At 400 °C, the kinetically favored but dynamic CO2 sorption at the MgO sites result in simultaneous formation and migration of CO32– ions to the neighboring CaO sites to yield CaCO3 and O2– ions. The O2– ions diffuse to the neighboring oxygen vacant MgO lattice and interact with CO2 forming CO32– ions.