One of the promising pathways for the directed separation of CO2 is via carbon mineralization in which CO2 is captured and converted to magnesium carbonate using oxides and silicates of Mg. However, the influence of the sizes of MgO and Mg2SiO4, in particular, nano-scale particles on the accelerated separation of CO2 has been less studied. In this study, we uncover the mechanisms underlying the synthesis of nano-scale MgO and Mg2SiO4 starting from colloidal precursors using in-operando Ultra Small/Small/Wide Angle X-Ray Scattering (USAXS/SAXS/WAXS) measurements. Detailed insights into the meso-scale, nano-meter scale, and sub-nanometer scale transformations are delineated using these measurements. The transitions of amorphous gels to crystalline nanoparticles on heating, and the temperatures that correspond to these transitions are described using this approach. To evaluate the feasibility of using these nanoparticles for capturing CO2 produced during the water gas shift reaction, we investigated the carbon mineralization kinetics in hydrothermal environments at 200 °C and CO2 partial pressure of 20 atm in DI water and 1 M NaHCO3 solution, respectively. These experimental conditions correspond to the Water-Gas-Shift (WGS) reaction in which CO and H2O (steam) are reacted to produce CO2 and H2. USAXS/SAXS/WAXS performed on the initial and final products revealed the morphology and composition of these materials. Near complete conversion of nano-scale MgO and Mg2SiO4 to magnesium carbonate is achieved by coupling our carbon mineralization pathway to the water-gas-shift reaction. This study illustrates the use of cross-scale scattering measurements to unlock fundamental insights into the science of CO2 separation via carbon mineralization.

Structural and microstructural transformations of amorphous magnesium silicate gels to nanoparticles and their applications in CO2 capture

ACS Fall 2020 Virtual Meeting

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