Time-Resolved synchrotron powder x-ray diffraction studies on the synthesis of L8 Si O6 and its reaction with CO2

Abstract

Lithium oxosilicate was synthesized via the solid-state method using Li 2 O and SiO 2 as starting reactants. In situ synchrotron powder X-ray diffraction (SPRXD) coupled with Rietveld refinement allowed describing the synthesis as a two-step process where Li 2 O and SiO 2 react to form Li 4 SiO 4 and, at higher temperatures, lithium orthosilicate reacts with the remaining Li 2 O to form Li 8 SiO 6 . Time-resolved measurements allowed determining the temperatures at which each phase transformation occurs as well as the time required to complete the synthesis. The CO 2 capture properties of Li 8 SiO 6 in the temperature range from room temperature to 770 °C were studied in detail by time-resolved in situ SPXRD. The crystallographic phases present during Li 8 SiO 6 carbonation were identified and quantified via Rietveld analysis. Results showed that, within the temperature range from 200 to 690 °C, Li 8 SiO 6 carbonation produces Li 4 SiO 4 and Li 2 CO 3 , while, at temperatures from 690 to 750 °C, a secondary reaction occurs, where previously formed Li 4 SiO 4 reacts with CO 2 , producing Li 2 SiO 3 and Li 2 CO 3. These findings allowed proposing a mechanism of reaction for Li 8 SiO 6 carbonation in the temperature range that is of interest for high temperature solid-state sorbents.