Alkali carbonates promote CO2 capture by sodium orthosilicate

Sodium orthosilicate was synthesized by a wet chemical method with further calcination at 600 °C. Mixtures of Na4SiO4 and alkali (Li/Na/K) carbonates were prepared by a mechanical mixing method. The CO2 capture performance of the samples was characterized by dynamic thermogravimetric analyses and in situ XRD and Raman spectroscopy in 80 vol% CO2 mixed with 20 vol% N2. It was found that sodium orthosilicate could be used for CO2 sorption, and its maximum capacity could reach up to 19.2 wt%. The addition of alkali carbonates, which serve as promoters, led to the enhancement of the CO2 capture performance of Na4SiO4, especially at low temperatures, because of the formation of C2O52−. The existence of C2O52− in the mixture exposed to 80 vol% CO2 was confirmed by in situ Raman spectra, and its geometric structure was presented by DFT calculations. The formation of C2O52− within carbonates exhibited a positive influence on the CO2 capture at low temperatures and the enhancement of CO2 diffusion by Grotthuss-like transport through the carbonate product shell at high temperatures besides the formation of eutectic carbonate melts.