In Situ XRD, Raman Characterization, and Kinetic Study of CO2 Capture by Alkali Carbonate-Doped Na4SiO4

Sodium silicate, a new type of CO2sorbent, has a relatively low cost, but its sorption reactivity is not yet good enough. Alkali carbonate doping is commonly used as an effective means to improve the CO2uptake reactivity of solid sorbents. In this study, sodium orthosilicate, Na4SiO4, was synthesized and mixed with 5, 10, and 20 mol% of Li2CO3–Na2CO3or Li2CO3–Na2CO3–K2CO3as CO2sorbents. The promotion of alkali carbonates on Na4SiO4in CO2capture was characterized using thermal analyses in an 80 vol% CO2–20 vol% N2atmosphere. The phase evolution and structural transformations during CO2capture were characterized by in situ XRD and Raman, and the results showed that the intermediate pyrocarbonate, C2O52−, which emerged from alkali carbonates, enhanced the CO2capture of Na4SiO4to form Na2CO3and Na2SiO3from 100 °C. Isothermal analyses showed that 10 mol% of Li2CO3–Na2CO3was the optimal additive for Na4SiO4to attain better CO2uptake performance. The alkali carbonates were effective in reducing the activation energy for both chemisorption and bulk diffusion, improving the cycle stability of Na4SiO4.Keywords:CO2capture;Na4SiO4;alkali carbonates;in situ XRD;in situ Raman;isothermal analysis;double exponential model;Eyring’s model