Lithium orthosilicate (Li4SiO4) is an attractive high-temperature CO2sorbent (>650◦C) because of itslarge theoretical absorption capacity of up to 36.7 wt%. However, slow kinetics and partial reactions withCO2hinder its proper operation as a sorbent under practical conditions. To allow the use of this sorbent atlower operation temperatures, the present studies explored the way to improve the CO2absorption kinet-ics and increase the degree of reaction of Li4SiO4. Porous carbon materials such as CMK-3 were introducedinto the sorbent to provide an internal gas pathway. Upon calcination conditions, the carbon amountwas controlled in the composites (Li4SiO4@CMK-X%, where X represents the amounts of CMK-3). InLi4SiO4@CMK-1.8%, CMK-3 is distributed over the whole solid; in contrast, the additive in Li4SiO4@CMK-0.5% is mainly observed near the surface of the solid. CO2gas sorption study of the composites showedthat pores of CMK-3 in Li4SiO4aid the diffusion of CO2. In addition, we found that the incorporation ofporous carbon provides more active sites for interactions with CO2through the formation of cavitiesbetween Li4SiO4and CMK-3. Li4SiO4@CMK-1.8% had an increased CO2absorption capacity (35.4 wt%)and rate (15.2 wt% for the first 5 min) at 600◦C, compared to the CO2absorption capacity (16.3 wt%) andrate (5.1 wt% for the first 5 min) of pristine Li4SiO4(p-Li4SiO4). To confirm the influence of porous carbonon the CO2absorption properties, multi-walled carbon nanotube (MWCNT) was also examined as anadditive instead of CMK-3. Li4SiO4@CNT showed similar trends with Li4SiO4@CMK sorbents.