Abstract
Calcium oxide (CaO) is a high-temperature CO2 capture sorbent. However, it suffers from CaO aggregation for CO2 scrubbing after looping cycles. To disperse and secure CaO, in this research, we pyrolyzed Ca-based metal-organic frameworks (MOFs) Ca-BTC for CaO on MOF-derived carbon (MDC). Furthermore, ceria or nitrogen was introduced into Ca-MDC by Ce2+ or DABA ligand addition to Ca-BTC. Compared to pure CaO, Ca-MDC maintained 30 % better CO2 adsorption stability after 10 cycles. In comparison, the CO2 uptake of CeO2-decorated Ca-MDC kept at about 100 % after 10 cycles, which could be attributed to oxygen vacancy in CeO2. The highest CO2 adsorption reached 17.10 mmol/g in N-doped Ca-MDC with 80 % stability. All CaO on MDC samples had CO2 adsorption exceeding the theoretical stoichiometric ratio 1:1 of CaO:CO2, implying plausible CO2 spillover from CaO to carbon matrix. For kinetics analyses, the pseudo-second order (PSO) model showed a better fit than the linear driving force (LDF) model, suggesting strong chemisorption in CaO as expected. The double exponential (DE) model was applied to differentiate CO2 chemisorption and surface diffusion and showed much higher diffusion rate constants in Ca-MDC than CaO, suggesting a possible CO2 spillover phenomenon.
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