Atomic-scale mechanism of incorporation of carbon dioxide in coal*

Global warming is attributed to the rise of CO$_{2}$ concentration in the atmosphere. Sequestration of CO$_{2}$ into geological formations has been suggested for mitigating this phenomenon. Coalbeds are investigated as potential storage sites. Numerous experimental studies have demonstrated that coal swelling occurs after the injection of CO$_{2}$ into coal seams. However, the atomic-scale mechanism of such a phenomenon has not been well established. We report first-principles density-functional-theory calculations for the interaction between CO$_{2}$ and the coal network. The calculations show that the activation energies for incorporation of CO$_{2}$ into the coal bonding network are low at $\sim$ 0.9-1.3 eV depending on the bonding sites. We have found that the incorporated configurations are stable at low temperatures. However, high temperatures could stimulate the dissociation of CO$_{2}$ from such configurations as the activation energies are low at $\sim$ 0.5-0.9 eV, suggesting that coal swelling is reversible at high temperatures.