Effect of calcium on gasification of carbonaceous materials with CO2: A DFT study

Calcium catalyzed carbon gasification with CO2 was investigated by using density functional theory calculations at the B3LYP/6-311G(d) level of theory. Non-catalyzed carbon gasification with CO2 was also studied for comparison purposes. It was found that once calcium is chemisorbed on the active sites it modifies the net charge of some carbon atoms making the CO2 dissociative chemisorption more favorable. We evaluated two possible pathways for carbon monoxide desorption: (1) direct gasification for both catalyzed and non-catalyzed reactions and (2) gasification via formation of a surface complex only for catalyzed reactions. Activation energies and rate constants for all carbon monoxide desorption pathways proposed here were calculated and compared with previous experimental and computational studies. Carbon monoxide desorption takes place with similar activation barriers for both catalyzed and non-catalyzed reaction. These findings along with calculated rate constants and NBO analysis suggests that the role of catalyst is to increase the rate of the reaction without significantly changing the activation energy.