Co2 Adsorption on Carbonaceous Surfaces: a Combined Molecular Modeling and Experimental Study

Introduction Gasification of coke, char and graphite with CO2 has been a research focus for several decades. However, our understanding on the mechanism of this industrial important process is still limited. For instance, the mode of adsorption of CO2 on carbanaceous surfaces, i.e. a molecular or dissociative adsorption, is not known for certain, Though, it is generally believed that CO2 is chemisorbed on the carbon surface to release a CO molecule to the gas phase leaving a chemisorbed oxygen atom on the carbon surface forming a CarbonOxygen complex.1,2 There have been a number of experimental studies attempting to identify surface oxygen complexes due to its importance in deducing the mechanism of these reactions.3-5 Surface oxygen complexes such as pyrone, semi-quinone, carbonyl, ether, lactone, and acid anhydride have been proposed so far. However, there has been no definitely conclusion regarding the relative significance of these oxygen complexes in the gasification reactions and the chemical transformations between them. In the present study, we have carried out a combined theoretical and experimental study on the adsorption of CO2 on char. In particularly, theoretical study using a state-of-the-art quantum chemistry method, namely non-local hybrid density functional theory, was performed to determine stable CO2 adsorption complexes and to characterize them. Such computational tool has been previously applied to gasification and combustion reactions.6-8 Heat of adsorption of CO2 on char was determined experimentally using the volumetric technique and it is compared to the theoretical prediction. Such comparison allows us to elucidate molecular structures and stability of the surface complexes.