The mechanism of CO2 chemisorption on zigzag carbon active sites: A computational chemistry study

A computational chemistry study was carried out to evaluate the various options for CO2 adsorption on one or two adjacent zigzag sites in a graphene layer. Density functional theory was used with the 6-31G(d) basis set, as implemented in the Gaussian software package in conjunction with GaussView and Chem3D. Various electronic environments of a four-ring model, with and without surface oxygen and with special emphasis on carbene-like structures, were analyzed. The resulting optimized geometries were quite sensitive to such electronic configurations. In agreement with long-standing experimental evidence, dissociative CO2 adsorption was found to be particularly favorable; furthermore, dissociation was found to be favored on isolated carbene-like zigzag sites. It is recommended that such a pathway, rather than dual-site adsorption and C-CO2 complex formation, deserves the dominant attention in further theoretical studies of adsorption, reaction and desorption processes during CO2 gasification of carbons.