Advances on Understanding Coke Gasification Process with CO2: A Report from Density Functional Theory

CO2 gasification process on different active edges of a particular coke model surface has been explored computationally. It is observed that the adsorption through carbon and oxygen end of CO2 (CO-mode) through formation of four- and five-membered ring on the active sites is the favoured one. Our calculation also reveals that the strength of adsorption depends on nature and position of the active sites. The exergonic adsorption energy of CO-mode drives the first CO release process and also makes it favoured compared to the adsorption mode where CO2 has been absorbed through its two-oxygen end (OO-mode). Among all the intermediates, intermediate having oxygen attached to the middle-carbon of the coke (middle-oxygenated coke) is found to be the most stable intermediate. The energy barrier for the second CO release also depends on the attachment sites of the oxygen on the coke surface. It is noteworthy that first principles investigations of coke gasification reactions with CO2 reported to date are found to consider different coke active sites separately on different coke model surfaces. In this context, our work is believed to be the first of its kind where complete characterization of CO2 gasification reactions has been performed considering all the active sites in a single coke model, thus providing a more coherent picture of it.