Theoretical investigation on reaction pathways for ethylene epoxidation on Ti-decorated graphene

The activities of atomic Ti-decorated graphene (Ti/dG) for ethylene epoxidation and competitive paths for acetaldehyde (AA) formation are investigated by means of density functional theory together with the D3 dispersion correction (UM06-L-D3). Two reaction mechanisms for ethylene epoxidation, namely concerted and stepwise mechanisms, were considered. The computational results reveal that the electron transfer from graphene can effectively enhance the catalytic activity of Ti atom. Without graphene support, atomic Ti becomes an inert metal for this reaction. Strong adsorption and significant activation of the reactant O₂ molecule were observed on the Ti-decorated graphene material. Over the O₂-adsorbed Ti/dG, the direct attack of the olefin on an peroxo oxygen center is preferred. The activation for this step is 10.9 kcal mol^?1. After the reaction, an ethylene oxide is formed with one atomic oxygen on top of Ti. Consequently, a gaseous ethylene reacts with the remaining O atom of TiO moiety for the formation of the second ethylene oxide molecule. The formation of ethylene oxide over the TiO/dG involves a two-step process which is the formations of oxametallacycle intermediate and EO, respectively. The calculated barriers for these two steps are 9.9 and 18.9 kcal mol^?1, respectively. Furthermore, the Ti/dG showed a lower activation barrier toward EO formation than that of AA. Therefore, our theoretical study suggests that atomic Ti-decorated graphene could possess catalytic activity for ethylene epoxidation comparable to that of potential catalysts.