The effect of surface carbon on ethylene dimerization

The oligomerization of olefins is important to the production of the high hydrocarbons. In the oligomerization process, it is always accompanied by the reaction of hydrogenation. In the present article, we report that surface carbon affects the ethylene (C2H4) hydrogenation on the supported cobalt catalysts. Co/SiO2 catalyst is carburized with CO and Co3C structure as well as Co structure is revealed with Transmission Electron Microscopy (TEM). We investigate ethylene hydrogenation on the Co/SiO2 catalyst and the carburized Co3C-Co/SiO2 catalyst. It exhibits a high selectivity of C4 products on the carburized Co3C-Co/SiO2 catalyst. We further apply Density Functional Theory (DFT) calculation to study the effect of surface carbon on the dimerization of ethylene. Co(0001) and Co3C(2 2 1) are chosen to represent the Co/SiO2 and Co3C-Co/SiO2 catalysts, respectively. The dimerization of ethylene occurs by CCH3* species coupling instead of CH2CH2* coupling. The effective barrier of CCH3* coupling on Co(0001) is higher than that on Co3C(2 2 1). This explains the high selectivity to C4 products on the carburized Co3C-Co/SiO2 catalyst. Our study provides experimental and theoretical insight for the effect of surface carbon to the reaction of ethylene with hydrogen. It may guide us to reasonable design of the catalyst for olefin oligomerization.