Theoretical insights into formation of ethylene, propylene and butylene in Co2C (020) catalyzed FTO process

Abstract

Fischer–Tropsch Synthesis to lower olefins (FTO) is an important non-petroleum route to produce lower olefins. Nanoprisms Co2C has been discovered as a promising FTO catalyst possessing high selectivity to olefins and low CH4 selectivity for its exposing (020) facet. Density Functional Theory (DFT) was used to understand the reason for inhibiting methane formation, the chain growth mechanism and dominant formation pathway of three main low olefins. The results show that the activation energy for CH2* to couple with CH* (0.51 eV) was much lower than that for further hydrogenation to form CH3* (0.66 eV), which was the key species to produce methane. Therefore, the mechanism inhibiting methane formation was Co2C(020) promoting CH2*-CH*coupling rather CH2* hydrogen. Moreover, it can be predict that the carbon chain would not grow too long, because the coupling activation energy for the C1-C1 coupling, C1-C2 coupling, C1-C3 coupling were 0.51 eV, 0.54 eV and 0.69 eV, respectively. At last, it can be predicted that propylene was the easiest to produce, followed by ethylene and butylene, because their barrier energy were 1.58 eV, 1.64 eV and 2.12 eV, respectively.