Conversion of methane to benzene in CVI by density functional theory study

A density functional theory (DFT) study was employed to explore the mechanism of the conversion of methane to benzene in chemical vapor infiltration (CVI) based on the concluded reaction pathways from C₁-species to C₆-species. The geometry optimization and vibrational frequency analysis of all the chemical species and transition states (TS) were performed with B3LYP along with a basis set of 6–311 +G(d, p), and Gaussian 09 software was used to perform the study. The rate constants were calculated by KiSThelP according to the conventional transition state theory (TST), and the Wigner method was applied to acquire the tunneling correction factors. Then the rate constants were fitted to the modified Arrhenius expression in the temperature range of 800–2000 K. As for the barrierless reactions calculated in this paper, the rate constants were selected from the relating references. Through the energetic and kinetic calculations, the most favorable reaction pathway for benzene formation from methane was determined, which were mainly made of the unimolecular dissociation. The conversion trend from C₁-species to C₄-species is mainly guided by a strong tendency to dehydrogenation and the pathways from C₄-species to C₆-species are all presumed to be able to produce C₆H₆ molecule.