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

Kun Li,Ningning Yan,Wei Li,Hejun Li,Qiang Song,Tiyuan Wang

doi:10.1038/s41598-019-56136-0

Kun Li, Ningning Yan + Show 4 more

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https://doi.org/10.1038/s41598-019-56136-0

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Journal: Scientific Reports	Publication Date: Dec 1, 2019
Citations: 7	License type: open-access

Affiliation: Northwestern Polytechnical University

Abstract

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.

Highlights

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 above researches studied the decomposition of methane, they were unable to illustrate the nature of the mechanism of the homogeneous reactions during the pyrolysis of methane, and these results could not be explained from the view of the molecular level
The primary goal of this section is to obtain the main reaction pathways of the decomposition of methane during Chemical vapor infiltration (CVI) by distinguishing the pathways collected from the previous researches[11,12,29,30,31,32,33,34,35,36,37,38,39,40]

Summary

Introduction

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. Chemical vapor infiltration (CVI) is a widely used method for the production of carbon/carbon (C/C) composites, which are mainly employed in the manufacture of solid rocket motor nozzles, brake discs of military and commercial aircraft, and spacecraft heat shields because of their excellent thermal and mechanical properties, like high specific modulus, high specific strength, and wear resistance at high temperature[1] It is one of the most important ways to prepare high performance C/C composites using methane as precursor[2,3,4,5,6,7,8,9,10], and the pyrolysis in the gas phase has been reported to play a significant role in the formation of C/C composites[8,11]. Despite the plenty of theoretical studies of the decomposition of methane published already, there are few DFT researches concerning the detailed conversion pathways of methane to benzene in CVI, and it is of great necessity to figure out the mechanism from the molecular level

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Discussion

Conclusion