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Reaction pathways and kinetics study on syngas combustion system: CO + HO2 in H2O environment

Abstract

The reaction between CO and HO2 plays a significant role in syngas combustion. In this work, the catalytic effect by single-molecule water on this reaction is theoretically investigated at the CCSD(T)/aug-cc-pV(D, T, Q)Z and CCSD(T)-F12a/jun-cc-pVTZ levels in combination with the M062X/aug-cc-pVTZ level. Firstly, the potential energy surface (PES) of CO + HO2 (water-free) is revisited. The major products CO2 + OH are formed via cis- or trans-transition state (TS) channel and the formation of HCO + O2 is minor. In the presence of water, the title reaction has three different pre-reactive complexes (i.e., RC2: CO…HO2 + H2O, RC3: CO…H2O + HO2, and RC4: HO2…H2O + CO), depending on the initial hydrogen bond formation. Compared to the water-free process, the reaction barriers of water-assisted process are reduced considerably, due to more stable cyclic TSs and complexes. The rate constants for the bimolecular reaction pathways CO + HO2, RC2, RC3, and RC4 are further calculated using conventional transition state theory (TST) with Eckart asymmetric tunneling correction. For reaction CO + HO2, our calculations are in good agreement with literature. In addition, the effective rate constants for water-assisted process decrease by 1–2 orders of magnitude compared to the water-free one at temperature below 600 K. In particular, the effective rate constants for water-assisted and water-free are 1.55 × 10-28 and 3.86 × 10-26 cm3 molecule−1 s−1 at 300 K, respectively. It implies that the contribution of single molecule water-assisted process is small and cannot accelerate the title reaction.

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Supplementary files

Article information


Submitted
10 Dec 2019
Accepted
06 Feb 2020
First published
07 Feb 2020

Phys. Chem. Chem. Phys., 2020, Accepted Manuscript
Article type
Paper

Reaction pathways and kinetics study on syngas combustion system: CO + HO2 in H2O environment

W. Li, Y. Shang, H. Ning, J. Li and S. Luo, Phys. Chem. Chem. Phys., 2020, Accepted Manuscript , DOI: 10.1039/C9CP06642J

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