Li Wenrui, Shang Yanlei, Ning Hongbo, Li Jun, Luo Sheng-Nian
Key Laboratory of Advanced Technologies of Materials, Ministry of Education, and Institute of Material Dynamics, Southwest Jiaotong University, Chengdu, Sichuan 610031, P. R. China.
School of Chemistry and Chemical Engineering & Chongqing Key Laboratory of Theoretical and Computational Chemistry, Chongqing University, Chongqing 401331, China.
Phys Chem Chem Phys. 2020 Mar 11;22(10):5797-5806. doi: 10.1039/c9cp06642j.
The reaction between CO and HO2 plays a significant role in syngas combustion. In this work, the catalytic effect of 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 a cis- or a 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: COHO2 + H2O, RC3: COH2O + HO2, and RC4: HO2H2O + CO), depending on the initial hydrogen bond formation. Compared to the water-free process, the reaction barriers of the 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 the literature. In addition, the effective rate constants for the water-assisted process decrease by 1-2 orders of magnitude compared to the water-free one at a temperature below 600 K. In particular, the effective rate constants for the water-assisted and water-free processes are 1.55 × 10-28 and 3.86 × 10-26 cm3 molecule-1 s-1 at 300 K, respectively. This implies that the contribution of a single molecule water-assisted process is small and cannot accelerate the title reaction.
一氧化碳（CO）与过氧化氢（HO₂）之间的反应在合成气燃烧中起着重要作用。在本工作中，采用CCSD(T)/aug-cc-pV(D,T,Q)Z和CCSD(T)-F12a/jun-cc-pVTZ理论水平，并结合M062X/aug-cc-pVTZ理论水平，从理论上研究了单分子水对该反应的催化作用。首先，重新考察了CO + HO₂（无水）的势能面。主要产物二氧化碳（CO₂）和羟基（OH）通过顺式或反式过渡态（TS）通道形成，而一氧化碳氢（HCO）和氧气（O₂）的形成较少。在有水存在的情况下，根据初始氢键的形成，该反应有三种不同的预反应复合物（即RC2：COHO₂ + H₂O、RC3：COH₂O + HO₂和RC4：HO₂H₂O + CO）。与无水过程相比，由于形成了更稳定的环状过渡态和复合物，水辅助过程的反应势垒显著降低。使用传统过渡态理论（TST）并结合埃卡特非对称隧穿校正，进一步计算了双分子反应路径CO + HO₂、RC2、RC3和RC4的速率常数。对于反应CO + HO₂，我们的计算结果与文献报道吻合良好。此外，在温度低于600 K时，水辅助过程的有效速率常数比无水过程降低了1 - 2个数量级。特别是，在300 K时，水辅助过程和无水过程的有效速率常数分别为1.55×10⁻²⁸和3.86×10⁻²⁶ cm³·分子⁻¹·秒⁻¹。这表明单分子水辅助过程的贡献较小，无法加速该反应。
