Yang Jeehyun, Smith Mica C, Prendergast Matthew B, Chu Te-Chun, Green William H
Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Phys Chem Chem Phys. 2021 Jul 7;23(26):14325-14339. doi: 10.1039/d1cp01565f.
The formation of polycyclic aromatic hydrocarbons (PAHs) during combustion has a substantial impact on environmental pollution and public health. The hydrogen-abstraction-acetylene-addition (HACA) mechanism is expected to be a significant source of larger PAHs containing more than two rings. In this study, the reactions of 1-naphthalenyl and 2-naphthalenyl radicals with acetylene (C2H2) are investigated using VUV photoionization time-of-flight mass spectrometry at 500 to 800 K, 15 to 50 torr, and reaction times up to 10 ms. Our experimental conditions allow us to probe the Bittner-Howard and modified Frenklach HACA routes, but not routes that require multiple radicals to drive the chemistry. The kinetic measurements are compared to a temperature-dependent kinetic model constructed using quantum chemistry calculations and accounting for chemical-activation and fall-off effects. We measure significant quantities of C14H10 (likely phenanthrene and anthracene), as well as 2-ethynylnaphthalene (C12H8), from the reaction of the 2-naphthalenyl radical with C2H2; these results are consistent with the predictions of the kinetic model and the HACA mechanism, but contradict a previous experimental study that indicated no C14H10 formation in the 2-naphthalenyl + C2H2 reaction. In the 1-naphthalenyl radical + C2H2 reaction system, the primary product measured is C12H8, consistent with the predicted formation of acenaphthylene via HACA. The present work provides direct experimental evidence that single-radical HACA can be an important mechanism for the formation of PAHs larger than naphthalene, validating a common assumption in combustion models.
燃烧过程中多环芳烃（PAHs）的形成对环境污染和公众健康有重大影响。氢提取-乙炔加成（HACA）机制被认为是含有两个以上环的较大PAHs的重要来源。在本研究中，使用真空紫外光电离飞行时间质谱仪在500至800K、15至50托以及最长10毫秒的反应时间下，研究了1-萘基和2-萘基自由基与乙炔（C2H2）的反应。我们的实验条件使我们能够探测比特纳-霍华德和改进的弗伦克拉赫HACA途径，但无法探测需要多个自由基驱动化学反应的途径。将动力学测量结果与使用量子化学计算构建并考虑化学活化和衰减效应的温度依赖动力学模型进行比较。我们测量到2-萘基自由基与C2H2反应产生了大量的C14H10（可能是菲和蒽）以及2-乙炔基萘（C12H8）；这些结果与动力学模型和HACA机制的预测一致，但与先前的一项实验研究相矛盾，该研究表明2-萘基 + C2H2反应中没有C14H10生成。在1-萘基自由基 + C2H2反应体系中，测量到的主要产物是C12H8，这与通过HACA预测生成苊烯的结果一致。本工作提供了直接的实验证据，表明单自由基HACA可能是形成比萘更大的PAHs的重要机制，验证了燃烧模型中的一个常见假设。
