Continuous Butadiyne Addition to Propargyl: A Radical-Efficient Pathway for Polycyclic Aromatic Hydrocarbons

Abstract

Polycyclic aromatic hydrocarbons (PAHs) play a crucial role in soot inception, interstellar evolution, and nanomaterial synthesis. Although several mechanisms, such as hydrogen-abstraction acetylene/vinylacetylene addition, have previously been proposed, PAH formation and growth are not yet fully understood. We propose an alternate PAH growth mechanism wherein propargyl radical reacts with butadiyne to form larger radicals containing newly fused aromatic rings. Butadiyne is an important intermediate in hydrocarbon oxidation and carbon rich stars, while propargyl is one of the most important resonantly stabilized radicals that persists for long times. Our proposed mechanism is validated by quantum chemical calculations, elementary reaction experiments, laminar flame analysis, and kinetic modeling. Our findings challenge the conventional wisdom that radical site regeneration, being central to PAH growth, requires sequential hydrogen elimination and/or abstraction. In our proposed mechanism, PAH growth does not depend on abundant free radical consumption, and could, therefore, help explain carbonaceous nanoparticle coalescence in radical-deficient reaction environments.

Temperature Effect on Formation of Polycyclic Aromatic Hydrocarbons in Acetylene Pyrolysis

“…using the reaction mechanism generator(RMG), are considered to supplement and update the elemental reactions. In the mechanism construction, the recent development and modified elementary reactions are also considered, including propargyl, [34–37] benzene and phenyl, [38,39] naphthalene [40] , acenaphthylene, [41–44] and the formation mechanism of various PAHs [30,45–49] . For chemical reactions not covered by the above mechanisms, the group additivity and density functional theory (B3LYP) of RMG are used to estimate the reactions.…”

“…For the process from C 6 hydrocarbon to coronene based on the mechanism proposed by Norinaga et al [31] and Tao et al [32] At the same time, the detailed reaction mechanism developed by Chemical Reaction Engineering and Chemical Kinetics Lab and the detailed acetylene pyrolysis mechanism automatically constructed by Liu et al [33] using the reaction mechanism generator(RMG), are considered to supplement and update the elemental reactions. In the mechanism construction, the recent development and modified elementary reactions are also considered, including propargyl, [34][35][36][37] benzene and phenyl, [38,39] naphthalene [40] , acenaphthylene, [41][42][43][44] and the formation mechanism of various PAHs. [30,[45][46][47][48][49] For chemical reactions not covered by the above mechanisms, the group additivity and density functional theory (B3LYP) of RMG are used to estimate the reactions.…”

Probing combustion and catalysis intermediates by synchrotron vacuum ultraviolet photoionization molecular-beam mass spectrometry: recent progress and future opportunities

“…A notable progress is the very recent works reported by Jin and co-workers. 66,67 In the regard of PAH formation, they proposed a radical efficient PAH growth pathway named as CBAC, wherein the propargyl radical reacts with butadiyne to form larger radicals containing newly fused aromatic rings. Fig.…”

“…Catalysis is directly applied in around 80% of the production of important industrial chemicals, among which heterogeneous 66 Reproduced with permission from the American Chemical Society. catalysts are often preferred for their advantages of easier recovery and recycling in industrial production.…”

“…All mass spectra were obtained at the photon energy of 8.5 eV. PIE curves for (d) m/z 89, (e) m/z 90, (f) m/z 139, and (g) m/z 140 66. Reproduced with permission from the American Chemical Society.…”