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Role of Phenyl Radicals in the Growth of Polycyclic Aromatic Hydrocarbons
文摘
To investigate the role of phenyl radical in the growth of PAHs (polycyclic aromatic hydrocarbons), pyrolysisof toluene with and without benzene has been studied by using a heatable tubular reactor couple with anin-situ sampling vacuum ultraviolet (VUV) single photon ionization (SPI) time-of-flight mass spectrometer(TOFMS) at temperatures 1155-1467 K and a pressure of 10.02 Torr with 0.56 s residence time. Whenbenzene was added, a significant increase of phenyl addition products (biphenyl, terphenyl, and triphenylene)was observed and the mass spectra showed a clear regular sequence with an interval of ~74 mass number,corresponding to the phenyl addition (+C6H5) followed by H-elimination (-H) and cyclization (-H2). Theanalysis showed that the PAC (phenyl addition/cylization) mechanism is efficient for the growth of PAHswithout a triple fusing site, for which the HACA (hydrogen abstraction/C2H2 addition) step is inefficient, andproduces PAHs with five-membered rings. The PAC process was also suggested to be efficient in the subsequentgrowth of PAHs with five-membered rings. The role of the PAC mechanism in combustion conditions isdiscussed in relation to the importance of disordered five-membered ring structure in fullerene or soot core.
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