Laser-Ionization TOF Mass Spectrometer Characterization of Benzene Destruction in Atmospheric Pressure Pulsed Discharge

Benzene is a major industrial air pollutant and can cause serious human health disorders. In this paper an investigation on benzene destruction, in an atmospheric-pressure fast-flow pulsed DC-discharge by means of laser ionization combined with time-of-flight (TOF) mass spectrometry, is reported. Most by-products including transient reactive species from the benzene discharge were characterized by molecular beam sampling combined with TOF mass spectrometry. It is showed that, with a gas mixture of 0.5% C6H6 in Ar, benzene can be effectively destroyed by discharge plasma. The intermediate species consisted of small fragments of CnHm (n=3 similar to 5, m=1 similar to 11), cycle-chain species of CnHm (n=6 similar to 9, m=7 similar to 10) and polycyclic species CnHm (n >= 9, m=8 similar to 12). The alternation of mass peaks (intensity) with even/odd electrons was observed in the measured mass spectra. The results indicated that the alternation is mainly due to the different ionization potentials of the open shell and close shell species. Based on the examination of the features of the species' composition, the primary reaction pathways are proposed and discussed.