Involvement of catalyst materials in nonthermal plasma chemical processing of hazardous air pollutants

Catalytic effects of metal oxides in nonthermal plasma chemical processing of hazardous air pollutants (HAPs) are discussed, relevant to their activities for the oxidation of HAPs in nonthermal plasma media and their selective control of active oxygen species derived from background O₂. In ferroelectric packed-bed reactors, the oxidation power of barium titanate (BaTiO₃) is not strong enough to oxidize HAPs and their carbon intermediates to CO₂. Only nitrous oxide (N2_O) was formed from background N₂ and lattice oxygen atoms in BaTiO₃. The catalytic effect of BaTiO₃ is negligible under aerated conditions. On the other hand, ozone (O₃) is formed from background O₂ in much higher concentrations in a silent discharge plasma reactor. Manganese dioxide (MnO₂)-catalyzed decomposition of O₃ promotes decomposition of benzene, which is less reactive than trichloroethylene and tetrachloroethylene. The acceleration of benzene consumption rate is ascribed to the promotion of its oxidative decomposition by the triplet oxygen atom. Catalytic control of in situ active oxygen species could be one of the most effective approaches to increase the energy efficiency of the nonthermal plasma reactor and to achieve the complete oxidation of the carbon atoms in HAPs.