Environmental plasma-catalysis for the energy-efficient treatment of volatile organic compounds

Nonthermal plasma (NTP) coupled with catalysis is a promising technique for the abatement of dilute volatile organic compounds (VOCs), because it is operable under mild reaction conditions, i.e., low temperature and atmospheric pressure. This review addresses the mechanistic aspects of catalyst activation by NTP, such as the generation and fixation of reactive species, facilitation of redox cycles, photocatalysis, and local heating, to clarify the combined effects of plasma and catalysis. The plasma-catalytic removal of VOCs preferentially requires the catalyst to have a large specific surface area, high surface oxygen storage capacity, and to be highly reducible. The energy consumption and deactivation of catalysts are considered by comparing continuous and cyclic operations in terms of specific input energy, VOC removal and energy efficiencies, and byproduct formation. Based on the information in the literature, a plasma-catalytic system operating in cyclic adsorption-oxidation mode is recommended for the treatment of air contaminated by dilute VOCs. Finally, the effects of NTP on the regeneration of deactivated catalysts are also discussed.