Plasma-Catalytic VOC Removal with Nonthermal Plasma Regeneration and Repetitive use of Catalysts

Catalysts used in nonthermal plasma (NTP)-catalytic removal of volatile organic compounds are often deactivated by coke deposits. Their regeneration and subsequent repetitive use are therefore essential for maintaining process efficiency and reducing operating costs. This work investigates the potential of NTP regeneration and repetitive use of coke-deactivated catalysts. Packed-bed dielectric barrier discharge reactors filled with TiO₂ and Pt/γ-Al₂O₃ pellets were used for toluene removal in atmospheric air. The catalysts deactivated during toluene decomposition were regenerated by NTP in oxygen to promote coke oxidation. This removal-deactivation-regeneration cycle was repeated 3 times. Two NTP regeneration strategies were studied: continuous plasma regeneration and sequential plasma regeneration, the latter combining shorter NTP exposures with pellet mixing. In addition, catalyst pre-treatment by NTP in oxygen was also performed before toluene removal. Reactor temperature and current waveforms were continuously monitored throughout the experiments. Toluene removal efficiency (TRE), energy cost, and production of gaseous products (CO₂, CO, HCOOH) were evaluated by Fourier-transform infrared absorption spectroscopy. The surface of catalytic pellets was analyzed by scanning electron microscopy coupled with energy-dispersive spectroscopy. The results revealed a strongly catalyst-dependent response to both NTP regeneration and pre-treatment. TiO₂ exhibited higher or comparable TRE after regeneration in repeated cycles of its use than fresh and non-regenerated catalysts, and its performance was further enhanced by the pre-treatment. In contrast, although the regeneration increased the TRE of Pt/γ-Al₂O₃ compared to the non-regenerated catalyst, its efficiency in repeated cycles remained lower than that of the fresh catalyst. Moreover, pre-treatment of Pt/γ-Al₂O₃ further reduced its TRE.