Effects of humidity on the plasma-catalytic removal of low-concentration BTX in air

Effects of relative humidity (30%, 50% and 80% RH) on the removal of low-concentration benzene, toluene and p-xylene (BTX mixture) in air by non-thermal plasma (NTP) and the combination of NTP and MnOx/Al2O3 catalyst (CPC) were systematically investigated in a link tooth wheel-cylinder plasma reactor. A long-term (150 h) CPC experiment under 30% RH was also conducted to investigate the stability of the catalyst. Results show that increasing humidity inhibits the O3 production in plasma and its decomposition over the catalyst. As for BTX conversion, increasing humidity suppresses the benzene conversion by both NTP and CPC; although higher humidity slightly promotes the toluene conversion by NTP, it negatively influences that by CPC; while the conversion of p-xylene by both NTP and CPC is insensitive to the humidity levels. Irrespective of the RH, the introduction of MnOx/Al2O3 catalyst significantly promotes BTX conversion and improves the energy efficiency. On the other hand, CPC under 30% RH shows the best performance towards COx formation during BTX oxidation processes. However, for a specific input energy of 10 J L-1 in this study, organic intermediates generated and accumulated over the catalyst surface, resulting in a slight deactivation of the MnOx/Al2O3 catalyst after 150-h reactions.