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

Abstract

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 MnO x /Al 2O 3 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 O 3 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 MnO x /Al 2O 3 catalyst significantly promotes BTX conversion and improves the energy efficiency. On the other hand, CPC under 30% RH shows the best performance towards CO x 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 MnO x /Al 2O 3 catalyst after 150-h reactions.