Adsorption-discharge plasma system for toluene decomposition over Ni-SBA catalyst: In situ observation and humidity influence study

Adsorption-discharge plasma system has been applied for catalytic removal of low concentration toluene over a series of Ni-SBA catalysts. Catalytic activity was evaluated towards different relative humidities of air (RH). Meanwhile, gas phase and catalyst surface by-products were investigated during oxidative decomposition of toluene using in situ Time of Flight-Mass spectrometry (TOF-MS), in situ Fourier Transform infrared spectroscopy (FT-IR) and GC–MS analysis technology. The results showed that 5% Ni-SBA sample exhibited higher toluene mineralization rate (71.8%) than that of other samples after 60 min plasma catalysis, and different RH (20–80%) had a negative impact on toluene degradation due to the competitive adsorption and the blocking of active sites on the catalysts surfaces. Interestingly, humidity decreased the yield of CO and increased in the production of CO2 due to the enhanced oxidation of both CO and other intermediates during the reaction. In situ TOF-MS spectra showed that several benzene series were detected in 5% Ni-SBA system during plasma catalysis, and suggested that Ni-SBA catalyst facilitated the benzyl oxidation but are not conducive to benzoic acid ring-opening reactions. In situ FT-IR analysis displayed many products that formed in the surface of Ni-SBA catalyst was degraded after 60 min plasma catalysis. Meanwhile, GC–MS result indicated that no nitrogen-containing byproducts were detected in the surface of Ni-SBA catalyst after 60 min plasma catalysis under 40% RH water vapor. The result may provide new insights for plasma catalysis removal of industrial VOCs at medium and high RH.