Efficient toluene abatement in indoor air by a plasma catalytic hybrid system

Numerous indoor sources emit volatile organic compounds, NOx and O3 which all have a negative effect on human health. Previous work proved that plasma technology seems promising. However, some disadvantages occur such as high energy cost and the formation of by-products.In this work in-plasma (IPC) and post-plasma (PPC) catalysis was investigated for indoor air purification. Introducing a TiO2 catalyst in-plasma was not effective in ozone reduction. Adding only 10 g of CuOMnO2/TiO2 post-plasma position, resulted in a reduction of the ozone outlet concentration by a factor 7. Humidity proved to have a limiting effect on ozone removal rates.In dry air toluene (Cin = 0.5 ppmv) was removed three times more efficient by introducing Aerolyst®7706 TiO2 (IPC). In humid conditions (RH = 27%) performance of this IPC decreased: toluene abatement was only 1.5 times more efficient compared with the non-catalytic plasma oxidation. For dry air inserting 10 g CuOMnO2/TiO2 down flow the plasma reactor modules (PPC), resulted in toluene removal efficiencies up to 40 times higher. In humid gas streams, PPC toluene removal efficiency decreased by competitive adsorption.NOx production by the corona discharge was monitored. In dry air and for an energy density of 10 J L−1, the NO2 outlet concentration was 1500 ppbv, while this is three times lower at 50% RH. Both heterogeneous catalysts (TiO2 and CuOMnO2/TiO2) proved capable to reduce NOx levels in the outlet gas stream by up to 90%.Deactivation of the catalyst material may be explained by the formation of HNO3 in the plasma discharge. These molecules adsorb on the catalyst, surface nitrate ion concentrations were 0.184 mg/m2 and 0.143 mg/m2 for TiO2 and MnO2–CuO/TiO2 catalysts, respectively.