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Abstract Processes based on non-thermal plasma (NTP) for indoor air treatment inevitably lead to the formation of toxic by-products such as ozone (O 3) and nitrogen oxides (NO x). Adding a step of heterogeneous catalysis in series with NTP could allow for the decomposition of the by-products. Therefore, different catalysts were developed based on transition metal oxides, such as NiO x , CoO x and MnO x with different weight percentage 1, 5 and 10 wt.%, deposited on a γ-Al 2 O 3 support. The O 3 removal efficiency (ORE) and the NO x removal efficiency (NRE) were very encouraging in dry air: about 65% and 80%, respectively, by using 2 g 5 wt.% MnO x /Al 2 O 3 catalyst under the experimental conditions. However, strongly negative effects of relative humidity (RH) on the catalytic decomposition performance were observed. To overcome this limitation, the catalyst surface was modified to make it hydrophobic using a cost-effective chemical grafting method. This treatment consisted in impregnating the 5 wt.% MnO x /Al 2 O 3 catalyst with different trichloro(alkyl)silanes (TCAS). The effects of different linker lengths and amounts of TCAS for the hydrophobicity and the decomposition performance of surface-modified catalysts under humid conditions were investigated. Our results show that the surface-modified catalyst with the shortest linker and 0.25 mmol/g cat of modifying agent represents the best catalytic decomposition performance for O 3. Its ORE is 41% at 60% RH, which is twice that of the non-modified catalyst. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

The use of non-thermal plasma, corona discharge, was studied for indoor air applications. Toluene at a very low to moderate concentration (a few ppbv–1000 ppbv) was used as the target compound. Both degradation of toluene and generation of by-products (intermediates and ozone) were investigated. Because of the very low concentrations implemented in this study, high levels of removal efficiency were reached with very low specific density (a few J L −1 ). It was found that the polarity of the discharge was the parameter having the greatest influence: at 8.2 ppbv, removal efficiency could reach 98.2% under negative polarity while only 62% removal efficiency was achieved under positive polarity. This result is consistent with the lower ozone concentration in positive polarity and hence the lower plasma reactivity. The relative humidity of the air is another highly important parameter. It was found that the number of intermediates detected at the outlet of the plasma and removal efficiency both increased when increasing the relative humidity from less than 2%–40%. At higher relative humidity, toluene removal efficiency remained on the same order of magnitude (close to 80%), while the number and the amount of intermediates decreased. A higher oxidative rate was expected. [ABSTRACT FROM AUTHOR]