Search

Highlights: [•] Complementary analysis of gas phase and adsorbed phase species using FTIR and DRIFTS. [•] Isopropanol and acetone oxidation using ozone on TiO2 catalyst. [•] Acetone is the main intermediate of isopropanol oxidation by ozone. [•] Limited number of sites selective toward acetone oxidation into CO2. [•] Similar oxidation mechanisms observed with ozone and with photocatalysis. [Copyright &y& Elsevier]

Highlights: [•] A quantitatively assessed adsorption mechanism of NO2 and TiO2 is proposed. [•] Quantitative ratio between adsorbed NO2, produced NO3 and evolved NO is 3:2:1. [•] NO initial formation time is controlled by TiO2 surface coverage. [ABSTRACT FROM AUTHOR]

Highlights: [•] Decane batch photocatalytic abatement on the ppb range. [•] Simultaneous monitoring: (i) decane, (ii) reaction intermediate, and (iii) CO and CO2. [•] Reaction pathway of decane oxidation. [•] Light aldehydes firstly the main gaseous intermediates, then mineralized into CO2. [•] Intermediates and CO2 formations are maximized by 50% RH. [Copyright &y& Elsevier]

Abstract: Environmental regulation on air quality requires the development of energetic efficient volatile organic compounds (VOCs) abatement techniques. Adsorption, photocatalysis, non-thermal plasma and their combinations have been widely studied for VOC treatment. Even if the plasma – material (sorbent or catalyst) association appears as one of the most efficient configuration for VOC removal, it mainly consists in operating continuously the discharge on the material surface as long as the effluent flows across the reactor. This work aims at investigating another approach of plasma – material association for VOC removal: in a first step, the material is used as a sorbent until the complete coverage of adsorption sites; in a second step, once VOC saturation is achieved, the discharge is ignited on the material surface. During both steps, the influence of air relative humidity (RH) is investigated in order to evaluate its impact on the process. The objectives of our approach are: (i) the reduction of energy consumption; (ii) the increase of sorbent life-times by efficient regeneration; (iii) the investigation of plasma interaction with VOC saturated materials; (iv) the investigation of air RH influence on such VOC treatment process. A packed bed reactor coated with TiO2 has been designed. IPA is used as a model VOC. First, injected power in the packed-bed reactor is characterized as a function of air RH. Complete coverage of TiO2 surface over 35% RH is suggested as a significant parameter. Then, adsorption of IPA on TiO2 was monitored until IPA breakthrough. The amount of IPA adsorbed per TiO2 surface unit is compared to values reported by other authors. The influence of air RH on reversibly and irreversibly adsorbed IPA fractions is investigated. Over 35% RH irreversible adsorption is favored, adsorption modes are discussed. Plasma regeneration of IPA saturated TiO2 surface leads simultaneously to IPA desorption and mineralization. Increasing air RH favors IPA mineralization and diminishes acetone production. Carbon balance obtained after 1h plasma treatment reaches 91% in the presence of 50% RH. A thermal treatment is performed after each plasma treatment in order to evidence plasma insensitive adsorbed species and to restore TiO2 initial surface state. 97% of the carbon balance is collected under 50% RH after thermal treatment. During the thermal step, acetone and CO2 are mainly produced, their formation pathways are discussed. [Copyright &y& Elsevier]

Abstract: An investigation of toluene photocatalytic oxidation was conducted with initial concentrations of toluene ranging from 50 to 800ppbv under dry and wet (50% RH) atmosphere in order to characterize photocatalysis performances close to indoor air conditions. A batch reactor system was developed in order to perform kinetic studies of (i) toluene removal, (ii) organic reaction intermediate formation and removal, (iii) CO and CO2 formation, at ppbv levels. The monitoring of CO and CO2 produced by a photocatalytic reaction in the air with ppbv levels of pollutant is reported for the first time. It appears that toluene removal follows, even at ppbv levels, a pseudo first order kinetic slightly improved by the presence of water vapour (50% RH). The determination of reaction intermediate temporal profiles confirmed that oxidized aromatic compounds (benzaldehyde, cresols) are toluene primary reaction intermediates. The fact that no benzoic acid was evidenced in the gas phase, and that benzaldehyde maximum concentration remains below 4ppbv indicate that several consecutive oxidation steps take place in the adsorbed phase with a low desorption of reaction intermediate. The diversity of aliphatic reaction intermediates obtained after toluene ring opening is coherent with former results obtained at ppmv initial levels of toluene. Nevertheless, the removal of the lightest carbonyls (acetone, acetaldehyde and formaldehyde) is not observed within 14h of reaction. Carbon mass balance calculations performed with all the quantified gas phase reaction intermediates evidenced that those compounds represent only from 1 to 1.5%. This portion is almost constant during the whole oxidation process. The precise determination of CO and CO2 concentrations gives a good overview of the oxidation/mineralization process. CO and CO2 measurements evidenced that the presence of water vapour (50% RH) considerably improves the formation of CO2 corresponding to a better mineralization of organic matter and an improved conversion of CO into CO2. Temporal profiles of CO2 concentration reveal that CO2 formation rate is highly dependent on the nature of the compounds to be treated. Between 10 and 12h of reaction, corresponding to 95% conversion of toluene, CO and CO2 represent only from 25 to 35% of the carbon mass balance. If the reaction is performed on longer times, the mineralization percentage constantly increases until 23h of irradiation, mainly corresponding to oxidation of compounds adsorbed on photocatalyst surface. After 22h of irradiation, the mineralization (CO+CO2) finally exceeds 70% of the carbon mass balance. [Copyright &y& Elsevier]