Plasma-Catalytic Mineralization of Toluene Adsorbed on CeO2

Zixian Jia,Frederic Thevenet,Xianjie Wang,Emeric Foucher,Antoine Rousseau

doi:10.3390/catal8080303

Abstract

In the context of coupling nonthermal plasmas with catalytic materials, CeO2 is used as adsorbent for toluene and combined with plasma for toluene oxidation. Two configurations are addressed for the regeneration of toluene saturated CeO2: (i) in plasma-catalysis (IPC); and (ii) post plasma-catalysis (PPC). As an advanced oxidation technique, the performances of toluene mineralization by the plasma-catalytic systems are evaluated and compared through the formation of CO2. First, the adsorption of 100 ppm of toluene onto CeO2 is characterized in detail. Total, reversible and irreversible adsorbed fractions are quantified. Specific attention is paid to the influence of relative humidity (RH): (i) on the adsorption of toluene on CeO2; and (ii) on the formation of ozone in IPC and PPC reactors. Then, the mineralization yield and the mineralization efficiency of adsorbed toluene are defined and investigated as a function of the specific input energy (SIE). Under these conditions, IPC and PPC reactors are compared. Interestingly, the highest mineralization yield and efficiency are achieved using the in-situ configuration operated with the lowest SIE, that is, lean conditions of ozone. Based on these results, the specific impact of RH on the IPC treatment of toluene adsorbed on CeO2 is addressed. Taking into account the impact of RH on toluene adsorption and ozone production, it is evidenced that the mineralization of toluene adsorbed on CeO2 is directly controlled by the amount of ozone produced by the discharge and decomposed on the surface of the coupling material. Results highlight the key role of ozone in the mineralization process and the possible detrimental effect of moisture.

Highlights

Volatile organic compounds (VOCs), from both natural sources and human activities such as transport, organic solvents and solvent-containing products, production processes and combustion processes [1], have environmental and health impacts [2,3]
Unlike the former study was centered on surface processes, this paper focuses on the performances of CeO2 coupled to Nonthermal plasma (NTP) in the oxidation of toluene through gas phase characterization
The oxidation of toluene adsorbed on CeO2 has been studied using two configurations: (i) in plasma-catalysis (IPC) and (ii) post plasma-catalysis (PPC), respectively

Summary

Introduction

Volatile organic compounds (VOCs), from both natural sources and human activities such as transport, organic solvents and solvent-containing products, production processes and combustion processes [1], have environmental and health impacts [2,3]. Toluene is widespread in the environment owing to its use in a wide variety of household and commercial products [4]. Toluene levels are higher than outdoor; this confinement effect is clearly enhanced by specific sources such as tobacco smoke [5]. The abatement of VOCs has motivated research toward an efficient and economical approach. Nonthermal plasma (NTP) technology, as an alternative to conventional. VOC abatement techniques, received increasing interest during recent decades [6,7,8,9,10,11,12,13,14,15]. The application of NTP for VOC abatement has three main drawback: first, the incomplete oxidation of primary pollutants with unwanted side-product emissions; second, the low mineralization rate of organic pollutants; and third, the low energy efficiency [16]. In order to overcome these weaknesses, Catalysts 2018, 8, 303; doi:10.3390/catal8080303 www.mdpi.com/journal/catalysts

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