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Hdr Année : 2015

Heterogeneous Oxidation of VOCs : from fundamentals to air quality

Oxydation hétérogène des COV : des fondamentaux à la qualité de l'air

Frederic Thevenet

Résumé

My main assignment as I was recruited in 2008 at Ecole des Mines in Dpt SAGE was to create a novel research activity focused on fundamentals and applications of air treatment processes. The development of this new topic was supported by the high level academic background of the laboratory in the field of environmental gas phase analysis. In that context, I brought my expertise in the domain of (i) adsorption, (ii) photocatalysis and (iii) non-thermal plasma coupling with catalytic materials. Heterogeneous physical and chemical phenomena are the meeting points of these air treatment technologies, they had to be addressed in details with innovative experimental approaches to be understood and enhanced. The modern context of indoor air and the dramatic decrease of indoor air quality have been identified as main issues where air treatment technologies could bring effective improvements. An overview of current existing technologies points out the fact that adsorption, photocatalysis and non-thermal plasma are the relevant technologies to face the pollution characteristics and the energetic requirements of indoor air. However, none of them were effectively investigated, developed or validated under typical indoor air conditions. The three air treatment techniques share the common characteristics of being heterogeneous processes. To that regard, scientific questions were still open about (i) heterogeneous interactions between pollutants, materials and non-thermal plasma in the plasma-material coupling, (ii) the effectiveness of photocatalytic oxidation at typical ppb in the presence of multi-polluted indoor atmospheres, and (iii) the sustainability these technologies. The approach I proposed to investigate plasma-material coupling through sequential adsorption of the pollutants and plasma regeneration of the saturated coupling material offered interesting insights from a fundamental as well as a process point of view. First, it improved the distinction between gas phase and adsorbed phase phenomena. The key role of coupling material surface chemistry has been quantitatively evidenced for (i) pollutant adsorption; (ii) plasma generated oxidizing species consumption and (iii) long term performances and potential deactivation. Second, from a process point of view, it evidenced that the plasma sequential regeneration was a relevant option regarding energy consumption and oxidation reaction advancement. Based on these results, future perspectives in plasma-material coupling are proposed toward material tailored synthesis and tuned surface chemistry. The detailed investigation of photocatalytic reaction at ppb level was required by the high development of such technologies for indoor air applications whereas its effectiveness was questioned. Based on analytical developments, gas phase and adsorbed phase have been addressed from primary VOC removal to gas phase reaction intermediate, CO2 and particle matter production. The efficacy of photocatalytic oxidation for VOC abatement under typical indoor air condition was shown. However, the variability of the reaction with the nature and the diversity of VOCs have been evidenced. Adsorption considerations are relevant to describe and predict the behavior of photocatalysis on multi-polluted air, but deeper investigations have to be carried out. The key point of future developments is the real scale assessment of photocatalytic air treatment devices to propose effective standards and protocols to ensure efficiency and innocuity of such a process. My research perspectives can be structured according to two main paths. First, at short and mid-term, the development of a large scale experimental room will make possible further investigation of indoor air treatment technologies and more generally indoor air chemistry, from a homogenous to a heterogeneous point of view. This innovative device will be used for the assessment of photocatalytic air treatment devices performances and innocuity and for the evaluation of the performances of designed sorbents and catalyst when used for specific VOC adsorption and subsequent plasma regeneration. Second, I plan to widen the scope of my research activities to atmospheric heterogeneous processes investigation. Typically, my involvement in the field of heterogeneous oxidation processes could lead to the development of innovative approaches to tackle the interaction of atmospheric VOCs with mineral dust from arid area and volcanoes and the subsequent air quality impacts.
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tel-04221607 , version 1 (30-09-2023)

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  • HAL Id : tel-04221607 , version 1

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Frederic Thevenet. Heterogeneous Oxidation of VOCs : from fundamentals to air quality. Chemical Sciences. Université de Lille, 2015. ⟨tel-04221607⟩
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