Abstract
The abatement of toluene was studied in a sequential adsorption-plasma catalysis (APC) process. Within this process, Hopcalite was used as bifunctional material: as adsorbent (storage stage) and as catalyst via the oxidation of adsorbed toluene (discharge stage). It was observed that the desorption and oxidation activity of the adsorbed toluene was significantly affected the process variables. In addition, the adsorption time influenced the CO2 selectivity and CO2 yield by changing the interaction between the catalyst and the plasma generated species. At least four APC sequences were performed for each examined condition suggesting that Hopcalite is very stable under plasma exposure during all the sequences. Consequently, these results could contribute to advance the plasma–catalyst system with an optimal VOC oxidation efficiency. The catalytic activity, amount of toluene adsorbed, amount of toluene desorbed and product formation have been quantified by FT-IR. Moreover, the catalyst was characterized by XRD, H2-TPR, N2 adsorption–desorption analysis and XPS. Hopcalite shows a good CO2 selectivity and CO2 yield when the APC process is performed with an adsorption time of 20 min and a plasma treatment with a discharge power of 46 W which leads to a low energy cost of 11.6 kWh·m−3 and energy yields of toluene and CO2 of 0.18 (±0.01) g·kWh−1 and 0.48 (±0.06) g·kWh−1 respectively.
Highlights
Owing to rapid industrialization and urbanization, the production of volatile organic compounds (VOCs) is increasing, which in turn is one of the main reasons for the development of photochemical smog [1,2]
At the beginning of the experiments, most of the toluene in the simulated exhaust gas is removed from the gas phase due to strong adsorption on the surface of Hopcalite
The energy cost rapidly decreases with an increase in the storage time t1
Summary
Owing to rapid industrialization and urbanization, the production of volatile organic compounds (VOCs) is increasing, which in turn is one of the main reasons for the development of photochemical smog [1,2]. The stored VOC is oxidized into CO2 by igniting the plasma (discharge stage) [9,10] This interesting approach helps to reduce the high energy consumption of classical inplasma catalysis systems which in turn contributes to an improved energy efficiency [11]. Considering its porosity and catalytic performances in total oxidation reactions, Hopcalite can be an effective candidate as a bifunctional material in an APC process, acting as an adsorbent in the storage phase and as a catalyst during the discharge stage. To reduce the VOC release at the exit of the reactor during the storage stage and to reduce the exothermicity of the NTP induced oxidation of adsorbed toluene over Hopcalite, the effect of low toluene storage stage time duration (t1) and of the applied discharge power P on the performance of the APC process have been studied in terms of catalytic and energetic performances. Different physicochemical characterizations including XRD, H2-TPR, N2 adsorption–desorption analysis and XPS have been conducted to detect eventual modifications of the bifunctional material
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