Lambert Benjamin

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Volatile organic compounds (VOCs) are poisonous and regarded as the paramount source for the formation of secondary organic aerosols, ozone, and photochemical smog, greatly affecting human health and environment quality. In order to abate VOC emission, catalytic oxidation is widely applied in industries and is believed to be an efficient and economically feasible way for the elimination of VOCs. This review is primarily concentrated on summarizing the recent progress and developments in the catalytic oxidation of various VOCs over Pd-supported catalysts. Despite their high catalytic performances at much lower temperatures, the wide use of Pd-supported catalysts in the industry has been limited by their high cost, low thermal stability, and incomplete oxidation of VOCs. Hence, the intrinsic properties of the active sites and supports, the reaction conditions, the deactivation mechanism, and the strategy to reveal the catalytic oxidation pathway are also systematically summarized. This review aims to give a deep comprehension and guidance for the development of efficient and cost-effective Pd-supported catalysts in the near future.Get more news about Acrylic Deoxidizer,you can vist our website!
It is well known that organic compounds with the boiling point below 250°C and saturated vapor pressure equivalent to the atmospheric pressure (101.325 kPa) are identified as volatile organic compounds (VOCs). The types of released VOCs include aromatics, aliphatic hydrocarbons, oxygenated VOCs, halogenated VOCs, sulfur- or nitrogen-containing VOCs, and so on. Although the release of VOCs originates from the nature and human activities, the anthropogenic source accounts for a large proportion for VOC emission. Urbanization and industrialization have further led to the continuous increase in the emission of VOCs (Boeglin et al., 2006; Qiu et al., 2014). The anthropogenic sources were usually linked with chemical industries, gas station, food processing, petrochemical processing, production of plastics, solvent use, and many other industrial activities (Liotta, 2010; Scire and Liotta, 2012; Liao et al., 2015). Due to the high volatility at ambient conditions, the majority of VOCs can be easily emitted into the atmosphere and be absorbed through the human respiratory tract, skin, and digestive tract, and are harmful to the respiratory system and central nervous system even at low concentrations (Srivastava et al., 2005; Boeglin et al., 2006; Ahn et al., 2017; Odoom-Wubah et al., 2019c). Furthermore, some of the VOCs are used in the formation of secondary organic aerosols (Boltic et al., 2013; Zang et al., 2019), reducing air quality, and may trigger stratospheric ozone depletion (Dumanoglu et al., 2014; Liang et al., 2017). Therefore, efficient VOC destruction is of paramount significance from the perspectives of environment and human health.

The techniques used for the elimination of VOCs include recovery and destruction. Recovery techniques such as absorption, adsorption, and membrane separation are more adaptable to efficient disposal of high concentration VOCs. However, execution of these techniques is restricted by a complicated process and high cost (Iranpour et al., 2005; Vu et al., 2009; Tomatis et al., 2016). Catalytic oxidation appears to be an effective way for the removal of VOCs due to its higher destructive efficiency and lower operating temperatures (Zhang et al., 2016). It can completely mineralize VOCs to carbon dioxide (CO2) and H2O instead of transforming them to by-products with high toxicity. Furthermore, catalytic oxidation can also be applied to eliminate extremely dilute VOC streams.

Preparation of catalysts with high activity and stability is critically important in VOC catalytic oxidation. Catalysts for VOC combustion can be divided into the following categories: 1) non-noble metal oxides (Kim and Shim, 2010), 2) supported noble metals (Liotta, 2010), and 3) alloy metal nanoparticle catalysts (Aguero et al., 2009; Zeng et al., 2015). Among these, noble metal catalysts (Au, Pt, Rh, Pd, etc.) possess superior catalytic activity and durability for VOC catalytic oxidation under low temperature (Gulsnet and Magnoux, 1997). Currently, Pd is preferred in the industrial application of VOC abatement over the other noble metals (Au, Pt, and Ru) (Bendahou et al., 2008; Aznárez et al., 2015; Xiong et al., 2018; Odoom-Wubah et al., 2019a) on account of its unique electron configuration and high chemical stability during VOC catalytic oxidation (Kamal et al., 2016). Significant achievements have been obtained by using Pd as a catalyst for the elimination of VOCs. It has been proved that the catalytic performance of Pd-based catalysts is highly dependent on the particle size, chemical state, loading amount of Pd, and physical and chemical properties of the supporting materials. However, deactivation phenomena frequently appear in the forms of coking, poisoning, and thermal sintering during catalytic VOC oxidation over Pd-based catalysts, which cause a decrease in catalytic activity. Complete understanding of the reaction mechanism is vital for the development of highly efficient catalysts for VOC oxidation. The present work mainly focuses on previous reviews of catalytic oxidation of VOCs over Pd-supported catalysts (Scheme 1). Moreover, the intrinsic properties of catalysts and the reaction conditions for the catalytic performance over Pd catalysts are described. The deactivation mechanism and the tactics to disclose the catalytic oxidation pathway are summarized in detail too. We believe that this review is meaningful in offering a deep understanding and guidance to the preparation of highly efficient and cost-effective Pd catalysts.

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