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    介孔铝耦合等离子体催化分解CF4研究

    Catalytic Decomposition of CF4 by Mesoporous Aluminum Coupled with Non-Thermal Plasma

    • 摘要: CF4是一种强温室气体,具有极强的热稳定性,铝电解工业烟气是CF4的主要排放源。现有基于铝基催化剂的热催化技术可实现CF4高效分解,但反应温度需达到600 ℃以上。由于实际铝电解过程中烟气最高温度仅有140 ℃,研发低温烟气CF4催化分解技术是铝电解行业减少温室气体排放的重要需求。针对CF4低温分解难题,提出铝基催化剂耦合低温等离子体分解CF4的思路,设计了富羟基介孔铝催化剂,实现了常温(25 ℃)下CF4的高效分解。围绕铝表面羟基位点构筑,以异丙醇铝为铝源,采用溶胶-凝胶法制备富羟基介孔铝,显著提升了CF4的分解效率。在CF4浓度为10%、流量为10 mL/min条件下,介孔铝耦合等离子体对CF4分解效率最高可达95%。流量提升至50 mL/min,最高分解效率仍可达70%。介孔铝的强酸性位点和羟基含量分别比商业Al2O3提高16.2%和118.0%。介孔铝表面酸碱性位点含量更高,其中弱碱性位为Al—OH,强碱性位为O2−等活性氧。反应后,介孔铝表面的Al—OH参与了CF4分解,转变为C和AlF3沉积在催化剂表面,导致孔隙堵塞,使CF4分解效率下降。羟基可在CF4分解反应过程中提供质子,扮演碱性位和B酸双重作用,从而提高CF4分解性能。

       

      Abstract: CF4 (tetrafluoromethane), a perfluorinated compound with high thermal stability and global warming potential, poses significant challenges for the conventional catalytic decomposition route due to its robust C—F bonds and chemical inertness. Current thermal catalytic technologies, primarily using aluminum-based catalysts, have demonstrated efficient CF4 decomposition but require reaction temperatures exceeding 600 ℃, which is far beyond the maximum temperature of flue gas from actual aluminum electrolysis (140 ℃). Consequently, there is an urgent need to develop low-temperature CF4 catalytic decomposition technologies to reduce greenhouse gas emissions from the aluminum electrolysis industry. To address this challenge, researchers have proposed the strategy of coupling aluminum-based catalysts with low-temperature plasma. Notably, the hydroxyl-enriched mesoporous aluminum catalyst exhibits remarkable CF4 decomposition efficiency even at room temperature (25 ℃). The key to this breakthrough lies in the formation of hydroxyl sites on the aluminum surface. Hydroxyl-enriched mesoporous aluminum has been successfully prepared through the sol-gel method using aluminum isopropoxide as the aluminum source, which significantly enhances CF4 decomposition efficiency. Experimental results show that, under the reaction conditions of 10% CF4 concentration and 10 mL/min flow rate, the highest decomposition efficiency of CF4 can reach 95% using a mesoporous aluminum catalyst coupled with plasma. Even at a flow rate of 50 mL/min, the decomposition rates can still reach 70%. These findings underscore the potential of this new catalyst in practical applications. Compared to commercial alumina, mesoporous aluminum demonstrates superior properties. Specifically, the strong acidic sites and hydroxyl content of mesoporous aluminum are 16.2% and 118.0% higher, respectively. The surface of mesoporous aluminum contains higher densities of acidic and basic sites, with the weak basic sites being Al—OH and strong basic sites being active oxygen species such as O2−. During the CF4 decomposition reaction, the Al—OH groups on the surface of mesoporous aluminum participate in the decomposition process, transforming CF4 into carbon (C) and aluminum fluoride (AlF3). These products deposit on the catalyst surface, leading to pore blockage and a subsequent decrease in CF4 decomposition efficiency after prolonged reaction. The hydroxyl group plays a pivotal role in CF4 decomposition by serving as a proton donor and an active site. Its dual functionality as a Brønsted acid and a base enhances the overall performance of CF4 decomposition. The presence of hydroxyl groups facilitates the breakdown of CF4 and improves the catalyst's stability and longevity, making it a promising solution for reducing greenhouse gas emissions from aluminum electrolysis processes in industrial applications.

       

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