Abstract:
CF
4 (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 CF
4 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 CF
4 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 CF
4 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 CF
4 decomposition efficiency. Experimental results show that, under the reaction conditions of 10% CF
4 concentration and 10 mL/min flow rate, the highest decomposition efficiency of CF
4 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 O
2−. During the CF
4 decomposition reaction, the Al—OH groups on the surface of mesoporous aluminum participate in the decomposition process, transforming CF
4 into carbon (C) and aluminum fluoride (AlF
3). These products deposit on the catalyst surface, leading to pore blockage and a subsequent decrease in CF
4 decomposition efficiency after prolonged reaction. The hydroxyl group plays a pivotal role in CF
4 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 CF
4 decomposition. The presence of hydroxyl groups facilitates the breakdown of CF
4 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.