Ultrastable ZnAlPO4 catalyst for stable CF4 hydrolysis over 3700 hours

Title : Ultrastable ZnAlPO4 catalyst for stable CF4 hydrolysis over 3700 hours

Abstract:

Tetrafluoromethane (CF₄) is among the most persistent and hazardous greenhouse gases emitted from semiconductor manufacturing processes. Due to its exceptionally high global warming potential of 7,380 and an atmospheric lifetime exceeding 50,000 years, the effective abatement of CF₄ has become a critical environmental imperative. Among various mitigation strategies, catalytic hydrolysis over cost-effective γ-Al₂O₃-based materials has received widespread attention as a practical option. However, conventional γ-Al₂O₃ catalysts readily react with byproduct hydrofluoric acid (HF) to transformation into catalytically inert α-Al₂O₃ phases, resulting in rapid deactivation and severely hindering their industrial application.
To address this challenge, we developed a novel pellet-type ZnAlPO₄ catalyst synthesized via an extrusion method, achieving simultaneous incorporation of phosphate (P) and zinc (Zn) into the γ-Al₂O₃ framework. Phosphoric acid treatment yields thermodynamically stable phosphate-alumina interactions at the surface region. This structural anchoring effectively shields the active framework from corrosive fluorine poisoning and suppresses the HF-induced phase transition to α-Al₂O₃. Concurrently, the introduction of Zn modulates the local electronic structures of alumina, promoting electron transfer that significantly increases the density of strong coordinatively unsaturated Lewis acidic Al sites. This electronic modification facilitates charge transfer to the chemisorbed CF₄ molecules, thereby lowering the kinetic barrier for C-F bond activation. Density functional theory (DFT) calculations substantiate these findings by confirming that the synergistic cooperative Zn-Al environments substantially stabilize CF₄ adsorption and diminish the activation penalty for subsequent dissociation.
Catalytic performance tests were executed using industrially relevant pelletized specimens under harsh conditions featuring 5,000 ppm CF_­4 and ~8% steam. The optimized Zn(20)AlPO₄ catalyst, containing 20 wt.% Zn, achieved complete CF₄ conversion at 700 ^oC, lowering the required reaction temperature by 50 ^oC compared to pristine AlPO₄. Most notably, the Zn(20)AlPO₄ catalyst exhibited exceptional long-term durability, maintaining 100% catalytic activity and complete morphological integrity for over 3,700 hours without any detectable crystalline degradation or irreversible phase changes. In contrast, phosphate-free γ-Al₂O₃ and ZnAl₂O₄ catalysts exhibited rapid and progressive deactivation, respectively, both accompanied by a distinct phase transformation into the inactive α-Al₂O₃ phase after the durability tests. Furthermore, a comparative cost analysis demonstrated that our Zn(20)AlPO₄ catalyst is highly cost-effective, being ~700 times less expensive than conventional gallium-based formulations. These findings represent a significant breakthrough in industrial PFCs abatement and provide an extendable design framework for engineering robust, HF-resistant catalysts for treating various fluorinated greenhouse gases.

Biography:

Eun-Han Lee is Ph.D. candidate in the Department of Chemical and Biomolecular Engineering at Yonsei University, Republic of Korea. His research focuses on the development of alumina-based catalysts for the abatement of non-CO₂ greenhouse gases, including CF₄, NF₃, SF₆, N₂O, and HFCs. He has authored several SCI publications in catalysis and environmental engineering and is actively involved in catalyst design, catalytic reaction engineering, and greenhouse gas mitigation technologies. His current work focuses on developing highly durable catalysts for the hydrolysis of fluorinated greenhouse gases.