Activity Test with Various AlF3 Nano-Structure for Catalytic Hydrolysis of NF3

Abstract

Extended Abstract Fluorine compounds have been highlighted as a warming gas caused the global warming. These Fluorine compounds, such as NF3, etc., are commonly emitted from semiconductor and LCD manufacturing industries. This study gave assessment of catalytic hydrolysis for the effective decomposition of NF3 [1, 2]. AlF3 nano-structures with various morphologies, which were synthesized by various synthesis methods, were used as the catalyst for the hydrolysis of NF3. AlF3 with a nano-needle type was synthesized by a gas-solid reaction, and AlF3 with a large-sized rod type was synthesized using the wet chemical method. The catalytic activity tests were carried out in a fixed-bed reactor, and the content of NF3 and GHSV were fixed to 5000 ppmv, and 15000 h, respectively. Steam was injected at a volumetric ratio of NF3 / H2O = 1 / 3 via syringe pump. The characterization of AlF3 used as the catalyst for hydrolysis of NF3 was observed by XRD (X-ray diffraction), SEM (scanning electron microscopy) and BET (Brunauer-Emmett-Teller) surface areas measurements. The AlF3 structures with various morphologies, such as rod, needle, and spherical types, were observed. The AlF3 samples of most structures had a very low surface area and their surface area showed no significant difference. On the other hand, the results of the activity tests for the hydrolysis of NF3 over AlF3 with different morphologies showed different catalytic activity. The conversion of NF3 over the spherical type AlF3 was kept at approximately 30 %. In contrast, the catalytic activity of needle-shaped AlF3 resulted in 100% NF3 conversion. The activity was maintained for more than 300 h in the long-term tests. The hexagonal crystal structure of AlF3 (25.321°, 42.715°, 51.997°, and 58.118° 2θ) was confirmed by XRD analysis of all AlF3 samples used in this study. The orthorhombic crystal structure of AlF3 (14.747°, 24.943°, 29.746°, 47.463°, and 52.790° 2θ) was confirmed only on the XRD peak pattern of AlF3 synthesized by the wet fluorination process. The commercial AlF3 and AlF3 nanostructure synthesized by the dry fluorination process exhibited a similar XRD peak pattern, but the peak intensity of the commercial AlF3 on the XRD peak pattern of the hexagonal crystal structure was higher than that of the other AlF3 samples. The hexagonal structure of AlF3 has higher catalytic activity for the hydrolysis of NF3 than the orthorhombic structure of AlF3. Although the hexagonal structure of AlF3 had a high catalytic activity for the hydrolysis of NF3, the needle-like shaped hexagonal structure of AlF3 had higher catalytic activity than the other shaped hexagonal structures. The hexagonal structure of AlF3 has higher catalytic activity for the hydrolysis of NF3 than the orthorhombic structure of AlF3. Therefore, the needlelike shaped AlF3 with high catalytic activity can be prepared by a dry fluorination process.