| Summary: | 碩士 === 國立臺灣大學 === 化學工程學研究所 === 90 === The objective of this thesis is to develop a process for immobilizing gold particles on “Pyrex” glass fibers in the chloroauric acid solution. It is expected that this material can possess high catalytic activity for CO oxidation at room temperature and can be utilized in the commercial CO safety gas masks. Because gold particles are hardly deposited on Pyrex glass fibers directly, and they can be on TiO2 surface, therefore, a process for coating TiO2 sol-gel on glass fibers was developed at the beginning of this research. TPT (tetrapropyl titanate) was used as a precursor in the sol-gel. Then gold particles were deposited on TiO2-Pyrex via a deposition-precipitation process. These synthesized catalysts were characterized by the instrments of ICP, SEM, TEM, XRD and XPS.
From the SEM images, TiO2 films were successfully coated on Pyrex. Nevertheless there existed many coagulated TiO2 pieces between Pyrex fibers. After lowered the concentration of TPT (TPT : i-PrOH : HCl = 2 : 42 : 3.4 in molar ratio) in the sol-gel and treated TiO2-Pyrex fibers with ultrasonic vibration after calcination at 450℃, these non-deposited TiO2 pieces were immensely decreased. Furthermore, TiO2-Pyrex prepared from a complete mixing as well as a double-coating process contained higher homogeneity and larger amount of TiO2 films.
Gold deposited on TiO2-Pyrex via deposition-precipitation indeed had the ability for oxidizing CO to CO2. From TEM results, gold catalysts prepared with gold concentration of 2x10-3 M contained gold particles with diameters around 15 nm, which were too large to exhibit high catalytic activity and had no resistance to moisture poison. When the gold concentration was lowered to 2 x10-4 M, the prepared catalyst exhibited extraordinary high activity for CO oxidation and had high resistance to moisture, owing to smaller gold particle in catalysts.
In order to prevent gold particles from sintering during drying at 60℃ for 6 h, gold catalyst dried at room temperature was prepared. However, it exhibited low activity for CO oxidation. From XPS of Au 4f, the fraction of metallic Au in catalysts dried at room temperature is much less than the one in the catalyst dried at 60℃, resulting in low catalytic activity.
Although gold catalyst exhibited high catalytic activity for CO oxidation, the decay in activity was observed in catalyst after storage for 2 months. Inferred from XPS of Cl, there were residues of Cl-, which acted as a poison to catalysts. Besides, compared XRD patterns between TiO2-Pyrex and Au/TiO2- Pyrex, TiO2 structure collapsed after gold deposition on it. The interaction between Cl- and Ti was suspected.
The catalytic activity of gold catalysts prepared with gold concentration of 2x10-4 M is high enough to reach the standard of commercialized gas mask. Nevertheless, the decay in activity is the problem and must be improved in the future.
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