https://scholars.lib.ntu.edu.tw/handle/123456789/61726
標題: | 原位紅外線偵測一氧化氮在光觸媒上之光催化氧化反應 In situ FT-IR Studies of Photocatalytic NO Oxidation on Photocatalysts |
作者: | 鄭宇廷 Cheng, Yu-Ting |
關鍵字: | 二氧化鈦;紅外線;光催化;一氧化氮;TiO2;FTIR;photocatalytic;nitric oxide | 公開日期: | 2005 | 摘要: | 本研究運用傅立葉轉換紅外線光譜儀,研究在紫外線照射下純二氧化鈦以及負載過渡金屬的二氧化鈦對於一氧化氮的光觸媒催化反應。利用改良式溶膠凝膠法水解鈦的醇氧化物製備二氧化鈦以及負載銅、釩、鉻金屬之二氧化鈦。在500°C 通入空氣進行前處理之後,觸媒表面偵測到大量過氧化物以及氫氧基。通入一氧化氮氣體後,發現一氧化氮會移除氫氧基、過氧化物,或過渡金屬與氧分子之間的雙鍵鍵結,並以雙齒亞硝酸基或硝酸基的型式吸附在觸媒表面。此外,一氧化氮也會以亞硝醯基的型式吸附在負載之過渡金屬離子上。觸媒在紫外光照射下受激發形成的電洞將過氧化物氧化成超氧化物;此超氧化物會將雙齒亞硝酸基氧化成硝酸基。當亞硝醯基存在於表面時,會因為亞硝醯基的優選氧化使得亞硝酸基的氧化受到抑制。 在熱穩定性測試中,400°C的高溫仍然無法移除雙齒硝酸基,且吸附在二氧化鈦的氫氧基因為與硝酸產生偶合而不受高溫影響。然而,氫氧基與雙齒亞硝酸基無法進行偶合,故氫氧基的熱穩定性表現與未吸附一氧化氮的二氧化鈦觸媒相同。再者,研究同時發現一氧化氮可再次吸附在存在有雙齒亞硝酸基及硝酸基的二氧化鈦表面。在光穩定性測試中,發現亞硝酸基的氧化是由觸媒照光後產生的中間物觸發進行,而非光觸媒受光反應後的產物對亞硝酸基進行氧化形成硝酸基。X光繞射分析、紫外光–可見光光譜分析證明觸媒的結構,以及對紫外光吸收的能力不會受高溫處理和一氧化氮的光觸媒催化反應影響。 由傅立葉轉換紅外線光譜儀的結果,可推測出一氧化氮在純二氧化鈦和負載過渡金屬的二氧化鈦上,進行光觸媒催化反應的可能機制。 Photocatalytic NO oxidation on TiO2 and transition metal-loaded TiO2 (M/TiO2) catalysts under UV irradiation was studied using in situ FT-IR spectroscopy. TiO2 and M/TiO2 catalysts were prepared by sol-gel method via controlled hydrolysis of titanium (IV) butoxide. Copper, vanadium or chromium was loaded onto TiO2 during sol-gel procedure. After treated at 500°C under air flow, a large amount of surface peroxo species and OH groups were detected on the TiO2 and M/TiO2 catalysts. Nitric oxides (NO) can be adsorbed on TiO2 and M/TiO2 in the form of bidentate nitrites, or nitrates via removing OH groups, peroxo species or M=O bonds. In addition, NO can also be adsorbed on Mn+ in the form of nitrosyls. Under UV irradiation, bidentate nitrites were oxidized to monodentate or bidentate nitrates. This transformation was probably triggered by superoxo species which were oxidized from peroxo species via photogenegrated holes. The existence of nitrosyls caused the inhibition of oxidation from nitrites to nitrates because of primary oxidation on nitrosyls. Thermal stability tests showed that even the temperatures were up to 400°C, bidentate nitrates still remained on TiO2 surface. It also showed that OH groups were coupled with nitrates so that the OH groups were not influenced even up to 400°C. However, for bidentate nitrite, it was not coupled with OH groups so the OH groups were influenced at high temperatures. In addition, further NO adsorption and photocatalytic NO oxidation were allowed on nitrite-adsorbed TiO2 and nitrate-adsorbed on TiO2. Photo stability tests evidently showed that it was photogenerated intermediates, not photocatalytic products that involved in the oxidation from nitrites to nitrates. XRD and UV-Visible tests showed that the structures and the abilities of absorbing UV light were not influenced by high temperature treatment and photocatalytic NO oxidation. Based on the FT-IR results, a possible mechanism was proposed for the photocatalytic NO oxidation on TiO2 and M/TiO2. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/52200 | 其他識別: | en-US |
顯示於: | 化學工程學系 |
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