In situ FT-IR Studies of Photocatalytic NO Oxidation on Photocatalysts
Date Issued
2005
Date
2005
Author(s)
Cheng, Yu-Ting
DOI
en-US
Abstract
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.
Subjects
二氧化鈦
紅外線
光催化
一氧化氮
TiO2
FTIR
photocatalytic
nitric oxide
Type
thesis
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