原位紅外線研究一氧化氮與甲烷在光觸媒上之光催化 反應

Abstract

氮氧化物(NOx)為一般人們所熟知的空氣污染物，本實驗欲探討 在低溫下(100℃以下)，以光驅動的方式是否也能達到選擇性還原的 目的，運用原位傅立葉轉換紅外線光譜儀(In situ Fourier Transform Infrared Spectroscopy)，可以觀察反應中間體，進而瞭解反應機制。 本實驗用熱水解法（thermal-hydrolysis method）製備光觸媒純二氧化 鈦和1wt%白金負載的二氧化鈦。光觸媒催化反應是以紫外光為光 源。本實驗觀察在25、50 及100℃下，甲烷與一氧化氮同時吸附在 二氧化鈦與1wt%白金負載的二氧化鈦上。照光後，大部分的甲烷在 光催化反應中形成了甲酸及二氧化碳。一氧化氮在吸附時變成二氧化 氮、雙牙基亞硝酸和單牙基硝酸，照光後雙牙基亞硝酸消失，取而代 之的是雙牙基硝酸、單牙基硝酸以及異氰酸鹽NCO 的產生，許多文 獻視其為選擇性吸附之中間產物，又加上本研究也觀察到NH2，故推 測在本實驗中，照光可以促進部分一氧化氮催化變成氮氣，進而達到 低溫選擇性還原的目的。

NOx is a well-known air pollutant. We propose to remediate NOx by photo catalytic reduction at low temperature (<100℃). In situ FTIR was used to observe reaction intermediates and to explore possible mechanisms. The thermal-hydrolysis method was used to prepare TiO2 and 1wt% Pt-TiO2 photocatalysts. UV light was used as light source. The reactants, CH4 and NO, are adsorbed on the photocatalyst (TiO2 or 1wt% Pt-TiO2), the reaction was performed at three temperatures (25, 50 and 100℃). Under light irradiation, most of the CH4 is converted to formic acid and CO2. When NO is adsorbed on the photocatalyst, it becomes NO2, bidentate nitrites and monodentate nitrate. After light irradiation, bidentate nitrite disappears, while bidentate nitrate, monodentate nitrate and isocyanate are generated. Literatures suggest that NCO is the main intermediate in the selective catalytic reduction (SCR) process. In addition, NH2 was also observed in this experiment. Finally it is concluded that NO can be reduced to N2 by low temperature SCR under light irradiation.