光催化選擇性還原一氧化氮污染物

Abstract

本研究探討室溫下以金屬負載的P25光觸媒選擇性光催化還原一氧化氮，並使用丙烷作為還原氣。二氧化鈦光觸媒利用初濕含浸法負載鈀及銠金屬，並使用流動式反應器探討其催化活性。在紫外光（波段350∼500nm）照射下，Pd/TiO2比PdRh/TiO2及Rh/TiO2具有較高的催化活性。研究並發現丙烷吸附在選擇性光催化還原一氧化氮中扮演重要的角色。Pd/TiO2的活性在經過2小時500°C氫氣還原下有顯著的提升。利用原位傅立葉轉換紅外線光譜分析的結果，可推測出一氧化氮及丙烷在金屬負載的二氧化鈦，進行光觸媒催化反應的可能機制。觀察吸附在含鈀觸媒的表面上有N2O，推測其有可能為中間物或副產物。化學氣相層析分析的結果未發現N2O的存在，其可能原因為沒有N2O生成或是其濃度低於氣相層析可偵測的範圍。結果顯示在紫外光照射下，使用Pd/TiO2光觸媒及丙烷還原氣，可以有效的將一氧化氮轉化為無害的氮氣。

Photo-assisted selective catalytic reduction of nitric oxide (NO) was studied over a series of metal-loaded P25 at room temperature. Propane was used as a reducing agent. The activities of metal-loaded M (Pd, Rh)/TiO2 photocatalysts, prepared via the incipient wetness impregnation method, were compared using a continuous flow reactor. Under UV (350-500nm) irradiation, Pd/TiO2 showed superior photo activity when compared to PdRh/TiO2 and Rh/TiO2. Propane adsorption on the photocatalyst plays a significant role in photo-SCR reaction to react with adsorbed NO. The activity of the Pd/TiO2 catalyst could be significantly increased after reduction with hydrogen at 500°C for 2hr. A possible reaction mechanism was proposed based on the product species found from IR spectroscopy. Nitrous oxide (N2O) was observed on the surface of catalysts loaded with palladium and could be a reaction intermediate or by-product. However N2O was either not present in the gas phase or its concentration was below the detection limit of gas chromatography. The results indicate that Pd/TiO2 under UV irradiation using propane reducing agent can effectively reduce NO pollutant at room temperature to harmless N2.