內照明蜂巢式反應器應用於光催化還原一氧化氮

Abstract

本研究探討以雙金屬氧化物(PdOPtOy)負載之TiO2光觸媒在不同溫度(25、70、120℃)，於蜂巢式載體上進行選擇性光催化還原一氧化氮，本實驗使用丙烷作為還原劑。二氧化鈦光觸媒使用熱水解法製備以利覆膜於蜂巢式反應器上，並使用連續式反應器探討其催化活性。在紫外光（波段320∼500nm）照射下，分別探討滯留時間，進料莫爾比，光強度以及溫度等對於反應之影響，於最適之反應條件下，NO去除率可達到89.5%，而計算所得之N2選擇率可達到99%以上。此外亦研究氧氣與水氣對於反應系統之影響，分別就溫度與光強度進行討論，發現利用光強度之增強或溫度之提升，能降低氧氣與水氣對於反應系統之抑制效果，最佳去除率分別可達67%和87%。利用原位傅立葉轉換紅外線光譜分析的結果，藉以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。觀察吸附在觸媒表面上之物質有丙酮，乙醛，甲酸，亞硝酸鹽以及硝酸鹽等，推測其有可能為中間物或副產物，但NCO和CN等並未於反應系統中觀察到。後續亦利用其結果推論出可能反應路徑，由NO的O提供氧化C3H8，結果將NO還原成N2。

Photocatalytic reduction of nitric oxide (NO) was studied over bi-metal loaded TiO2 in a monolith reactor at various temperatures (25, 70 and 120℃). The bi-metal oxide-loaded PdOPtOy/TiO2 photocatalyst, prepared by the thermal hydrolysis method, were used in a continuous system using C3H8 as the reductant. A monolith photoreactor was adopted to provide better light illumination on photocatalyst by using optical fibers, thus the efficiency of photoreaction was improved. The effects such as reductant molar ratio, retention time, light intensity and temperature on the activity of photocatalyst in NO reduction were investigated. Under the optimal reaction condition, C3H8 was able to reduce 89.5% of NO with N2 selectivity 99%. In the presence of O2 and water vapor, 67% and 87% NO conversion can be reached respectively if higher temperature or higher light intensity was used, indicating the adverse effects of O2 and water vapor on NO reduction over PdOPtOy /TiO2 photocatalyst. The intermediates of NO/C3H8 photoreaction were studied with respect to the behavior of adsorbed species on the surface of PdOPtOy/TiO2 using in-situ FTIR. The results indicated that acetone, acetaldehyde, formate and CO species were the intermediates formed during the photoreaction. Neither NCO nor CN was observed during the reaction period. Reaction paths were proposed. The role of NO was to supply oxygen atom for C3H8 oxidation, resulting in the reduction of NO to N2.