先導級光反應器進行升溫輔助光催同時淨化VOCs和NOx

Abstract

近年來，空氣污染日益嚴重，因此提升空氣品質已成為國際議題。在空氣污染物中，氮氧化物（NOx）以及揮發性有機化合物(VOCs)的去除引起了廣泛關注。NOx 與 VOCs 會導致酸雨和光化學煙霧等空氣污染問題，且共存的 NOx 和 VOCs在陽光照射下還會生成臭氧（O3）造成二次汙染，但陽光同時也是光催化劑可以利用的能量來源。光催化會改變 NOx 和 VOCs 之間的反應途徑，協同將它們轉化為小分子（如 CO2、H2O）。然而，大多數研究僅關注單一污染物的降解，未能滿足實際情境中多種污染物共存的要求。 因此，本研究以 TiO2 作為光觸媒主要的基底，並以 Pd 修飾，利用覆膜浸漬法負載於 α-Al2O3 載體上。透過 SEM BSE 圖像搭配 EDS mapping 成像顯示 Pd 粒子分布於 TiO2 層內且 TiO2 成功負載於 α-Al2O3 載體上，然而由於 Pd 重量百分比過低，於 XPS、EDS 元素分析內並無 Pd 的訊號；UV-Vis 顯示具有 Pd 修飾的 TiO2於可見光波長區域能吸收較多的可見光。 之後，分別在實驗室規模與先導級規模光反應器進行光催化反應，在不同初始濃度、反應溫度與光強度下，比較 NOx 與 VOCs 的去除率。結果發現在室溫下光觸媒具有最佳的 NOx 和 VOCs 去除率，但當溫度提高時 NOx 和 VOCs 去除率因為吸附能力下降而下降。另外，於先導級反應系統中，最佳 NOx 去除率能達到100%，最佳丙酮去除率約為 85%；最佳甲苯去除率能達到接近 100%的表現，然而丙烷因為分子結構較穩定，去除率僅有 5~10%。這顯示本研究所合成之觸媒具有良好的 NOx 與 VOCs 的光催化能力並能應用於更大規模的反應器內。透過 FTIR顯示當 NO 與 VOCs 同時進行光催化反應時，於觸媒表面上不會生成 N-O 鍵結，表示能減緩 NO 光氧化反應速率，降低氧化副產物的生成而造成光觸媒毒化。此現象與活性測試結果吻合。綜上所述，我們的研究成功地放大光反應到先導級光反應系統，經由一系列的實驗，證實光觸媒能顯著有效的去除 NOx 和 VOCs。

In recent years, air pollution has become increasingly severe so improving air quality is an international concern. Removing nitrogen oxides (NOx) and volatile organic compounds (VOCs) has attracted widespread attention as key pollutants. The coexistence of NOx and VOCs leads to air pollution issues such as acid rain and photochemical smog. In addition, sunlight triggers the generation of secondary pollutants like ozone (O3). However, sunlight also serves as an energy source for photocatalysis. Photocatalysts can modify the reaction pathways between NOx and VOCs, thus synergistically converting them into small molecules (e.g., CO2, H2O). So far, most studies focus on the degradation of a single pollutant, lacking to address the complexity of multiple pollutants in real situations. Therefore, this study utilizes TiO2-based photocatalyst, loaded with Pd and coated onto an α-Al2O3 support using dip-coating method. Scanning electron microscopy (SEM) by back-scattering electrons (BSE) imaging combined with energy-dispersive X-ray spectroscopy (EDS) mapping shows that Pd particles are dispersed within the TiO2 layer, and successfully loaded onto the α-Al2O3 support. However, due to the low weight percentage of Pd, there is no signal for Pd in X-ray photoelectron spectroscopy (XPS) and EDS elemental analysis. UV-Vis analysis indicates that Pd-modified TiO2 absorbs more visible light. Subsequently, photocatalytic reactions were conducted in both lab-scale and pilot scale photocatalytic reactors to compare the removal efficiency of NOx and VOCs under different initial concentrations, reaction temperatures, and light intensities. The results indicate that the photocatalyst exhibits optimal NOx and VOCs removal at room temperature while the removal decreases at higher temperatures due to low adsorption capacity. In the pilot-scale reaction system, the NOx removal reached 100%, while the optimalacetone removal was approximately 85%. The toluene removal approached 100%, but propane exhibited a removal of only 5-10% attributed to its stable molecular structure. Our research demonstrates that the synthesized catalyst in this study possesses excellent photocatalytic capabilities for the removal of NOx and VOCs, and can be applied in larger-scale reactors. FTIR reveals that, during simultaneous photocatalytic reactions with NO and VOCs, no N-O bonds are formed on the catalyst surface, indicating the inhibition of NO photo-oxidation thus reducing the generation of oxidation byproducts, which will occupy active sites and result in catalyst deactivation. This is consistent with the results of activity tests. In summary, this study successfully scaled up the photo reaction to a pilot-scale system through a series of experiments, achieving significant and effective removal of NOx and VOCs.