以即時性漫反射傅立葉轉換紅外光譜儀探討乙醇氧化蒸氣重組在(Co, Rh)/(CeO2, YSZ)上之反應機制

Abstract

在我們目前的研究中，我們使用即時性漫反射傅立葉轉換紅外光譜儀(in situ DRIFTS IR)，系統式的檢測不同水醇比和氧氣比例之(Co, Rh)/CeO2和Rh/(CeO2, YSZ)催化劑在乙醇氧化蒸氣重組的反應，而我們透過這方式，來推測不同催化劑以及不同反應條件下之反應機構。催化劑使用含浸法合成，並透過X-ray粉末繞射分析儀(XRD)、能量散射光譜儀 (EDS)、程序升溫還原反應(TPR)和光電子能譜儀 (XPS)來鑑定其晶格、成分以及氧化態。比較（Rh，Co）/ CeO2的乙醇氧化蒸氣重組反應，我們的結果發現，在Rh / CeO2上容易快速脫氫而形成酰基陽離子（CH3CO）中間體，進而分解成CH4和CO，顯示了Rh擁有優良的斷碳碳鍵活性。比較Rh /（CeO2 ，YSZ）上的反應，Rh / CeO2上的大量CO脫附，確定了氧化物載體的優良儲氧能力;另外，乙醛與乙酸顯著的反應，對於Rh / CeO2催化劑產生CO2也有明顯的影響，這也代表著它有助於氧化的過程。而反應的結果顯示，大量的水氣比例增加會使氫氣的產率升高以及得到較低的CO和較高的CH4選擇率，而較高的氧氣含量，會使得反應產生更多的氧化產物，比如CO和CO2。

In our present study, we systematically examined the reaction of oxidative steam reforming on (Co, Rh)/CeO2 and Rh/(CeO2, YSZ) at various ethanol/steam/oxygen ratios by in situ Diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) to reveal the mechanisms in the different catalysts at varied operational conditions. The catalysts were initially fabricated by impregnation method and characterized by X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDS), Temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) to identify their lattice, composition and oxidation states. Comparing reforming reactions on (Rh,Co)/CeO2, our results found the quick formation of acyl cation (CH3CO) intermediate, which easily decomposes to CH4 and CO, on Rh/CeO2, revealing the mechanism behind the excellent C-C bond cleavage activity of Rh. Comparing the reactions on Rh/(CeO2/YSZ), the abundant CO desorption from Rh/CeO2 identifies the superior oxygen storage capability of the oxide support; additionally, the obvious reaction of acetaldehyde to acetic acid, ultimately to CO2 on Rh/CeO2 ¬also suggests the capability assisting the oxidation process. The operational condition tests showed that higher steam ratio results better hydrogen yield as well as less CO and more CH4 selectivities, while the higher oxygen content yields more oxidative products of CO and CO2.