氧化鈦擔載奈米金觸媒應用於甲醇部分氧化產製氫氣之研究; Production of hydrogen via partial oxidation of methanol over Au/TiO2 catalysts

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Title:	氧化鈦擔載奈米金觸媒應用於甲醇部分氧化產製氫氣之研究;Production of hydrogen via partial oxidation of methanol over Au/TiO2 catalysts
Authors:	余心印;Hsin-Yin Yu
Contributors:	化學工程與材料工程研究所
Keywords:	氫氣;甲醇部分氧化反應;金觸媒;二氧化鈦;gold catalyst;titania support;partial oxidation of methanol;deposition-precipitation;hydrogen
Date:	2005-06-28
Issue Date:	2009-09-21 12:24:52 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	本研究以二氧化鈦為擔體，利用沈澱固著法製備成二氧化鈦擔載奈米金觸媒，目的在發展甲醇部分氧化反應(CH3OH + 1/2O2 → 2H2 + CO2)製備氫氣的程序，同時利用感應耦合電漿質譜分析儀（ICP-AES）、熱重分析儀（TGA）、X射線繞射儀（XRD）、穿透式電子顯微鏡（TEM）、掃瞄式電子顯微鏡（SEM）、X射線光電子分析儀（XPS）等各項儀器與分析技術，分別對擔體及觸媒進行鑑定，藉以評估觸媒應用於質子交換膜燃料電池的可行性。從TEM的分析結果發現，以沈澱固著法製備出的觸媒，金晶粒呈現半圓球型，以平的那一面吸附在擔體上。金顆粒的大小會因為製備過程不同而有所差異，當製備時的pH值為9到6時，Au大小為1.8 nm?3.9 nm。煅燒過後的觸媒Au顆粒也會增加，未煅燒時金顆粒為3.0 nm，在673 K下煅燒後，Au顆粒則為4.7 nm。由XPS的結果中發現，未煅燒過的觸媒中，Au以三種狀態存在，金屬態（Au0）、非金屬態（Auδ+）以及Au2O3，而在573K煅燒過的觸媒，則只有金屬態的金（Au0）存在。經過活性測試後發現，觸媒的活性與金顆粒的大小有絕對的關係，當金的顆粒越小時，氫氣選擇率越高；在pH＝8製備的觸媒，未煅燒的Au/TiO2觸媒有最佳的氫氣選擇率。另外進料中氧與甲醇的比例也是影響反應的一個因素，當O2/CH3OH = 0.3時一氧化碳的產量達到極低，不到500 ppm，無法由GC偵測出來。當增加反應溫度時，甲醇轉化率與氫氣選擇率都會同時增加。反應路徑假設為由連續的甲醇部分氧化、甲醇直接分解與甲醇蒸汽重組反應構成。最後和文獻上的銅觸媒以及鈀觸媒催化結果做比較，Au/TiO2觸媒的催化活性較佳，且CO的產率極微小，但是氫氣選擇率比銅觸媒及鈀觸媒來的差，未來仍須進行改質，以期提升氫氣選擇率。 Selective production of hydrogen by partial oxidation of methanol (CH3OH + 1/2O2 → 2H2 + CO2) over Au/TiO2 catalysts, prepared by deposition-precipitation method was studied. The catalysts were characterized by ICP-AES, TGA, XRD, TEM, and XPS analyses. TEM observations show that the Au/TiO2 catalysts exhibit hemispherical gold particles, which are strongly attached to metal oxide support at their flat planes. The size of the gold particles decreases from 3.9 nm to 1.8 nm with the rise in pH during preparation of the catalysts 6 to 9 and increases from 3.0 nm to 4.7 nm with the rise in calcination temperature up to 673 K. XPS analyses demonstrate that in uncalcined catalysts gold existed in three different states i.e. metallic gold (Au0), non-metallic gold (Auδ+) and Au2O3 and in catalysts calcined at 573 K only in metallic state. The catalytic activity is strongly dependant on the gold particle size, with smaller particles produces higher hydrogen selectivity. The catalyst precipitated at pH 8 and uncalcined catalysts show highest activity for hydrogen generation. The partial pressure of oxygen plays an important role in determining the product distribution. There is no carbon monoxide detected, when the O2/CH3OH molar ratio in the feed is 0.3. Both hydrogen selectivity and methanol conversion increase with increasing the reaction temperature. The reaction pathway is suggested to consist of consecutive methanol partial oxidation, methanol decomposition, and methanol steam reforming.
Appears in Collections:	[National Central University Department of Chemical & Materials Engineering] Electronic Thesis & Dissertation

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