水在NiAl(100)表面上的反應; XPS,TPD與LEED的研究

Abstract

在催化劑與催化劑基材中，金屬氧化物佔有一個非常重要的地位，雖然我們廣泛的使用這些系統，但是對其詳盡的化學機構仍然不是非常了解。我們利用光電子能譜、程溫脫附法以及低能電子繞射來研究氧化NiAl(100)表面所生成的γ-Al2O3薄膜。在程溫脫附(TPD)的實驗中指出，物理吸附的水會在165K時從表面上脫附，而H(ad)會在200-400K之間從表面上脫附。在光電子能譜(XPS)的實驗中，發現在100K下水分子吸附於表面上，會部份產生分解成OH (ad) 與 H(ad)，當溫度升高到173K時，水分子會產生出脫附於表面或是分解成OH(ad)兩種反應途徑，當溫度達到700K時，在表面上已經形成Al2O3氧化層。在低能電子繞射(LEED)的研究之中，在清潔的NiAl(100)表面上，我們可以發現P(1x1)與c(√2 x 3√2)R45o兩種不同的LEED pattern，這是因為鋁與鎳共存在表面上的結果，當我們曝露水於表面並且再加熱至1000K後，我們可以發現Al2O3氧化層在表面上形成P(2x1)與P(1x2)的LEED pattern。在我們的論文之中，我們也會討論水與氧對於氧化NiAl(100)所形成的Al2O3氧化層與其氧化機構是否的不同。

Metal and metal oxide play an important role as catalyst and catalyst support. While the system is widespread used, but the detail chemical mechanism are not well understood. Ultra-thin of γ-Al2O3 grown on NiAl(100) were investigated by using X-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD), and low-energy electron diffraction (LEED). Our TPD results showed that water of physical adsorption desorps from surface at 165K and H(ad) desorps between 200K and 400K. XPS data show that water partially dissociate to form OH (ad) and H(ad) at 100K. When heating to 173K, water will desorp from surface or dissociate to form OH (ad) and H(ad). The Al2O3 are formed on NiAl(100) surface at 700K. We found two kinds of patterns on the investigation of LEED. One is P(1x1) and the other is c(√2 x 3√2)R45o. This is due to nickel coexist with aluminum on surface. After we dose water on surface at 100K and anneal to 1000K, we found that the LEED patterns of aluminum oxide are P(2x1) and P(1x2). In our investigation, we also discussed the difference of aluminum oxide formed by water or oxygen and the difference of mechanism of oxidation.