Methanol Decomposition on Au-Rh Bimetallic Nanoclusters supported by Al2O3/NiAl(100): A combined IRAS and TPD study

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/71675

Title:	Methanol Decomposition on Au-Rh Bimetallic Nanoclusters supported by Al2O3/NiAl(100): A combined IRAS and TPD study
Authors:	李璿;Lee,Hsuan
Contributors:	物理學系
Keywords:	甲醇分解;金銠合金;熱脫附;紅外光吸收能譜;Methanol decomposition;Au-Rh bimetallic nanoclusters;Au-Rh alloy;TPD;IRAS
Date:	2016-08-22
Issue Date:	2016-10-13 13:29:35 (UTC+8)
Publisher:	國立中央大學
Abstract:	我們藉由熱脫附質譜(TPD)和紅外光反射吸收能譜(IRAS)表面探測技術利用一氧化碳分子來探測在室溫下蒸鍍於θ相氧化鋁薄膜上的金-銠合金奈米粒子的表面結構和組成。將金原子鍍在銠奈米團簇上，銠在合金奈米粒子的表面位置數會隨著金的鍍量線性遞減。當銠原子鍍在金奈米團簇上，我們會發現銠原子跟金原子會在表面交換形成銠核-金殼的結構，隨著銠原子鍍量的增加我們發現吸附在金原子上的一氧化碳對紅外光的吸收會明顯增強。不論蒸鍍金或銠的先後順序如何，我們都觀察到一氧化碳分子的脫附不會改變金-銠合金奈米粒子的表面組成，且當金原子吸附一氧化碳分子時會降低吸附在銠原子上的一氧化碳分子對紅外光的吸收。在合金奈米粒子的熱穩定性實驗中我們發現不論蒸鍍金或銠的先後順序如何，450 K時位於合金表面的金原子會將銠原子覆蓋的更好，700 K時合金表面的金與銠相對於300 K都有明顯的減少。甲醇在金-銠合金奈米粒子上的分解途徑為脫氫反應，主要在銠的位置上進行。大尺寸的銠金屬團簇(1.00 ML)對於甲醇分解的產率會因鍍上少量的金(0.25 ML)而明顯降低，是因為金原子傾向於佔據銠團簇較具有活性的低配位數位置，但並不會對甲醇脫氫產生一氧化碳的活化能造成明顯改變。但是小尺寸(0.25 ML)的銠團簇對於甲醇分解的產率不會隨著鍍上金原子而有變化，主因是金原子佔據的都是銠團簇較具有活性的低配位數位置。當銠鍍在黃金奈米團簇上時，對甲醇分解的產率會隨著銠的鍍量增加而降低，且產率隨著銠鍍量的演化關係相似於甲醇分解的產率對於純銠奈米團簇鍍量的演化關係，主要原因是由於銠鍍在金奈米粒子上的配體效應並不明顯，故產率隨著銠鍍量的演化關係會與純銠奈米粒子的情形相似。;We probe the surface structure and composition of Au-Rh bimetallic nanoclusters on thin-film Al2O3/NiAl(100) at 300K with molecular CO, temperature programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS). For the deposition of Au onto Rh nanoclusters, the numbers of Rh sites decrease linearly with Au deposition. For the metal deposition in the reverse order, Au segregates at the surface and then forms Rh core – Au shell structure. The infrared absorption for CO on Au sites was significantly enhanced with Au deposition. We observed that no CO induces structural change for Au-Rh bimetallic nanoclusters during the CO desorption whereas CO adsorbed on Au sites suppresses the IR absorption of CO on Rh sites, despite the order of the metal deposition. For the investigation of thermal stability, we discovered that in the bimetallic clusters, the Au atoms preferentially covered Rh core at 450 K but both Au and Rh attenuated significantly at 700 K. The decomposition of methanol proceeded through dehydrogenation, primarily on Rh sites of Au-Rh bimetallic nanoclusters. The reactivity of methanol decomposition dramatically decreases for the bimetallic clusters formed by small coverages of Au ( 0.5 ML) deposited onto Rh clusters of large size (1.0 ML) because the Au atoms prefer to occupy the low-coordinated sites of Rh clusters. Nevertheless, the activation energy of methanol decomposition on the bimetallic clusters changes insignificantly. The reactivity of methanol decomposition to CO on small Rh clusters (0.25 ML) does not be change with Au deposition because all the Au atoms occupy the low coordinated Rh sites. The reactivity of methanol decomposition on the bimetallic clusters formed by Rh deposited onto Au clusters gradually attenuates with Rh deposition. The revolution of the reactivity with following Rh deposition is similar to that with Rh deposited on pure Rh clusters.
Appears in Collections:	[Graduate Institute of Physics] Electronic Thesis & Dissertation

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