Methanol Decomposition on Pt nanoclusters supported by Graphene on Pt(111)：A combined RHEED, IRAS and TPD study

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/71660

Title:	Methanol Decomposition on Pt nanoclusters supported by Graphene on Pt(111)：A combined RHEED, IRAS and TPD study
Authors:	蔡佩仰;Cai,Pei-Yang
Contributors:	物理學系
Keywords:	甲醇分解;白金(111);石墨烯;高能電子繞射;紅外光吸收儀;熱程控脫附術;Methanol Decomposition;Pt(111);Graphene;RHEED;IRAS;TPD
Date:	2016-06-30
Issue Date:	2016-10-13 13:28:35 (UTC+8)
Publisher:	國立中央大學
Abstract:	Pt金屬的奈米團簇利用蒸鍍的方法成長在 Pt(111) 為基底的石墨烯(graphene)上，利用高能電子繞射儀(reflection high energy electron diffraction, RHEED)來研究。我們發現 Pt 金屬的奈米團簇有很好的排列行為而且結構及晶格間距受到底層石墨烯的影響，經由高能電子繞射儀的結構研究，我們發現石墨烯會以非常多不同的方向生長，其中主要的方向是石墨烯晶格平行於 Pt(111) 晶格，和一個次要方向石墨烯晶格與 Pt(111) 晶格相差30°。Pt 金屬的奈米團簇是 fcc 的結構並且沿著平行 Pt(111) 表面以 (111) 面方向成長，Pt 金屬的奈米團簇會也會隨著石墨烯以非常多不同的方向生長的，但有一個主要方向是 [11-2] 方向平行於 Pt(111) 的 [11-2] 方向。而 Pt 金屬奈米團簇在表面法向量方向的晶格常數(4.02 – 4.34 Å)相對於 fcc 結構的 Pt 塊材(3.92 Å)較為膨脹，這樣會使 Pt 金屬奈米團簇的 (111) 面有比較好的晶格去吻合表面的石墨烯。晶格常數會因鍍量而有所下降，但不會隨退火溫度改變。我們利用熱脫附質譜術及反射式紅外線光譜吸收儀來研究甲醇於白金奈米粒子上的分解反應之觸媒模型。從 IR 吸收光譜上以 CO 作為探測物的結果發現 CO 傾向於吸附在 Pt 奈米粒子的 on-top site 上，沒有其他像是 bridge或是 hollow的吸附被探測到。由被探測到。由 CO 的 TPD脫附譜線則顯示CO 的脫附有兩個峰值：一位於 390 K（在 Pt 單晶上也有出現），一個則位於 470 K（我們認為是來自於較小的 Pt 奈米粒子上脫附的 CO ）。然而，無論反射式紅外線光譜及熱脫附質譜術的結果都指出，單層吸附的甲醇會在 136 K 左右完全脫附光，低於甲醇分解反應在 Pt(111) 單晶的溫度(200 K). 沒有任何甲醇分解反應的產物被偵測到，暗示著甲醇在以石墨烯/ Pt(111) 為基底上的白金奈米粒子上不會進行分解反應。 ;The Pt nanoclusters grown from vapor deposition on single layer graphene have been studied by reflection high energy electron diffraction (RHEED). The results show that the Pt nanoclusters are highly crystalline and their structures and lattice constant are significantly affected by the graphene/Pt(111) substrate. Structural analysis based on the RHEED patterns indicates that graphene grow with varied orientations but two are primary: graphene[1000]//Pt(111)[11-2] and graphene[1-100]//Pt(111)[11-2]. Pt nanoclusters grew as fcc phase, with their (111) facets parallel to the graphene surface and with varied orientations with respect to graphene/Pt(111); the primary one has its [11-2] direction parallel to [11-2] direction of Pt(111), denoted as Pt(111) clusters [11-2]//Pt(111)[11-2]. The clusters grew with two kinds. Their orientations differ by 60˚ from each other. Since fcc Pt clusters in (111) orientation has six-fold symmetry, the two kinds of clusters are at the same orientation with respect to the substrate. The lattice constant of the Pt nanoclusters is expanded only in surface normal direction (4.02 – 4.34 Å), relative to that of fcc bulk Pt (3.92 Å). The lattice constant decreases with the coverages, but indenpent of annealing temperature. Methanol decomposition on Pt nanoclusters supported by graphene as a model system is studied by IRAS and TPD. The study contained two parts: surface structures of Pt clusters probe with CO and methanol decomposition on Pt nanoclusters. The IRAS spectra with CO as a probe show that the CO adsorbed on on-top site of Pt nanoclusters; no other site such as bridge or hollow site have been detected. The CO TPD spectra show that CO desorbed with two distinct peaks, one at 390 K for CO on terrace sites, which is observed for CO on Pt single crystal results and the other at about 470 K for CO on low-coordinated site, which is observed for CO on small Pt clusters. Both IRAS and TPD spectra for methanol experiments show that the monolayer methanol on the clusters compeletly desorb about 136 K, significantly lower than that for methanol desorption from Pt(111) single crystal (170 K) and also that for methanol decomposition on Pt(111) single crystal (200 K). No CO and hydrogen produced from decomposition is detected, indicating that methaol on the Pt nanoclusters on graphene/Pt(111) does not decompose.
Appears in Collections:	[Graduate Institute of Physics] Electronic Thesis & Dissertation

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