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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/82807


    Title: Inactivity of Pt nanoclusters Modified by Atomic Oxygen and Au on Graphene/Pt(111) in the Decomposition of Methanol-d4
    Authors: 吳雨蓉;WU, YU-JUNG
    Contributors: 物理學系
    Keywords: 甲醇;金屬奈米團簇;白金;分解反應;原子氧;methanol;nanoclusters;Pt;decomposition;atomic oxygen
    Date: 2020-05-18
    Issue Date: 2020-06-05 17:15:12 (UTC+8)
    Publisher: 國立中央大學
    Abstract: 以Pt(111)為基底的石墨烯(graphene)上的Pt金屬奈米粒子對甲醇分解的催化在之前的研究已經透過熱脫附質譜(TPD)和紅外光反射吸收能譜(IRAS)研究,研究顯示甲醇幾乎沒有分解並直接脫附,沒有中間產物甲氧基(CH3O)的產生,這些結果和甲醇在Pt(111)上的結果有很大的不同,這個不同由於Pt奈米粒子有較Pt(111)小的晶格常數導致甲醇在Pt奈米粒子上的吸附能較在Pt(111)上來的小。
    在這個研究中我們以兩種方法來調整Pt金屬奈米粒子,一個是預先吸附氧原子在Pt奈米粒子上,另一個是在蒸鍍Pt金屬奈米粒子前先蒸鍍Au金屬奈米粒子,形成Au-Pt合金奈米粒子。在Pt奈米粒子上的氧原子的效果被預期為協助甲醇脫氫形成中間產物甲氧基,我們藉由XPS、TPD、IRAS研究甲醇在氧原子預吸附的Pt奈米粒子上的分解反應,經由XPS知道氧原子預吸附的Pt奈米粒子可以透過將Pt奈米粒子加熱到570K曝露在氧氣中的方法製備,並且隨著氧氣曝量的上升,在飽和前氧原子的覆蓋率也會大致隨之上升。從TPD脫附譜線得到甲醇在氧原子預吸附的Pt奈米粒子上仍然沒有分解形成CO及D2; IR吸收光譜顯示了在0.014O_sat 氧原子覆蓋率的Pt奈米粒子上,甲醇在150K到200K會脫氫形成中間產物甲氧基,然而甲氧基不會進一步分解為CO及D2,在飽和氧原子覆蓋率O_sat的Pt奈米粒子上,則沒有甲氧基的生成,因為飽和的氧原子會覆蓋Pt奈米粒子造成甲醇吸附量減少。
    Au塊材的晶格常數為4.08 Å 較Pt塊材的晶格常數3.92Å大,Au金屬奈米粒子在Au-Pt合金奈米粒子中的效果被預期為可以使Pt金屬奈米粒子的晶格常數增加,然而TPD脫附譜線顯示吸附的甲醇在Au-Pt合金奈米粒子上沒有產物的生成,暗示著甲醇在Au-Pt合金奈米粒子上仍然不會進行分解反應。
    ;The decomposition of methanol-d4 on Pt nanoclusters grown by metal deposition on graphene/Pt(111) has been studied with TPD and IRAS previously. The results show that methanol-d4 did not decompose but desorbed mostly, and no methoxy intermediates observed which is in contrast with those on Pt(111) surface. This disparate results from the smaller adsorption energy of methanol on the Pt clusters than on Pt(111) which is owing to the smaller lattice constant of Pt clusters than Pt(111).
    In this study, Pt nanoclusters on graphene/Pt(111) were modified by two methods, one is pre-adsorption of atomic oxygen on Pt clusters, and the other is the addition of Au deposition prior to Pt deposition to form Au-Pt bimetallic clusters. The effect of atomic oxygen on the Pt clusters, expected to assist the formation of methoxy via abstracting d from methanol-d4, on the reaction was clarified by comparison with the reaction on Pt clusters. Using XPS, TPD, and IRAS, we have investigated the reactivity of methanol-d4 on atomic oxygen pre-adsorbed Pt nanoclusters on graphene/Pt(111). Atomic oxygen pre-adsorbed Pt nanoclusters prepared by exposing Pt clusters to oxygen doses at 570K confirmed with XPS; higher dose of oxygen mostly lead to larger coverages of atomic oxygen. The TPD spectra exhibit no evidence of methanol decompose to CO and D2. The IRAS spectra show formation of methoxy from methanol-d4 only on Pt clusters with 0.014O_sat coverage of atomic oxygen pre-adsorbed at the temperature from 150K to 200K. Saturation coverage of atomic oxygen block Pt sites lead to no formation of methoxy.
    The lattice constant of Au bulk is 4.08 Å which is larger than that of Pt bulk(3.92Å). The effect of Au in Au-Pt bimetallic clusters are expected to expand the lattice constant of Pt clusters on graphene/Pt(111). The reaction of methanol on Au-Pt bimetallic clusters was monitored with TPD still like that on Pt clusters show no decomposition of methanol to CO and D2. Both Pt clusters with atomic oxygen pre-adsorbed Pt nanoclusters and Au-Pt bimetallic clusters on graphene/Pt(111) are inactive in Methanol-d4 decomposition .
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