Manipulating catalytic performance of layered PdTe2 by engineering surface defects

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题名:	Manipulating catalytic performance of layered PdTe2 by engineering surface defects
作者:	郭來翔;Kuo, Lai-Hsiang
贡献者:	物理學系
关键词:	二碲化鈀;表面催化;缺陷控制;超高真空催化;近常壓催化;PdTe2;surface catalysis;defects manipulating;UHV catalysis;near ambient pressure catalysis
日期:	2022-09-12
上传时间:	2022-10-04 11:17:38 (UTC+8)
出版者:	國立中央大學
摘要:	我們以氬氣轟擊PdTe2的表面以製造表面Te缺陷，藉由控制氬氣的量，表面Te缺陷的濃度同樣也能被控制；若以反射式高能電子繞射儀(reflected high energy electron diffraction RHEED)進行表面晶格的量測時，樣品本身的晶格結構並未發生變化，但缺陷使得繞射條紋變的模糊；另外以同步輻射光源的光電子能譜術(synchrotron-based photoelectrons spectroscopy PES)對表面進行同樣的量測，我們發現經過氬氣轟擊後，Pd 3d的能譜中觀測到額外的電子，同時Te 4d的能譜並沒有發生變化。結合RHEED以及PES的資料，我們得知經過氬氣轟擊後的表面產生了Te空缺，此空缺使晶格的對稱性變弱，留下的空缺使隔壁產生了未鍵滿的Pd(Pduc)，而被氬氣轟擊後的表面在經過520 K的加熱後，表面能回復成原來尚未經過轟擊前的狀態。在超高真空環境下，我們個別做了水和甲醇的吸附催化反應，以更進一步探討表面缺陷對催化效應的影響，不管是在乾淨或缺陷的表面上，水皆不會分解；我們也將甲醇曝到有缺陷及乾淨的PdTe2表面上，甲醇經過升溫後會發生C-O及C-H的斷鍵並產生CHxO 和 CHx ，隨著越多的Pduc以氬氣轟擊的方式被產生，甲醇的分解量也隨之上升，此結果反應出Pduc是甲醇分解反應的反應位置。當我們把甲醇的量上升到近常壓的狀態，PdTe2對甲醇的分解效應也發生了改變，不管是乾淨或缺陷的表面，皆可以進行甲醇分解反應，並觀測到氫氣及水/甲烷的產生，甲醇在近常壓的狀態下不只會分解，分解的同時表面上的Te原子也隨之減少，進而產生Te的空缺，使Pduc被觀測到，而同時Pduc又是促進甲醇分解的反應位置，這種甲醇及Pduc互相催化的連鎖效應使得表面的化學結構發生了劇烈的變化，並使得Pduc最終會占滿整個表面，此結果反應出只需以乾淨表面本身所具備的樣品固有缺陷便足夠進行甲醇分解反應，最後當我們將系統抽回超高真空並同樣升溫到520 K，表面的PdTe2鍵結又重新出現並開始回復。 ;We studied PdTe2 surface Te defects engineering and catalytic properties by synchrotron-based photoelectrons spectroscopy (PES), quadrupole mass spectrometer (QMS) in both UHV and near ambient pressure conditions, and reflected high energy electron diffraction (RHEED) system in UHV condition. To generate the Te defects on the surface, we produce Ar+ bombardment process. By controlling the dosages of Ar+, the numbers of Te defects can be engineered. From the PES results, after Te defects are produced, under-coordinated Pd (Pduc) is observed in Pd 3d core level PES spectrum. The surface can recover back to the pristine surface through the 520 K annealing process, which is monitored by both RHEED and PES. The formation of Pduc promotes the methanol decomposition reaction compared with the inert as-cleaved PdTe2 surface. The methanol decomposes into CHxO and CHx through the temperature increase which indicated the C-H and C-O bonds are broken at the same time. The production grows when the numbers of Pduc increase. Pduc is determined as the active site in the methanol decomposition reaction. The water dissociative reaction is also produced. In both as-cleaved and defected surfaces, the reactivity remains inert. In the near ambient condition, the methanol decomposed on the as-cleaved and defected surface. The formation of hydrogen and water/methane is observed and increase through pressure increase. The Te atoms are removed from the surface and generates more Te vacancies which are recognized as Pduc through the pressure increase. Since Pduc is the active site of methanol decomposition reaction. The inducement of Pduc promotes more methanol decomposing. This chain effect can lead to surface chemical environments processing an extreme change which leads to the Pduc dominating the whole surface. Namely, even the intrinsic vacancies can produce the reaction. The surface also can be recovered through the annealing process after pumping back to UHV.
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