Decomposition of Methanol on Rhodium and Rhodium-Gold Bimetallic Nanoclusters Supported by Al2O3/NiAl(100): Studies under Ambient Pressure Conditions

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题名:	Decomposition of Methanol on Rhodium and Rhodium-Gold Bimetallic Nanoclusters Supported by Al2O3/NiAl(100): Studies under Ambient Pressure Conditions
作者:	廖冠智;Liao, Guan-Jr
贡献者:	物理學系
关键词:	甲醇分解;近室壓;銠;銠金雙金屬合金;近室壓 X 光光電子能譜;質譜法;methanol decomposition;near-ambient pressure conditions;Rh;Rh-Au bimetallic alloy;APXPS;mass spectroscopy
日期:	2022-08-23
上传时间:	2022-10-04 11:17:07 (UTC+8)
出版者:	國立中央大學
摘要:	我們研究在近室壓條件下，甲醇於銠、銠金奈米團簇上的反應及氣壓對奈米團簇結構之影響。實驗中甲醇氣壓範圍為10-6 – 0.5 mbar。此研究使用近室壓X射線光電子能譜學、紅外光反射-吸收光譜法、熱脫附質譜法、質譜法來進行實驗。實驗使用之基板為單晶鎳鋁合金NiAl(100)。為承載奈米團簇，會先曝氧氣於鎳鋁合金上並加溫形成氧化鋁薄膜。之後使用鍍槍將銠或金粒子蒸鍍於氧化鋁上，形成銠或銠金奈米團簇。樣品準備過程皆在超高真空環境中進行以降低可能的污染。實驗結果顯示在近室壓條件下，甲醇在氧化鋁表面有反應發生：吸附於氧化鋁表面的甲醇會部分分解並參與含有OCO結構物質之形成。在近室壓環境中，甲醇在銠奈米團簇表面的分解方式主要是通過脫氫，其終端產物為一氧化碳和氫氣。銠奈米團簇對甲醇分解的反應能力具有尺寸相依性，與之前在超高真空環境下觀察到的結果相似：對於直徑小於 1.5 奈米的團簇，每單位吸附位置的產量約是直徑大於 1.5 奈米團簇的四倍大。在近室壓條件下，甲醇在銠金奈米團簇上的分解也主要是通過脫氫。銠金奈米團簇的反應性與表面銠原子的數量有關。在近室壓反應環境中，銠金奈米團簇的結構變得不穩定：無論蒸鍍的順序為何，一部分的銠原子從銠金奈米團簇的內層移動到表面，導致銠/金訊號比增加。 ;We studied the decomposition of methanol on Rhodium and Rhodium-Gold bimetallic nanoclusters supported on thin-film Al2O3/NiAl(100) under near-ambient pressure (NAP) conditions (methanol partial pressure 10-6 – 0.5 mbar), with NAP photoelectron spectroscopy, infrared reflection absorption spectroscopy, and quadrupole mass spectrometer. In this study, the Al2O3 thin films were grown on the oxidation of NiAl(100) surface, and the clusters were formed by deposition of Rh and Au vapors onto the oxide films under ultrahigh vacuum (UHV) conditions. The results show that the thin film Al2O3/NiAl(100) was not inert toward methanol decomposition under NAP conditions; adsorbed methanol was partially decomposed and involved in forming OCO species. Decomposition of methanol on Rh nanoclusters under NAP conditions is predominantly through dehydrogenation, with CO and H2 as terminal products. The Rh nanoclusters exhibited size-dependent reactivity toward methanol decomposition, resembling that observed under UHV conditions; for clusters with a diameter smaller than 1.5 nm, the production per Rh surface site is 4 times that of clusters with a diameter larger than 1.5 nm. Decomposition of methanol on Rh-Au bimetallic clusters under NAP conditions is mainly through dehydrogenation, too. The reactivity of the Rh-Au bimetallic clusters was enhanced with the surface Rh. The structures of the Rh-Au bimetallic clusters became unstable under NAP reaction conditions; regardless of the order of deposition, a fraction of Rh atoms moved from the core to the surface of the bimetallic nanoclusters, leading to an increase in the Rh-to-Au signal ratio.
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