銠(111)對硝酸的還原及鉑銠合金對甲醇催化之研究

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/80418

Title:	銠(111)對硝酸的還原及鉑銠合金對甲醇催化之研究
Authors:	梁鈞郁;Liang, Chun-Yu
Contributors:	化學學系
Keywords:	電化學;銠單晶;硝酸還原;鉑奈米沉積;甲醇氧化
Date:	2019-08-14
Issue Date:	2019-09-03 14:29:12 (UTC+8)
Publisher:	國立中央大學
Abstract:	接續先前實驗室製備的Pt/Pd(111)對甲醇氧化有提升效果，改以銠當載體探討 : (1)故以含氧性高的銠金屬與鉑製備成合金，研究對甲醇氧化的活性；(2)作為常用於還原反應的催化材料之一，及近期有許多以銠對硝酸鹽催化的文獻，故研究特定晶面的銠對硝酸鹽的活性。本研究以無電鍍和電鍍兩種簡易方法製備鉑銠合金，由掃描式穿隧電子顯微鏡(STM)和X射線光電子能譜儀(XPS)觀察兩者表面的結構型態，發現兩種方式的鉑都以奈米尺度沉積於銠(111)上，但XPS的Pt 4f訊號卻有所不同，並藉以循環伏安法(CV)探討催化甲醇的活性，實驗結果顯示無電鍍的Pt NPs/Rh(111)相比Pt(111)的正掃氧化電位提前280 mV，且負掃的氧化峰能提前在0.1 V(vs. Ag/AgCl)出現；再經由氧化CO實驗，也觀察到Pt NPs/Rh(111)的CO氧化電位相比Pt(111)能提前35~115 mV，推論銠金屬能在低電位貢獻OH，使CO毒化能力降低，所以提升甲醇氧化活性是藉由鉑銠的協同作用 — Pt-CO + Rh-OH →Pt + Rh + CO2 + H+ + e−，還會以XPS、粗糙度等方向分析影響甲醇氧化電位與電流大小的因素。從STM和紅外反射吸收光譜儀(IRRAS)探討硝酸吸附於銠(111)的結構與反應過程；發現晶面的不同導致硝酸還原活性也有所不同，分別對(111)和(100)晶面的硝酸還原CV做Tafel slope，得出114和180 mV dec-1 ，認為都以硝酸根吸附接著還原成亞硝酸為速率決定步驟(RDS)，因此活性表現較差的(100)晶面，原因可能是幾何結構的影響(Geometric effect) — 三角平面結構的NO3-不易吸附於簡單四方的(100)晶面；還探討不同pH值和陰離子對硝酸鹽活性是否有改變。 ;The Pt/Pd(111) prepared in the previous laboratory has the effect of improving the oxidation of methanol. It is changed to the carrier of the rhodium : (1) The alloy prepared from a high oxygen-containing rhodium and platinum to Study the activity toward methanol oxidation; (2) As one of the catalytic materials commonly was used in the reduction reaction, and there are many literature on the catalysis of nitrate by rhodium recently; therefore, the nitrate reductive activity on specific crystal facets is studied. In this study, platinum-rhodium alloy was prepared by two methods: electroless plating and electroplating. The structure of the surface was observed by scanning tunneling electron microscopy (STM) and X-ray photoelectron spectroscopy (XPS). It was found that both platinum were deposited on the Rhodium (111) with nanometer scale, but the XPS Pt 4f signal is different, and the activity toward MOR was investigated by cyclic voltammetry (CV). The experimental results show that oxidative potential of Pt NPs/Rh(111) from electroless plating moved up 280 mV than that of Pt(111), and the oxidation peak of the backward sweep can appear in advance at 0.1 V (vs. Ag/AgCl). Through the oxidation of CO experiment, it was also observed that the CO oxidation potential of Pt NPs/Rh(111) was 35~115 mV ahead of Pt(111), it is inferred that rhodium can contribute OH group at low potential, which reduces CO poisoning, so the methanol oxidation activity is enhanced by the synergistic effect of platinum and rhodium—Pt-CO + Rh-OH →Pt + Rh + CO2 + H+ + e−. XPS and roughness also analyzed factors affecting the oxidation potential and current of methanol. The structure and reaction process of nitric acid adsorption on rhodium (111) were investigated from STM and infrared reflectance absorption spectrometer(IRRAS). It is found that the difference in crystal facet results in different nitrate reduction activities, Tafel slope was performed on the nitrate reduction CV of the (111) and (100) facets, respectively, and 114 and 180 mV dec-1 were obtained, it is considered that the nitrate adsorbed and followed by reduction to nitrite as a rate determining step (RDS), therefore, the (100) crystal plane with poor activity may be due to the geometric effect—the triangular plane structure of NO3- is not easy to adsorb to the simple tetragonal (100) plane. It is also explored whether different pH values and anions have a change in nitrate activity.
Appears in Collections:	[Graduate Institute of Chemistry] Electronic Thesis & Dissertation

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