【作者】 郭睿劼；

【导师】 张宝泉；

【作者基本信息】 天津大学 ， 工业催化， 2007， 博士

【摘要】 有序纳米结构金属材料在催化、电池、燃料电池及传感器等领域有潜在的应用前景,溶致液晶模板法是合成这种新型材料的主要方法之一。本文以非离子表面活性剂Brij56形成的溶致液晶为模板,在不同基体上分别采用化学沉积和电化学沉积法合成了有序纳米结构金属/双金属膜,模拟了它们在膜反应器中对丙烷脱氢反应的催化性能。以非离子表面活性剂分别与金属盐、双金属盐水溶液构建层状、六方相液晶,用偏光显微镜、低角XRD等手段研究金属盐性质、水相组成对液晶结构及其稳定性的影响。在多孔α-Al2O3基体上,利用水合肼与溶解在液晶水相的金属前驱物的反应,制得与基体紧密结合、结构高度有序的层状及六方纳米结构金属(Pd、Pt)膜。在多孔α-Al2O3基体上,用水合肼同时还原液晶水相中的两种金属前驱物,合成沉积在多孔基体上的层状和六方纳米结构PdAg、PdPt双金属膜。分析了产物组成及两种组分在其中的分布情况。用化学镀法在多孔α-Al2O3基体上制备致密Pd膜,考察合成条件对Pd膜性能的影响。以表面处理后的Pd膜为基体,在其上电化学沉积六方纳米结构金属Pt膜,制得Pt-Pd/α-Al2O3复合材料。分析产物组成,通过低角XRD、TEM等手段表征产物结构,考察沉积电势、液晶水相中金属前驱物浓度等对Pt膜结构及结构参数的影响,用循环伏安法测定纳米结构Pt膜比表面积为13.8 m2 g-1。研究产物与液晶模板之间结构对应关系,初步探讨引起二者尺寸不匹配的原因。分析认为,化学沉积或电化学沉积时基体提供的沉积界面、液晶模板中金属前驱物浓度等对产物结构参数有一定影响。该结果为调控纳米结构提供了一种新的、简便的方法。以丙烷催化脱氢为模型反应,模拟氧化铝基体上Pt膜及Pt-Pd双层膜在膜反应器中的行为,并与固定床反应器及传统Pd膜反应器进行比较,考察吹扫气流量、压力、温度及反应体积等对丙烷转化率的影响。模拟结果显示,除可免除填充催化剂颗粒外,双层膜反应器可在更加微小的反应器中保持较高的丙烷转化率,具有传统膜反应器不可比拟的优势。更多还原

【Abstract】 Well-defined periodic nanostructured metal materials are promising candidates with potential applications in catalysis, batteries, fuel cells and sensors. Lyotropic liquid crystalline templating strategy is a versatile approache for the synthesis of this new kind of materials. In this thesis, ordered nanostructured metal / bimettalic films were deposited chemically or electrochemically on different substrates by using lyotropic liquid crystalline templates exhibited by the nonionic surfactant Brij56. The performance of the as-resulted membrane reactors composed of nanostructured Pt films on Al2O3 or on dense Pd membranes was compared with that of conventional fixed-bed and Pd membrane reactors for the catalytic dehydrogenation of propane. The major research works might be summarized as follows:Lamellar and hexagonal liquid crystalline phases were formed by mixing Brij56 and aqueous precursor solutions containing one or two metal salts. The effects of the precursor nature and the composition of the templating mixture on the nanostructure and stability of the liquid crystalline phase were investigated by means of POM and low-angle XRD.Reactions between hydrazine hydrate and metal salts dissolved in aqueous domains of the liquid crystalline templates resulted in the nanostructured metal Pd and Pt films chemically deposited on porousα-Al2O3 substrates. These films possessed well-defined lamellar or hexagonal nanostructure and strongly adhered to the substrates.Co-reduction of two-metal species in the presence of liquid crystalline phase by hydrazine hydrate produced lamellar nanostructured PdAg and hexagonal nanostructured PdPt bimetallic films chemically deposited onα-Al2O3 substrates. Composition and distribution of two metals in the as-resulted bimetallic films were analyzed.Dense Pd membrane was electrolessly plated onα-Al2O3 substrates and the effect of plating procedure on the quality of the Pd coating was studied. Electrochemical deposition of nanostructured Pt films on the surface of post-treated dense Pd membrane produced Pt-Pd two-layer films. The composition was analyzed and the nanostructure of Pt films was characterized with low-angle XRD and TEM. Effects of deposition potentials and precursor concentration in aqueous domains of liquid crystalline templates on the nanostructure and lattice parameter were investigated. Cyclic voltammetry experiments gave the active specific surface areas of Pt films of 13.8 m2 g-1.Relations between the template media and the templated inorganic structures were discussed with focus on the reasons leading to size mismatch between them. In fact, this founding might be a simple and convenient way controlling over nanostructure.Simulation of the propane dehydrogenation process in the mesoporous Pt membrane reactors and Pt-Pd two-layer membrane reactors was employed. The performance of the two types of membrane reactors had been compared with that of fixed-bed reactors and conventional Pd membrane reactors using this simulation. Comparative studies were carried out to analyze the performances of reactors containing different membranes in terms of sweep gas, pressure, temperature, space time and reactors inner tube radius. The results show that the Pt-Pd two-layer membrane reactors are superior to the conventional ones in that they retain higher propane conversion even in minuscule reactor chamber as well as prevent from packing granular catalysts.更多还原