Synthesis of Nano-structured Materials Using Hybrid Mesoporous Templates and their Application to Advanced Catalytic Devices

纳米粒子和纳米线是纳米技术自下而上方法中高度有序的纳米结构材料的关键前体。迄今为止，人们对纳米颗粒的合成及其在磁性、光学、电子、分离和催化等方面的应用进行了大量的研究。然而，纳米线的化学是一个新的领域，近年来由于其基于低维结构的潜在的独特性能而引起了人们的极大兴趣。在纳米线的应用中，吸附和催化等化学反应性研究较少。在本研究中，我们成功地以介孔二氧化硅FSM-16、HMM和薄膜为模板合成了单金属和合金纳米线和纳米颗粒。采用物理化学方法对纳米线和纳米粒子进行了表征；金属丝直径为3nm，长度为25 μm，结晶度高。研究了Pt纳米线的形成机理，其中前驱体Pt离子在介孔通道中的迁移是纳米线生长的关键。有机硅材料HMM-1中的铂丝具有纳米项链结构，而硅材料FSM-16中的铂丝具有纳米棒结构。作为纳米线和纳米颗粒在非均相催化中的应用，我们对PEM燃料电池进行了CO在过量H_2中的优先氧化（PROX）。在298 ~ 373 K下，FSM-16中的Pt纳米线和纳米颗粒的CO转化率为80 ~ 100%，而Pt/ hm -1、Pt/Al_2O_3和Pt/SiO_2的CO转化率为10 ~ 20%（图2）。Pt/FSM-16催化剂的CO选择性高达90-100%，有效抑制了H_2+O_2反应。从FSM-16中提取Pt丝，并将其再次沉积在FSM-16的外表面。然而，所得Pt/FSM-16催化剂的催化活性较低，表明Pt在介孔中的包封对PROX反应很重要。通过XAFS、XPS、IR和化学吸附对Pt/FSM-16的结构进行表征，我们认为Pt/FSM-16的高活性是由于Pt表面缺乏电子，从而促进了CO的部分解吸和O_2的吸附生成CO_2。少

Nanoparticles and nanowires are key precursors to highly ordered, nanostructured materials in the bottom-up approach in nanotechnology. So far much work has been devoted to the synthesis and application of nanoparticles in magnetism, optics, electronics, separation and catalysis. However, the chemistry of nanowire is a new area, and the nanowires have attracted great interest in recent years due to potential unique properties based on the low-dimensionality. In the applications of nanowires, the chemical reactivity such as adsorption and catalysis is less explored. In this study, we have succeeded in synthesizing monometallic and alloy nanowires and nanoparticles in mesoporous silicas FSM-16, HMM, and thin film as a template. The nanowires and -particles were characterized by physicochemical methods ; the wires are 3 nm in diameter and 25 μm in length with high crystallinity. The mechanism for formation of Pt nanowires was studied, in which migration of precursor Pt ions in the mesopor … More ous channels is the key to growth of nanowires. The Pt wires in organosilica HMM-1 have a nanonecklace structure, while the wires in siliceous FSM-16 have a nanorod structure.As an application of nanowires and -particles in heterogeneous catalysis, we performed preferential oxidation (PROX) of CO in excess H_2 for PEM fuel cells. The Pt nanowires and nanoparticles in FSM-16 showed 80-100% CO conversion at 298-373 K, while Pt/HMM-1, Pt/Al_2O_3 and Pt/SiO_2 gave 10-20 % of CO conversion (Figure 2). Also CO selectivity was as high as 90-100% for the Pt/FSM-16 catalysts, indicating that the H_2+O_2 reaction is effectively suppressed. The Pt wires were extracted from FSM-16, and the wires were again deposited on the external surface of FSM-16. However, the resulting Pt/FSM-16 catalyst gave low catalytic activity, showing that the encapsulation of Pt in the mesopores is important for the PROX reaction. From the structural characterization by XAFS, XPS, IR and chemisorption, we propose that the high activity of Pt/FSM-16 is due to the electron-deficiency at the Pt surface, which enhances partial desorption of CO and adsorption of O_2 to give CO_2. Less