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

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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