Template Synthesis of Alloy Nanowires in Mesoporous Materials by Photoreduction and Their Applications

在介孔二氧化硅材料如FSM-16和有机-无机杂化HMM（孔径3 nm）中合成了单纳米线和双纳米线。研究了纳米线的形成机理、规模化合成和分离方法。结果表明，当金属离子的迁移速度比光还原速度快时，纳米线在介孔空隙中形成。相反，当迁移比还原慢时形成纳米颗粒。考虑到这一机制，我们发现了一种有效的和通用的方法，在大规模合成纳米线，其中水蒸气在高温下添加到氢气流。迄今为止，我们已经合成了铂、钯、铑和铂-金的纳米线。通过用稀氢氟酸溶解二氧化硅基质，分离和隔离金属纳米线。在TEM和STM观察中，线的直径为3 nm，长度可达25 μm（纵横比为8300）。纳米线具有项链结构。我们还研究了利用超临界流体制备金属纳米粒子催化剂。在介孔氧化硅浸渍步骤金属盐，如铑和Rh/Pt，样品与超临界二氧化碳的氧化。处理后的样品具有高分散的金属颗粒内的空隙，和所得的RhPt催化剂在丁烷氢解乙烷的高产率。

Mono- and bimetallic nanowires were synthesized in mesoporous silica materials such as FSM-16 and organic-inorganic hybrid HMM (pore diameter 3 nm). The formation mechanism, large-scale synthesis, and separation of nanowires were studied. It is revealed that, when migration of metal ions is faster than photoreduction, nanowires are formed in the mesoporous voids. In contrast, nanoparticles are formed when migration is slower than reduction. By considering this mechanism, we have discovered an effective and versatile method to synthesize nanowires in large-scale, in which water vapor is added to hydrogen flow at high temperature. To date we have synthesized nanowires of platinum, palladium, rhodium, and platinum-gold. By dissolving silica matrix with diluted hydrofluoric acid, the metal nanowires were separated and isolated. In TEM and STM observations, the diameter of wires is 3 nm and the length is up to 25 μm (aspect ratio 8300). The nanowires have a necklace-structure. We have also studied the preparation of metal nanoparticle catalysts by usuing supercritical fluids. After the impregnation of mesoporous silica with step metal salts such as Rh and Rh/Pt, the samples were terated with supercritical carbon dioxide. The treated samples have high dispersion of metal particles inside the voids, and the resulting RhPt catalysts shows high yields of ethane in butane hydrogenolysis.