Bifunctional heterogeneous catalysts for selective epoxidation and visible light driven photolysis: Nickel oxide-containing porous nanocomposite
Bifunctional heterogeneous catalysts for selective epoxidation and visible light driven photolysis: Nickel oxide-containing porous nanocomposite
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DOI：
10.1002/adma.200701677
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发表时间：
2008-02-04
影响因子：
29.4
通讯作者：
Choy, Jin-Ho
中科院分区：
文献类型：
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作者：
Kim, Tae Woo;Hwang, Seong-Ju;Choy, Jin-Ho
在过去的几十年里，人们一直致力于开发高效的多相催化剂，因为它们使用方便，易于回收。([1])特别地，多孔过渡金属氧化物作为有前途的催化剂材料已经引起特别的关注，因为过渡金属离子可以对氧化还原反应和光诱导反应显示出高催化活性，而且通过制造多孔结构来扩大表面积可以提供大量的催化活性位点。([2])在制备多孔无机固体的各种方法中，最有效的方法之一是无机前驱体在表面活性剂分子或嵌段共聚物的帮助下的自组装。([3])这种合成路线对于制备介孔二氧化硅基催化剂如MCM-41和MCM-48非常有效，然而在制备热稳定的多孔过渡金属氧化物方面不太成功。作为替代途径，金属氧化物嵌入层状无机固体中的插层反应可用于合成多孔过渡金属氧化物。([4])此外，该方法可以提供将两种不同的金属氧化物混合成多孔晶格的独特优点，导致两种物理化学性质的协同组合。近年来，微波法制备的纳米多孔磷酸镍对烯烃环氧化反应表现出很高的催化活性。([5])此外，纳米氧化镍作为助催化剂被广泛用于提高光催化材料的光催化活性。([6])在这方面，含氧化镍的多孔化合物不仅作为氧化还原催化剂，而且作为光催化剂都是有活性的。然而，迄今为止，还没有关于氧化镍纳米颗粒和层状无机固体的多孔插层化合物的合成的报道。先前尝试将少量的氧化镍（< 1wt%）掺杂到层状钙钛矿金属氧化物的层间空间中或表面上，在制备多孔NiO基材料中是不成功的。([7])最近有报道称，大体积有机分子的插入导致过渡金属氧化物剥离成胶体纳米管。([8])由于所得的单个单层带负电荷，因此预期它们容易与带正电荷的氢氧化镍纳米团簇重新组装，（[9]）导致多孔氧化镍基材料的形成（方案1）。在本工作中，我们成功地合成了[GRAPHICS]第一次多孔氧化镍-氧化钛（以下称为NT）纳米复合材料与剥离的氧化钛纳米片，并表征了其多功能催化活性和化学键合性质。
Over the last decades, intense research activities have been devoted on the development of efficient heterogeneous catalysts because of their convenient use and facile recycling.([1]) In particular, porous transition metal oxides have attracted special attention as promising catalyst materials since transition metal ions can show high catalytic activity for redox- and photoinduced-reactions, and moreover the expansion of surface area through the fabrication of porous structure can provide a large number of catalytically active sites.([2]) Among various synthetic routes to porous inorganic solids, one of the most powerful methods is the self-assembly of inorganic precursors with the help of surfactant molecules or block copolymers.([3]) This synthetic route is very effective for creating mesoporous silica-based catalysts like MCM-41 and MCM-48, however it is less successful in preparing thermally stable porous transition metal oxides. As an alternative route, the intercalation reaction of metal oxide into layered inorganic solids is useful for synthesizing porous transition metal oxides.([4]) Furthermore, this method can provide a unique merit of hybridizing two different metal oxides into a porous lattice, leading to the synergetic combination of two physicochemical properties. Recently nanoporous nickel phosphate prepared by microwave irradiation has been reported to show high catalytic activity for the epoxidation of olefin molecules.([5]) Moreover, nanocrystalline nickel oxide has been widely used as a co-catalyst for improving the photocatalytic activity of semiconductive materials.([6]) In this regard, nickel oxide-containing porous compound is expected to be active not only as a redox catalyst but also as a photocatalyst. Up to date, however, there have been no reports on the synthesis of porous intercalation compound of nickel oxide nanoparticle and layered inorganic solids. A previous attempt to dope a small amount of nickel oxide (< 1wt%) into the interlayer space or on the surface of layered perovskite metal oxide was unsuccessful in producing porous NiO-based materials.([7]) Recently it was reported that the intercalation of bulky organic molecules leads to the exfoliation of transition metal oxides into colloidal nanoshects.([8]) Since the resultant individual monolayers are negatively charged, they are expected to easily be reassembled with positively charged nickel hydroxide nanoclusters,([9]) leading to the formation of porous nickel oxide-based materials (Scheme 1). In the present work, we are successful in synthesizing for the[GRAPHICS]first time porous nickel oxide-titanium oxide (hereafter it is called as NT) nanocomposites with exfoliated titanium oxide nanosheets and characterized their multifunctional catalytic activities and chemical bonding nature.