Oxygen Insertion Catalysis by sp2 Carbon
Oxygen Insertion Catalysis by sp2 Carbon
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DOI：
10.1002/anie.201103340
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发表时间：
2011-01-01
影响因子：
16.6
通讯作者：
Schloegl, Robert
中科院分区：
文献类型：
--
作者：
Frank, Benjamin;Blume, Raoul;Schloegl, Robert
具有sp2杂化的元素碳在我们的生活中无处不在，并且以其天然形式，石墨是铅笔，电池，润滑剂，钢和电动机刷的组成部分。高科技电子设备和核电站中的中子减速器是由具有低密度缺陷（六方晶格中碳原子位错的数量）的合成石墨制成的。纳米结构sp2碳用作颜料（炭黑）和聚合物填料。非平面碳同素异形体（如碳纳米管（CNT）和富勒烯）的发现和合成[1]开创了元素碳尖端应用的新时代。基本结构单元是石墨烯，[2]具有边缘缺陷和由非六元碳环引起的曲率。在化学中，石墨形式的碳具有令人感兴趣的催化潜力，其应用范围广泛，包括氢化，氧化，聚合和氯化反应。[3，4] Dreyer和Bielawski最近审查了增加的反应范围，[5]他们自己研究了氧化石墨烯在液相中温和条件下的几种反应中的催化活性。[6]碳材料的非均相气相催化的最突出的例子是通过位于堆叠的石墨烯片的棱柱边缘或（0001）石墨表面中的表面缺陷处的亲核氧原子将石墨烯选择性氧化脱氢（ODH）为苯乙烯[7，8]-一种具有高度工业相关性的反应。对于无氧途径（DH），包覆有缺陷石墨烯壳的纳米晶金刚石，即所谓的“巴基金刚石”，其活性甚至超过工业上的钾促进的铁催化剂。[9]轻质烷烃的ODH具有低得多的选择性并不令人惊讶，因为产物分子中的C2 OH键比底物中的C2 OH键弱[10]-这是选择性氧化反应中的常见问题。[11]充满亲电氧的点缺陷可能引发非选择性燃烧途径。纳米结构碳材料的低维性提供了修改和优化活性位点的化学环境的可能性，从而获得明确的结构-反应性相关性。强路易斯酸性金属阳离子的不存在使焦炭的沉积最小化，从而使催化剂的失活最小化。这又可以通过不需要添加蒸汽或通过焦炭燃烧定期再生催化剂来降低工艺成本。[9]在ODH和DH催化中的这种进展鼓励我们测试纳米结构碳催化剂用于在丙烯醛选择性气相氧化为丙烯酸（AA）中插入氧作为模型反应[Eq. 1]。
Elemental carbon with sp2 hybridization is omnipresent in our lives, and in its natural form, graphite, an integral part of pencils, batteries, lubricants, steel, and electric motor brushes. High-tech electronic devices and the neutron moderators in nuclear power plants are made of synthetic graphite with a low density of defects (the number of carbon atom dislocations in the hexagonal lattice). Nanostructured sp2 carbon is used as a pigment (carbon black) and as a polymer filler. The discovery and synthesis of nonplanar carbon allotropes, such as carbon nanotubes (CNTs) and fullerenes,[1] ushered in a new era of cutting-edge applications for elemental carbon. The basic structural unit is graphene,[2] with edge defects and a curvature induced by non-six-membered carbon rings. In chemistry, graphitic forms of carbon have an intriguing potential for catalysis, with a broad spectrum of application covering hydrogenation, oxidation, polymerization, and chlorination reactions.[3, 4] The increased reaction scope has recently been reviewed by Dreyer and Bielawski,[5] who themselves investigated the catalytic activity of graphene oxide in several reactions under mild conditions in the liquid phase.[6] The most prominent example of heterogeneous gasphase catalysis by carbon materials is the selective oxidative dehydrogenation (ODH) of ethylbenzene to styrene [7, 8]—a reaction of high industrial relevance—by nucleophilic oxygen atoms located at the prismatic edges of stacked graphene sheets or at surface defects in the (0001) graphitic surface. For the oxygen-free pathway (DH), the activity of nanocrystalline diamonds coated with defective graphene shells, so-called “bucky diamonds”, even exceed the industrial potassiumpromoted iron catalyst.[9] It is not surprising that the ODH of light alkanes suffers from a much lower selectivity because the CÀH bond in the product molecule is weaker than in the substrate [10]—a common problem in selective oxidation reactions.[11] Point defects filled with electrophilic oxygen likely initiate nonselective combustion pathways. The lowdimensionality of nanostructured carbon materials offers the possibility to modify and optimize the chemical environment of the active sites, and thus to obtain well-defined structure–reactivity correlations. The absence of strongly Lewis-acidic metal cations minimizes the deposition of coke and thus deactivation of the catalyst. This in turn can reduce process costs by not necessitating the addition of steam or periodic regeneration of the catalyst by coke burning.[9] Such progress in ODH and DH catalysis encouraged us to test nanostructured carbon catalysts for oxygen insertion in the selective gas-phase oxidation of acrolein to acrylic acid (AA) as a model reaction [Eq. 1].