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碳纳米管内的限制对催化的影响。

The effects of confinement inside carbon nanotubes on catalysis.

机构信息

State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Zhongshan Road 457, Dalian 116023, China.

出版信息

Acc Chem Res. 2011 Aug 16;44(8):553-62. doi: 10.1021/ar100160t. Epub 2011 Jun 27.

Abstract

The unique tubular morphology of carbon nanotubes (CNTs) has triggered wide research interest. These structures can be used as nanoreactors and to create novel composites through the encapsulation of guest materials in their well-defined channels. The rigid nanotubes restrict the size of the encapsulated materials down to the nanometer and even the sub-nanometer scale. In addition, interactions may develop between the encapsulated molecules and nanomaterials and the CNT surfaces. The curvature of CNT walls causes the π electron density of the graphene layers to shift from the concave inner to the convex outer surface, which results in an electric potential difference. As a result, the molecules and nanomaterials on the exterior walls of CNTs likely display different properties and chemical reactivities from those confined within CNTs. Catalysis that utilizes the interior surface of CNTs was only explored recently. An increasing number of studies have demonstrated that confining metal or metal oxide nanoparticles inside CNTs often leads to a different catalytic activity with respect to the same metals deposited on the CNT exterior surface. Furthermore, this inside and outside activity difference varies based on the metals used and the reactions catalyzed. In this Account, we describe the efforts toward understanding the fundamental effects of confining metal nanoparticles inside the CNT channels. This research may provide a novel approach to modulate their catalytic performance and promote rational design of catalysts. To achieve this, we have developed strategies for homogeneous dispersion of nanoparticles inside nanotubes. Because researchers have previously demonstrated the insertion of nanoparticles within larger nanotubes, we focused specifically on multiwalled carbon nanotubes (MWCNTs) with an inner diameter (i.d.) smaller than 10 nm and double-walled carbon nanotubes (DWCNTs) with 1.0-1.5 nm i.d. The results show that CNTs with well-defined morphology and unique electronic structure of CNTs provide an intriguing confinement environment for catalysis.

摘要

碳纳米管(CNTs)独特的管状形态引发了广泛的研究兴趣。这些结构可用作纳米反应器,并通过将客体材料封装在其限定的通道中,来创造新颖的复合材料。刚性的纳米管将封装材料的尺寸限制在纳米甚至亚纳米尺度内。此外,被封装的分子和纳米材料与 CNT 表面之间可能会发生相互作用。CNT 壁的曲率导致石墨烯层的π电子密度从凹入的内表面转移到凸起的外表面,从而产生电势差。因此,CNT 外壁上的分子和纳米材料可能表现出与 CNT 内部受限分子和纳米材料不同的性质和化学反应性。最近才开始探索利用 CNT 内部表面进行的催化作用。越来越多的研究表明,将金属或金属氧化物纳米粒子限制在 CNT 内部通常会导致与沉积在 CNT 外表面上的相同金属相比,催化活性不同。此外,这种内外活性差异取决于所使用的金属和催化的反应。在本专题介绍中,我们描述了理解将金属纳米粒子限制在 CNT 通道内的基本效应的努力。这一研究可能为调节其催化性能提供新方法,并促进催化剂的合理设计。为此,我们开发了在纳米管内部均匀分散纳米粒子的策略。由于研究人员之前已经证明了可以将纳米粒子插入较大的纳米管中,所以我们特别关注内径(i.d.)小于 10nm 的多壁碳纳米管(MWCNTs)和 1.0-1.5nm i.d.的双壁碳纳米管(DWCNTs)。结果表明,具有明确形态和独特 CNT 电子结构的 CNT 为催化提供了引人入胜的限制环境。

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