Nature. 2016 Jul 7;535(7610):131-5. doi: 10.1038/nature18284. Epub 2016 Jun 29.
Three-dimensional graphene architectures with periodic nanopores—reminiscent of zeolite frameworks—are of topical interest because of the possibility of combining the characteristics of graphene with a three-dimensional porous structure. Lately, the synthesis of such carbons has been approached by using zeolites as templates and small hydrocarbon molecules that can enter the narrow pore apertures. However, pyrolytic carbonization of the hydrocarbons (a necessary step in generating pure carbon) requires high temperatures and results in non-selective carbon deposition outside the pores. Here, we demonstrate that lanthanum ions embedded in zeolite pores can lower the temperature required for the carbonization of ethylene or acetylene. In this way, a graphene-like carbon structure can be selectively formed inside the zeolite template, without carbon being deposited at the external surfaces. X-ray diffraction data from zeolite single crystals after carbonization indicate that electron densities corresponding to carbon atoms are generated along the walls of the zeolite pores. After the zeolite template is removed, the carbon framework exhibits an electrical conductivity that is two orders of magnitude higher than that of amorphous mesoporous carbon. Lanthanum catalysis allows a carbon framework to form in zeolite pores with diameters of less than 1 nanometre; as such, microporous carbon nanostructures can be reproduced with various topologies corresponding to different zeolite pore sizes and shapes. We demonstrate carbon synthesis for large-pore zeolites (FAU, EMT and beta), a one-dimensional medium-pore zeolite (LTL), and even small-pore zeolites (MFI and LTA). The catalytic effect is a common feature of lanthanum, yttrium and calcium, which are all carbide-forming metal elements. We also show that the synthesis can be readily scaled up, which will be important for practical applications such as the production of lithium-ion batteries and zeolite-like catalyst supports.
具有周期性纳米孔的三维石墨烯结构——类似于沸石骨架——由于有可能将石墨烯的特性与三维多孔结构结合在一起，因此受到了关注。最近，人们通过使用沸石作为模板和可以进入狭窄孔径的小分子烃来合成这种碳。然而，烃的热解碳化（生成纯碳的必要步骤）需要高温，并且会导致在孔外非选择性地沉积碳。在这里，我们证明嵌入沸石孔中的镧离子可以降低乙烯或乙炔碳化所需的温度。通过这种方式，可以在沸石模板内选择性地形成类石墨烯的碳结构，而不会在外部表面沉积碳。碳化后沸石单晶的 X 射线衍射数据表明，对应于碳原子的电子密度沿沸石孔壁产生。去除沸石模板后，碳骨架表现出比无定形中孔碳高两个数量级的电导率。镧催化允许在直径小于 1 纳米的沸石孔中形成碳骨架；因此，可以用对应于不同沸石孔径和形状的各种拓扑结构再现微孔碳纳米结构。我们展示了用于大孔沸石（FAU、EMT 和β）、一维中孔沸石（LTL）甚至小孔沸石（MFI 和 LTA）的碳合成。这种催化作用是镧、钇和钙的共同特征，它们都是形成碳化物的金属元素。我们还表明，这种合成可以很容易地扩大规模，这对于锂离子电池和沸石样催化剂载体等实际应用将非常重要。
