摘要/Abstract

由于纳米催化剂的独特催化活性, 因而开发稳定的超细纳米催化剂的制备方法引起了广大科研工作者们的关注. 然而, 复杂的合成过程和结构的不稳定性已经成为纳米催化剂研究和实际应用的瓶颈. 本工作通过原位还原氯铂酸和十甲基五元瓜环(Me₁₀CB[5])构筑的超分子晶体材料, 成功制备了粒径尺寸约为3.0 nm的超细铂纳米粒子. Me₁₀CB[5]的空间限域效应成功抑制铂纳米颗粒的团聚; 瓜环端口羰基氧与铂纳米粒子表面的相互作用防止铂纳米粒子脱落, 确保催化剂的高稳定性. 该铂纳米催化剂对于温和条件下催化加氢硝基苯反应具有优良的催化活性、高稳定性和高化学选择性. 这项工作为纳米催化剂的制备开辟了一条新途径, 为纳米催化剂在电化学、能源科学和环境保护等许多重要领域的应用提供了基础.
关键词: 超分子晶体, Pt纳米颗粒, 硝基芳烃, 催化加氢
The development of a general synthetic approach for stable ultrafine heterogeneous nanocatalysts has attracted extensive attentions worldwide. However, the complex synthetic process and structure unstability have been recognized as the bottleneck of their investigation and practical application. Herein, a convenient and high selective platinum nanocatalyst was developed based from crystalline supramolecular hybrid solid materials. The macrocyclic decamethylcucurbit[5]uril (Me₁₀CB[5]) and [PtCl₆]^2– anions were firstly self-assembled into cyrstalline supramolecular solid in the presence of different alkali metal ions (Li⁺, Na⁺, K⁺). Then, ultrafine platinum (Pt) nanoparticles (NPs) have been successfully synthesized through in-situ reduction of cyrstalline supramolecular assemblies under mild thermal treatment at H₂atmosphere. Uniform Pt NPs (ca.3.0 nm) are produced and deposited on Me₁₀CB[5] substrate to form M-Pt@Me₁₀CB[5] (M=Li⁺, Na⁺, K⁺) composite materials. The obtained Pt NPs are characterized extensively by a range of physical measurements including X-ray powder diffractions (PXRD), thermogravimetric analyses (TGA), inductively coupled plasma emission spectrometer (ICP), X-ray photoelectron spectroscopy (XPS) and transmission electron microscope (TEM). The morphology and size of Pt NPs can be easily tuned through changing the original supramolecular structures. The different interaction between [PtCl₆]^2– and Me₁₀CB[5] capsulates affects the morphology and size of Pt NPs greatly. Such differences in geometric structures of Pt NPs have a significant impact on their catalytic performance. Moreover, the unique confinement effect provided by the supramolecular assembly as well as the special steric effect offered by macrocyclic Me₁₀CB[5] suppresses the growth of Pt NPs during the reduction process. In addition, the atomic level uniform dispersion of Pt ions in ordered crystalline structure of the supramolecular assembly assures the uniform distribution of the final Pt NPs on the intact Me₁₀CB[5], which acts as both a stabilizer and support. The Pt NPs obtained from Na⁺ and K⁺ constructed supramolecular assemblies exhibit high activity and chemoselectivity in catalytic hydrogenation of substituted nitrobenzenes to corresponding anilines under mild conditions. Meanwhile, the final Pt NPs also show an excellent stability in recycle test without dramatic loss of activity. This work demonstrates a novel, high-performance catalyst for the chemoselective hydrogenation reaction, and opens up a new approach for the preparation of nanocatalysts, which can be used in many other important fields, such as electrochemistry, energy science and environmental protection.
Key words: supramolecular crystalline materials, Pt nanoparticles, nitroarenes, catalytic hydrogenation


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