Chen Fengfeng, Shen Kui, Yang Yitao, Huang Haigen, Li Yingwei
State Key Laboratory of Pulp and Paper Engineering, School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, China.
ACS Appl Mater Interfaces. 2020 Oct 28;12(43):48691-48699. doi: 10.1021/acsami.0c15344. Epub 2020 Oct 19.
The facile fabrication of porous solid acids is highly desired for replacing hazardous liquid acids for many acid-catalyzed reactions in the industry. Herein, we present a bottom-up strategy to construct ultrastable mesoporous CrO/SiO nanohybrids (denoted as Meso-Cr-Si-O) with highly dispersed Lewis acid sites by pyrolysis of a SiO@MIL-101 precursor prepared via nanocasting by a reverse double-solvent approach, which can guarantee the efficient encapsulation of SiO nanoparticles (NPs) inside the MIL-101 pores. The pore environment of Meso-Cr-Si-O can be well tuned by simply controlling the amount of silica within the MIL-101 pores and the pyrolysis temperature. Pyridine adsorption experiments demonstrate that the density of Lewis acidic sites in the obtained Meso-Cr-Si-O is much higher than that of MIL-101-derived CrO NPs. Benefitting from its highly mesoporous nanostructure with abundant acid sites, the optimal Meso-Cr-Si-O exhibits a significantly improved catalytic activity for the Lewis-acid-catalyzed Meerwein-Ponndorf-Verley reduction of cyclohexanone with 4.5 times higher yield of cyclohexanol than that of the MIL-101-derived CrO NPs, representing the first efficient CrO-based catalytic system for this reaction.
在工业中，许多酸催化反应都迫切需要简便地制备多孔固体酸来替代危险的液体酸。在此，我们提出一种自下而上的策略，通过对经由反向双溶剂法纳米浇铸制备的SiO@MIL-101前驱体进行热解，构建具有高度分散路易斯酸位点的超稳定介孔CrO/SiO纳米杂化物（记为Meso-Cr-Si-O），这能够确保SiO纳米颗粒（NPs）有效封装在MIL-101孔内。通过简单控制MIL-101孔内二氧化硅的量和热解温度，可以很好地调节Meso-Cr-Si-O的孔环境。吡啶吸附实验表明，所得Meso-Cr-Si-O中路易斯酸位点的密度远高于MIL-101衍生的CrO NPs。得益于其具有丰富酸位点的高度介孔纳米结构，最佳的Meso-Cr-Si-O对环己酮的路易斯酸催化Meerwein-Ponndorf-Verley还原反应表现出显著提高的催化活性，环己醇产率比MIL-101衍生的CrO NPs高4.5倍，代表了该反应首个高效的基于CrO的催化体系。
