Integration of Au nanoparticles and metal-organic frameworks in hollow double-shelled nanoreactor for efficient tandem catalysis

Abstract

Tandem reactions make it possible to convert simple raw materials into desired products without separating and purifying intermediates. Integrating metal–organic frameworks (MOFs) and highly reactive metal nanoparticles (NPs) into a tandem system promises the synthesis of a prospective multifunctional nanoreactor due to their synergistic catalytic effects. However, conventional catalysts are difficult to spatially distribute the active sites in a controlled manner, preventing efficient tandem catalysis. Herein, we designed a mesoporous silica-stabilized double-shelled microcapsule nanoreactor for a two-step catalytic Knoevenagel condensation-hydrogenation reaction. The microcapsule is composed of hollow structured ZIF-8 as the inner shell, mesoporous SiO2 as the outer shell, and Au nanoparticles (Au NPs) confined between the two shell layers and is named H-ZIF-8/Au@mSiO2. Furthermore, the nanoreactor exhibited excellent catalytic performance for the two-step reaction under mild conditions, reaching 99.8% conversion of p-nitrobenzaldehyde and 99.6% yield of 2-(4-aminobenzylidene) malononitrile (C). Turnover frequency (TOF) of the nanoreactor was as high as 275.0 h−1. Importantly, the catalytic activity of H-ZIF-8/Au@mSiO2 was maintained after ten cycles due to the protective effect of the double-shell layer. This work exploits a unique structure that integrates multiple active sites through spatial separation, offering possibilities for designing multifunctional nanoreactors for other complex molecules.