Sinter-resistant gold nanoparticles encapsulated by zeolite nanoshell for oxidation of cyclohexane

Abstract

A large surface-to-volume ratio is a prerequisite for highly effective heterogeneous catalysts. Making catalysts in the form of nanoparticles provides a good way to realize this aim. However, agglomeration of such nanoparticles during the preparation and catalytic reaction remains a formidable problem. In the present work we have synthesized gold nanoparticles-coated with different zeolites, ZSM-5 and MCM-22, by hydrothermal route. The method adopted is generic where gold nanoparticles were firstly encapsulated by silica utilizing Stober's process and further these silica coated gold nanoparticles are transformed into Au@MCM-22 and Au@ZSM-5 by modified hydrothermal route. The sinter resistant gold nanoparticle core encapsulated by zeolitic nanoshell showed enhanced conversion for the test reaction of oxidation of cyclohexane to KA-oil, which is an important intermediate in the production of nylon-6 and nylon-6,6. The nano-capsules act as bifunctional catalyst, with the nanoparticles prevented from agglomeration during synthesis or catalytic applications, and the zeolitic-shell enhanced conversion and reusability of the nano-catalyst.