A generalized strategy for the ultrafast encapsulation of metal oxide nanoclusters into zeolites

Abstract

Encapsulating metal oxide nanoclusters into zeolites creates bifunctional catalysts that combine the high activity of metal oxide nanoclusters and unique shape selectivity of zeolites. The one-pot encapsulation in the process of zeolite synthesis is preferable for its high efficiency; however, this method is largely hindered by the mismatch in the time scale between the fast precipitation of metal species and the slow crystallization of zeolites. We herein put forward a generalized strategy to address the mismatch issue, which can lead to the ultrafast, one-pot encapsulation of metal oxide nanoclusters into zeolites in just a few minutes. The encapsulation of nanoclusters of different metal oxides, including CuO, ZnO, NiO and CoO, into a pure-silica MFI zeolite (silicalite-1) was used to prove the concept. Taking the CuO case as an example, the factors influencing the ultrafast encapsulation, such as synthesis temperature, aging time and precursor composition, were systematically examined. The CuO@silicalite-1 zeolite synthesized via the ultrafast encapsulation method showed satisfactorily high activity and stability in the dehydrogenation of ethanol to acetaldehyde. On the basis of the ultrafast encapsulation, we further established the continuous-flow encapsulation with a high space–time yield, which offers a promising route for the large-scale preparation of this class of catalysts.