State-of-the-art strategies for the synthesis of zeolite-encapsulated subnanometric metal clusters

Abstract

The review is devoted to the analysis of the strategies used for the design and preparation of zeolite-encapsulated subnanometric metal clusters. Nowadays this topic is often considered as one of the most rapidly developing in heterogeneous catalysis. On the one hand, it is due to the great fundamental interest to the structure and properties of such materials and, on the other hand, it is related to their unique catalytic properties and great perspectives for their application in a number of important heterogeneous catalytic reactions aimed at the conversion of non-conventional feedstocks and building a low-carbon (decarbonized) economy. The application of metal-containing zeolites allows the challenges related to the development of novel tandem processes, which require simultaneous proceeding of several catalytic reactions over one catalyst, to be addressed. The coupling of zeolites and metals in a single catalyst allows for fine-tuning the properties of tandem catalysts both by engineering the nature, state and localization of the metal active sites, and by mastering the unique porous structure of the zeolites with active sites of different nature. The contribution presents the methodological aspects of the synthesis of the described systems, highlighting their advantages, limitations and problems related to their applications. In particular, both novel methods of metal encapsulation and conventional ones known for decades are analyzed and systematized. Special attention is paid to the conditions under which simple conventional methods allow the encapsulation of nanoclusters in zeolite. As a result, the recommendations on the most preferable approaches for obtaining specific zeolite–metal combinations are given and promising directions for the development of synthesis methods are highlighted.