Recent advances in the synthesis, characterization, and catalytic consequence of metal species confined within zeolite for hydrogen-related reactions

Zeolites-encapsulated metal and metal oxide species are important heterogeneous catalysts. They give performances that steadily outperform traditional supported catalysts in many important reactions and have become a research hotspot. Remarkable achievements have been made with respect to the synthesis, characterization, and performances of metal species (typically metal and metal oxide clusters) confined in zeolites. The development in the strategies for the encapsulation of metal species including post-treatment and in situ synthesis method are introduced and compared. For the characterization of zeolite-encapsulated metal catalysts, the structural and surface properties of metal species are studied by several useful techniques, such as electron microscopy, X-ray absorption (XAS), Fourier transform infrared spectroscopy of CO (FTIR-CO), and chemisorption, which confirm the successful confinement of metal species in zeolites and their unique physiochemical properties. In addition, the encapsulation fraction can be determined by a probe molecular titration reaction. For the catalytic performance of zeolite-encapsulated metal catalysts, the activity, selectivity, and stability are emphasized. Finally, applications of zeolite-encapsulated metal catalysts in hydrogen-related reactions are summarized. Keywords: Zeolite; Encapsulation; Metal species; Synthesis; Characterization; Catalytic performance. We summarize and discuss the progress in the synthesis and characterization of zeolite-encapsulated metal catalysts, and the consequences of encapsulation in terms of activity, selectivity, and stability for the hydrogen-related catalytic reactions.