Desing of Homometallic Nanosites-Confined Hierarchical and Bulk Zeolites for Tandem Catalysis

The ability to confine multiple metal species within the cage and pore structures of a zeolite as isolated subnanometric metal nanosites (MNS), thereby preventing the formation of bimetallic nanoclusters, is a significant objective in chemical science and catalytic research. In this study, a general synthesis strategy is presented by integrating the ethylenediamine (en) ligand protection method into the seed-assisted crystallization approach. This strategy is exemplified by subnanometric catalyst systems in which hierarchical and bulk mordenite zeolites are decorated with individual MNS of Pd–Co, Pd–Ni, and Pd–Cu metal pairs and the combinations of Pd–Co–Ni metals. For this purpose, a hierarchical zeolite synthesis was optimized, in which a tetra-quaternary ammonium structure-directing agent (SDA) acted as a mesostructure-directing agent, while bulk mordenite served as a microstructure-directing seed. By incorporating the en-ligand protection method into this synthesis procedure, metal nanocatalysts were confined into the MOR framework, forming nanosheets approximately 20 nm in width and 10 nm in thickness, and subsequently stabilized by thermal treatment. These monometallic M@hMOR products were used in the synthesis of catalysts containing multiple metal species in the role of seed as a source of other metal species. In the synthesis of bulk forms of the same catalysts, only SDA was removed from the procedure.