Synthetic Chemistry and Multifunctionality of an Amorphous Ni-MOF-74 Shell on a Ni/SiO₂ Hollow Catalyst for Efficient Tandem Reactions

Abstract

Core–shell particles, a unique class of functional materials, have received increasing research interest for the past 2 decades owing to their exceptional performance in many technological fields. For catalysis, coating a core catalyst with a shell could effectively enhance core stability and catalytic activity, provide reactant/product selectivity, add stimuli-responsive smart features, and so forth. Despite the rapid advancement made for core–shell materials, it is rare to see such shells displaying more than one or two functional roles in a single reaction system. Herein, we have developed an amorphous Ni-MOF-74 coating process for a hollow sphere made of silica-supported Ni nanoparticles. Multifunctional catalysts prepared by integration of metal–organic frameworks (MOFs) and metals were mainly limited to noble metals, whereas our catalyst successfully integrates highly dispersed transition-metal nanoparticles with MOFs. Our MOF shell possesses four distinct functionalities for tandem imination: to prevent detachment and segregation of catalytic Ni nanoparticles, to act as an acid catalyst, to avoid over-hydrogenation of the desired product via molecular sieving, and to suppress the undesired byproduct via promoting competitive reaction with a size-sieveable product. As a result, this MOF shell enables Ni/SiO2 to serve as a potential alternative to noble metal catalysts in this tandem reaction, and chemical transformation of the reactant substrate to a targeted product can be achieved more effectively.