Effects of Mono-, Di- and Tri-Amino Groups on Physicochemical Properties of Palladium Ions Supported by Dendritic Mesoporous Silica Nanospheres

Abstract

Palladium(Pd)-based catalysts have been broadly applied in modern industry. The ideal ones should be robust enough against leaching, load Pd to the maximum degree, and possess outstanding dispersity against aggregation. As for SiO₂-supported Pd catalysts, aminosilane coupling reagents have been commonly utilized to introduce interfacial self-assembled layers which can chemically bond SiO₂ substrates with siloxy (-SiOH) groups and firmly link Pd with amino groups. However, up to now, the influences of variable aminoalkyl chains on physicochemical properties and catalytic performances of palladium ions (Pd(II)) supported by dendritic mesoporous silica nanospheres (DMSNs) have not been contrasted and revealed. In this work, three types of aminosilane-functionalized DMSNs-based Pd(II) catalysts have been prepared, including DMSNs-1N-Pd(II) within mono-amino group, DMSNs-2N-Pd(II) with di-amino, and DMSNs-3N-Pd(II) with tri-amino ones. For the first time, the effects of mono-, di- and tri-aminosilanes on their basic properties have been thoroughly exploited, including the morphologies, architectures, compositions of crystal phases, surface functional groups, loading contents of Pd, Pd(II) and Pd(0) percentages, etc. Moreover, catalytical performances have been evaluated by Pd-catalyzed Heck reaction as well.