Unconventional Pd nanoparticles' growth induced by a competitive effect between temperature-dependent coordination and reduction of grafted amino ligands for Heck reaction

A useful and interesting unconventional phenomenon of Pd nanoparticle formation, i.e., significantly inhibited particle growth at elevated temperatures, has been observed for the first time by growing Pd nanoparticles on a type of nonreactor, amino group-functionalized hollow mesoporous silica nanoparticles (amino-HMSNs). Such an unconventional effect is evidenced to be a competitive result between temperature-dependent coordination and reduction action of amino groups on the shell of HMSNs based on a series of experiments of probing the coordination and reduction capability of the amino groups to a Pd precursor K₂PdCl₆. A possible mechanism has been proposed to demonstrate and clarify the unconventional growth of Pd nanoparticles on the shell of amino-HMSNs. The as-synthesized Pd nanoparticles on the amino-HMSNs, therefore, show a tunable temperature-dependent small size range (<10 nm) and high dispersity, and can be used as efficient Heck reaction catalysts. Such a finding of unconventional particle growth effect may offer a novel protocol for particle size modulation during materials design and fabrication.