Synthesis of Ultrasmall Platinum Nanoparticles on Polymer Nanoshells for Size-Dependent Catalytic Oxidation Reactions

It is highly desirable for the synthesis and stabilization of noble metal nanoparticles of uniform, precisely tunable sizes, especially in the range of angstroms to a few nanometers, for many catalytic applications in pursuit of optimal activity and selectivity. Herein, we report a novel strategy for the synthesis of uniform platinum (Pt) nanoparticles of ultrasmall sizes (average size: 0.9-2.3 nm), which are stabilized on hollow polymer nanoshells formed by polymerization of sodium dodecyl benzenesulfonate (SDBS) at the interface of an ethanol/water emulsion. The resulting composite represents a highly active catalyst for effective oxidation of alcohols under ambient conditions. Strong size-dependent catalytic activity of Pt nanoparticles has been revealed in aerobic oxidation of 1-phenylethanol to yield acetophenone, demonstrating a volcano-shape profile, with Pt nanoparticles of ∼1.7 nm showing the highest activity. The size effect has been attributed to the size-dependent d-band electron structure of the Pt nanoparticles. This work reveals the size effect of Pt nanoparticles in general organic oxidation reactions, and thus provides a general methodology and a lot of opportunities in the design of metal-nanoparticle-based catalysts for fine-chemical production.