Switchable Surfactants for the Preparation of Monodisperse, Supported Nanoparticle Catalysts.

Abstract

Synthesis methods for the preparation of monodisperse, supported nanoparticles remain problematic. Traditional synthesis methods require calcination following nanoparticle deposition to remove bound ligands and expose catalytic active sites. Calcination leads to significant and unpredictable growth of the nanoparticles resulting in polydisperse size populations. This undesired increase in nanoparticle size leads to a decrease in catalytic activity due to a loss of total surface area. In this work, we present the use of silylamines, a class of switchable solvents, for the preparation of monodisperse, supported nanoparticles. Silylamines are switchable molecules that convert between molecular and ionic forms by reaction with CO2. Upon addition of an alkane, the switchable solvent behaves as a switchable surfactant (SwiS). The SwiS is used to template nanoparticles to aid in synthesis and subsequently used to release nanoparticles for deposition onto a support material. The use of SwiS allowed for the preservation of nanoparticle diameter throughout the deposition process. Finally, it is demonstrated that supported gold nanoparticle catalysts prepared using SwiS are up to 300% more active in the hydrogenation of 4-nitrophenol than their traditionally prepared analogues.