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 CO. 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.

Ionic Liquid Aggregation Mechanism for Nanoparticle Synthesis

“…57,58 It has been shown previously that RevILs are effective in the synthesis of monodisperse nanoparticles without the use of additional capping agents and that by leveraging the switchable nature of the silylamine, sizecontrolled and highly active nanoparticles can be deposited onto a support material. 61,62 Nanoparticle synthesis in RevIL systems was hypothesized to proceed through a reverse micelle templating mechanism, in which the ion pairs of the IL selfassemble into organized structures possessing an aqueous core. The basis for this hypothesis came from the utilization of methyl orange as a micellar probe molecule.…”

Triethylamine–Water as a Switchable Solvent for the Synthesis of Cu/ZnO Catalysts for Carbon Dioxide Hydrogenation to Methanol

“…There are a wide variety of switchable systems that have been applied, using switchable hydrophilicity [18,21], switchable surfactants [22] and switchable water [23]; where the additive increases its ionic strength under different atmospheres and can be used to precipitate out compounds. The switching of the solvent properties is relatively slow using low pressure gases, although in theory this could be used as a way of precipitating a dissolved component from solution.…”

Preparation and Application of CO2-Triggered Switchable Solvents in Separation of Toluene/n-Heptane

“…Novel extraction techniques based on reversible response materials may be able to mitigate many of the problems that are frequently encountered in common industrial processes, such as the difficulty associated with solvent recovery and high costs. Reversible response materials are compounds having molecular structures that can be changed in response to external conditions, and can include surfactants, , catalysts, gels, − polymers, − and solvents. The properties of these materials can be significantly different before and after the structural change, and so they may be easily separated from other substances.…”