SWITCHABLE SURFACTANTS FOR THE PREPARATION OF SUPPORTED NANOPARTICLE CATALYSTS

Kristin Nicole Bryant

Synthesis methods for the preparation of monodisperse, supported nanoparticles remain problematic. Traditional synthetic methods require the use of stabilizing agents (i.e. ligands, surfactants, etc.) to prevent over growth and aggregation of nanoparticles. However, the presence of these stabilizers on catalytic surfaces can be detrimental to activity and therefore are typically removed via a high-temperature calcination. While necessary for ligand removal, calcination leads to significant and unpredictable growth of the nanoparticles, resulting in a decrease in total surface area of the active phase and ultimately a decrease in catalytic activity. 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 via reaction with CO2. Upon addition of an alkane, the switchable solvent behaves as a switchable surfactant (SwiS) that can be used to stabilize nanoparticles throughout synthesis and subsequently used to release nanoparticles for deposition onto a support material. The use of SwiS allows for the preservation of nanoparticle diameter throughout the deposition process to an extent that is not achieved using traditional methods. We demonstrate using X-ray photoelectron spectroscopy (XPS) that supported nanoparticles prepared with SwiS are surface-clean immediately after deposition, eliminating the need for traditional activation steps. It is shown that even low-temperature thermal activations have detrimental effects on the catalyst properties beyond those associated with changes in surface area. For this reason, supported nanoparticle catalysts prepared using SwiS are up to 300% more active in the hydrogenation of 4-nitrophenol than their traditionally prepared analogs. Previous work hypothesized nanoparticles synthesized with SwiS are formed via a reverse micelle mechanism in which nanoparticles are stabilized and templated within the aqueous core of the organized structures. In this work, diffusion-ordered nuclear magnetic resonance spectroscopy (DOSY-NMR) is used to demonstrate that nanoparticles synthesized with SwiS are not formed through a reverse micelle mechanism but rather a “switchable aggregation” of the ionic liquid in solution. Manipulation of the ionic liquid concentration and structure affords excellent control over the resulting nanoparticle size in SwiS systems.

SWITCHABLE SURFACTANTS FOR THE PREPARATION OF SUPPORTED NANOPARTICLE CATALYSTS

Files and links (1)

Abstract

Metrics

Details