(198j) The Synthesis of Monodisperse, Supported Nanoparticle Catalysts with Switchable Surfactants and the Effects of Calcination on Nanoparticle Characteristics

Established methods of preparing supported nanoparticle catalysts do not provide sufficient control over nanoparticle morphology. Classical methods typically require organic surfactants to passivate the nanoparticle surface to limit undesired size changes. Stabilizing ligands bound to the nanoparticle surface compete with reagents for active sites and typically significantly hinder catalytic activity. Commonly used methods of ligand removal, such as calcination, have detrimental effects on the catalyst as exposure to high temperatures often results in significantly increased nanoparticle size and, thus, decreased total surface area for catalysis. Previously, we demonstrated a novel method for synthesizing highly active, monodisperse, supported nanoparticles using a switchable surfactant (SwiS) system. In this method nanoparticle size is finely controlled throughout synthesis and deposition. Here, we show with X-ray photoelectron spectroscopy (XPS) that supported nanoparticles prepared with SwiS are completely surface-clean after deposition, eliminating the need for any traditional activation steps such as calcination. Additionally, it is demonstrated that a low-temperature calcination at 230°C of surface-clean supported nanoparticles has detrimental effects on nanoparticle size, dispersion, and catalytic activity. Supported nanoparticles prepared with SwiS are up to 700% more active in the hydrogenation of 4-nitrophenol than their calcined counterparts. Further, calcination results in the formation of an induction time in 4-nitrophenol reduction, demonstrating that calcination causes surface structure rearrangements unfavorable for catalysis.