(771b) Switchable Surfactants for the Preparation of Monodisperse, Surface-Clean Supported Nanoparticle Catalysts and the Impacts of Calcination

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 catalyst properties 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 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 even a low-temperature calcination of surface-clean supported nanoparticles has detrimental effects on nanoparticle size, dispersion, catalytic activity, and surface chemistry. 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, reduces activation energy, and reduces surface hydrophilicity demonstrating that calcination causes changes to catalyst properties beyond those associated with nanoparticle morphology.