Traditional supported nanoparticle synthesis methods require the use of stabilizing ligands to passivate the nanoparticle surface to protect from nanoparticle growth and agglomeration. These ligands often deactivate the catalyst by blocking metallic active sites. Thus, stabilizing ligands typically must be removed prior to use most commonly through a high-temperature annealing step. In traditional systems, it is reported that exposure of nanoparticles to high temperatures causes significant and uncontrollable nanoparticle growth, however; the fundamental causes for this growth have not been investigated.  In a previous work, we showed that ligand-free, supported nanoparticles grew significantly less during calcination than those prepared via traditional methods. In this work, we demonstrate that nanoparticle growth during calcination in traditionally-prepared, supported nanoparticle catalysts is a result of weakened nanoparticle-support attractive forces caused by the presence of the stabilizing ligand that separates the nanoparticle from the support material. Here, silica gel support material was functionalized with triethoxysilane monolayers of varying thicknesses. Ligand-free nanoparticles were then deposited on top of the monolayers by utilizing a switchable surfactant system in which the stabilizing ligand is easily removed from the nanoparticle surface during deposition. The supported nanoparticles were then calcined and imaged with transmission electron microscopy.  Image analysis shows that the nanoparticles separated from the support by the thickest monolayer grew significantly more during calcination than those separated from the support by a shorter distance.  These results demonstrate that nanoparticle growth during calcination in traditionally prepared supported nanoparticle catalysts is a result of weakened nanoparticle-support interactions caused by the presence of stabilizing ligands on the metallic surface. <br/>

Effects of stabilizing ligands on nanoparticle sintering during calcination in supported nanoparticle catalysts

2019 Spring National Meeting

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