(751a) Efficient Removal of Organic Ligands from Supported Nanocrystals By Fast Thermal Annealing Enables Catalytic Studies on Well-Defined Active Phases

A variety of uniform nanocrystals (NCs) and heterostructured materials with different sizes, shapes and compositions can be prepared with nanometer precision using surfactant-assisted organic- or aqueous-based techniques. This nanoscale control over a wide variety of different crystallographic surfaces and compositions is very appealing for catalytic studies because it allows accurate structure-activity relationships and mechanisms to be made. The major drawback of colloidal synthetic methods is that they often require surface-bound surfactants to achieve colloidal stability and to control size and shape. Catalysis relies on having clean surfaces where reactants can bind to surface atoms and undergo chemical transformations into the desired products. Even small amounts of ligands left on the surface might be extremely detrimental for catalysis.

In this contribution, a simple yet efficient method to remove organic ligands from supported nanocrystals is reported for activating uniform catalysts prepared by colloidal synthesis procedures. The method relies on a fast thermal treatment in which ligands are quickly removed in air, before sintering can cause changes in the size and shape of the supported nanocrystals. A short treatment at high temperatures is found to be sufficient for activating the systems for catalytic reactions. We show that this method is widely applicable to nanostructures of different sizes, shapes and compositions. Being rapid and effective, this procedure allows the production of monodisperse heterogeneous catalysts for studying a variety of structure-activity relationships. Highlighted are results on methane steam reforming, where the particle size controls the CO/CO₂ ratio on alumina-supported Pd, demonstrating the applications of the method in catalysis.