Silver based nanoclusters for applications in catalysis

Research Project, 2015 – 2017

One of the main challenges the world is facing today is the climate change and how to lead the society towards a sustainable future. One avenue towards sustainability is by efficiently converting low value, bio-based waste feedstock into high value chemicals for fuels and other materials by environmentally friendly means. Towards this goal, new and innovative catalysts and catalytic reactions are required, which can reduce the activation barrier for the desired reaction or facilitate new reaction pathways towards the target product. Oxidation reactions are of fundamental importance as they are key transformations in many syntheses at the bench scale as well as the industrial scale. Nevertheless, stoichiometric amounts of toxic reagents and transition metals (e.g. Cr(VI)) are still employed in the production of many important chemical intermediates and products. It is imperative that new catalytic routes for sustainable oxidation transformations are developed which use environmentally benign precursors, are selective for the desired product(s), are energy efficient and limit the generation of unwanted by-products. The selective, partial oxidation of hydrocarbons is a key step in many synthetic processes where the main challenge is to prevent the total oxidation of the precursor, while concurrently increase activity and selectivity for the targeted reaction pathway.

In recent years, there have been several exciting developments with the use of atomically precise gold clusters, which have demonstrated remarkably high activity and selectivity for a wide range of reactions.[1]  The employment of metal clusters in catalysis, with sizes of just a few atoms up to 2 nm, provides a unique and important route to studying catalytically active sites and metal-support interaction in a precise fashion.[2] At the same time, also providing a way to elucidate how minor changes in cluster size, composition and support can influence catalytic activity. Silver is an excellent target catalytic material as traditional silver based catalysts are already relevant for a range of industrially significant partial oxidation reactions, such as ethene epoxidation. The silver based systems have also generated notable interest for applications in automotive emission control where partially oxidized hydrocarbons can be used to remove NOx emissions from the exhaust. Recent work has shown that the activity of supported silver catalysts has a significant dependence on the size of the silver species, with a significantly increased activity and selectivity for small silver species, further motivating our study of silver clusters for catalytic applications. More recently it was demonstrated that small, mass selected, silver clusters have uniquely high activity for alkene oxidation[3] Even though some studies on selective oxidation reactions over ligand protected metal clusters are reported in the literature, there are no reports particularly on silver-based ligand protected clusters for catalysis and not for the use of clusters in lean NOx reduction catalysis.