Ligand and support effect on supported gold nanoclusters in selective hydrogenation of alkynes

Abstract

Hydrogenation reactions are integral to many industries, from oil and gas to pharmaceuticals.Traditionally, platinum group metals have been used as catalysts, offering satisfactory conversion rates. However, these catalysts often require modification or poisoning to achieve desired selectivity, reducing overall efficiency. Additionally, a detailed atomic-level understanding of the catalytic process is still lacking, necessitating exploring new catalytic systems.Ligand-protected gold nanoclusters represent a relatively novel class of atomically precisematerials with highly tunable properties. The choice of size of the cluster, support material,and possible heteroatom doping can significantly affect the structure, stability, and properties of these clusters. One promising application of these metal nanoclusters is in catalysis, where they provide well-defined active sites, making them ideal for studying the structure-reactivity relationship.This thesis explores supported gold nanoclusters as catalysts for the selective semihydro-genation of alkynes, more specifically phenylacetylene to produce styrene. The study focuseson the effect of silver doping in Au25 nanoclusters and the role of different support materials, namely Hydrotalcite (HT) and Zeolite (Zeo), in both gas and liquid phase reactions.A combination of catalytic studies and X-ray absorption fine structure (XAFS) analysis was employed to examine the catalysts’ structural stability and identify the reaction dynamics atthe active sites.The results indicate a strong correlation between the cluster-support interaction and catalytic activity, showing that both Au25 and Au11 offered higher yields with different supports.Additional trends were observed in conversion while comparing liquid and gas phase reactions. The introduction of Ag into the structure of Au25 did not enhance the catalytic activity,though supporting these clusters on Zeo offered higher stability, as revealed by the XAFSanalysis.The findings highlight the critical role of nanocluster size, doping, and support material ininfluencing catalytic activity and stability.