The properties of monolayer protected Au nanoclusters are known to be size-dependent, and strongly related to the nature of the protecting ligand. Modification of the surface ligands can be accomplished by a ligand exchange reaction. This represents a valuable pathway for tuning the cluster properties, as well as alternative synthetic pathways of cluster species, which cannot be easily obtained from standard precursor materials. For applications such as catalysis or sensing, the clusters are usually immobilized on metal oxides. For a better understanding of these processes and of Au nanoclusters in general, studying the interaction between cluster and support is crucial. One approach is provided by comparison of ligand exchange reactions of dissolved and deposited clusters. However, so far only ligand exchange reactions with Au nanoclusters in solution have been published. Within this thesis, ligand exchange of immobilized Au11(PPh3)7Cl3 clusters and thiol ligands is reported for the first time. The reactions were studied using three different systems: (1) free clusters in solution, (2) cluster dropcast films on planar Al2O3 or ZnSe and (3) clusters supported on SiO2 or Al2O3 powders. For the reaction in solution, growth of the cluster core from Au11 to Au25 was observed, whereas no major change in size was found for reactions with cluster dropcast films or clusters supported on oxide powder material. Only incomplete exchange was observed for system (1) and (2), with all triphenylphosphine, thiol and chloride being present in the ligand shell of the product. For the powder-supported clusters, the number of exchanged ligands remains to be identified in future work. In addition, ligand exchange in solution, starting from crude Au15 with a large excess of 2-phenylethanethiol was investigated, resulting in the formation of Au20(SC2H4Ph)16. This presents a new, facile approach for synthesizing Au20 clusters in high yield.