Synchrotron XPS was used to investigate a series of chemically synthesised, atomically precise gold clusters Au(n)(PPh3)y (n = 8, 9 and 101, y depending on the cluster size) immobilized on anatase (titania) nanoparticles. Effects of post-deposition treatments were investigated by comparison of untreated samples with analogues that have been heat treated at 200 °C in O2, or in O2 followed by H2 atmosphere. XPS data shows that the phosphine ligands are oxidised upon heat treatment in O2. From the position of the Au 4f(7/2) peak it can be concluded that the clusters partially agglomerate immediately upon deposition. Heating in oxygen, and subsequently in hydrogen, leads to further agglomeration of the gold clusters. It is found that the pre-treatment plays a crucial role in the removal of ligands and agglomeration of the clusters. ; David P. Anderson, Rohul H. Adnan, Jason F. Alvino, Oliver Shipper, Baira Donoeva, Jan-Yves Ruzicka, Hassan Al Qahtani, Hugh H. Harris, Bruce Cowie, Jade B. Aitken, Vladimir B. Golovko, Gregory F. Metha and Gunther G. Andersson