Chemically synthesised atomically precise gold clusters deposited and activated on titania. Part II

Abstract

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.

Toward Control of Gold Cluster Aggregation on TiO2 via Surface Treatments

“…It is believed that the processes of aggregation and ligand removal upon deposition of the cluster onto the substrate are concurrent: this has been observed previously in XPS studies of phosphine-protected gold clusters deposited on titanium dioxide. 6,9 Of particular note, our studies show that gold clusters deposited on untreated commercial P-25 undergo ligand removal and aggregation even without specific post-deposition treatment, confirming reproducibility of our previous findings. 9…”

“…These results strongly mirror our previous findings. 9 None−TiO 2 −∆ shows a very low-intensity HBP around 85.3 eV, approximately 0.5 eV higher than for None−TiO 2 −None. The low intensity peak can be attributed to discrete clusters showing interaction with the titania substrate.…”

“…6,9 Our earlier studies have also highlighted the 5 important role support pre-treatment plays in the aggregation of gold clusters. Here, by using atomically-precise Au 9 clusters as a probe sensitive to aggregation, we have been able to focus on exactly how various pre-treatment methods of the same, popular support affect nanoparticle aggregation, both during cluster deposition and upon post-deposition treatments.…”

Factors influencing the catalytic oxidation of benzyl alcohol using supported phosphine-capped gold nanoparticles

“…Our earlier study using synchrotron XPS and NEXAS also confirmed presence of significant fraction of supported Au 9 clusters on TiO 2 . 47 The gold loading of 0.17 wt% on TiO 2 was chosen to minimise the For 0.5 wt% Au 101 /SiO 2 catalyst, a significant agglomeration of gold cluster occurred upon deposition: the gold clusters in the 0.5 wt% Au 101 /SiO 2 -untreated catalyst aggregated to form gold nanoparticles of mean size 3.6 ± 1.2 nm. The observed particle size is almost twice the size of pristine Au 101 cluster and 10 substantially larger than size of gold particles (2.0 ± 0.4 nm) in the case of Au 101 immobilized on TiO 2 at the same surface coverage.…”

Understanding ligand effects in gold clusters using mass spectrometry

“…In comparison with the more widely studied thiolates, phosphines coordinate the gold cores less strongly resulting in a reduced amount of structural distortion and more facile ligand removal to expose the underlying active metal surfaces for applications. [213][214][215] In addition, the charge donating and steric properties of In addition, ESI-MS may be employed to identify mixed ligand clusters that are formed through ligand exchange reactions onto preformed species. CID provides qualitative insight into cluster structure and the relative binding energies of differently substituted phosphines to gold cores.…”