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

David P Anderson,Baira Donoeva,Hugh H Harris,Jade B Aitken,Rohul H Adnan,Gregory F Metha,Vladimir B Golovko,Hassan Al Qahtani,Gunther G Andersson,Oliver Shipper,Jan-Yves Ruzicka,Jason F Alvino,Bruce Cowie

doi:10.1039/c3cp52497c

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.

Highlights

Gold particles with a size reduced below 5 nanometres are known to be catalytically active.[1,2,3] it has been demonstrated that the onset of catalytic activity of gold often coincides with the loss of metallic properties of Au nanoparticles at around 1.5–2 nm
The aim of the present work is an investigation of the influence of oxidative treatments on the size and environment of gold clusters deposited on untreated titania
The X-ray photoelectron spectroscopy (XPS) results from the 0.08 wt% Au samples are effectively the same as that observed for the 0.17 wt% Au, indicating that a two-fold reduction in the loading does not affect the behaviour of gold clusters

Summary

Introduction

Gold particles with a size reduced below 5 nanometres are known to be catalytically active.[1,2,3] it has been demonstrated that the onset of catalytic activity of gold often coincides with the loss of metallic properties of Au nanoparticles at around 1.5–2 nm. This size-threshold is established for both naked clusters prepared under UHV conditions[4] and chemically-synthesised[5,6] well-defined metal nanoparticles immobilized onto inert supports. Removal of ligands is often postulated as a necessary step for making the adsorption sites at the surface of the clusters catalytically active

Objectives

Results

Conclusion