Atomically Precise Gold Catalysis - Atomically-Precise Methods for Synthesis of Solid Catalysts - page 96

d n 9 r 4 n g | 7

Figure 4.5 Proposed reaction mechanism for CO oxidation on a commercial
Au/TiO 2 catalyst.
(Reproduced with permission from ref. 33, Copyright Elsevier, 2013).

.

mechanism of epoxidation still need to be addressed. The development of
atomically precise gold catalysts now offers a unique opportunity to study
the fundamental aspects of gold catalysis, in particular regarding how
structure and the electronic properties of nanoclusters influence their
catalytic performance.
Au 25 (SR) 18 nanoclusters immobilized on hydroxyapatite support was re-
ported by Tsukuda and co-workers 35 for the selective oxidation of styrene in
toluene. They achieved

100% conversion of styrene with 92% selectivity
towards epoxide product. Recently, Jin and co-workers 37 have reported
selective oxidation of styrene using three different sized nanoclusters
(i.e., Au 25 ,Au 38 and Au 144 ). They found that the catalytic activity of the
catalysts exhibited a strong dependence on the cluster size. In general,
smaller nanoclusters exhibited higher conversions. With a catalyst loading
of

B

1% for all the three cluster sizes, the Au 25 nanoclusters showed the
highest conversion of styrene, followed by Au 38 and Au 144 respectively. They
also compared the catalysis results with larger crystalline

B

3nmsizedgold
nanocrystals which were not atomically monodisperse and were capped by
octylthiolates. The 3-nm gold nanocrystals showed a much lower con-
version. They investigated the effect of the nature of thiolate ligands, aro-
matic versus long-chain alkanethiolates, and found that the chemical

B