Atomically Precise Gold Nanoclusters: Synthesis and Catalytic Application - Atomically-Precise Methods for Synthesis of Solid Catalysts - page 131

d n 9 r 4 n g | 3

Figure 5.7 Reversible conversion between [Au 25 (SR) 18 ] 0 and [Au 25 (SR) 18 ] .
Adapted with permission from ref. 29.

also found in the case of the water-soluble Au 25 (SG) 18 nanocluster. Both the
organic-solubleandtheaqueousAu 25 (SR) 18 (where R ¼ -CH 2 CH 2 Ph, -C 6 H 13 or
-G (glutathione)) have been utilized in catalytic work.

5.5.2 Catalytic Oxidation
The activation of oxygen (O 2 ) plays an important role in the gold nanocluster-
catalyzed selective oxidation processes. 1,30 As discussed above, Au n (SR) m
nanoclusters can interact with oxidants (e.g., O 2 ,H 2 O 2 , etc.) even at room
temperature. 29 The oxidation reactivity of Au 25 (SR) 18 nanoclusters inspired
us to pursue their catalytic application. Below we discuss the various oxi-
dation reactions that have been found to be catalyzed by gold nanoclusters.

.

5.5.2.1 Catalytic Oxidation of CO to CO 2
CO oxidation has been extensively investigated in nanogold catalysis. 1,31 In
previous work, the support was found to largely affect the nanogold activity,
and TiO 2 is generally the most effective support in the nanogold catalyzed
oxidation of CO to CO 2 . When it comes down to the case of Au n (SR) m
nanoclusters, surprisingly Nie et al. 32 found that the Au 25 (SR) 18 /TiO 2 catalyst
was the least active, which had no catalytic activity even up to 200 1C
(Figure 5.8a). By comparing several oxide supports, Au 25 (SR) 18 /CeO 2 was
found to exhibit moderate activity (CO conversion onset temperature 60 1C,
62% conversion at 160 1C). These results imply that some striking differ-
ences exist between conventional (bare) Au/TiO 2 catalysts 31 and ligand-on
Au 25 (SR) 18 /TiO 2 catalyst. 32
To enhance the catalytic activity of Au 25 (SR) 18 /TiO 2 , pretreatment was
performed. Significantly, Nie et al.

found that pretreatment of the