216
13 Metal Cluster Catalysis
On the other hand, to employ the superatom concepts to quantitatively identify
electronic energy states for promising catalysts to investigate iso-valent species is also
important to determine if the superatomic concepts carry over to catalytic reaction
behavior. This is also an important class of catalysts likely without precious metals.
Presented in this chapter are several classes of studies using clusters to unravel
fundamental catalytic reaction mechanisms, including a few of those using identified superatoms and the concepts of element mimics to tailor catalysts with desired
functionality [35].
13.2 Gold Cluster Catalysis
Although bulk gold is known to be chemically inert metal, gold nanoparticles have
demonstrated powerful catalytic capability in various chemical reactions, such as
in CO oxidation [36], epoxidation [37, 38], selective hydrogenation/reduction [39],
C–C bond formation [40], and water-gas shift [41]. There are also many examples of
catalysis in solution by cationic complexes of gold, in particular, gold catalysts such
as Au
I and Au
III salts are powerful for C–H activation [42], in which the Au
I /Au
III
catalytic cycle is very likely to be involved [43]. Cationic, neutral, and anionic gold
clusters and complexes have also been identified in supported gold catalysts [23, 44,
45]. Among these catalytic reactions, it was suggested that gold may switch its role
between electron donator and electron acceptor; for instance, doping atomic clusters
(e.g., metal oxide clusters) with gold atoms may cause charge redistribution within
the clusters during reactions. Thereby, the correlative reactivity such as the C–H
activation which depends heavily on the effects of local charges can be effectively
tuned by the gold-based catalysis (Fig. 13.1) [1, 23, 27, 42, 44–46]. Gold is known as
a very versatile redox catalyst [36, 47–57]. It also shows potential for both selective
and nonselective oxidation of hydrocarbons, for methanol synthesis by hydrogenation
of carbon monoxide or dioxide, and for the reduction of nitric oxide by hydrogen,
propene, or carbon monoxide, etc. [55]. Besides, the supported gold chloride was
found to be the most active catalyst for the hydrochlorination of ethyne, and the
hydrogenation of unsaturated hydrocarbons also occurs on highly dispersed gold
catalysts [55].
13.2.1 Catalysis of Supported Gold Clusters
Together with the bonding nature of gold, the Au clusters and Au-contained
heteroatomic systems have been extensively studied [58–76]. As well as the interesting relativistic effect involved in gold clusters [77–79], extensive investigations
have been reported on the catalysis of gold clusters, including those (both homogeneous and heterogeneous) with gold as a key component [80–88]. The catalysis
13 Metal Cluster Catalysis
On the other hand, to employ the superatom concepts to quantitatively identify
electronic energy states for promising catalysts to investigate iso-valent species is also
important to determine if the superatomic concepts carry over to catalytic reaction
behavior. This is also an important class of catalysts likely without precious metals.
Presented in this chapter are several classes of studies using clusters to unravel
fundamental catalytic reaction mechanisms, including a few of those using identified superatoms and the concepts of element mimics to tailor catalysts with desired
functionality [35].
13.2 Gold Cluster Catalysis
Although bulk gold is known to be chemically inert metal, gold nanoparticles have
demonstrated powerful catalytic capability in various chemical reactions, such as
in CO oxidation [36], epoxidation [37, 38], selective hydrogenation/reduction [39],
C–C bond formation [40], and water-gas shift [41]. There are also many examples of
catalysis in solution by cationic complexes of gold, in particular, gold catalysts such
as Au
I and Au
III salts are powerful for C–H activation [42], in which the Au
I /Au
III
catalytic cycle is very likely to be involved [43]. Cationic, neutral, and anionic gold
clusters and complexes have also been identified in supported gold catalysts [23, 44,
45]. Among these catalytic reactions, it was suggested that gold may switch its role
between electron donator and electron acceptor; for instance, doping atomic clusters
(e.g., metal oxide clusters) with gold atoms may cause charge redistribution within
the clusters during reactions. Thereby, the correlative reactivity such as the C–H
activation which depends heavily on the effects of local charges can be effectively
tuned by the gold-based catalysis (Fig. 13.1) [1, 23, 27, 42, 44–46]. Gold is known as
a very versatile redox catalyst [36, 47–57]. It also shows potential for both selective
and nonselective oxidation of hydrocarbons, for methanol synthesis by hydrogenation
of carbon monoxide or dioxide, and for the reduction of nitric oxide by hydrogen,
propene, or carbon monoxide, etc. [55]. Besides, the supported gold chloride was
found to be the most active catalyst for the hydrochlorination of ethyne, and the
hydrogenation of unsaturated hydrocarbons also occurs on highly dispersed gold
catalysts [55].
13.2.1 Catalysis of Supported Gold Clusters
Together with the bonding nature of gold, the Au clusters and Au-contained
heteroatomic systems have been extensively studied [58–76]. As well as the interesting relativistic effect involved in gold clusters [77–79], extensive investigations
have been reported on the catalysis of gold clusters, including those (both homogeneous and heterogeneous) with gold as a key component [80–88]. The catalysis