active for liquid-phase oxidations. In contrast to the Au/reducible MO x catalysts,
size of Au NPs and acid-base properties of MO x become more important for Au/nonreducible MO x catalysts. Low-coordinated sites on the Au NPs would be the active
sites for O 2 activation and the adsorption sites of the substrate [77]. Au/γ-Ga 2 O 3
catalyzed base-free oxidation of benzyl alcohol in mesitylene to give benzaldehyde
with 99% selectivity at >99% conversion [40]. In addition, the catalytic activity of
Au/γ-Ga 2 O 3 exceeded those of Au/TiO 2 , Au/CeO 2 , and Au/Fe 2 O 3 . The remarkable
high activity was speculated by dehydrogenation activity, and temperatureprogrammed surface reaction (TPSR) of 2-propanol was examined for Au/γ-Ga 2 O 3 .
As the temperature increased, 2-propanol adsorbed on the catalysts was converted to
acetone together with the formation of H 2 . Accordingly, more intense H 2 desorption
peak was observed for γ-Ga 2 O 3 itself than those observed for Au/CeO 2 (the H 2
desorption was not observed for Au/TiO 2 and Au/Fe 2 O 3 ). In addition, H 2 desorption
peak for Au/γ-Ga 2 O 3 was shifted to lower temperature from that for γ-Ga 2 O 3 itself,
indicating that γ-Ga 2 O 3 has high activity for the dehydrogenation and Au NPs
facilitate the reaction. Ga-Al mixed oxides were also examined and Au/Ga 3 Al 3 O 9
showed the higher activity than Au/Ga 2 O 3 and other Au/Ga x Al y O z catalysts. The
catalytic activity order was consistent to the order of dehydrogenation activity which
was elucidated by the amount of desorbed H 2 from 2-propanol by TPSR [41]. Au
NPs supported on MgO [43], Mg x Al y O z , Cu-containing Mg x Al y O z spinel-type
oxides [44, 45], and MgFe 2 O 4 [46] also promoted the oxidation of alcohols in the
absence of base. For Cu-containing Mg x Al y O z , the introduction of redox-active Cu
might change the surface basicity, affect the electronic state of Au, and add the redox
properties of Cu in some extent, which led to the improved activity from
Au/Mg x Al y O z without Cu [44].
2.3 Non-oxides
2.3.1 Role of Supports
Metal hydroxides, phosphates, and carbonates are classified as non-oxides inorganic
supports. Au NPs on basic hydrotalcite (HT: Mg 6 Al 2 (OH) 16 CO 3 ÁnH 2 O) exhibited
high catalytic activity for oxidation of various alcohols in the absence of base
[47, 48]. Au/HT exhibited superior activity and selectivity (99% at 99% conversion)
to Au/Al 2 O 3 and Au/MgO, reported by Kaneda et al. [47]. Au/MgCr-HT (Cr
3+
substituted HT) improved the catalytic activity from Au/HT [49]. The oxidation of
a primary aliphatic alcohol, 1-octanol, did not proceed to give octanal over Au/HT in
the absence of base [47] but proceed over Au/MgCr-HT, whereas the conversion
was lower than those for aromatic alcohols. Au/MgCr-HT also recorded extremely
high TOF (81,000 h
À1 ) for solvent-free oxidation of 1-phenyl ethanol to give
acetophenone (Table 2).
A series of Au clusters (ca. 1.5 nm in diameters) on M 3 Al-LDH (M ¼ Ni, Co,
Mg) exhibited high catalytic activity for base-free oxidation of 1-phenylethanol to
give TOF of 46,500 h
À1 over Au/Ni 3 Al-LDH (Table 2) [50]. Both strong acidic and
10
T. Ishida et al.
size of Au NPs and acid-base properties of MO x become more important for Au/nonreducible MO x catalysts. Low-coordinated sites on the Au NPs would be the active
sites for O 2 activation and the adsorption sites of the substrate [77]. Au/γ-Ga 2 O 3
catalyzed base-free oxidation of benzyl alcohol in mesitylene to give benzaldehyde
with 99% selectivity at >99% conversion [40]. In addition, the catalytic activity of
Au/γ-Ga 2 O 3 exceeded those of Au/TiO 2 , Au/CeO 2 , and Au/Fe 2 O 3 . The remarkable
high activity was speculated by dehydrogenation activity, and temperatureprogrammed surface reaction (TPSR) of 2-propanol was examined for Au/γ-Ga 2 O 3 .
As the temperature increased, 2-propanol adsorbed on the catalysts was converted to
acetone together with the formation of H 2 . Accordingly, more intense H 2 desorption
peak was observed for γ-Ga 2 O 3 itself than those observed for Au/CeO 2 (the H 2
desorption was not observed for Au/TiO 2 and Au/Fe 2 O 3 ). In addition, H 2 desorption
peak for Au/γ-Ga 2 O 3 was shifted to lower temperature from that for γ-Ga 2 O 3 itself,
indicating that γ-Ga 2 O 3 has high activity for the dehydrogenation and Au NPs
facilitate the reaction. Ga-Al mixed oxides were also examined and Au/Ga 3 Al 3 O 9
showed the higher activity than Au/Ga 2 O 3 and other Au/Ga x Al y O z catalysts. The
catalytic activity order was consistent to the order of dehydrogenation activity which
was elucidated by the amount of desorbed H 2 from 2-propanol by TPSR [41]. Au
NPs supported on MgO [43], Mg x Al y O z , Cu-containing Mg x Al y O z spinel-type
oxides [44, 45], and MgFe 2 O 4 [46] also promoted the oxidation of alcohols in the
absence of base. For Cu-containing Mg x Al y O z , the introduction of redox-active Cu
might change the surface basicity, affect the electronic state of Au, and add the redox
properties of Cu in some extent, which led to the improved activity from
Au/Mg x Al y O z without Cu [44].
2.3 Non-oxides
2.3.1 Role of Supports
Metal hydroxides, phosphates, and carbonates are classified as non-oxides inorganic
supports. Au NPs on basic hydrotalcite (HT: Mg 6 Al 2 (OH) 16 CO 3 ÁnH 2 O) exhibited
high catalytic activity for oxidation of various alcohols in the absence of base
[47, 48]. Au/HT exhibited superior activity and selectivity (99% at 99% conversion)
to Au/Al 2 O 3 and Au/MgO, reported by Kaneda et al. [47]. Au/MgCr-HT (Cr
3+
substituted HT) improved the catalytic activity from Au/HT [49]. The oxidation of
a primary aliphatic alcohol, 1-octanol, did not proceed to give octanal over Au/HT in
the absence of base [47] but proceed over Au/MgCr-HT, whereas the conversion
was lower than those for aromatic alcohols. Au/MgCr-HT also recorded extremely
high TOF (81,000 h
À1 ) for solvent-free oxidation of 1-phenyl ethanol to give
acetophenone (Table 2).
A series of Au clusters (ca. 1.5 nm in diameters) on M 3 Al-LDH (M ¼ Ni, Co,
Mg) exhibited high catalytic activity for base-free oxidation of 1-phenylethanol to
give TOF of 46,500 h
À1 over Au/Ni 3 Al-LDH (Table 2) [50]. Both strong acidic and
10
T. Ishida et al.