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Chemistry Letters Vol.37, No.12 (2008)
Coprecipitated Gold–Tricobalt Tetraoxide Catalyst
for Heterogeneous Hydroformylation of Olefins
Xiaohao Liu,1;3 Masatake Haruta,2;3 and Makoto Tokunagaꢀ1;3
1Department of Chemistry, Graduate School of Science, Kyushu University,
6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581
2Materials Chemistry Course, Faculty of Urban Environmental Sciences, Tokyo Metropolitan University,
1-1 Minami-osawa, Hachioji, Tokyo 192-0397
3JST (Japan Science and Technology Cooperation) CREST
(Received September 8, 2008; CL-080854; E-mail: mtok@chem.kyushu-univ.jp)
The combination of gold (Au0) and tricobalt tetraoxide
(Co3O4) prepared by coprecipitation gives high-performance
heterogeneous catalysts for hydroformylation reaction with se-
lectivity above 85% in desired aldehydes, although neither
Au0 nor Co3O4 have been demonstrated in this reaction and
show poor activities. The Au/Co3O4 catalysts can be recycled
by simple decantation with slight decrease in catalytic activity
along with recycle times. The role of Au may mainly promote
in situ reduction of Co3O4 to Co0 catalyzing the hydroformyla-
tion reaction.
H2 + CO
(3-5 MPa)
100-130 °C
CHO
CHO
+
R
R
R
Au/Co3O4
linear
branched
Scheme 1. Au/Co3O4-catalyzed hydroformylation of 1-olefins.
catalyst was performed by introducing an aqueous solution of
cobalt(II) nitrate hexahydrate and HAuCl4 into a sodium car-
bonate solution at room temperature. The coprecipitates were
washed, dried overnight at 100 ꢁC, and calcined at 400 ꢁC for
4 h. The Co3O4 was prepared in the same way.
Hydroformylation, also known as ‘‘oxo synthesis,’’ is an im-
portant homogeneous industrial process for the production of al-
dehydes from alkenes.1 This process has witnessed continuous
growth since its invention in the 1930s. Notwithstanding a num-
ber of advantages over their heterogeneous counterparts such as
high accessibility of all catalytic sites and possibility of tuning
selectivity, homogeneous systems have problems inevitably as-
sociated with separating the catalyst from the products and its re-
cycling use.2 In addition, the cost of dominantly used rhodium
catalysts are about 4000 times as that of cobalt.
Thus, possible solutions to the problems are to heterogenize
Co0 metal or Co0 complex catalysts by anchoring the catalyst on
a support such as polymer,3 silica,4 and active carbon.5 Active
sites can be fixed on the support through strong bonding or phys-
ical interaction to form heterogeneous catalysts to develop eco-
nomically and environmentally friendly green processes.
Recently, gold has been proven to be an effective catalytic
component for many reactions.6 The most important key is to
support nanoparticles of gold on select metal oxides or to design
bimetallic structures. The fact that gold nanoparticles exhibit
markedly high catalytic activity and selectivity by the synergy
with the metal oxide supports have motivated us to prepare a het-
erogeneous hydroformylation catalyst based on Co3O4. Gold
nanoparticles deposited on base metal oxides can adsorb CO7
moderately and are active for CO oxidation, water gas shift reac-
tion, olefin hydrogenation, and methanol synthesis.
As shown in Table 1, Au/AC (activated carbon), Au/Al2O3,
Au/TiO2, and Au/Fe2O3 showed only little or no hydroformyla-
tion activities (Table 1, Entries 1–4). The reactant 1-olefin intro-
duced mainly remained unchanged and the major products were
isomerized olefins or hydrogenated paraffin depending on the
catalyst component and the reaction conditions. The Co3O4
did not exhibit any activity for 1-hexene conversion (Table 1,
Entry 5). In contrast, very interestingly, supported nanoparticu-
late gold catalysts 5 or 10 atom % Au/Co3O4 exhibit noticeably
high hydroformylation activity (Table 1, Entries 6–9) and the se-
lectivity to aldehydes was in the range of 85–90%. The catalytic
activity is appreciably increased with increasing gold loading
(Table 1, Entries 6 and 8). A chemical yield >80% (Table 1,
Entry 9) of desired aldehydes was obtained with 10 atom %
Au/Co3O4 catalyst.
Taking into account the catalytic activity order in hydrofor-
mylation widely accepted (Rh, Co, Ir, Ru, Os, Pt, Pd, Fe, Ni,
etc.), we may assume that the remarkably enhanced catalytic ac-
tivity of Au/Co3O4 compared to Co3O4 or other supported Au
nanoparticles (Au on AC, Al2O3, TiO2, and Fe2O3) may be as-
cribed to active Co0 metal generated on the surface8 by spillover
hydrogen from gold nanoparticles, or to other synergistic effects
between gold and cobalt.
As evidenced with XRD data (Figure S1),9 the fresh
10 atom % Au/Co3O4 catalyst gives only Co3O4 peaks at
2ꢀ ¼ 19:0, 31.4, 36.9, 44.7, 55.7, 59.3, 65.2, and 77.5 and gold
peaks at 2ꢀ ¼ 38:2, 44.4, 64.7, and 77.6. When the catalyst is re-
duced with H2 (100 ꢁC, 2.0 MPa, 3 h) in 2.0 mL of heptane, its
XRD patterns are composed of a CoO peak at 2ꢀ ¼ 42:4 and
strong Co0 peaks at 2ꢀ ¼ 44:1, 47.6, and 75.9, but not of Co3O4
peaks. This reduction behavior is consistent with a temperature-
programmed reduction (TPR) experiment that the reduction of
Co3O4 in Au/Co3O4 to elemental cobalt took place at a temper-
ature about 200 ꢁC lower than the reduction temperature for pure
In a similar manner to these reactions, for the seventy-year-
old hydroformylation reaction (Scheme 1), various supported
gold-containing catalysts were prepared for reaction test. The
5 atom % Au/Fe2O3 and Au/Co3O4 were prepared by coprecipi-
tation. The 3 wt % Au/TiO2 and 1.5 wt % Au/AC (activated car-
bon) were prepared by deposition–precipitation. The 1 wt % Au/
Al2O3 was prepared by directly grinding dimethylgold(III) ace-
tylacetonate with Al2O3. In details, the preparation of Au/Co3O4
Copyright Ó 2008 The Chemical Society of Japan