Bimetallic synergistic Au/CuO-hydroxyapatite catalyst for aerobic oxidation of alcohols

Article abstract of DOI:10.1016/S1872-2067(15)60854-3

A catalyst consisting of Au supported on copper oxide-modified hydroxyapatite (Au/CuO-HAP) was prepared using a homogeneous deposition-precipitation method. The catalyst was characterized using atomic absorption spectrometry, N₂ adsorption-desorption, powder X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The catalytic performance in liquid-phase aerobic oxidation of alcohols was investigated. The catalytic activity and benzaldehyde selectivity in benzyl alcohol oxidation with the bimetallic Au/CuO-HAP catalyst were significantly better than those with monometallic Au/HAP and CuO-HAP catalysts. The conversion of benzyl alcohol and selectivity for benzaldehyde at 120 °C for 1.5 h under aerobic oxidation conditions were 99.7% and 98.4%, respectively. Various aromatic alcohols were selectively converted to their corresponding aldehydes or ketones over Au/CuO-HAP. The Au/CuO-HAP catalyst could be reused at least four times without loss of activity.

Full text of DOI:10.1016/S1872-2067(15)60854-3

Chinese Journal of Catalysis 36 (2015) 1358–1364
a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / c h n j c
Article
Bimetallic synergistic Au/CuO-hydroxyapatite catalyst for aerobic
oxidation of alcohols
Tao Tian, Ying Liu, Xungao Zhang *
College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, Hubei, China
A R T I C L E I N F O
A B S T R A C T
Article history:
A catalyst consisting of Au supported on copper oxide-modified hydroxyapatite (Au/CuO-HAP) was
prepared using a homogeneous deposition-precipitation method. The catalyst was characterized
using atomic absorption spectrometry, N2 adsorption-desorption, powder X-ray diffraction, trans-
mission electron microscopy, and X-ray photoelectron spectroscopy. The catalytic performance in
liquid-phase aerobic oxidation of alcohols was investigated. The catalytic activity and benzaldehyde
selectivity in benzyl alcohol oxidation with the bimetallic Au/CuO-HAP catalyst were significantly
better than those with monometallic Au/HAP and CuO-HAP catalysts. The conversion of benzyl
alcohol and selectivity for benzaldehyde at 120 °C for 1.5 h under aerobic oxidation conditions were
99.7% and 98.4%, respectively. Various aromatic alcohols were selectively converted to their cor-
responding aldehydes or ketones over Au/CuO-HAP. The Au/CuO-HAP catalyst could be reused at
least four times without loss of activity.
Received 10 February 2015
Accepted 27 March 2015
Published 20 August 2015
Keywords:
Heterogeneous catalysis
Gold-copper bimetallic catalyst
Aerobic oxidation of alcohols
Hydroxyapatite
Reusability
© 2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
below 10 nm) supported on TiO2 show high activity in the
low-temperature CO oxidation. In the last two decades, na-
Liquid-phase oxidation of alcohols to the corresponding ke-
tones or aldehydes is important in organic functional group
conversion reactions [1]. Traditionally, stoichiometric oxidants
such as dichromate and permanganate have been used in the
oxidation of alcohols [2–5]. However, excessive use of these
stoichiometric oxidants raises environmental and safety con-
cerns. In addition, many by-products are generated because of
over oxidation. In terms of cost saving and environmental pro-
tection, new routes to aldehydes and ketones using benign
oxidizing agents such as organic peroxides, hydrogen peroxide,
and molecular oxygen are of significant interest [6–8]. Nano-
materials based on noble metals such as Pd, Au, Pt, and Ru have
been widely studied as potential catalysts [9–12].
nosized Au catalysts have attracted much attention because of
their high catalytic activity in various reactions [15,16]. Re-
cently, bimetallic Au catalysts have been found to have better
catalytic activity and selectivity than monometallic catalysts,
because of their tunable and synergistic properties; for exam-
ple, Au-Pd/TiO2 catalysts have been used in the oxidation of
primary carbon-hydrogen bonds in toluene [17], oxidation of
primary alcohols [18], cinnamaldehyde hydrogenation [19],
and direct hydrogen peroxide synthesis [20]. Zhao et al. [21]
reported that the stability and catalytic lifetime of a Au/γ-Al2O3
catalyst could be improved by the addition of Bi. Zhang et al.
[22] found that Au in cooperation with Co gave superior cata-
lytic activity and long-term stability in acetylene hydrochlorin-
ation.
Au was considered to be an inert material until Haruta et al.
[13,14] showed that well-dispersed Au nanoparticles (NPs,
Supported bimetallic Au-Cu catalysts have been widely used
* Corresponding author. Tel/Fax: +86-27-68752136; E-mail: xgzhang66@whu.edu.cn
This work was supported by Natural Science Foundation of Hebei Province of China (2013CFB291).
DOI: 10.1016/S1872-2067(15)60854-3 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 36, No. 8, August 2015

Tao Tian et al. / Chinese Journal of Catalysis 36 (2015) 1358–1364
1359
in CO preferential oxidation [23], CO2 reduction [24], hydro-
genation of cinnamaldehyde [25], and gas-phase oxidation of
benzyl alcohol [26]. Recently, Li et al. [27] reported that sili-
ca-supported Au-Cu alloy NPs showed good activity and selec-
tivity for aldehydes in liquid-phase oxidation of alcohols under
mild and base-free conditions, but rigorous post-processing
such as reduction with H2 at 550 °C was necessary for catalyst
recovery. A CuO-supported Au catalyst with high selectivity and
activity for benzyl alcohol oxidation under mild conditions has
been reported [28]. In this study, we prepared and character-
ized Au supported on CuO-modified hydroxyapatite
(Au/CuO-HAP), and investigated its catalytic properties in the
oxidation of alcohols. The Au/CuO-HAP performance was bet-
ter than those of monometallic Au/HAP and CuO-HAP, and it
had excellent recyclability. Various aromatic alcohols were
efficiently converted to their corresponding aldehydes or ke-
tones over Au/CuO-HAP under aerobic conditions.
solution) in the supernatant. The solid was dried at 90 °C over-
night and calcined at 300 °C for 4 h in air flow (30 mL/min ).
The obtained purple catalysts were denoted by Au/HAP and
Au/CuO-HAP.
2.3. Catalyst characterization
The Au and Cu contents of the catalysts were determined
using atomic absorption spectrometry (AAS; Perkin-Elmer
PEAA800). The specific surface areas of the catalysts were de-
termined from their N2 adsorption-desorption isotherms at
196 °C by the Brunauer-Emmett-Teller method, using a Tris-
tar II 3020 V1.02 instrument (Micromeritics Instrument Cor-
poration, USA). The pore size distributions were obtained from
the desorption branch of the N2 adsorption-desorption iso-
therms using the Barrett-Joyner-Halenda (BJH) method. The
crystal structure of the catalysts were examined using powder
X-ray diffraction (XRD; X’Pert Pro, PANalytical, Cu Kα radiation
(λ = 0.15406 nm), operated at 40 mA and 40 kV). Transmission
electron microscopy (TEM) and high-resolution TEM (HRTEM)
were performed using a JEOL JEM-2010-HR microscope oper-
ated at 200 kV. Before the TEM experiments, the samples were
ultrasonically dispersed in ethanol and transferred to a Cu grid
coated with a holey carbon film. The chemical states of the sur-
face elements were determined using X-ray photoelectron
spectroscopy (XPS; ESCALAB 250Xi, Thermo Fisher) with
monochromic Al Kα radiation; all binding energies were cali-
brated using the C 1s line at 284.8 eV.
2. Experimental
All reagents were analytical grade and purchased from the
Sinopharm Chemical Reagent Co., Ltd. They were used without
further purification unless otherwise specified. Deionized wa-
ter was used in all experiments.
2.1. Preparation of HAP and CuO-HAP supports
HAP was prepared as follows. Phosphoric acid aqueous so-
lution (300 mL, 0.1 mol/L) was added dropwise to an aqueous
suspension (300 mL) of calcium hydroxide (3.71 g, 0.05 mol)
under vigorous mechanical stirring. The dropping speed was
controlled at 4 mL/min, the temperature of the suspension
solution was set at 80 °C, and the pH of the suspension solution
was adjusted to 9.0 with aqueous ammonia. After addition of
the phosphoric acid solution, the mixture was stirred at 80 °C
for 3 h. The resulting precipitate was collected by filtration and
washed with deionized water. The solid was dried at 105 °C
overnight, and then calcined at 500 °C for 3 h.
The CuO-HAP support was prepared by dropwise addition
of an aqueous solution (300 mL) of phosphoric acid (3.68 g,
purity 85%) and copper(II) chloride dihydrate (0.571 g) to an
aqueous suspension (300 mL) of calcium hydroxide (3.71 g),
with vigorous mechanical stirring; the molar ratio of (Ca +
Cu)/P was set at 1.67. The subsequent procedures were the
same as those for HAP preparation. The resulting product was
denoted by CuO-HAP.
2.4. Catalytic reaction
The alcohol aerobic oxidations were performed in
a
bath-type reactor under oxygen (101.3 kPa). In a typical reac-
tion, a 25 mL three-necked round-bottomed flask containing
alcohol (3 mmol), K2CO3 (1 mmol), a certain amount of catalyst,
and p-xylene (10 mL) was kept at 120 °C, with magnetic stir-
ring (1200 r/min). Oxygen was flowed into the suspension at a
rate of 20 mL/min. The liquid products were obtained by cen-
trifugation, and then analyzed using a gas chromatograph
(GC-1690, Hangzhou Jiedao Technology Instrument Co., Ltd)
equipped with a flame ionization detector (FID) and an AT
OV-1701 capillary column, to determine the conversion and
selectivity. Gas chromatography-mass spectrometry (GC-MS;
450GC-320MS, Varian) was used to confirm the product com-
positions.
The catalysts were recovered by centrifugation, washed al-
ternately with ethanol and water several times, and dried at 90
°C overnight. The recovered catalyst was used to investigate
the recycling performance under the same reaction conditions.
2.2. Preparation of Au/HAP and Au/CuO-HAP catalysts
The Au/HAP and Au/CuO-HAP catalysts were prepared us-
ing the homogeneous deposition-precipitation method devel-
oped by Zanella et al. [29], using urea as the precipitating agent.
HAP or CuO-HAP (0.5 g) was added to an aqueous solution (20
mL) of HAuCl4·4H2O (5.3 × 10–3 mol/L) and urea (0.84 mol/L).
The suspension was heated to 90 °C and stirred for 4 h. The
solid was separated by centrifugation and washed with deion-
ized water until no chloride ions were detected (using AgNO3
3. Results and discussion
3.1. Catalyst characterization
The N2 adsorption-desorption isotherms of Au/HAP,
CuO/HAP, and Au/CuO-HAP are shown in Fig. 1(a). The relative
pressure was set in the range 0.01–1.0. The surface areas of

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Tao Tian et al. / Chinese Journal of Catalysis 36 (2015) 1358–1364
Au/HAP, CuO-HAP, and Au/CuO-HAP were 53.8, 50.8, and 53.7
m2/g, respectively. There were no significant differences
among the specific surface areas, and sickle-shaped N2 adsorp-
tion-desorption isotherms were observed for all three catalysts.
Fig. 1(b) shows that the major peak for the three catalysts was
located at 27 nm. However, after loading with Cu species, a
shoulder peak appeared at about 39 nm for both CuO-HAP and
Au/CuO-HAP, indicating that the Cu species altered the porous
structure; these results are consistent with those in the litera-
ture [30].
dispersed on nanosized HAP, with an average diameter of 3.8
nm. The measured interplanar distances of 0.235 and 0.343 nm
correspond to the spacing of the (111) plane of face-centered
cubic Au NPs (PDF No. 04-0784) and the spacing of the (002)
plane of HAP (PDF No. 09-0432), respectively (Fig. 2(d)). It is
clear from Fig. 2(b) that a large number of small particles of
average diameter (2.7 nm) are uniformly dispersed on the
support; most of the particles are of size 2 to 3.5 nm. The lattice
spacing of 0.232 nm corresponds to the (111) plane of mono-
clinic CuO NPs (PDF No. 48-1548; Fig. 2(e)). The TEM and
HRTEM images of CuO-HAP confirm that a large number of CuO
NPs were generated during support preparation, and that the
support has the typical HAP structure, although some Cu2+ ions
Fig. 2 shows the TEM and HRTEM images of Au/HAP,
CuO-HAP, and Au/CuO-HAP and their metal particle size dis-
tribution diagrams. Fig. 2(a) shows that the Au NPs are well
(a)
(b)
(3)
(3)
(2)
(1)
(2)
(1)
0.0
0.2
0.4
0.6
0.8
1.0
20
40
60
80
100
Pore diameter (nm)
Relative pressure (p/p0)
Fig. 1. N2 adsorption-desorption isotherms (a) and BJH pore size distributions (b) of Au/HAP (1), CuO/HAP (2), and Au/CuO-HAP (3).
(a)
(b)
(c)
20 nm
(d)
20 nm
20 nm
0.269 nm
0.235 nm
Au(111)
(e)
(f)
HAP(300)
0.235 nm
Au(111)
0.230 nm
CuO(111)
Au
(111)
CuO
(111)
0.230 nm
CuO(111)
0.343 nm
HAP(002)
5 nm
5 nm
0.232 nm
CuO(111)
5 nm
Fig. 2. TEM images and corresponding particle size distributions of Au/HAP (a), CuO-HAP (b), and Au/CuO-HAP (c); HRTEM images of Au/HAP (d),
CuO-HAP (e), and Au/CuO-HAP (f).

Tao Tian et al. / Chinese Journal of Catalysis 36 (2015) 1358–1364
1361
might dope into the HAP network. When the solution of cop-
per(II) chloride and phosphoric acid was added dropwise to
the calcium hydroxide suspension at 80 °C (as described in the
experimental section), copper hydroxide was more easily pre-
cipitated than copper phosphate, because the former is less
soluble at pH = 9.0. As a result, large amounts of CuO NPs were
generated when copper hydroxide decomposed at high tem-
perature. Fig. 2(c) shows that Au and CuO NPs of average di-
ameter (3.5 nm) are finely dispersed on the CuO-HAP support.
Little NPs aggregation was observed, possibly because of the
high surface area of the porous structure of CuO-HAP or the
sinter-resistant properties of CuO. The HRTEM image of
Au/CuO-HAP shows the presence of CuO NPs and bimetallic
Au-CuO NPs. The interplanar distance of 0.269 nm corresponds
to the (300) crystal plane of the HAP support (Fig. 2(f)).
 Au

(3)
(2)
(1)
20 25 30 35 40 45 50 55 60 65 70 75 80
2/(o)
XPS was used to determine the surface chemical states of Au
and Cu in the samples. Fig. 3 shows the Au 4f and Cu 2p3/2 XPS
profiles of Au/HAP, Au/CuO-HAP, and CuO-HAP. The Au 4f
spectra of Au/HAP and Au/CuO-HAP (Fig. 3(a)) show that the
binding energies of Au in Au/HAP at 87.5 and 83.8 eV are at-
tributable to Au 4f5/2 and 4f7/2, respectively, the Au 4f5/2 and
4f7/2 binding energies in Au/CuO-HAP shifted to 87.8 and 84.1
eV, respectively. The 0.3 eV positive shift for Au/CuO-HAP
compared with Au/HAP was probably caused by interactions
between Au NPs and CuO NPs. After four runs of benzyl alcohol
oxidation, the Au chemical state of the used Au/CuO-HAP was
almost unchanged. The asymmetric Cu 2p3/2 peaks in the spec-
tra of fresh Au/CuO-HAP and CuO-HAP can be fitted to two
peaks, at 933.5 and 935.0 eV, which are attributed to the bind-
ing energies of Cu 2p3/2 in CuO and copper phosphate, respec-
tively [30,31]. The characteristic shake-up satellite peak at the
higher binding energy of 944 eV for Cu2+ also indicates that the
main components were Cu2+ species. The peak-fitting results
indicate that the atomic ratio of Cu from CuO to Cu from copper
phosphate in both CuO-HAP and Au/CuO-HAP was close to 4:1,
i.e., in Au/CuO-HAP and CuO-HAP, Cu was mainly present in the
CuO state, with a small amount of Cu doped into the HAP net-
work; these results are consistent with the TEM images. How-
ever, in Fig. 3(b), the peak in the Cu 2p3/2 spectrum of the used
Fig. 4. XRD patterns of CuO-HAP (1), Au/HAP (2), and Au/CuO-HAP (3).
Au/CuO-HAP shifted from 933.6 to 933.0 eV, and was fitted to
three peaks, at 935.0, 933.5, and 932.5 eV, which correspond to
the binding energies of Cu 2p3/2 in copper phosphate, CuO, and
Cu2O, respectively. The weakened shake-up satellite peak also
indicates that the Cu2+ was partially reduced. Area integration
showed that about 50% of surface Cu was transformed into
Cu2O in the used Au/CuO-HAP. It is easy to see that CuO was
partially reduced to Cu2O in the presence of benzyl alcohol un-
der alkaline conditions; during this process, CuO could supply
active oxygen for the reaction [28].
Fig. 4 shows the XRD patterns of CuO-HAP, Au/HAP, and
Au/CuO-HAP. The major diffraction peaks for CuO-HAP,
Au/HAP, and Au/CuO-HAP, at 2θ = 25.9°, 31.9°, 33.1°, and
34.1°, are almost identical, and in good agreement with the
typical HAP structure (PDF No. 09-0432). These results show
that the prepared CuO-HAP and HAP were stable during Au
NPs loading, and the HAP structure was not changed by the
small amount of Cu doping. Although the Au and Cu contents in
Au/CuO-HAP were both 4%, only a weak and broad diffraction
peak at 2θ = 38.2°, associated with the Au (111) plane, can be
(b)
(1)
(a)
(1)
(2)
(2)
(3)
(3)
92
90
88
86
84
82
80
78
948
944
940
936
932
928
Binding energy (eV)
Binding energy (eV)
Fig. 3. (a) Au 4f XPS profiles of Au/HAP (1), fresh Au/CuO-HAP (2), and used Au/CuO-HAP (3), and (b) Cu 2p3/2 XPS profiles of CuO-HAP (1), fresh
Au/CuO-HAP (2), and used Au/CuO-HAP (3).

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Tao Tian et al. / Chinese Journal of Catalysis 36 (2015) 1358–1364
identified; this is attributed to the effect of the small finely dis-
persed Au and CuO NPs.
Table 2
Results for oxidation of various alcohols over Au-CuO/HAP in p-xylene.
Conversiona Aldehyde/ketone Time TOFb
Entry
1
Substrate
selectivitya (%) (h) (h–1)
3.2. Catalytic performance in benzyl alcohol oxidation
(%)
99.7
98.4
>99.9
99.7
1.5 548
3.5 414
3.5 405
In the aerobic oxidation of benzyl alcohol catalyzed by
monometallic Au catalysts, by-products such as toluene, ben-
zoic acid, and benzyl benzoate are easily formed [15,32]. Bime-
tallic Au catalysts have enhanced activity and selectivity in al-
cohol oxidation [18,27]. The catalytic performance of the
Au/HAP, CuO-HAP, and Au/CuO-HAP catalysts in the aerobic
oxidation of benzyl alcohol are summarized in Table 1. When
CuO-HAP was used, only 4.5% of benzyl alcohol was converted
to benzaldehyde after reaction for 1.5 h, indicating that this
catalyst had low catalytic activity in this reaction. Under the
same reaction conditions, Au/HAP exhibited higher catalytic
activity, and 53.2% and 98.9% conversions of benzyl alcohol
were achieved after 1 and 4 h, respectively. However, the selec-
tivity for benzaldehyde decreased from 96.2% to 91.4%, and
about 9% benzyl benzoate was generated as a by-product, be-
cause of over oxidation. Benzyl alcohol was quantitatively con-
verted to benzaldehyde over Au-CuO/HAP after 1.5 h, and the
selectivity for benzaldehyde remained greater than 98.4%,
without over oxidation. The calculated turnover frequencies
OH
2
3
99.7
99.8
4c
5
94.5
89.8
>99.9
97.5
7.0 119
9.0 99
6
7
99.6
99.9
99.5
4.0 254
1.5 536
>99.9
Reaction conditions:
3 mmol alcohol, 1 mmol K2CO3, 50 mg
Au/CuO-HAP catalyst, 10 mL p-xylene, 20 mL/min O2, 120 °C.
a Products conducted by GC-FID. b TOF value was calculated as: mol of
alcohol converted at the first 15 min/(mol of total loading of Au × reac-
tion time). c 0.1 g Au/CuO-HAP catalyst.
(TOFs) of Au/CuO-HAP and Au/HAP were 548 and 460 h−1
,
electron-withdrawing group (entry 4). Although the catalytic
activity in the reaction with 2-furanmethanol was low, the se-
lectivity for furfuraldehyde was greater than 97.5% (entry 5).
Cinnamyl alcohol and diphenylmethanol were also quantita-
tively converted to their corresponding aldehyde and ketone
with high TOF values (entries 6 and 7).
respectively, indicating that Au/CuO-HAP had higher catalytic
activity in the aerobic oxidation of benzyl alcohol. We suggest
that the enhanced catalytic performance of Au/CuO-HAP in the
aerobic oxidation of benzyl alcohol is the result of a synergistic
effect between the supported Au and CuO NPs.
3.3. Scope of Au/CuO-HAP-catalyzed alcohol oxidation
3.4. Reusability of Au/CuO-HAP catalyst
The scope for the Au/CuO-HAP-catalyzed aerobic oxidation
of alcohols was investigated. Table 2 lists the results for aerobic
oxidation of various alcohols catalyzed by Au/CuO-HAP. The
oxidation of benzyl alcohol and its derivatives with elec-
tron-donating groups to the corresponding aldehydes (entries
1–3) was easier than the oxidation of benzyl alcohol with an
Catalyst reusability is important in industry. As a result of
aggregation, particle size enlargement, and support instability,
the catalytic performance of heterogeneous Au catalysts in
liquid-phase oxidation of alcohols deteriorate in recycling ex-
periments [15,33,34]. The recycling performance of the
Au/CuO-HAP catalyst in the oxidation of benzyl alcohol was
investigated. Table 3 lists the benzyl alcohol conversion and
selectivity for benzaldehyde over recycled Au/CuO-HAP at 120
°C after reaction for 1.5 h. Under the same aerobic conditions,
the catalytic performance of Au/CuO-HAP from the second to
the fourth runs was almost unchanged, and the benzyl alcohol
conversion and selectivity for benzaldehyde was above 95%
and 99%, respectively, i.e., similar to those with the fresh cata-
lyst (the first run). The TEM image of Au/CuO-HAP after the
fourth run (Fig. 5) shows that the Au particle size had not no-
ticeably altered, most of the Au NPs were of size 2.5 to 4.5 nm,
and no aggregation was observed. The XPS results show that
the chemical state of Au did not change and about 50% of sur-
face Cu was transformed into Cu2O in the catalyst after the
fourth run (see Fig. 3). The change in the surface Cu structure
did not significantly affect the catalytic activity of the reused
Au/CuO-HAP, indicating that the activity was dominated by Au,
with a minor contribution from CuO. CuO NPs on the HAP sur-
Table 1
Catalytic performance of Au/HAP, CuO-HAP, and Au/CuO-HAP in oxi-
dation of benzyl alcohol.
Benzalde-
hyde
selectivityb (h )
Conver-
sionb
(%)
Aua Cua Size Time
(%) (%) (nm) (h)
TOFc
Catalyst

1
(%)
CuO-HAP
Au/HAP
—
3.9
—
2.7
3.8
1.0
1.5
1.0
1.5
4.0
1.0
1.5
1.5
4.5
0
100
96.2
93.1
91.4
98.6
98.4
—
4.3
53.2
75.7
98.9
95.9
99.7
460
Au/CuO-HAP 4.7 3.7
3.5
548
Reaction conditions: 3 mmol benzyl alcohol, 1 mmol K2CO3, 50 mg cat-
alyst, 10 mL p-xylene, 20 mL/min O2, 120 °C.
a The contents of Au and Cu were measured by AAS. b Products con-
c
ducted by GC-FID. TOF value was calculated as: mol of benzyl alcohol
converted at the first 15 min/(mol of total loading of Au × reaction
time).

Tao Tian et al. / Chinese Journal of Catalysis 36 (2015) 1358–1364
1363
alytic performance of Au/CuO-HAP in the aerobic oxidation of
benzyl alcohol was better than that of monometallic Au/HAP
and CuO-HAP catalysts, because of the bimetallic synergistic
effect. Various aromatic alcohols were converted to their cor-
responding aldehydes or ketones over Au/CuO-HAP, with high
catalytic activity and excellent selectivity. The Au NPs were
anchored on the support by CuO NPs, and had excellent size
stability. The prepared Au/CuO-HAP catalyst can be reused at
least four times without loss of its activity.
Table 3
Au/CuO-HAP recycling experiments.
Conversion of
Run number
Benzaldehyde
selectivity (%)
98.4
benzyl alcohol (%)
1st
99.7
95.8
97.2
96.3
2nd
3rd
4th
99.2
99.5
99.2
Reaction conditions: 3 mmol benzyl alcohol, 1 mmol K2CO3, 50 mg
Au/CuO-HAP catalyst, 10 mL p-xylene, 20 mL/min O2, 120 °C, 1.5 h.
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Graphical Abstract
Chin. J. Catal., 2015, 36: 1358–1364 doi: 10.1016/S1872-2067(15)60854-3
Bimetallic synergistic Au/CuO-hydroxyapatite catalyst for aerobic oxidation of alcohols
Tao Tian, Ying Liu, Xungao Zhang *
Wuhan University
Benzyl alcohol conversion
Benzaldehyde selectivity
Benzaldehyde yield
100
80
60
40
20
0
O2
Au
Au
Au
Au
CuO
CuO-HAP
Au/HAP
CuO-HAP
Au/CuO-HAP
The catalytic activity and benzaldehyde selectivity of bimetallic Au/CuO-HAP in the oxidation of benzyl alcohol were better than those of
monometallic Au/HAP and CuO/HAP catalysts.

1364
Tao Tian et al. / Chinese Journal of Catalysis 36 (2015) 1358–1364
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