Promotion effect of nickel for Cu–Ni/γ-Al2O3 catalysts in the transfer dehydrogenation of primary aliphatic alcohols

Article abstract of DOI:10.1007/s13738-016-0963-2

Cu–Ni/γ-Al₂O₃ bimetallic catalysts were developed for anaerobic dehydrogenation of non-activated primary aliphatic alcohols to aldehydes. Systematic investigation about the promotion effect of nickel on the catalytic performance was carried out. Hydrogenation of C=C bond rather than C=O bond, was significantly improved over Cu–Ni/γ-Al₂O₃ catalyst by introducing nickel, which interprets the good conversion of primary aliphatic alcohols. This work would contribute to design new catalysts for dehydrogenation of primary aliphatic alcohols.

Full text of DOI:10.1007/s13738-016-0963-2

J IRAN CHEM SOC
DOI 10.1007/s13738-016-0963-2
ORIGINAL PAPER
Promotion effect of nickel for Cu–Ni/γ‑Al O catalysts in the
2
3
transfer dehydrogenation of primary aliphatic alcohols
1
1
2
2
2
Xiaomei Yang · Xiaomin Fu · Ningning Bu · Li Han · Jianfeng Wang ·
2
1
1
2
Chengying Song · Yunlai Su · Lipeng Zhou · Tianliang Lu
Received: 20 April 2016 / Accepted: 11 August 2016
©
Iranian Chemical Society 2016
Abstract Cu–Ni/γ-Al O bimetallic catalysts were devel-
toward aldehydes because of facile oxidation of aldehydes
into acids in presence of molecular oxygen and transi-
tional metal catalysts [1–3, 11–13]. Catalytic dehydroge-
nation of alcohols is an attractive method [14] in which
further oxidation of aldehydes into acids is limited under
an inert atmosphere. Although various monometallic cata-
lysts including Ag [15, 16], Co [17] and Cu [18–21] have
been reported for efficient liquid-phase dehydrogenation of
secondary aliphatic alcohols, catalytic dehydrogenation of
non-activated primary aliphatic alcohols into aldehydes is
rather difficult.
2
3
oped for anaerobic dehydrogenation of non-activated pri-
mary aliphatic alcohols to aldehydes. Systematic investiga-
tion about the promotion effect of nickel on the catalytic
performance was carried out. Hydrogenation of C=C bond
rather than C=O bond, was significantly improved over
Cu–Ni/γ-Al O catalyst by introducing nickel, which inter-
2
3
prets the good conversion of primary aliphatic alcohols.
This work would contribute to design new catalysts for
dehydrogenation of primary aliphatic alcohols.
Keywords Heterogeneous catalysis · Alcohols ·
Dehydrogenation
In catalytic transfer dehydrogenation of alcohols, a read-
ily available unsaturated organic compound is often used
as hydrogen acceptor [22, 23]. Generally, both dehydroge-
nation of alcohols and hydrogenation of carbonyl product
would occur simultaneously, and an equilibrium would be
temporarily established without hydrogen acceptor (unsatu-
rated organic compounds). The competitive hydrogenation
of hydrogen acceptor with C=O bond of aldehydes would
be crucial in catalytic transfer dehydrogenation of primary
aliphatic alcohols. To obtain high yield of aliphatic alde-
hydes, a catalyst is desired with preference for catalytic
hydrogenation of hydrogen acceptor rather than aliphatic
aldehyde.
Introduction
The selective oxidation of non-activated primary aliphatic
alcohols is one of the most challenging reactions. Stoi-
chiometric oxidizing agents such as chromium and man-
ganese salts are traditionally used which often result in
large amount of toxic wastes. Development of catalytic
aerobic oxidation of alcohols attracts much attention for
both environmental and economic reasons [1–10]. How-
ever, it is rather challenging to obtain high selectivity
Monometallic copper catalysts exhibit good perfor-
mance on catalytic dehydrogenation of alcohols [18–21,
2
4–27]. Enhancing the catalytic activity on hydrogenation
*
Tianliang Lu
of hydrogen acceptor would be favorable for production
of aliphatic aldehydes for copper catalysts. Considering
the high C=C bond hydrogenation activity and selectivity
of nickel [28–31], and similar lattice parameters between
copper and nickel [32–35], a copper–nickel bimetallic
catalyst had been explored by our group [36]. Hydrogena-
tion of hydrogen acceptor (styrene) would be accelerated
when the nickel was introduced into the copper catalyst,
lutianliang@zzu.edu.cn
1
College of Chemistry and Molecular Engineering,
Zhengzhou University, 100 Kexue Road, Zhengzhou 450001,
People’s Republic of China
2
Research Center of Heterogeneous Catalysis and Engineering
Sciences, School of Chemical Engineering and Energy,
Zhengzhou University, 100 Kexue Road, Zhengzhou 450001,
People’s Republic of China
1
3

J IRAN CHEM SOC
Table 1 Physical properties of different catalysts
and formation of aliphatic aldehydes would be enhanced.
In this work, we present systemic and specific evidence
to understand the promotion effect of nickel for Cu–Ni/γ-
Al O catalysts in the transfer dehydrogenation of primary
Cu/Nia
b
BET
2
−1
c
−1
(mL g )
Catalyst
S
(m g
)
V
pore
γ-Al O
–
201.2
170.3
166.5
180.3
214.0
150.2
161.9
0.31
0.32
0.31
0.35
0.38
0.30
0.28
2
3
2
3
6
6
6
6
6
.6Cu/γ-Al O
–
aliphatic alcohols into aldehydes.
2
3
.6Ni/γ-Al O
–
2
3
.6Cu–1Ni/γ-Al O
6.6
5.0
3.3
1.7
2
3
.6Cu–1.3Ni/γ-Al O
Experimental section
Materials
2
3
.6Cu–2Ni/γ-Al O
2
3
6.6Cu–4Ni/γ-Al2O3
a
Mass ratio of Cu/Ni
Deionized water used in all experiments was purified by
b
Surface area was determined by the BET method at a relative pres-
a Milli-Q system (Millipore). γ-Al O , Cu(NO ) ·3H O,
2
3
3 2
2
sure of 0.05–0.30
c
Ni(NO ) ·6H O and ammonia solution (25 %) were pur-
3
2
2
Total pore volume
chased from Sinopharm Chemical Reagent Co., Ltd.
,3-Dimethyl-1-butanol, styrene and mesitylene were of
3
2
analytic grade and obtained from Aladdin Chemical Rea-
gent Corporation.
(TEM) images were obtained on FEI Tecnai G Spirit
electron microscope at an accelerating voltage of 120 kV.
Temperature-programmed reduction (TPR) of the samples
−
was conducted at a heating rate of 10 °C min in an H /Ar
2
1
Preparation of Cu/γ‑Al O and Cu–Ni/γ‑Al O catalysts
2
3
2
3
−1
atmosphere at a flowing rate of 50 mL min . Before meas-
urements, sample of the catalyst was degassed at 150 °C in
an atmosphere of Ar for 0.5 h. Sample weight was about
Cu/γ-Al O was prepared with a reported method [18, 19].
2
3
Cu(NO ) ·3H O (7.6 g) was dissolved in 100 mL of deion-
3
2
2
ized water, and the pH value of the solution was adjusted
to 9 using ammonia solution (25 %). Then, the solution
was transferred into an ice-water bath. After that, γ-Al O
0.10 g, and the consumption of H was monitored by
2
TCD detector. X-ray fluorescence (XRF) was performed
on a Philips Margix X-ray fluorescence spectrometer. N2
adsorption–desorption isotherms were measured with a
2
3
(
2
20.0 g) was added to the above solution. After stirring for
0 min, the suspension was diluted by a large quantity of
Quantachrome Autosorb using N as adsorbate at 77 K.
2
water. The solid was separated from the suspension by fil-
tration and washed with deionized water for three times.
Finally, the solid was dried at 110 °C overnight and cal-
cined at 400 °C for 4 h in air. Cu loading of Cu/γ-Al O
Samples were outgassed at 423 K for 2 h before measure-
ments. The surface area was calculated according to Bar-
rett–Emmet–Taller (BET) method. The physical parameters
of the samples are shown in Table 1.
2
3
was 6.6 wt% determined by XRF.
A series of Cu–Ni bimetallic catalysts with varying Cu/
Typical procedure for catalytic dehydrogenation
Ni ratios supported on γ-Al O were prepared through
2
3
introducing nickel to the above Cu/γ-Al O by incipi-
ent wetness impregnation. Firstly, calculated amount of
Typically, the dehydrogenation reactions were performed
in a stainless steel autoclave equipped with an automatic
temperature controller, a thermocouple, a magnetic stirrer
and a pressure gauge. Taking catalytic dehydrogenation
of 3,3-dimethyl-1-butanol as an example: 3,3-dimethyl-
1-butanol (2 mmol), 6.6Cu–2Ni/γ-Al O (0.4 g), styrene
2
3
Ni(NO ) ·6H O was dissolved in deionized water (1.4 mL).
3
2
2
Then, Cu/γ-Al O (2.0 g) was added to the solution. After
2
3
stirring for 3 h, the slurry was dried at 80 °C for 8 h and
calcined at 400 °C for 4 h in air. Before used in catalytic
reactions, all the as-prepared materials were reduced in an
2
3
(8 mmol) and mesitylene (2 mL) were added to the auto-
atmosphere of H at 500 °C for 5 h unless stated otherwise.
clave. After the autoclave was sealed, N was charged to
2
2
We denoted the Cu–Ni bimetallic catalyst as xCu–yNi/γ-
Al O , where x and y were denoted as the weight percent of
replace the air. Then, the autoclave was heated to 150 °C
under magnetic stirring within 20 min. After 24 h, the reac-
tor was cooled down to room temperature. The liquid reac-
tion mixture was diluted and analyzed.
2
3
Cu and Ni relative to γ-Al O .
2
3
Characterization
Product analysis
X-ray diffraction analysis was performed using Rigaku D/
Max 2500/PC powder diffractometer with Cu-Kα radia-
tion (λ = 0.15418 nm) at 40 kV and 200 mA with a scan-
The reaction mixture was analyzed by gas chromatogra-
phy (GC) method. Gas chromatography measurements
were performed on an Agilent 7890A GC with an DB-225
−
1
ning rate of 5° min . Transmission electron microscopy
1
3

J IRAN CHEM SOC
Fig. 2 H -TPR profiles of 6.6Cu/γ-Al O , 6.6Cu–1Ni/γ-Al O ,
2
2
3
2
3
6
.6Cu–1.3Ni/γ-Al O , 6.6Cu–2Ni/γ-Al O , 6.6Cu–4Ni/γ-Al O and
2 3 2 3 2 3
6
.6Ni/γ-Al O
2
3
precursor of γ-Al O . Thus, after H reduction at 500 °C,
2
3
2
diffraction peaks of AlO(OH) disappeared completely
Fig. 1e). The 6.6Ni/γ-Al O without reduction exhibited a
(
2
3
weak diffraction peak of NiO, and this peak corresponded
to the reflection from (2 0 0) plane of the monoclinic NiO
(
Fig. 1b). When 6.6Ni/γ-Al O was exposed to hydrogen
2 3
at 500 °C for 5 h, the diffraction peak of NiO disappeared
and characteristic peaks at 2θ = 44.5°, 51.9° and 76.4°
were observed (Fig. 1f). These peaks corresponded to the
reflection from (1 1 1), (2 0 0) and (2 2 0) planes of the
0
cubic Ni . The changes between Fig. 1b, f indicated that the
0
NiO species was reduced to Ni by H reduction at 500 °C.
2
The 6.6Cu/γ-Al O sample without reduction showed a
2
3
Fig. 1 XRD patterns of samples without reduction: a γ-Al O ; b
2
3
diffraction peak at 2θ = 35.7° which was ascribed to the
6
.6Ni/γ-Al O ; c 6.6Cu/γ-Al O ; d 6.6Cu–2Ni/γ-Al O and reduced
2 3 2 3 2 3
by H at 500 °C: e γ-Al O ; f 6.6Ni/γ-Al O ; g 6.6Cu/γ-Al O ; h
reflection from (−1 1 1) plane of the monoclinic CuO
2
2
3
2
3
2
3
6
.6Cu–2Ni/γ-Al O3
2
(Fig. 1c). After reduction under H at 500 °C, the char-
2
acteristic line of CuO disappeared and diffraction peaks
at 2θ = 43.3°, 50.5° and 74.2° appeared (Fig. 1g). These
peaks were ascribed to the reflection from (1 1 1), (2 0 0)
capillary column and a flame ionization detector. Conver-
sion and selectivity were determined by the area normali-
zation method. Products were identified by using Agilent
0
and (2 2 0) planes of the cubic Cu . Thus, the CuO species
0
could also be converted to Cu after H reduction at 500 °C.
2
6
890 N GC/5973MS and the comparison with authentic
The 6.6Cu–2Ni/γ-Al O sample without reduction showed
2
3
samples.
the characteristic peak of CuO, and the diffraction peak of
NiO was not observed (Fig. 1d). After reduction, peaks of
0
0
Cu appeared and that of Ni were absent (Fig. 1h). The
0
Results and discussion
absence of NiO and Ni in 6.6Cu–2Ni/γ-Al O indicates
2
3
that they were highly dispersed or too small to be detected.
Characterization
Figure 2 shows the H -TPR profiles of the samples. When
2
Ni was introduced into the Cu-based catalyst, the H con-
2
X-ray diffraction patterns (XRD) of the samples are
sumption peak corresponding to CuO reduction shifted to
displayed in Fig. 1. Crude γ-Al O3 without reduction
a higher temperature, and the H consumption peak corre-
2
2
showed diffraction peaks of cubic Al O and orthorhom-
sponding to NiO reduction shifted to a lower temperature,
which indicates an interaction between Cu and Ni.
2
3
bic AlO(OH) (Fig. 1a), as AlO(OH) (Al O ·H O) was the
2
3
2
1
3

J IRAN CHEM SOC
Fig. 4 Time courses of 3,3-dimethyl-1-butanol dehydrogenation over
Fig. 3 Effect of Cu/Ni mass ratio on catalytic activity of different
catalysts on dehydrogenation of 3,3-dimethyl-1-butanol. Reaction
conditions: 3,3-dimethyl-1-butanol (2 mmol), catalyst (0.20 g), sty-
6
.6Cu/γ-Al O and 6.6Cu–2Ni/γ-Al O catalysts. Reaction condi-
2 3 2 3
tions: 3,3-dimethyl-1-butanol (2 mmol), catalyst (0.20 g), styrene
(
4 mmol), mesitylene (2 mL), T = 130 °C, N atmosphere
2
rene (4 mmol), mesitylene (2 mL), T = 130 °C, t = 5 h, N atmos-
2
phere
shown in Fig. 4. 6.6Cu–2Ni/γ-Al O showed much higher
2
3
conversion than 6.6Cu/γ-Al O under the same reaction
2
3
Effect of Cu/Ni mass ratio
conditions. Even when the reaction time was prolonged to
8 h, 36 and 69 %, conversions of 3,3-dimethyl-1-butanol
were obtained using 6.6Cu/γ-Al O and 6.6Cu–2Ni/γ-Al O
4
Catalytic performance of the prepared catalysts was tested in
the dehydrogenation of 3,3-dimethyl-1-butanol to 3,3-dime-
thyl-1-butanal which is a key intermediate for synthesis of
the novel high-intensity sweetener of neotame [37]. Fig-
ure 3 shows the effect of the Cu/Ni mass ratio on the cata-
lytic activity of Cu–Ni/γ-Al O in the dehydrogenation of
2
3
2
3
as catalyst, respectively. Above results further confirmed
the promotion effect of nickel for the 6.6Cu–2Ni/γ-Al O
2
3
catalyst in the dehydrogenation of 3,3-dimethyl-1-butanol.
Selectivities of 3,3-dimethyl-1-butanal for the dehydrogena-
tion reactions mentioned above were all >99 %.
2
3
3,3-dimethyl-1-butanol. The conversion was controlled below
3
0 %. As expected, monometallic catalyst of 6.6Cu/γ-Al O
Effect of hydrogen acceptor
2
3
and 6.6Ni/γ-Al O showed lower catalytic activity than the
2
3
bimetallic Cu–Ni/γ-Al O catalysts. Only 11 and 1 % of
In transfer dehydrogenation, unsaturated organic com-
pounds are usually used as hydrogen acceptor to facilitate
the reaction [22, 23]. In this study, various olefins were
selected as hydrogen acceptors and the results are summa-
rized in Table 2. Without a hydrogen acceptor, the conver-
sion of 3,3-dimethyl-1-butanol was only 2 % in 24 h. When
vinyl acetate and methyl acrylate were used as hydrogen
acceptor, no promotion effect was observed. Cyclohex-
ene, 1-decene, styrene and diphenylethylene could accel-
erate the dehydrogenation of 3,3-dimethyl-1-butanol, and
the reactivity order is styrene > 1-decene > diphenylethyl-
ene > cyclohexene. Delocalization effect of benzene ring
made C=C bond in styrene more reactive to be hydro-
genated. That is why the highest conversion was obtained
when styrene was used as hydrogen acceptor. However,
lower conversion was observed when diphenylethylene
was applied as hydrogen acceptor. This might be related to
its bigger molecular size which made it difficult to contact
with the active site for hydrogenation on catalyst.
2
3
3,3-dimethyl-1-butanol can be converted to 3,3-dimethyl-
1
-butanal over monometallic 6.6Cu/γ-Al O and 6.6Ni/γ-
2
3
Al O ,respectively. For bimetallic Cu–Ni/γ-Al O catalysts,
2
3
2 3
when the content of nickel was raised from zero to 2 %,
conversion of 3,3-dimethyl-1-butanol increased from 11 to
2
5 %; however, higher nickel content (6.6Cu–4Ni/γ-Al O )
2 3
afforded lower conversion of 3,3-dimethyl-1-butanol than that
of 6.6Cu–2Ni/γ-Al O . Introduction of the nickel into Cu–
2
3
Ni/γ-Al O catalysts promoted the dehydrogenation activity
2
3
obviously. All the selectivities of 3,3-dimethyl-1-butanal for
the reaction mentioned above were higher than 99 %.
Time courses of the dehydrogenation
of 3,3‑dimethyl‑1‑butanol over 6.6Cu/γ‑Al O3
2
and 6.6Cu–2Ni/γ‑Al O
2
3
Time courses of the dehydrogenation of 3,3-dimethyl-
-butanol over 6.6Cu/γ-Al O and 6.6Cu–2Ni/γ-Al O are
1
2
3
2
3
1
3

J IRAN CHEM SOC
Table 2 Dehydrogenation of 3,3-dimethyl-1-butanol with different
hydrogen acceptor over 6.6Cu–2Ni/γ-Al O catalyst
Effect of reaction conditions
2
3
Entry Hydrogen acceptor Conversion of
Selectivity of
The influence of reaction time, reaction temperature, amount
of catalyst and styrene on the dehydrogenation of 3,3-dime-
thyl-1-butanol over 6.6Cu–2Ni/γ-Al O is illustrated in
3
,3-dimethyl-1-bu- 3,3-dimethyl-
tanol (%)
1-butanal (%)
2
3
Table 3. When the reaction time was prolonged from 5 to
4 h, conversion of 3,3-dimethyl-1-butanol was increased
1
2
None
2
2
>99
>99
2
from 25 to 52 % (Table 3, entries 1, 2 and 3). Then, elevat-
ing the reaction temperature to 150 °C, 79 % conversion
was obtained (Table 3, entry 5). The catalytic performance
of 6.6Cu–2Ni/γ-Al O also improved when the amount of
2
3
3
4
3
8
>99
>99
catalyst and styrene was increased (Table 3, entries 4, 6 and
). After optimization of reaction conditions, 93 % conver-
sion of 3,3-dimethyl-1-butanol with 99 % selectivity of
,3-dimethyl-1-butanal can be obtained at 150 °C after 24 h
Table 3, entry 8). Under the optimized reaction conditions
7
3
(
5
6
28
52
>99
>99
7
17
>99
Fig. 5 Effect of reduction temperature of 6.6Cu/γ-Al O3 and
2
Reaction conditions: 3,3-dimethyl-1-butanol (2 mmol), 6.6Cu–2Ni/γ-
6.6Cu–2Ni/γ-Al O . Reaction conditions: 3,3-dimethyl-1-butanol
2
3
Al O (0.20 g), hydrogen acceptor (4 mmol), mesitylene (2 mL),
(2 mmol), catalyst (0.20 g), styrene (4 mmol), mesitylene (2 mL),
2
3
T = 130 °C, t = 24 h, N atmosphere
T = 130 °C, t = 5 h, N atmosphere
2
2
Table 3 Dehydrogenation of
Entry
Amount of catalyst (g)
Reaction temperature (°C)
Reaction time (h)
Conversion (%)
3
,3-dimethyl-1-butanol over
6
.6Cu–2Ni/γ-Al O under
2
3
1
2
3
4
5
6
7
8a
0.2
0.2
0.2
0.1
0.4
0.2
0.4
0.4
130
130
130
130
130
150
150
150
5
15
24
24
24
24
24
24
25
42
52
37
70
79
84
93
different reaction conditions
Reaction conditions: 3,3-dimethyl-1-butanol (2 mmol), styrene (4 mmol), mesitylene (2 mL), N atmos-
2
phere. Selectivity of 3,3-dimethyl-1-butanal >99 % for all entries
a
Mole ratio of styrene/substrate = 4
1
3

J IRAN CHEM SOC
Fig. 6 TEM images of 6.6Cu–2Ni/γ-Al O : a without reduction; b reduced at 270 °C; c reduced at 400 °C; d reduced at 500 °C; e reduced at
2
3
6
00 °C
(same as Table 3, entry 8), dehydrogenation of some other
6.6Cu/γ-Al O and 6.6Cu–2Ni/γ-Al O showed compara-
2 3 2 3
primary aliphatic alcohols including isoamyl alcohol, n-amyl
alcohol and n-hexyl alcohol was carried out. 89, 91 and 91 %
conversions of isoamyl alcohol, n-amyl alcohol and n-hexyl
alcohol were obtained, respectively, and all the selectivity of
the corresponding aldehydes was more than 99 %.
ble activity after H reduction at 270 °C. When the reduc-
2
tion temperature was between 270 and 500 °C, an increase
in the conversion of 3,3-dimethyl-1-butanol was observed
over 6.6Cu–2Ni/γ-Al O and a decrease in conversion was
2
3
obtained over 6.6Cu/γ-Al O . Lower activity of 6.6Cu/γ-
2
3
Al O reduced at 500 °C was obtained than 270 °C which
2
3
Effect of reduction temperature
might be related to the bigger Cu particle size. However,
.6Cu–2Ni/γ-Al O reduced at 270, 400 and 500 °C showed
6
2
3
Figure 5 shows the effect of reduction temperature on the
similar metal particle size (Fig. 6). Thus, particle size was not
catalytic activity of 6.6Cu/γ-Al O and 6.6Cu–2Ni/γ-Al O .
the only factor affecting the activity of 6.6Cu–2Ni/γ-Al O
2
3
2
3
2 3
1
3

J IRAN CHEM SOC
Scheme 1 Proposed reaction pathways in the transfer dehydrogena-
tion of 3,3-dimethyl-1-butanol over Cu–Ni/γ-Al O catalyst
2
3
Scheme 2 Hydrogenation of styrene over different catalysts. Reac-
tion conditions: styrene (4 mmol), catalyst (0.2 g), mesitylene (8 mL),
H (0.6 MPa)
2
Fig. 7 Hydrogenation of mixture of 3,3-dimethyl-1-butanol,
,3-dimethyl-1-butanal, styrene and ethylbenzene over 6.6Cu–2Ni/γ-
Al O and 6.6Cu/γ-Al O . a, b were denoted as below: a amount
3
in range of 270–500 °C. Figure 2 shows that CuO species
2
3
2
3
0
of styrene/(amount of styrene and ethylbenzene) × 100; b amount
could be reduced to Cu under H at 270 °C completely, how-
2
of 3,3-dimethyl-1-butanal/(amount of 3,3-dimethyl-1-butanal and
ever, reduction of NiO occured at higher temperature. The
3
,3-dimethyl-1-butanol) × 100. Reaction conditions: 3,3-dime-
0
presence of Ni might be important for the high activity of
thyl-1-butanal (2 mmol), catalyst (0.4 g), mesitylene (10 mL),
T = 100 °C, t = 30 min, H (0.6 MPa)
6
.6Cu–2Ni/γ-Al O .
2
2
3
Figure 6 shows the TEM images of the 6.6Cu–2Ni/γ-
Al O reduced by H at different temperatures. Most parti-
2
3
2
cles in the 6.6Cu–2Ni/γ-Al O samples reduced at 270, 400
be one of the key steps in the transfer dehydrogenation of
3,3-dimethyl-1-butanol.
2
3
and 500 °C exhibited similar particle size ranges (5–15 nm)
Fig. 6a–d). However, higher temperature (600 °C) led
(
As mentioned above, the catalytic activity of 6.6Cu/γ-Al O
2
3
to larger particle size (Fig. 6e). These results indicate that
metal particle size was not affected significantly by reduc-
tion temperature in a broad range (270–500 °C) when Ni
was introduced into the Cu–Ni/γ-Al O catalyst. This might
in dehydrogenation of 3,3-dimethyl-1-butanol was significantly
enhanced by introduction of nickel. We are interested in the
role of nickel during the transfer dehydrogenation reaction.
Hydrogenation of styrene over different catalysts was carried
out (Scheme 2). Conversion of styrene on 6.6Cu/γ-Al O and
2
3
be related to the interaction between copper and nickel
2
3
which was also observed in the H -TPR results (Fig. 2).
6.6Ni/γ-Al O was 28 and 40 % in 30 min at 100 °C, respec-
2
2 3
tively, indicating that 6.6Ni/γ-Al O was more active than
2
3
Promotion effect of nickel in Cu–Ni bimetallic catalyst
on hydrogenation of styrene
6.6Cu/γ-Al O in the catalytic hydrogenation of styrene. More-
2 3
over, conversion of styrene over 6.6Cu–2Ni/γ-Al O catalyst
2
3
increased significantly to 80 %, which was much higher than
On the basis of the previous work [18–21, 24–27], we pro-
posed reaction pathways in transfer dehydrogenation of
that over 6.6Cu/γ-Al O or 6.6Ni/γ-Al O . This result suggests
that introduction of nickel enhanced the hydrogenation activ-
2
3
2 3
3
,3-dimethyl-1-butanol over Cu–Ni/γ-Al O catalyst in this
ity of 6.6Cu–2Ni/γ-Al O dramatically. The literature also
2
3
2 3
study (Scheme 1): (1) conversion of 3,3-dimethyl-1-butanol
into 3,3-dimethyl-1-butanal directly by dehydrogenation;
reported that the catalytic activity of nickel was much higher
than that of copper for hydrogenation of styrene [38].
(
2) rehydrogenation of 3,3-dimethyl-1-butanal; (3) hydro-
genation of the styrene. An equilibrium would be tempo-
rarily established between reactions (1) and (2) without
styrene (take styrene as an example). The immediate trans-
fer of hydrogen would affect the equilibrium significantly.
Hydrogenation of hydrogen acceptor like styrene would
Selective hydrogenation of C=C bond over Cu–
Ni/γ‑Al O catalyst
2
3
Generally, hydrogenation of hydrogen acceptor like sty-
rene is supposed to compete with that of aldehyde in
1
3

J IRAN CHEM SOC
3,3-dimethyl-1-butanal would be impeded and the formation
of 3,3-dimethyl-1-butanal was promoted.
Conclusions
In summary, we report Cu–Ni bimetallic catalysts for
high selective dehydrogenation of 3,3-dimethyl-1-butanol
in liquid phase, which exhibited higher activity than that
of monometallic copper catalyst under the same reaction
conditions. Selective hydrogenation of C=C bond, rather
than C=O bond, was significantly improved over Cu–Ni/γ-
Al O catalyst by introducing nickel, which accounted for
2
3
the enhanced activity in catalytic dehydrogenation of pri-
mary aliphatic alcohols.
Fig. 8 GC traces for hydrogenation of crotonaldehyde over
.6Cu–2Ni/γ-Al O3 and 6.6Cu/γ-Al O . The retention times cor-
6
2
2
3
respond to the following compounds: 6.14 min (n-butanal),
.05 min (crotonaldehyde), 8.24 min (crotyl alcohol), and 8.56 min
Acknowledgments This work was supported by the National Natural
Science Foundation of China (Grant: U1304209), the Key Scientific
Research Projects for University in Henan Province (16A530009) and
the Foundation for University Young Key Teacher by Henan Province
8
(
(
n-butanol). Reaction conditions: crotonaldehyde (4 mmol), catalyst
0.30 g), mesitylene (10 mL), T = 90 °C, t = 1 h, H (1.5 MPa)
2
(
Grant: 2014GGJS-005).
transfer dehydrogenation of alcohols. We carried out a con-
trol experiment to test and verify the assumption. Firstly,
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