Highly efficient dehydrogenation of primary aliphatic alcohols catalyzed by Cu nanoparticles dispersed on rod-shaped La2O2CO 3

Article abstract of DOI:10.1021/cs400255r

Copper nanoparticles dispersed rod-shaped La₂O ₂CO₃ efficiently catalyzed transfer dehydrogenation of primary aliphatic alcohols with an aldehyde yield of up to 97%. This high efficiency was achieved by creating a catalyti

Full text of DOI:10.1021/cs400255r

Letter
pubs.acs.org/acscatalysis
Highly Efficient Dehydrogenation of Primary Aliphatic Alcohols
Catalyzed by Cu Nanoparticles Dispersed on Rod-Shaped La O CO
3
2
2
†
†
†
,‡
‡
‡
†
†
Fei Wang, Ruijuan Shi, Zhi-Quan Liu,* Pan-Ju Shang, Xueyong Pang, Shuai Shen, Zhaochi Feng,
,
,†
Can Li,* and Wenjie Shen*
†
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
‡
Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016,
China
*
S Supporting Information
ABSTRACT: Copper nanoparticles dispersed rod-shaped
La O CO efficiently catalyzed transfer dehydrogenation of
2
2
3
primary aliphatic alcohols with an aldehyde yield of up to 97%.
This high efficiency was achieved by creating a catalytically active
nanoenvironment for effective reaction coupling between alcohol
dehydrogenation and styrene hydrogenation via hydrogen transfer.
The {110} planes on the La O CO nanorods not only provided
2
2
3
substantial amounts of medium-strength basic sites for the
activation of alcohol but also directed the selective dispersion of
hemispherical Cu particles of about 4.5 nm on their surfaces,
which abstracted and transferred hydrogen atoms for styrene
hydrogenation. This finding provides a new strategy for developing highly active alcohol-dehydrogenation catalysts by tuning the
shape of the oxide support and consequently the metal-oxide interfacial nanostructure.
KEYWORDS: heterogeneous catalysis, dehydrogenation, primary aliphatic alcohol, reaction coupling, Cu/La O CO catalyst,
2
2
3
crystal-facet selective deposition, active nanoenvironmental
ehydrogenation of primary aliphatic alcohols to aldehydes
dehydrogenation of secondary aliphatic alcohols using styrene
7
8
9
D
is of great importance in synthetic chemistry and fine
chemical industry. This conversion is traditionally accomplished
by oxidizing alcohols with stoichiometric amounts of chromate
as the hydrogen acceptor. Hydrotalcite-supported Ag, Au,
10
11
and Cu particles and water-soluble Ru nanoparticles
effectively catalyzed oxidant-free dehydrogenations of secon-
dary aliphatic and benzylic alcohols. Recently, copper particles
supported on basic metal oxides were found to show
1
or permanganate, generating large amounts of highly toxic
heavy metal wastes. Oxidative dehydrogenation of alcohols
using solid catalysts and atmospheric air or molecular oxygen
avoids the environmental problem, producing water as the only
2b
12
remarkably enhanced activities in alcohol dehydrogenation.
Even though, efficient dehydrogenation of primary aliphatic
alcohols is still challenging. In a previous study, we reported
that a Cu/La O catalyst offered a 1-octanal yield of 63% in
2
3
4
5
byproduct in principle. Supported Au, Pd, Pt, and Ru
catalysts are basically active for oxidative dehydrogenation of
benzylic and allylic alcohols, known as activated alcohols, but
are less active for primary aliphatic alcohols that are generally
viewed as nonactivated alcohols. The practical application of
oxidative dehydrogenation of alcohols is still hindered by the
unsatisfied selectivity toward carbonyls and the safety concern
linked with the use of flammable solvents under oxidative
atmospheres.
2
3
12c
transfer dehydrogenation of 1-octanol.
Here, we further
demonstrate that precisely tuning the chemical phase and the
shape of the oxide support could significantly promote the
efficiency of the Cu particles of 4−5 nm for transfer
dehydrogenation of primary aliphatic alcohols, attaining an
aldehyde yield of 97% under the optimized reaction conditions.
We started with the synthesis of La(OH) nanorods using a
3
Transfer dehydrogenation of alcohols that uses recyclable
solid catalysts and unsaturated organic compounds as the
hydrogen acceptors improves the selectivity of carbonyls and
overcomes the safety problem, providing a new route for
alcohol transformation. However, only a few heterogeneous
catalysts are known to be effective for this novel conversion of
alcohols, mostly activated alcohols. Pd nanoparticles catalyzed
transfer dehydrogenation of allylic and aromatic alcohols using
ethylene, cyclohexene, and nitrobenzene as the hydrogen
hydrothermal process. The nanorods had widths of 10−15 nm
and lengths of 200−400 nm (Supporting Information, Figure
S1). Calcination of this lanthanum hydroxide precursor at 773
K for 4 h in air yielded La O CO nanorods with straight sides
2
2
3
and regular ends (Supporting Information, Figure S2). Figure
a is a high-resolution transmission electron microscopy
1
Received: April 5, 2013
Published: April 9, 2013
6
acceptors. Cu catalysts showed high activities in transfer
©
2013 American Chemical Society
890
dx.doi.org/10.1021/cs400255r | ACS Catal. 2013, 3, 890−894

ACS Catalysis
Letter
Meanwhile, the favorable lattice matching between the Cu
(
111) and the La O CO (110) may also result in a selective
2 2 3
deposition of copper particles.
The Cu/La O CO catalyst showed exceptionally high
2
2
3
activity in transfer dehydrogenation of 1-octanol, the most
frequently used representative of primary aliphatic alcohols. In
a preliminary test, 1-octanol was dehydrogenated to 1-octanal
with a yield of 8% at 373 K; the yield of 1-octanal increased
when raising the temperature and reached 64% at 413 K
(
Supporting Information, Table S1). Optimization of the
styrene/1-octanol molar ratio and the reaction time resulted in
-octanal yield of 97% at 423 K (Table 1). By adding styrene as
1
Table 1. Transfer Dehydrogenation of 1-Octanol on the Cu/
a
La O CO Catalyst at 423 K
2
2
3
b
entry
time (h)
S/O (ratio)
conv. (%)
select. (%)
yield (%)
1
2
3
4
5
3
3
1.0
2.0
4.0
4.0
4.0
72
84
87
94
98
100
>99
99
72
83
86
93
97
3
8
99
10
99
a
Reaction conditions: Cu/La O CO (200 mg), 1-octanol (2 mmol),
2
2
3
b
mesitylene (8 mL), styrene (2−8 mmol), N atmosphere. Styrene/1-
octanol molar ratio.
2
Figure 1. HRTEM images of the La O CO nanorod viewed along the
2
2
3
(
̅
a) [001], (b) [110], and (c) [010] orientations. The arrow-heads in
the hydrogen acceptor in an equimolar ratio with respect to 1-
octanol, the yield of 1-octanal was 72% and increased to 83% by
using 2 equivalent moles of styrene. Further increasing the
styrene/1-octanol molar ratio to 4.0 only slightly promoted 1-
octanal yield to 86%. When prolonging the reaction time, the
yield of 1-octanal increased moderately from 86% at 3 h to 97%
at 10 h. In these experiments, the number of moles of
ethylbenzene produced approximately equaled to that of 1-
octanol converted. This result evidenced the effective reaction
coupling between 1-octanol dehydrogenation and styrene
hydrogenation through hydrogen transfer.
panel c indicate the steps on the (001) plane, noticing that at these
steps La and O atoms in the (110) plane are exposed to the surface.
(
near the [110] orientation. (e) Illustration of the real shape of the
La O CO nanorod. (f) Hemispherical Cu particles with a mean size
of about 4.5 nm on the La O CO nanorod viewed along the [001]
orientation; the dotted circles referred to the copper nanoparticles on
the (001) flat plane.
d) A rectangular cross-section (10 × 15 nm) of the nanorod viewed
2
2
3
2
2
3
(
HRTEM) image of a single La O CO nanorod viewed along
2 2 3
the [001] orientation. The nanorod grew along the [110]
direction and was enclosed by (110), (100), and (010) planes.
The Cu/La O CO catalyst was also highly active for transfer
2
2
3
HRTEM images viewed along the [11
(
(
̅
dehydrogenation of other primary aliphatic alcohols (Table 2).
Dehydrogenations of 1-butanol and 1-hexanol produced the
corresponding aldehydes with the yields of 84% and 93%,
respectively. For the dehydrogenation of higher C-chain
alcohols, like 1-decanol and 1-dodecanol, the aldehyde yields
approached 74−85%. These slightly lowered yields might be
due to the relatively slow surface migration of the bulky
[
̅
2
2
3
assumed to be a square block that was terminated by two (001)
flat planes, two (110) side planes, and two (110) end planes, as
14
̅
substrates on the catalyst surface. The scope of the substrate
could be extended to primary aromatic and cycloaliphatic
alcohols. Transfer dehydrogenation of benzyl alcohol, the
typical substrate of primary aromatic alcohols, provided
benzylaldehyde yields of 58% at 383 K for 6 h and 100% at
423 K for 1 h. Moreover, primary cycloaliphatic alcohols, like
cyclohexanol and cyclooctanol, were easily dehydrogenated to
cycloaliphatic aldehydes with yields of 61−99% at 383 K. Most
interestingly, the Cu/La O CO catalyst was also effective for
illustrated in Figure 1e where the hexagonal unit was outlined.
The width of the flat (001) plane was about 15 nm while that of
̅
the side (110) plane was about 10 nm. Hemispherical Cu
nanoparticles with an average size of 4.5 nm were then
dispersed on the La O CO nanorods by a deposition-
2
2
3
precipitation method. Figure 1f shows a HRTEM image of
the Cu/La O CO catalyst. There were only a few Cu particles
2
2
3
deposited on the (001) flat planes as indicated with dotted
2
2
3
circles; most Cu nanoparticles were preferentially anchored on
transfer dehydrogenation of primary benzylic alcohols. 2-
Phenyl-ethanol, whose dehydrogenation is more challenging
than that of primary aliphatic alcohols, was converted to 2-
acetonaphthone with the yields of 11% at 383 K for 7 h and
52% at 423 K for 6 h. As expected, secondary aliphatic alcohols
(2-octanol) and activated aromatic alcohols (1-phenyl-2-
the {110} surfaces, including the (11
110) end planes (Supporting Information, Figure S3),
showing a distinct crystal-facet selective deposition pattern.
̅
0) side planes and the
(
13
Since the {110} facet have a high energy, preferential
deposition of Cu particles minimized the overall surface energy.
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ACS Catalysis
Letter
a
Table 2. Transfer Dehydrogenation of Alcohols on the Cu/La O CO Catalyst
2
2
3
a
Reaction conditions: Cu/La O CO (200 mg), alcohol (2 mmol), styrene (8 mmol), mesitylene (8 mL), N atmosphere.
2
2
3
2
ethanol) were fully dehydrogenated to the corresponding
carbonyls at 383 K within 1 h on the Cu/La O CO catalyst.
atoms only (Figure 2b and Supporting Information, Figure S4).
Since the surface area of the {110} planes was about 40% of the
2
2
3
2
−
The outstanding performance of the Cu/La O CO catalyst
total surface area, the coordinatively unsaturated O sites or
2
2
3
3+
2−
in transfer dehydrogenation of primary aliphatic alcohols is
understandable on the basis of the reaction mechanisms derived
from classical studies carried out for homogeneous and
heterogeneous dehydrogenations of alcohols. In homogeneous
catalysis, to achieve satisfactorily high alcohol conversion and/
or aldehyde selectivity, organic bases or alkaline compounds
were often added to the reaction media for expediting the
La -O pairs on the {110} facets predominantly contributed
to the overall basicity of the La O CO nanorods.
2
2
3
Infrared spectroscopy of 1-octanol adsorption on the catalyst
evidenced that the La O CO nanorod activated alcohol while
2
2
3
the Cu nanoparticle facilitated hydrogen transfer (Figure 2c and
Supporting Information, Figure S5). On bare La O CO
3
2
2
nanorods, 1-octanol was dissociatively activated through the
15
3+
2−
deprotonation of the alcoholic group. When heterogeneous
catalysts are used, alcohol was activated by interacting with the
surface oxygen on the supporting oxides, acting as a Brønsted
base. The high activities of gold, silver, and copper nano-
particles in oxidant-free dehydrogenation of alcohols were
interaction of its O−H bond with the surface La -O pairs at
423 K, forming alkoxide species (La−O−CH −R at 1046
2
−
1
17a
cm ).
On the Cu/La O CO catalyst, however, the
2 2 3
stretching modes of the −CH groups have blue-shifted by 5
2
−
1
cm ; the La−O−CH −R band on bare La O CO vanished,
2
2
2
3
8c
−1
primarily assigned to the basic sites on the hydrotalcites. Our
previous study on a Cu/La O catalyst for transfer dehydrogen-
but a new band at 1078 cm representing Cu−O−CH −R-like
2
17b
species
appeared, indicating that the copper particle
2
3
ation of 1-octanol verified the importance of the basic sites on
abstracted another hydrogen atom from the α-C−H bond
and activated the C−O bond in the adsorbed alkoxide
intermediate. These results suggest that transfer dehydrogen-
ation of 1-octanol on the Cu/La O CO catalyst follows a
the La O surface covered by La O CO species and the
2
3
2
2
3
maximum yield of 1-octanal approached 63% under the optimal
1
2c
conditions.
Here, tuning the shape of the supporting
2
2
3
La O CO further promoted the 1-octanal yield to a level of
bifunctional mechanism involving both the Cu nanoparticle and
2
2
3
97% under the optimized conditions, presumably due to the
the La O CO nanorod (Figure 2d). The first hydrogen atom
2
2
3
variations in the basic properties associated with the dominant
exposure of the {110} facets. Temperature-programmed
desorption of CO on the Cu/La O CO catalyst showed an
was removed from the alcoholic group by the basic sites on the
La O CO nanorod, forming alkoxide species. The abstraction
2
2
3
of the α-hydrogen from the alkoxide was then accomplished on
the nearby copper particle, producing aldehyde. Simulta-
neously, the Cu particle catalyzed styrene hydrogenation
using the hydrogen atoms released from the alcohol, driving
the reaction equilibrium toward aldehyde. In such a reaction
model, the {110} plane on the La O CO nanorod not only
2
2
2
3
intense desorption peak at about 560 K (Figure 2a), indicating
the presence of substantial amounts of medium-strength basic
3
+
2−
16
sites (La -O pairs). Crystallographically, La O CO has a
2
2
3
3
+
hexagonal structure where each La cation is surrounded by
seven oxygen anions: four in tetrahedral and three in octahedral
coordinations. As mentioned above, the La O CO nanorod
2
2
3
provided sufficient basic sites for the primary activation of the
alcohol but also directed the preferential dispersion of Cu
particles on its surface, creating a synergetic nanoenvironment
for the efficient reaction coupling between 1-octanol dehydro-
genation and styrene hydrogenation through hydrogen transfer.
2
2
3
̅
was enclosed by two end (110) planes, two (110) side planes,
and two (001) flat planes. Our density-functional theory
calculations identified that the {110} planes were made up of O
and La atoms whereas the {001} plane contained O and C
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ACS Catalysis
Letter
Recycling tests verified that the current catalyst maintained high
activity for five consecutive runs without decrease in the
selectivity of 1-octanal (more than 99%). The slight decrease in
1
-octanol conversion was assigned to the minor aggregation of
copper nanoparticles (Supporting Information, Figure S7).
On the basis of these findings, we conclude that Cu
nanoparticles selectively dispersed on the {110} facets of
La O CO nanorods are highly active for transfer dehydrogen-
2
2
3
ation of primary aliphatic alcohols. The medium-strength basic
sites on the {110} facets of the rod-shaped La O CO
3
2
2
interacted strongly with Cu nanoparticles, generating a
catalytically active nanoenvironment for the reaction coupling
between alcohol dehydrogenation and styrene hydrogenation.
This strategy raises the prospect of using nanostructured solid
catalysts for the efficient dehydrogenation of alcohols to
functionalized carbonyls, and consequently contributes to the
sustainable development of green chemistry.
ASSOCIATED CONTENT
■
*
S
Supporting Information
Materials and methods; additional experimental results in the
structural analyses of the catalysts, dehydrogenations of
different types of alcohols, reaction kinetics, and recycle tests.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Figure 2. Possible reaction pathway of 1-octanol transfer dehydrogen-
AUTHOR INFORMATION
■
ation. (a) Profiles of temperature-programmed desorptions of CO on
2
Corresponding Author
the La O CO nanorods (black curve) and the Cu/La O CO catalyst
2
2
3
2
2
3
(
red curve); the intense desorption peaks at about 560 K represented
*E-mail: shen98@dicp.ac.cn (W.S.), zqliu@imr.ac.cn (Z.-Q.L.),
3+
2−
the medium-strength basic sites (La -O pairs) with a total amount
of 0.16 mmol·g on the La O CO nanorods and 0.11 mmol·g on
the Cu/La O CO catalyst. (b) Hexagonal unit of La O CO crystal
canli@dicp.ac.cn (C.L.).
−1
−1
2
2
3
Notes
2
2
3
2
2
3
The authors declare no competing financial interest.
(
left) in which the C and O atomic sites are 1/3 occupied at the arrow-
indicated sublayers (the gray ball refers as to the vacancies), and the
atomic arrangements (right) of the {001} and {110} planes. (c) IR
spectra of 1-octanol adsorption on bare La O CO nanorods (black
ACKNOWLEDGMENTS
■
2
2
3
This work was supported by the National Natural Science
Foundation of China (20923001, 21025312) and the National
Basic Research Program of China (2010CB631006,
2013CB933100).
curve) and the Cu/La O CO (red curve) at 423 K. (d) A depicting
2
2
3
scheme of 1-octanol dehydrogenation on the Cu nanoparticle and the
{
110} plane of the La O CO . (e) Arrhenius plot of the reaction rate
2
2
3
on the Cu/La O CO catalyst at 373−423 K. (f) TOFs as a function
2
2
3
of copper particle size at 423 K.
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■
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