Robust cobalt oxide catalysts for controllable hydrogenation of carboxylic acids to alcohols

Article abstract of DOI:10.1016/S1872-2067(17)63003-1

The selective catalytic hydrogenation of carboxylic acids is an important process for alcohol production, while efficient heterogeneous catalyst systems are still being explored. Here, we report the selective hydrogenation of carboxylic acids using earth-abundant cobalt oxides through a reaction-controlled catalysis process. The further reaction of the alcohols is completely hindered by the presence of carboxylic acids in the reaction system. The partial reduction of cobalt oxides by hydrogen at designated temperatures can dramatically enhance the catalytic activity of pristine samples. A wide range of carboxylic acids with a variety of functional groups can be converted to the corresponding alcohols at a yield level applicable to large-scale production. Cobalt monoxide was established as the preferred active phase for the selective hydrogenation of carboxylic acids.

Full text of DOI:10.1016/S1872-2067(17)63003-1

Chinese Journal of Catalysis 39 (2018) 250–257
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
Robust cobalt oxide catalysts for controllable hydrogenation of
carboxylic acids to alcohols
Song Songa,†, Dong Wangc,†, Lu Dia, Chuanming Wangc, Weili Daia, Guangjun Wua, Naijia Guana,b,
Landong Lia,b,*
a School of Materials Science and Engineering & National Institute for Advanced Materials, Nankai University, Tianjin 300350, China
b Key Laboratory of Advanced Energy Materials Chemistry of Ministry of Education, Collaborative Innovation Center of Chemical Science and Engineering,
Nankai University, Tianjin 300071, China
c SINOPEC, Shanghai Research Institute of Petrochemical Technology, Shanghai 201208, China
A R T I C L E I N F O
A B S T R A C T
Article history:
The selective catalytic hydrogenation of carboxylic acids is an important process for alcohol produc‐
tion, while efficient heterogeneous catalyst systems are still being explored. Here, we report the
selective hydrogenation of carboxylic acids using earth‐abundant cobalt oxides through a reac‐
tion‐controlled catalysis process. The further reaction of the alcohols is completely hindered by the
presence of carboxylic acids in the reaction system. The partial reduction of cobalt oxides by hy‐
drogen at designated temperatures can dramatically enhance the catalytic activity of pristine sam‐
ples. A wide range of carboxylic acids with a variety of functional groups can be converted to the
corresponding alcohols at a yield level applicable to large‐scale production. Cobalt monoxide was
established as the preferred active phase for the selective hydrogenation of carboxylic acids.
© 2018, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Received 6 October 2017
Accepted 21 November 2017
Published 5 February 2018
Keywords:
Selective hydrogenation
Carboxylic acids
Alcohols
Cobalt oxides
Reaction‐controlled catalysis
Published by Elsevier B.V. All rights reserved.
1. Introduction
iridium and rhodium [7], and cobalt [8], have been reported,
and a delicately designed catalyst system, including metal pre‐
Alcohols are known as simple but important building blocks
in the fine chemistry industry and have increasing global de‐
mand. The catalytic hydrogenation of carboxylic acids with
dihydrogen is the most straightforward and green process for
the production of alcohols, which is a fundamental transfor‐
mation in laboratory organic synthesis and is also applied on an
industrial scale [1–3]. However, the low electrophilicity of the
carbonyl carbon and the weak polarizability of the carbonyl
group make the hydrogenation of carboxylic acids very difficult.
In the past decades, the hydrogenation of carboxylic acids has
been well‐investigated with a focus on catalysis [4–13]. Homo‐
geneous organometallic complexes based on ruthenium [4–6],
cursor, ligand, and additive, is the key point to achieve high
activity for carboxylic acid hydrogenation. The interaction of
the carboxylic acid with the active transition metal center may
result in the critical deactivation of the organometallic catalyst.
Heterogeneous catalysts based on platinum group metals,
e.g., ruthenium [9–11] and platinum [12], have also been suc‐
cessfully developed for the hydrogenation of carboxylic acids.
However, the selectivity toward alcohols is usually ~90%,
which is insufficient for alcohol production from carboxylic
acid hydrogenation [1,14,15]. Moreover, the use of precious
metals will undoubtedly increase the cost for the hydrogena‐
tion process. Despite current achievements, hydrogenation
* Corresponding author. Tel/Fax: +86‐22‐23500341; E‐mail: lild@nankai.edu.cn
This work was supported by the National Natural Science Foundation of China (21421001, 21573113) and Sinopec Corp.
† Two authors contributed equally to this work.
DOI: 10.1016/S1872‐2067(17)63003‐1 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 39, No. 2, February 2018

Song Song et al. / Chinese Journal of Catalysis 39 (2018) 250–257
251
catalysts are still being explored and the efficient hydrogena‐
tion of carboxylic acids to the corresponding alcohols remains
challenging.
Herein, we report partially reduced cobalt oxides as robust
nonprecious catalysts for the controllable hydrogenation of
carboxylic acids to the corresponding alcohols. A wide range of
carboxylic acids with different functional groups can be hydro‐
genated to alcohols under relatively mild conditions at yields
applicable to large‐scale production.
tific ESCALAB 250Xi spectrometer using a monochromatic
Al‐Kα X‐ray source (hν = 1486.6 eV) as the excitation source.
The Co3O4 sample was reduced in situ in the reaction chamber,
evacuated, and transferred for analysis under vacuum. All
spectra were recorded by using an aperture slot of 300×700
micrometers. Accurate binding energies (±0.1 eV) were deter‐
mined with respect to the position of the adventitious C 1s peak
at 284.8 eV.
2.3. Catalytic evaluation and product analysis
2. Experimental
The hydrogenation of carboxylic acids or other substrates
was performed in a high‐pressure stainless‐steel autoclave
(Xinyuan Chemical Machinery, Series CJK, 300 mL) with a
maximum stirring rate of 1500 r/min. In a typical experiment,
0.2 g of catalyst (or without catalyst for the control experi‐
ment), 3 mmol of the substrate, and 100 mL alkane solvent
(n‐hexane, n‐heptane, i‐octane, or n‐dodecane) were well mixed
in the autoclave and purged with pure nitrogen at room tem‐
perature. The gas supply and discharge were carried out man‐
ually through needle valves. The autoclave was rapidly heated
to the desired temperature and hydrogen was introduced at 2
MPa to initiate the reaction. The reaction pressure was kept at
2 MPa with a small negative deviation (~0.2 MPa) owing to the
consumption of hydrogen. Samples of the liquid phase were
continuously taken through a sampling tube with a filter at
certain intervals. The stirring rate was kept at 750 r/min dur‐
ing the reaction.
The liquid organic products were analyzed by gas chroma‐
tography (Shimadzu GC‐2010) and gas chromatography–mass
spectrometry (Shimadzu GCMS‐QP2010 SE), both with a
RXI‐5MS column (30 m, 0.25 mm internal diameter, stationary
phase thickness 0.25 μm). n‐Eicosane was used as an internal
standard for quantification through the internal standard
method. For the hydrogenation of dioic acids, the substrates
and liquid organic products were analyzed by
high‐performance liquid chromatography (Shimadzu LC‐20AT)
with a Carbomix H‐NP column (7.8 × 300 mm, stationary phase
thickness 10 μm). The gas products were analyzed with a mass
spectrometer (Pfeiffer Omnistar GSD 320).
2.1. Catalyst preparation
The Co3O4 sample was prepared by a precipitation method.
In a typical process, diffluent cobalt salt (cobalt nitrate, cobalt
chloride, or cobalt acetate) was dissolved in 200 mL distilled
water and a precipitator (1 mol/L of Na2CO3 solution) was
added dropwise into the cobalt salt aqueous solution under
vigorous stirring until the pH of the mother liquid reached ap‐
proximately 9. The suspension was aged for 2 h with stirring at
room temperature and the precipitate was collected by filtra‐
tion and thoroughly washed with distilled water. The solid
product was dried at 353 K overnight and then calcined in air
at 773 K for 6 h to obtain Co3O4.
The as‐prepared Co3O4 was further reduced in 5 vol% H2/Ar
(flow rate = 20 mL/min) at a designated temperature (473–773
K) for 2 h and the obtained reduced cobalt oxides were labeled
as Co3O4‐n, in which n indicates the reduction temperature in
Kelvin. (Note: The reduced cobalt oxides were extremely active
and self‐ignition could occur upon contact with air. All experi‐
ments with reduced cobalt oxides should be performed in a
glove box.)
2.2. Characterization techniques
The specific surface areas of samples were determined by
N2 adsorption/desorption isotherms at 77 K collected on a
Quantachrome iQ‐MP gas adsorption analyzer. Transmission
electron microscopy (TEM) images of selected samples were
taken on a FEI Tecnai G2 F30 electron microscope at an accel‐
eration voltage of 200 kV. A few drops of the alcohol suspen‐
sion containing the sample were placed on a carbon‐coated
copper grid, followed by evaporation at ambient temperature.
The temperature‐programmed reduction (TPR) experiments of
selected samples were performed on a chemisorption analyzer
(Chemisorb 2720, Micromeritics) with 5 vol% H2/Ar in the
temperature range of 300–1000 K at a heating rate of 10
K/min. Prior to reduction, the sample was pretreated in Ar at
573 K for 1 h. The X‐ray diffraction (XRD) patterns of Co3O4
during the in situ reduction process (473–773 K) were record‐
ed on a Thermo ARL SCINTAG X’TRA diffractometer with Anton
Parr XRK 900 reaction chamber using Cu‐Kα radiation (λ=
0.1541 nm) at a scanning rate of 4o/min in the region of 2θ =
10–80o. The sample chamber atmosphere was maintained un‐
der flowing 5 vol% H2/Ar at a flowrate of 20 mL/min. X‐ray
photoelectron spectra (XPS) were recorded on a Thermo Scien‐
For recycling tests, the catalyst sample was separated from
the liquid phase by configuration in the glove box (without a
washing step) and then mixed with the desired amount of stea‐
ric acid for the next reaction cycle.
2.4. Computational methods and modeling
All the spin‐polarized calculations were performed with the
Perdew‐Burke‐Ernzerhof (PBE) functional using the VASP
software [16,17]. The project‐augmented wave (PAW) method
was used to represent the core‐valence electron interaction.
The valence electronic states were expanded in the plane wave
basis sets with energy cutoff at 450 eV, and the occupancy of
the one‐electron states was calculated using Gaussian smear‐
ing. The ionic degrees of freedom were relaxed using the BFGS
minimization scheme until the Hellman‐Feynman forces on
each ion were less than 0.3 eV/nm. Transition states were

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Song Song et al. / Chinese Journal of Catalysis 39 (2018) 250–257
searched using a dimer method [18,19], and were verified
when (i) all forces on the atoms vanished; and (ii) the total en‐
ergy was a maximum along the reaction coordination but a
minimum with respect to the rest of the degrees of freedom.
The dipole correction was applied throughout the calculations
to take the polarization effect into account.
The CoO (111) surface was modeled as a four‐Co‐layer
p(44) periodic slab consisting of 128 atoms, and a corre‐
sponding 1×1×1 k‐points mesh was used during calculations.
Atoms in the bottom two layers were fixed, and all other atoms
were fully relaxed. For the calculations for CoO, the on‐site
coulomb correction was used to describe the electronic and
geometric structure, i.e., the so‐called DFT+U method [20,21].
The effective U value was set to 7 eV for Co 3d orbitals, as sug‐
gested in previous works [21]. In addition, we tested the effect
of the spin state of 3d electrons in Co2+ in the optimization of
CoO, and found that the high‐spin antiferromagnetic arrange‐
ment was the most stable state, which was consistent with lit‐
erature reports [22,23].
For the model construction, two types of CoO (111) surface
were initially considered, as shown in Fig. S1. Model I was ex‐
posed and had a fully reduced upper surface (Co‐terminated)
and a fully oxidized bottom surface (O‐terminated), whereas
Model II was terminated with two identical partially oxidized
(or reduced) surfaces. Thermodynamic calculations showed
that the surface energy of Model II was 1.23 J/m2 more stable
than that of Model I. Thus, Model II was used as the theoretical
model for the CoO (111) surface to explore the reaction mech‐
anism throughout the calculations. The detailed intermediate
structures (including transition states) for the optical pathway
are shown in Fig.s S2 & S3.
lyst with a reaction rate of 1.2 mmol/h/g at 473 K and under 2
MPa hydrogen, comparable with platinum group metal cata‐
lysts Pd/C (0.6 mmol/(h·g)) and Pt/C (1.8 mmol/(h·g)). Fur‐
thermore, perfect selectivity of >99.9% toward the alcohol was
observed over Co3O4, which was superior to Pd/C (89.6%) and
Pt/C (97.9%). The precursors for the preparation of Co3O4 can
influence the catalytic performance of cobalt oxides to some
extent (Fig. S4). The Co3O4 was further treated in hydrogen at
different temperatures to derive partially reduced cobalt oxides
for the hydrogenation of stearic acid. The activity of pristine
Co3O4 was significantly enhanced through partial reduction and
the perfect selectivity toward 1‐octadecanol was well pre‐
served. Typically, a high reaction rate of 7.3 mmol/(h·g) with
>99.9% 1‐octadecanol selectivity was obtained on Co3O4 re‐
duced at 573 K, i.e., Co3O4‐573. Because the reaction occurs on
the surface of the oxides, the surface specific activity was cal‐
culated and the intrinsic activity of Co3O4‐573 (0.447
mmol/(h·m2)) was more than 30 times higher than that of
Co3O4 (0.014 mmol/(h·m2)). Undoubtedly, partially reduced
cobalt oxides were robust catalysts for the selective hydro‐
genation of stearic acid to 1‐octadecanol and the reduction
treatment in hydrogen was the key step for achieving the high
activity. According to the time‐dependent behavior of stearic
acid hydrogenation (Fig. S5), the complete conversion of stearic
acid to 1‐octadecanol can be achieved before the further con‐
version of 1‐octadecanol to alkanes. Hot filtration experiments
(Fig. S6) revealed the heterogeneous nature of the stearic acid
hydrogenation catalytic reaction by Co3O4‐573, which also ex‐
hibited good recycling ability (Fig. S7).
The effects of the reaction temperature on the stearic acid
hydrogenation were investigated. As expected, increasing the
reaction temperature significantly promoted the conversion of
stearic acid over Co3O4‐573. Kinetic plots of the stearic acid
conversion (Fig. S8) indicated a linear increase in stearic acid
conversion with reaction time at the early stage of the reaction
and perfect selectivity toward 1‐octadecanol was obtained be‐
fore the total conversion of stearic acid, independent of the
reaction temperatures. After the total conversion of stearic
acid, the product 1‐octadecanol was further converted to
n‐octadecane and n‐heptadecane (Fig. S6) through a hydrogen‐
olysis route [24–27]. Therefore, the selective hydrogenation of
3. Results and discussion
Biomass‐derived stearic acid (C17H35COOH) was initially
chosen as a model substrate and the hydrogenation of stearic
acid was investigated by using various transitional metal oxides
as catalysts. As shown in Table 1, the selective hydrogenation of
stearic acid to 1‐octadecanol was achieved by using simple
transition metal oxides such as Fe3O4, Co3O4, and NiO as cata‐
lysts. Co3O4 appeared to be a more active hydrogenation cata‐
Table 1
Catalysts and their performance in the hydrogenation of stearic acid to 1‐octadecanol a.
SBET
(m2/g)
Reaction rate
(mmol/(h·g))
Selectivity b
(%)
Specific activity
(mmol/(h·m2))
Catalyst
Phase
Fe3O4
NiO
Co3O4
Co3O4‐473
Co3O4‐573
Co3O4‐573 d
Co3O4‐673
Co3O4‐773
Pd/Ce
75.5
98.9
83.2
71.0
16.3
16.9
12.6
12.1
223.6
219.7
Fe3O4
NiO
Co3O4
Co3O4
CoO
CoO
CoO & Co
Co
1.0c
0.9
1.2
2.2
7.3
7.4
6.4
1.7
0.6
1.8
>99.9
>99.9
>99.9
>99.9
>99.9
>99.9
>99.9
>99.9
89.6
0.012
0.008
0.014
0.031
0.447
0.438
0.508
0.141
0.003
0.008
—
—
Pt/Cf
97.9
a Reaction conditions: 3 mmol stearic acid, 0.2 g catalyst, 100 mL alkane solvent, reaction temperature = 473 K, hydrogen pressure = 2 MPa; b At stea‐
ric acid conversion of ~10%, closest time point employed; c Serious deactivation observed after reaction for 3 h; d Repeated experiment; e 5% Pd on
activated carbon from Alfa Aesar; f 5% Pt on activated carbon from Alfa Aesar.

Song Song et al. / Chinese Journal of Catalysis 39 (2018) 250–257
253
stearic acid to 1‐octadecanol over Co3O4‐573 was realized
through a reaction control process. The apparent activation
energies, calculated by using the Arrhenius equation (Fig. S7),
were 70 and 85 kJ/mol for the stearic acid hydrogenation to
1‐octadecanol and subsequent 1‐octadecanol hydrogenolysis
over Co3O4‐573, respectively.
ed by XPS analysis. As shown in Fig. 1(c), binding energy values
at 794.7 and 779.7 eV corresponding to Co 2p1/2 and 2p3/2 of
Co3+ and/or Co2+ were observed for Co3O4. The satellite fea‐
tures at ~805 and ~786 eV indicated the presence of Co2+ [31],
and a mixture of Co2+ and Co3+ with a Co2+/Co3+ ratio of ~1/3
(owing to surface enrichment of Co3+ in Co3O4) was obtained
according to the nonlinear least‐squares fitting results.
Through the reduction in hydrogen at 573 K, exclusive Co2+ is
observed for Co3O4‐573. The ratio of Co/O was measured to be
1/1, which confirmed the homogeneous distribution of cobalt
and oxygen species in stoichiometric CoO. The morphology and
lattice structure of the cobalt oxides were investigated by elec‐
tron microscopy. The pristine Co3O4 samples appeared to be
nanoparticles or nanorods with a size of several tens of na‐
nometers. Hydrogen reduction at 573 K could induce the
growth of nanoparticles or nanorods to some extent (Fig. S11),
accompanied by the decrease in surface area (Table 1). In the
high‐resolution transmission electron microscope (TEM) image
of Co3O4 (Fig. 1(d)), adjacent lattice distances of 0.467 and
0.244 nm were observed, corresponding to the (111) and (311)
planes, respectively [32–34]. For Co3O4‐573, the typical adja‐
cent lattice distance was measured to be 0.246 nm, corre‐
sponding to the (111) plane in cubic CoO [34].
To establish the structure‐activity relationship in the selec‐
tive hydrogenation of stearic acid, a series of spectroscopic
characterization techniques were performed on the cobalt ox‐
ide catalysts. In situ XRD patterns (Fig. 1(a)) revealed that the
bulk phase changed from Co3O4 (JCPDS 43‐1003) to CoO
(JCPDS 43‐1004) and then to metallic cobalt (JCPDS 05‐0727)
during the reduction of Co3O4 at increasing temperatures. The
temperature‐programmed reduction by hydrogen (H2‐TPR)
profile of Co3O4 (Fig. 1(b)) revealed a two‐stage reduction of
the cobalt species, i.e., the reduction of Co3+ to Co2+ at 500–700
K (H/Co≈2/3) and the reduction of Co2+ to Co0 at 600–800 K
(H/Co≈2/1) [28,29]. For Co3O4‐573, the dominant reduction of
Co2+ to Co0 at 600‒900 K (H/Co≈2/1) was observed in the
H2‐TPR profile [30]. The results from the XRD and H2‐TPR
analysis suggested that the pristine hexagonal Co3O4 was
transformed into cubic CoO upon hydrogen reduction at 573 K.
The surface states of the cobalt oxides were further investigat‐
On the basis of the above‐mentioned characterization and
catalytic results, the pristine Co3O4 could be partially reduced
to pure‐phase nanostructured CoO under controlled conditions
and the as‐obtained Co3O4‐573 was established as a robust
catalyst for the selective hydrogenation of stearic acid to
1‐octadecanol. Heterogeneous cobalt catalysts have been re‐
ported to be very active in several important reactions, e.g.,
carbon monoxide oxidation [32], oxygen evolution reaction
[35], electroreduction of carbon monoxide [36], alcohol oxida‐
tion and nitroarenes hydrogenation [37,38]. The structure sen‐
sitivity of reactions on cobalt‐based catalysts is widely
acknowledged and has triggered significant debates
[32,33,35–40]. In this study, CoO was definitely identified as
the active species for the hydrogenation reaction. Hereafter,
CoO (111) is used as a model surface for stearic acid hydro‐
genation and the reaction pathway was investigated through
first‐principles periodic density functional theory (DFT) calcu‐
lations.
(a)
(b)
Co2+‐ Co0
Co3O4
*
CoO
#
Co +
+
+
+
+
+
Co3O4‐773
Co3O4‐673
Co3O4‐573
+
Co3+‐ Co2+
+
#
+
#
#
#
#
#
Co3O4
*
*
*
*
*
Co O ‐473
*
*
*
*
3
4
Co3O4‐573
Co3O4
*
400
500
600
700
800
900
10 20 30 40 50 60 70 80
2o
Temperature (K)
(c)
(d)
Co2+
Co3+
To convert carboxylic acids into alcohols, a few hydrogena‐
tion (+H) and C–O dissociation (dis) steps that proceed in the
right sequence are required. The optimal pathways for the se‐
lective conversion of stearic acid into 1‐octadecanol (blue),
n‐octadecane (green), and n‐heptadecane (yellow) on the CoO
(111) surface are shown in Fig. 2. As the stearic acid adsorbs on
the surface, the direct dissociation of both the C=O and the
C–OH bonds are not favored thermodynamically. Alternatively,
the hydrogenation step proceeds first with a H atom preferen‐
tially bonding at the α‐C site instead of the carbonyl oxygen,
overcoming a barrier of 0.96 eV. Then, the removal of the OH
group is ready to occur with a small barrier (0.36 eV) and large
energy release (–0.62 eV), generating the surface‐adsorbed
stearic aldehyde intermediate. By further saturating the C=O
bond with two H atoms, whereby the α‐C site again has the
priority over the carbonyl oxygen, the 1‐octadecanol is gener‐
Co3O4
Co3O4‐573
(e)
810 805 800 795 790 785 780 775
Binding energy (eV)
Fig. 1. Characterization of cobalt‐based catalysts employed in this study
(a) In situ XRD patterns of Co3O4 during hydrogen reduction; (b) H2‐TPR
profiles of Co3O4 and Co3O4‐573; (c) XPS of Co3O4 and Co3O4‐573;
High‐resolution TEM images of Co3O4 (d) and Co3O4‐573 (e). Scale bar =
5 nm.

254
Song Song et al. / Chinese Journal of Catalysis 39 (2018) 250–257
CH2R
C
0.73 eV). In contrast, in the hydrogenolysis process, the bond
+ 1.16
+ 2.61
O
OH
O
R-CH2
OH
+
+
breaking of both the C–O and C–C bonds costs a lot energy (en‐
dothermic 0.67 and 0.53 eV, respectively) with high barriers of
~1.2 eV. Therefore, the branching reaction of alkanes produc‐
tion would be temporarily blocked (~0% selectivity) as long as
the main route of 1‐octadecanol production proceeded. The
subsequent hydrogenolysis of 1‐octadecanol started to emerge
only when the stearic acid was exhausted in the system
(~100% conversion), which was consistent with the experi‐
mental observations shown in Fig. S5. Therefore, our DFT re‐
sults demonstrate that CoO (111) is a good catalyst for the hy‐
drogenation of stearic acid, and the selective hydrogenation to
alcohols can be realized by controlling the concentration of acid
substrates.
dis
O
CH2R
HO C
+H
+ 1.63
Ea = 0.96
H =-0.05
R-CH2
OH
O
H
R-CH2
CH
R-CH2
+ H
+ 1.04
CH
O
OH
HO OH
dis
+ 2.02
Ea = 0.36
H =-0.62
CH2R
HO CH
O
+
R-CH2
HC
CH2R
O C
deH + 1.49
H
+
RCH2CH dis
O
Inspired by the successful catalysis of the partially reduced
cobalt oxides in the model reaction, we further investigated the
selective hydrogenation of a wide range of carboxylic acids
with different structures and functional groups (Table 2 & Fig.
S12). As expected, Co3O4‐573 exhibited high activity in most
cases and appeared to be an efficient catalyst for the controlla‐
ble hydrogenation of various carboxylic acid substrates. For the
hydrogenation of biomass‐derived saturated fatty acids, satu‐
rated fatty alcohols were obtained with yields of >97.5 % (En‐
try 1–7). We also performed stearic acid hydrogenation on a
larger scale (10 mmol stearic acid) and the isolated yield was
determined to be 95.8% (Fig. S10), in accordance with the GC
yield (97.9%). In the case of oleic acid, the hydrogenation of the
carbon‐carbon double bond occurred before the hydrogenation
of the carbon‐oxygen bond and 1‐octadecanol was obtained as
the final product with a yield of >99.9% (Entry 8, Fig. S12). The
hydrogenation of cycloalkyl carboxylic acids, i.e., cyclopentane‐
and cyclohexane‐carboxylic acid, proceeded in slightly lower
yields than the straight‐chain fatty acids and cycloalkyl alco‐
hols, which were produced in quantitative yields (Entry 9 &
10). If the carbon atom in the cycloalkyl ring was substituted
with an oxygen atom, the derivatives, e.g., tetrahy‐
dro‐furan‐3‐carboxylic acid and tetrahydropyran‐4‐carboxylic
acid, also smoothly underwent hydrogenation and the desired
alcohols were produced with the epoxy structure well pre‐
served (Entry 11 & 12). The hydrogenation of carboxylic acid in
O
OH
+
+
+ 2.75
+H
+ 1.31
Ea = 0.68
H = 0.05
CH2R
HO CH
RCH2CH2
+ 2.17
R-CH2
O
+
+
dis
CH2
O
CH2
O
Ea = 1.17
RCH2
+H

H = 0.53
CH4
Ea = 0.57
+H

H = 0.03
Ea = 0.81
RCH3
Ea = 0.54

H =-0.49

H =-0.03
deH
RCH2
R-CH2
CH2
+ 2.36
HO CH2
OH
+
+
dis
desorb + 0.33
adsorb - 0.33
RCH2CH2OH
O
RCH2CH2
+H
H
Ea = 1.25

H = 0.67
Ea = 0.81
RCH2CH3
H =-0.49

Fig. 2. Proposed reaction mechanism for stearic acid hydrogenation on
the CoO (111) surface using DFT calculations. The blue arrows indicate
the reaction route for 1‐octadecanol generation, whereas the green and
yellow arrows are for n‐octadecane and n‐heptadecane production,
respectively. Other disfavored pathways are indicated by dashed ar‐
rows. The reaction energetics, including the reaction barriers for the
favored pathways, are also listed.
ated. The conversion of 1‐octadecanol into alkanes proceeds
through one and/or two elementary steps that are in common
with the 1‐octadecanol generation pathway, and then splits
into two branches yielding the n‐octadecane and
n‐heptadecane. For the production of n‐octadecane, the C–O
bond cleavage starts as the 1‐octadecanol adsorbs on the sur‐
face by direct detachment of the OH group. For the generation
of n‐heptadecane, the C–C bond breaks between the α‐C and
β‐C of the deprotonated 1‐octadecanol species, forming the
heptadecyl group and formaldehyde on the surface. After‐
wards, the as‐formed octadecyl and heptadecyl species can be
hydrogenated into alkanes by overcoming a reaction barrier of
0.81 eV. We also investigated other possible pathways for the
production of alkanes, which were all proven to be thermody‐
namically prohibited on the CoO (111) surface (dashed squares
in Fig. 2).
the
presence
of
a
hydroxyl
group,
e.g.,
4‐hydroxyhexanecarboxylic acid, occurred to produce the cor‐
responding 4‐(hydroxymethyl) cyclohexanol in quantitative
yield (Entry 13). A very interesting example was the hydro‐
genation of monomethyl adipate, i.e., a carboxylic acid in the
presence of an ester group, to methyl 6‐hydroxyhexanoate
(Entry 14). The carboxyl group was hydrogenated to a carbinol
group and the ester group was well preserved, by which the
hydrogenation of the ester group is easier then the carboxyl
group [8]. DFT calculations revealed that the carboxyl group
adsorbs more easily on CoO (111) (adsorption energy: –1.11
eV) than the ester group (adsorption energy: –0.84 eV). That is,
4‐monomethyl adipate adsorbs on the CoO (111) surface
through the carboxyl group. Moreover, owing to the influence
from thermodynamic entropy at a reaction temperature of 473
K (~0.9 eV), the adsorption of the ester group on CoO (111)
was difficult, which hindered its hydrogenation. The selective
Kinetically, as driven by the favorable energetics, it was ex‐
pected that the conversion of stearic acid into 1‐octadecanol
would be quick and efficient, although the computed effective
barrier was slightly higher than the experimental value (0.96 vs

Song Song et al. / Chinese Journal of Catalysis 39 (2018) 250–257
255
Table 2
Controllable catalytic hydrogenation of biomass‐derived and other carboxylic acids to corresponding alcohols a.
Temp.
(K)
Time Select. Yield En‐
(h)
Temp. Time Select. Yield
(K)
Entry Substrate
Product
Substrate
Product
(%) b (%) c try
(h) (%) b (%) c
1
473
3
98.3
98.3 13 d, e
453
6
6
>99.9 >99.9
O
2
473
473
473
2.5
2.5
2.5
>99.9 97.7 14 f
>99.9 98.8 15
473
>99.9 >99.9
OH
10
3
4
433 10
98.1
98.1
97.8
95.6
97.8
97.8 16
433 6.5 97.8
433 8.5 94.6
5
6
473
473
2.5
9
98.9
98.7
98.9 17
98.7 18 d
423 14
86.1 g 86.1
>99.9 99.6
7
8
473
473
2
6
>99.9 >99.9 19 f
>99.9 >99.9 20 f
453
7
OH
483 9.5 98.5
483 6.5 96.1
98.5
96.1
16
9
473
473
10
10
>99.9 >99.9 21 f
10
>99.9 >99.9 22 d, f
>99.9 >99.9 23 f
463 10
483 10
94.8
94.8
11
12
473
473
9
>99.9 >99.9
10
98.9
98.9
a Reaction conditions: 3 mmol substrate, 0.2 g Co3O4‐573, 100 mL alkane solvent, hydrogen pressure= 2 MPa, unless otherwise stated; b When maxi‐
mal product yield is obtained; c GC yields, carbon balance > 95%; d Hydrogen pressure= 4 MPa; e Substrate in trans configuration, product enantiose‐
lectivity: trans/cis > 99%; f Dioxane as solvent; g Ethyl cyclohexane (13.9 %) observed as byproduct.
hydrogenation of aromatic acids, i.e., phenylpropionic acid and
phenylbutyric acid, can proceed at a low temperature of 433 K,
leading to the formation of phenylpropanol and phenylbutanol
in good yields (Entry 15 & 16). The cinnamic acid underwent a
preferential hydrogenation of the carbon‐carbon double bond,
followed by hydrogenation to phenylpropanol (Entry 17), sim‐
ilar to the case of oleic acid. The hydrogenation of phenylacetic
acid did not lead to the formation of phenethyl alcohol as the
xpected product. Instead, the aromatic hydrogenation products
cyclohexylethanol (86.1%) and ethyl cyclohexane (13.9%)
were formed (Entry 18). Clearly, the synergy effects can effec‐
tively activate the benzene ring and lead to the products from
hydrogenation of the benzene ring. With an oxygen insertion
between the carboxyl and the benzene ring, the selective hy‐
drogenation of 2‐methoxyphenylaceticacid was successfully
performed with both the benzene ring and methoxy groups
well preserved (Entry 19). Moreover, the hydrogenation of
dioic acids, i.e., adipic acid and suberic acid, was achieved
through a step‐by‐step process and the diols were obtained as
the final products in good yields (Entry 20–22). An esterifica‐
tion‐hydrogenolysis process with ring formation‐opening was
observed during the conversion of adipic acid (Fig. S12). The
hydrogenation of succinic acid proceeded through a dehydra‐
tion‐decarbonylation route, resulting in γ‐butyrolactone in‐
stead of 1, 4‐butanediol as the final product in a quantitative
yield of >99.9%, (Entry 23; Fig. S12). The further hydrogenoly‐
sis of γ‐butyrolactone to 1,4‐butanediol did not occur under the
employed reaction conditions because the five‐membered ring
γ‐butyrolactone was very stable against ring‐opening. The
Co3O4‐573 catalyst was finally employed for the hydrogenation
of carboxylic acids with halide, nitrile, or keto groups. The
Co3O4‐573 was not tolerant to these groups, and nonselective
hydrogenations occurred (not shown here).
4. Conclusions

256
Song Song et al. / Chinese Journal of Catalysis 39 (2018) 250–257
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Graphical Abstract
Chin. J. Catal., 2018, 39: 250–257 doi: 10.1016/S1872‐2067(17)63003‐1
Robust cobalt oxide catalysts for controllable hydrogenation
of carboxylic acids to alcohols
Song Song, Dong Wang, Lu Di, Chuanming Wang, Weili Dai,
Guangjun Wu, Naijia Guan, Landong Li *
Nankai University; Shanghai Research Institute of Petrochemical
Technology
22 Samples; 94.6‐99.9 % Yields
The selective hydrogenation of a wide range of carboxylic acids
using earth‐abundant cobalt oxides through a reaction‐controlled
catalysis process.

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高效钴氧化物催化羧酸可控加氢制醇
宋 松 a,†, 王 栋 c,†, 狄 璐 a, 王传明 c, 戴卫理 a, 武光军 a, 关乃佳 a,b, 李兰冬 a,b,*
a南开大学, 材料科学与工程学院, 国家新材料研究院, 天津 300350
b南开大学, 先进能源材料化学教育部重点实验室, 化学化工协同创新中心, 天津 300071
c中国石油化工集团公司, 上海石油化工研究院, 上海 201208
摘要: 羧酸选择加氢是合成醇的重要方法, 廉价高效的催化体系仍然在探索中. 我们利用地球上储量丰富的钴氧化物作为
催化剂, 通过控制催化反应过程, 进而实现高选择性地催化羧酸加氢制备醇. 一系列含有不同官能团的羧酸可以被选择加
氢至相应的醇类化合物, 反应选择性可以满足工业生产要求. 通过一系列的谱学表征以及理论计算, 我们证实了钴氧化物
在羧酸选择加氢反应中的优选活性位点位为氧化亚钴, 从而建立了催化剂与反应活性之间的构效关系, 为催化剂的理性设
计提供指导.
首先, 我们选取硬脂酸加氢反应作为模型反应, 通过对地球上储量丰富的氧化镍、四氧化三铁和四氧化三钴的催化活
性对比发现, 四氧化三钴催化剂活性最高, 在 473 K, 2 MPa 氢气条件下, 反应速率可以达到 1.2 mmol/(h·g). 对四氧化三钴
催化剂进行不同温度的预还原处理, 我们发现催化剂的活性得到显著提高, 其中 573 K 还原的样品活性最高, 反应速率可
以达到 7.3 mmol/(h·g), 要远远高于贵金属催化剂 Pd/C(0.6 mmol/(h·g)) 和 Pt/C(1.8 mmol/(h·g)).
XRD 结果表明, 随着还原处理温度的不断升高, 催化剂由四氧化三钴变为氧化亚钴, 最终变为金属态的钴. 当还原温
度为 573 K 时, 催化剂的组成为单一相氧化亚钴. XPS 测试结果表明, 当还原温度为 573 K 时, 样品中只含有 Co2+的信号
峰, 并且 Co/O 的比例为 1/1, 进一步证明样品是纯态的氧化亚钴. 从 TEM 照片中可以发现, 在原始的四氧化三钴样品中观
察到晶面间距为 0.467 和 0.244 nm, 分别对应四氧化三钴的 (111) 和 (311) 晶面. 而对于 573 K 还原的样品只观察到一种
晶面间距 (0.246 nm), 对应氧化亚钴的 (111) 晶面.
结合表征手段和硬脂酸催化加氢活性结果, 我们得出氧化亚钴是 573 K 还原样品催化羧酸加氢反应的活性位点. 理论
计算结果进一步证实了这个实验结论. 理论计算结果表明, 在氧化亚钴 (111) 晶面, 硬脂酸加氢转换为十八醇是非常快速
和高效的, 然而, 对于氢解 C‒C 键和 C‒O 键, 需要耗费更高的能量, 能垒约为 1.2 eV. 因为硬脂酸的吸附远远强于十八醇
的吸附, 硬脂酸的存在会抑制十八醇氢解形成烯烃的反应, 只有当硬脂酸酸完全转化为十八醇, 才会发生随后的氢解反应.
通过控制催化反应过程, 可以实现在氧化亚钴 (111) 晶面高选择性催化酸加氢至醇, 也就是反应控制催化过程. 基于氧化
亚钴在硬脂酸加氢制备十八醇上的优异催化性能, 我们进一步研究了一系列含有不同官能团的羧酸化合物的催化加氢, 发
现氧化亚钴表现出良好的官能团容忍度, 可以实现高效、广谱的酸选择加氢至醇反应.
关键词: 选择加氢; 羧酸; 醇; 氧化钴; 反应控制催化
收稿日期: 2017-10-06. 接受日期: 2017-11-21. 出版日期: 2018-02-05.
*通讯联系人. 电话/传真: (022)23500341; 电子信箱: lild@nankai.edu.cn
†共同第一作者.
基金来源: 国家自然科学基金 (21421001, 21573113); 中石化.
本文的电子版全文由Elsevier出版社在ScienceDirect上出版(http://www.sciencedirect.com/science/journal/18722067).