Efficient oxidation of cycloalkanes with simultaneously increased conversion and selectivity using O2 catalyzed by metalloporphyrins and boosted by Zn(AcO)2: A practical strategy to inhibit the formation of aliphatic diacids

Article abstract of DOI:10.1016/j.apcata.2020.117904

The direct sources of aliphatic acids in cycloalkanes oxidation were investigated, and a strategy to suppress the formation of aliphatic acids was adopted through enhancing the catalytic transformation of oxidation intermediates cycloalkyl hydroperoxides to cycloalkanols by Zn(II) and delaying the emergence of cycloalkanones. Benefitted from the delayed formation of cycloalkanones and suppressed non-selective thermal decomposition of cycloalkyl hydroperoxides, the conversion of cycloalkanes and selectivity towards cycloalkanols and cycloalkanones were increased simultaneously with satisfying tolerance to both of metalloporphyrins and substrates. For cyclohexane, the selectivity towards KA-oil was increased from 80.1% to 96.9% meanwhile the conversion was increased from 3.83 % to 6.53 %, a very competitive conversion level with higher selectivity compared with current industrial process. This protocol is not only a valuable strategy to overcome the problems of low conversion and low selectivity lying in front of current cyclohexane oxidation in industry, but also an important reference to other alkanes oxidation.

Full text of DOI:10.1016/j.apcata.2020.117904

Applied Catalysis A, General 609 (2021) 117904
Contents lists available at ScienceDirect
Applied Catalysis A, General
journal homepage: www.elsevier.com/locate/apcata
Efficient oxidation of cycloalkanes with simultaneously increased
conversion and selectivity using O2 catalyzed by metalloporphyrins and
boosted by Zn(AcO)2: A practical strategy to inhibit the formation of
aliphatic diacids
Hai-Min Shen, Xiong Wang, Lei Ning, A-Bing Guo, Jin-Hui Deng, Yuan-Bin She*
College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China
A R T I C L E I N F O
A B S T R A C T
Keywords:
The direct sources of aliphatic acids in cycloalkanes oxidation were investigated, and a strategy to suppress the
formation of aliphatic acids was adopted through enhancing the catalytic transformation of oxidation in-
termediates cycloalkyl hydroperoxides to cycloalkanols by Zn(II) and delaying the emergence of cycloalkanones.
Benefitted from the delayed formation of cycloalkanones and suppressed non-selective thermal decomposition of
cycloalkyl hydroperoxides, the conversion of cycloalkanes and selectivity towards cycloalkanols and cyclo-
alkanones were increased simultaneously with satisfying tolerance to both of metalloporphyrins and substrates.
For cyclohexane, the selectivity towards KA-oil was increased from 80.1% to 96.9% meanwhile the conversion
was increased from 3.83 % to 6.53 %, a very competitive conversion level with higher selectivity compared with
current industrial process. This protocol is not only a valuable strategy to overcome the problems of low con-
version and low selectivity lying in front of current cyclohexane oxidation in industry, but also an important
reference to other alkanes oxidation.
Cycloalkanes
Oxidation
Metalloporphyrins
Oxygen
Selectivity
1. Introduction
air as oxidant. Among them, one useful, important and commercial
process is the oxidation of cyclohexane, in which the commercially
The practical, efficient and selective transformation of abundant al-
kanes in petroleum products to corresponding high value-added oxy-
genous organic compounds with clean molecular oxygen (O2) as oxidant
in the absence of any solvent, has been the pursuit of scientists and
technicians in both of the theoretical study and industrial application all
available and low-cost cyclohexane is converted to a mixture of
high-value cyclohexanol and cyclohexanone known as KA-oil [18–21].
Both of cyclohexanol and cyclohexanone are common organic solvents
applied widely in chemical industry [22,23], and essential raw materials
in the syntheses of pharmaceuticals [24,25], pesticides [26,27], dyes
[28,29], plasticizers [30,31] and other fine chemicals. The other enor-
mous demand for KA-oil is to produce hexanedioic acid and capro-
lactam, that are employed widely as the irreplaceable synthetic
precursors in manufacture of polyamide fibers (Nylon-66, Nylon-6) [21,
32–35]. Annually, more than 3.5 million tons of hexanedioic acid is
produced to meet the demand of its downstream products and nearly 3.0
million tons of cyclohexanone is consumed to prepare caprolactam [33,
36]. For the tremendous and increasing market demand for KA-oil, and
the irreplaceable role, the oxidation of cyclohexane has become a
fundamental pillar industry in modern chemical society and attracted
the most extensive research interest from chemical scientists and
technicians.
–
the time [1–4]. To insert oxygen atoms into C–H bonds or C C bonds in
alkanes directly employing O2, not only provides the shortest reaction
route to form these important oxygen containing compounds, but also
possesses the highest atom economy with environmentally-friendly
water being the sole by-product from oxidant reduction, which is in
complete consistence with the requirements of green chemistry for
“Prevent wastes” and “Atom economy” [5–8], compared with other
oxidants, such as iodosylbenzene (PhIO) [9,10], m-chloroperoxybenzoic
acid [11,12], tert-butyl hydroperoxide (t-BuOOH) [13,14], hydrogen
peroxide (H2O2) [15–17] and so on. In addition, O2 is readily available,
low-cost, non-toxic and biocompatible in nature. Thus, most of the in-
dustrial processes in alkanes oxidation are conducted employing O2 or
* Corresponding author.
E-mail address: haimshen@zjut.edu.cn (Y.-B. She).
https://doi.org/10.1016/j.apcata.2020.117904
Received 19 August 2020; Received in revised form 26 October 2020; Accepted 26 October 2020
Available online 2 November 2020
0926-860X/© 2020 Elsevier B.V. All rights reserved.

H.-M. Shen et al.
Applied Catalysis A, General 609 (2021) 117904
In the current industrial process, oxidation of cyclohexane to KA-oil
or air as oxidants. The main means to keep the selectivity towards KA-oil
at a satisfying level is controlling the conversion not too high. Therefore,
it has become a critical need in the industrial oxidation of cyclohexane
to develop a practical process with high conversion and selectivity
employing O2 as oxidant under solvent-free conditions considering the
requirement of low production cost and low environmental impact.
In our pursuit of oxidative transformation of cyclohexane to KA-oil
with O2 catalyzed by metalloporphyrins, the following issues became
the key points to consider based on our previous work [68–73] and
others’ mentioned above. (1) Lowering the reaction temperature,
because when the reaction temperature reaches up to higher than
120 ◦C, the autoxidation of cyclohexane without selectivity will become
obvious [70]. The unselective autoxidation will inevitably decrease the
selectivity to KA-oil. (2) Inhibiting the formation of hexanedioic acid.
Based on our previous work, in the oxidation of cyclohexane catalyzed
by metalloporphyrins at 120 ◦C, hexanedioic acid and its derivatives are
the main by-products. The formation of hexanedioic acid in cyclohexane
oxidation will not only block the pipes in the industrial installations and
interrupt the industrial production, but also bring about a lot of other
by-products derived from hexanedioic acid and lower the selectivity
towards KA-oil. Thus, it is considered as an efficient strategy to obtain
the increased selectivity to KA-oil through inhibiting the formation of
hexanedioic acid. (3) Catalytic transformation of the oxidation inter-
mediate cyclohexyl hydroperoxide to KA-oil selectively rather than
traditional unselective thermal-decomposition with the purpose to
decrease the formation of undesired hexanedioic acid and its de-
rivatives, and increase the selectivity towards KA-oil. For these reasons,
the selective oxidation of cyclohexane to KA-oil in our group is con-
ducted at the temperature of 120 ◦C with the attempt to inhibit the
unselective autoxidation and the formation of troublesome hexanedioic
acid. Considering the decreased catalytic activity of heterogeneous
metalloporphyrins compared to the homogeneous ones, the homoge-
neous metalloporphyrins were selected as catalysts in our work. And in
order to control the transformation of cyclohexyl hydroperoxide, sec-
ondary catalytic center is employed whose function mainly is to adjust
the transformation of cyclohexyl hydroperoxide. Benefited from these
strategies, some satisfying results were obtained, especially the simul-
taneous increase in the selectivity towards KA-oil and the conversion of
cyclohexane. Thus, in this work, the source of hexanedioic acid in se-
lective oxidation of cyclohexane utilizing O2 as oxidant and metal-
loporphyrins as catalysts under solvent-free conditions was explored and
revealed systematically, and based on which, commercially available Zn
(II) was employed to adjust the conversion of oxidation intermediate
cyclohexyl hydroperoxide with the purpose to suppress the formation of
hexanedioic acid and its derivatives. Exhilaratingly, not only the selec-
tivity was boosted to 96.9 % from 80.1 %, but also the conversion was
boosted to 6.53 % from 3.83 %, a comparable level with the industrial
conversion of cyclohexane to KA-oil with higher selectivity. The simul-
taneously boosted conversion and selectivity were mainly ascribed to
the lower reaction temperature and the enhancement on the conversion
of oxidation intermediate cyclohexyl hydroperoxide to cyclohexanol by
Zn(II) instead of the traditional thermal-decomposition to cyclohexanol
and cyclohexanone, which delayed the formation of hexanedioic acid
and its derivatives resulting in high selectivity to KA-oil. This strategy to
achieve the simultaneous boosting on the conversion and selectivity in
cyclohexane oxidation through catalytic transformation of cyclohexyl
hydroperoxide and inhibiting the formation of hexanedioic acid and its
derivatives is very applicable to a large scope of metalloporphyrins and
cycloalkanes. To the best of our knowledge, the study demonstrated
herein is a very innovative and significant case in cycloalkane oxidation,
in which not only the direct source of aliphatic diacids in cycloalkane
oxidation was confirmed as cycloalkanone clearly, but also a practical
and efficient strategy to inhibit the formation of aliphatic diacids was
presented, resulting in the simultaneously increased conversion and
selectivity in the cycloalkane oxidation employing O2 as oxidant. Thus
this work will be a very efficient and practical example in oxidative
is usually conducted in the temperature of 150ꢀ 200 ◦C under
1.0–2.0 MPa employing homogeneous cobalt or manganese salts as
catalysts and O2 or air as oxidants with cyclohexane conversion of 3–5 %
and KA-oil selectivity of 75–85 % [32,34,37–42]. Due to the inherent
inertness of C–H bonds in cyclohexane and triplet O2, in the activation of
the C–H bonds and molecular oxygen, high reaction temperature is
employed [20], and causes the unselective autoxidation of cyclohexane
happen. And in order to achieve a higher selectivity, the conversion is
controlled at a lower level (3–5 %) to inhibit the deep oxidation of KA-oil
in the current industrial oxidation of cyclohexane [32]. The increase in
conversion would consume the selectivity to KA-oil dramatically
because of the higher reactivity of KA-oil than cyclohexane. For the
lower conversion, a large quantity of unconverted cyclohexane needs to
be circulated and reused, resulting in high energy consumption, low
production efficiency and some environmental pollution, which make
the current oxidation process of cyclohexane not so compatible with the
requirement of green chemistry and green engineering [5–8]. And the
main drawbacks in the current process to produce KA-oil through
cyclohexane oxidation are summarized as the high reaction tempera-
ture, low selectivity and low conversion. Therefore, it is still a urgent
and challenging tasks to achieve the oxidation of cyclohexane to KA-oil
with increased conversion and selectivity, and smooth the process,
especially the simultaneous increase in the conversion and selectivity.
To obtain a mild industrial process with higher conversion and
selectivity for the cyclohexane oxidation, several strategies have been
developed and adopted, which can be divided into two categories based
on the activity of oxidants involved. One is the employment of O2 or air
as oxidant boosted by various catalytic systems such as transition-metal
complexes catalysis [38,39,43,44], metal nanoparticles catalysis [4,45,
46], metal-oxide catalysis [40,47,48], non-metal materials catalysis
[49] and so on [50], under solvent-free conditions. In these catalytic
systems, the chemical model compounds of Cytochrome P-450, metal-
loporphyrins have been considered as a series of efficient catalysts in the
cyclohexane oxidation for their high performance in the activation of O2
and insertion of oxygen atom into C–H bonds of alkanes under both of
the heterogeneous conditions and homogeneous conditions [38,43,
51–60]. Homogeneous metalloporphyrins just in the mole ratio of one in
a million to substrates would realize the oxidation of cyclohexane with
satisfying results, especially in the conversion, and the conversion of
cyclohexane could reach up to more than 30 % with the selectivity of
less than 70 % to KA-oil [38,43,51–56]. A large amount of aliphatic
diacids and their derivatives were produced from the deep oxidation of
KA-oil. And the increase in conversion consumed the selectivity towards
KA-oil for the higher reactivity of KA-oil than cyclohexane and the
higher reaction temperature (usually above 150 ◦C). There is no doubt
that the formation of aliphatic diacids and their derivatives will result in
low selectivity to KA-oil, and cause troublesome separation problem,
high energy consumption and massive discharge of pollutants, which
hampers the wide industrial application of metalloporphyrins in the
oxidation of cyclohexane seriously. In fact, it is still a challenging issue
to increase the conversion without consumption of the selectivity to-
wards KA-oil in the oxidation of cyclohexane. It is nearly a consensus
that the increase in the conversion is followed by the decrease in
selectivity in many chemical transformations. The other strategy to
smooth the process of cyclohexane oxidation, and to achieve higher
conversion and selectivity is the utilization of more active oxidants, such
as H2O2 [61–64], t-BuOOH [14,65,66], and iodosylbenzene [9,10,67].
For the high reactivity of oxidants, the oxidation of cyclohexane could
be conducted in the temperature of 70ꢀ 80 ◦C with the conversion of
more than 70 % and selectivity of nearly 100 % towards KA-oil, even at
room temperature [61–63,65,66]. But the presence of solvent makes this
strategy not suitable for the commodity chemicals like KA-oil. Hence,
the industrial oxidation of cyclohexane at present still is conducted
utilizing the traditional process in 150ꢀ 200 ◦C and 1.0–2.0 MPa
employing homogeneous cobalt or manganese salts as catalysts and O2
2

H.-M. Shen et al.
Applied Catalysis A, General 609 (2021) 117904
Scheme 1. The syntheses of porphyrins, metalloporphyrins and their corresponding structures.
functionalization of C–H bonds to boost the conversion and selectivity
simultaneously through adjusting the transformation of cycloalkyl hy-
droperoxide by Zn(II) and inhibiting the formation of aliphatic acids,
and could act as a practical and efficient reference to boost the catalytic
oxidation of C–H bonds in various alkanes with O2. This work also is a
tremendous promotion in the realization of green chemistry in alkane
oxidation.
2.2. Syntheses of porphyrins
Tetraphenylporphyrin (TPP), tetrakis(2-chlorophenyl)porphyrin (T
(2-Cl)PP), tetrakis(3-chlorophenyl)porphyrin (T(3-Cl)PP), tetrakis(4-
chlorophenyl)porphyrin
(T(4-Cl)PP),
tetrakis(4-fluorophenyl)
porphyrin (T(4-F)PP), tetrakis(4-methylphenyl)porphyrin (T(4ꢀ CH3)
PP), tetrakis(4-methoxyphenyl)porphyrin (T(4ꢀ OCH3)PP), tetrakis
(naphthalen-2-yl)porphyrin
(T(2-Na.)P)
and
tetrakis(4-
2. Experimental section
methoxycarbonylphenyl)porphyrin (T(4ꢀ COOCH3)PP) were synthe-
sized through condensation of the corresponding aromatic aldehyde
with freshly distilled pyrrole in propionic acid according to the Adler-
Longo method after some modifications (Eq. 1 in Scheme 1) [74–76].
In the synthesis process, aromatic aldehyde (100 mmol) was dissolved in
propionic acid (300 mL) with stirring at the room temperature under the
atmosphere of nitrogen. Then, the resultant solution was heated to
refluxing (145 ◦C), and freshly distilled pyrrole (100 mmol) was added
dropwise. After stirring and refluxing for 2.0 h under the protection of
tin foil from ambient light, the resultant reaction mixture was cooled to
room temperature and kept standing at room temperature for 24.0 h.
The collected precipitate from suction filtration was suspended in
methanol (200 mL) with stirring at room temperature for 6.0 h and
washed with methanol (2 × 100 mL) successively. At last, silica column
chromatography was employed for further purification using the
mixture of cyclohexane and dichloromethane as eluent (Vcyclohexane :V
dichloromethane = 6 : 1). All the obtained porphyrins were dried at 75 ◦C for
12.0 h under reduced pressure and characterized through FT-IR, 1H
NMR, 13C NMR and ESI-MS. Details could be seen in the Electronic
Supplementary Information.
2.1. Materials
Benzaldehyde (99 %), 2-chlorobenzaldehyde (99 %), 3-chloroben-
zaldehyde (96 %), 4-chlorobenzaldehyde (98 %), 2, 6-dichlorobenzalde-
hyde (98 %), 2, 3, 6-trichlorobenzaldehyde (97 %), 2, 3, 4, 5, 6-
pentafluorobenzaldehyde (98 %), 4-fluorobenzaldehyde (98 %), 4-
methylbenzaldehyde (98 %), 4-methoxybenzaldehyde (98 %), 2-naph-
thaldehyde (98 %), methyl 4-formylbenzoate (98 %), pyrrole (99 %),
cyclopentane (98 %), cycloheptane (98 %), cyclooctane (99 %) cyclo-
pentanol (99 %), cyclopentanone (99 %), cyclohexanol (99 %) and
cyclohexanone (99 %) were the commodities of Energy Chemical.
Anhydrous cobalt (II) acetate (98 %), anhydrous zinc (II) acetate (99 %),
triphenylphosphine (99 %) and triphenylphosphine oxide (99 %) were
the commodities of Adamas Reagent. Cyclohexane (99 %) was the
commodity of Hangzhou Shuanglin Chemical Reagent. Cycloheptanol
(96 %), cycloheptanone (99 %), cyclooctanol (98 %), cyclooctanone (98
%), butanedioic acid (99 %), pentanedioic acid (99 %), hexanedioic acid
(99 %), heptanedioic acid (99 %) and octanedioic acid (99 %) were the
commodities of TCI. Other conventional chemicals were analytical re-
agents. The cycloalkanes were dried over sodium and redistilled before
use. All of the other chemicals were utilized as purchased with no further
treatment except where noted.
Tetrakis(2, 6-dichlorophenyl)porphyrin (T(2, 6-diCl)PP), tetrakis(2,
3, 6-trichlorophenyl)porphyrin (T(2, 3, 6-triCl)PP) and tetrakis(2, 3, 4,
5, 6-pentafluorophenyl)porphyrin (T(2, 3, 4, 5, 6-pentaF)PP, TPFPP)
were synthesized through condensation of the corresponding aromatic
aldehyde with freshly distilled pyrrole in dichloromethane according to
the Lindsay method after some modifications (Eq. 2 in Scheme 1)
3

H.-M. Shen et al.
Applied Catalysis A, General 609 (2021) 117904
Table 1
The formation sequence of oxygenous products in oxidation of cyclohexanea.
Yield (%)b
R1-OH
Entry
Temperature (ºC)
Reaction time (h)
R1=O
R1-OOH
R2-COOH
R3-COOH
1
0.50
1.00
1.50
2.00
4.00
6.00
0.50
1.00
1.50
2.00
4.00
6.00
0.50
1.00
1.50
2.00
4.00
6.00
6.00
6.00
N. D.c
0.04
0.06
0.06
0.30
0.58
0.07
0.11
0.13
0.17
0.53
0.87
0.11
0.18
0.32
0.51
1.09
1.50
N. D.
N. D.
0.07
0.08
0.08
0.09
0.26
0.53
0.08
0.09
0.10
0.13
0.49
0.82
0.10
0.11
0.18
0.26
1.02
1.96
3.05
2.63
0.12
0.13
0.17
0.20
0.26
0.33
0.14
0.24
0.28
0.29
0.31
0.31
0.19
0.28
0.38
0.54
0.20
0.18
2.53
2.23
N. D.
N. D.
N. D.
N. D.
0.07
0.09
N. D.
N. D.
N. D.
0.08
0.14
0.40
N. D.
0.02
0.06
0.10
0.20
0.40
N. D.
N. D.
N. D.
N. D.
N. D.
N. D.
N. D.
N. D.
N. D.
N. D.
N. D.
N. D.
N. D.
N. D.
N. D.
N. D.
N. D.
N. D.
N. D.
0.08
2
3
110
4
5
6
7
8
9
115
120
10
11
12
13
14
15
16
17
18
19
20
N. D.
N. D.
aConditions: cyclohexane (200 mmol, 16.83 g), T(4-Cl)PPCo (1.2 × 10ꢀ 3%, mol/mol, 0.0019 g), O2 (1.40 MPa), 600 rpm.
bAll the yields were calculated through GC and HPLC analyses as illustrated in Electronic Supplementary Information.
cNo obvious product detected.
dCyclohexane (2.0 mmol, 0.1683 g) in acetone (20 mL).
eCyclohexane (2.0 mmol, 0.1683 g) in acetonitrile (20 mL).
[77–79]. In the synthesis process, aromatic aldehyde (6.0 mmol) and
freshly distilled pyrrole (6.0 mmol) were dissolved in dichloromethane
dried over CaH2 (600 mL) and stirred under the atmosphere of nitrogen
3.0 h shielded from ambient light. Then, p-chloranil (6.0 mmol) was
added followed by stirring at room temperature for another 3.0 h, and
triethylamine (2.0 mL) was added to quench the reaction. The crude
products were obtained through rotary evaporation of solvent, and
neutral alumina column chromatography was utilized for further
•
at room temperature for 15 min. BF3OEt2 (2.0 mmol) was added quickly,
and the resultant reaction mixture was stirred at room temperature for
Table 2
The formation sequence of oxygenous products in oxidation of cyclohexanola.
Yield (%)b
Entry
Temperature (ºC)
Reaction time (h)
R1=O
R2-COOH
R3-COOH
1
1.00
2.00
3.00
4.00
6.00
8.00
1.00
2.00
3.00
4.00
6.00
8.00
1.00
2.00
3.00
4.00
6.00
8.00
0.20
N. D.c
N. D.
N. D.
N. D.
0.23
0.53
N. D.
N. D.
0.44
0.66
1.43
3.60
N. D.
0.31
0.87
0.99
8.26
11.40
N. D.
N. D.
N. D.
N. D.
N. D.
N. D.
N. D.
N. D.
N. D.
N. D.
N. D.
0.55
2
0.35
3
0.41
110
4
0.54
5
3.18
6
9.35
7
0.30
8
0.59
9
8.77
115
120
10
11
12
13
14
15
16
17
18
16.94
22.78
32.96
0.71
N. D.
N. D.
N. D.
N. D.
0.85
6.55
12.86
24.58
43.70
51.69
1.38
a
Conditions: cyclohexanol (50 mmol, 5.01 g), T(4-Cl)PPCo (2.4 × 10ꢀ 3%, mol/mol, 0.0010 g), O2 (1.40 MPa), 600 rpm.
All the yields were calculated through GC and HPLC analyses as illustrated in Electronic Supplementary Information.
No obvious product detected.
b
c
4

H.-M. Shen et al.
Applied Catalysis A, General 609 (2021) 117904
Table 3
The formation sequence of products in oxidation of cyclohexanonea.
Yield (%)b
R2-COOH
Entry
Temperature (ºC)
Reaction time (h)
R3-COOH
1
2
1.00
2.00
3.00
4.00
6.00
8.00
1.00
2.00
3.00
4.00
6.00
8.00
1.00
2.00
3.00
4.00
6.00
8.00
0.96
0.99
1.38
1.51
2.38
3.75
1.86
2.36
2.77
3.11
5.67
7.69
2.11
2.70
3.76
5.46
7.51
9.90
N. D.c
N. D.
N. D.
N. D.
0.11
0.47
N. D.
0.09
0.16
0.18
1.51
2.47
0.14
0.22
0.48
1.62
2.47
3.03
3
70
4
5
6
7
8
9
80
10
11
12
13
14
15
85
16
17
18
a
Conditions: cyclohexanone (50 mmol, 4.91 g), T(4-Cl)PPCo (2.4 × 10ꢀ 3%, mol/mol, 0.0010 g), O2 (1.40 MPa), 600 rpm.
All the yields were calculated through GC and HPLC analyses as illustrated in Electronic Supplementary Information.
No obvious product detected.
b
c
purification with dichloromethane as eluent. It was collected of all the
2 in Scheme 1) [79–81]. In a typical procedure, porphyrin synthesized in
2.2 (0.30 mmol) was dissolved in DMF (120 mL) and heated to refluxing
(150 ◦C) under the protection of nitrogen. Then anhydrous cobalt (II)
acetate (3.0 mmol) was added in one portion followed by stirring and
refluxing for another 24.0 h. After the solvent being evaporated under
reduced pressure, the obtained purple residue was dissolved in
dichloromethane (50 mL), washed with water (5 × 200) and dried over
anhydrous Na2SO4. At last, silica column chromatography was utilized
in further purification of the purple solid obtained after rotary evapo-
ration of the solvent, with the mixture of cyclohexane and dichloro-
methane as eluent (Vcyclohexane :V dichloromethane = 4 : 1ꢀ 1 : 1). All the
obtained porphyrin cobalts (II) were dried at 75 ◦C for 12.0 h under
reduced pressure before used and characterized through FT-IR and
ESI-MS. Details could be seen in the Electronic Supplementary
Information.
eluent from black to red. After concentration of the collected eluent,
silica column chromatography was employed for further purification of
the obtained crude products utilizing the eluent of cyclohexane and
dichloromethane (Vcyclohexane :V dichloromethane = 4 : 1ꢀ 1 : 1). All the
obtained porphyrins were dried at 75 ◦C for 12.0 h under reduced
pressure and characterized through FT-IR, 1H NMR, 13C NMR and
ESI-MS. Details could be seen in the Electronic Supplementary
Information.
2.3. Syntheses of metalloporphyrins
All the porphyrin cobalts (II) were obtained through metallation of
the corresponding porphyrin with anhydrous cobalt (II) acetate in N,N-
dimethylformamide (DMF) following the procedure reported (Eqs. 1 and
Fig. 1. The formation sequence of products in cyclohexane oxidation using O2 catalyzed by metalloporphyrins.
5

H.-M. Shen et al.
Applied Catalysis A, General 609 (2021) 117904
Fig. 2. Effect of temperature on oxidation of cyclohexane with O2 catalyzed by T(4-Cl)PPCo.
Conditions: cyclohexane (200 mmol, 16.83 g), T(4-Cl)PPCo (1.2 × 10ꢀ 3 %, mol/mol, 0.0019 g), O2(a. 0.80 MPa, b. 1.00 MPa, c. 1.20 MPa, d. 1.40 MPa, e. 1.60 MPa, f.
1.80 MPa, g. 2.00 MPa), 8.0 h, 600 rpm.
6

H.-M. Shen et al.
Applied Catalysis A, General 609 (2021) 117904
Fig. 3. Effect of catalyst loading on oxidation of cyclohexane with O2 catalyzed by T(4-Cl)PPCo.
Conditions: cyclohexane (200 mmol, 16.83 g), T(4-Cl)PPCo, O2 1.40 MPa, 8.0 h, 600 rpm, a. 110 ◦C, b. 115 ◦C, c. 120 ◦C.
2.4. The procedure of catalytic oxidation
by-products in the cyclohexane oxidation utilizing O2 catalyzed by
metalloporphyrins. And when the oxidation was conducted at 120 ◦C
with suppressed autoxidation of cyclohexane [70,73], the by-products
were only hexanedioic acid and pentanedioic acid with KA-oil and
cyclohexyl hydroperoxide as desired products, no other oxygenous
product being detected. Thus, in the attempt to increase the selectivity
towards KA-oil in our research, it has become the key point to inhibit the
formation of hexanedioic acid and pentanedioic acid. In order to explore
the emergence of hexanedioic acid and pentanedioic acid, the formation
sequence of the oxygenous products in the cyclohexane oxidation uti-
lizing O2 as oxidant and metalloporphyrins as catalysts was investigated
systematically. T(4-Cl)PPCo was employed as representative catalyst for
its satisfying performance in the oxidation of alkanes [72,73,82]. And
the formation sequence of products in the oxidation of cyclohexane with
O2 was illustrated in Table 1.
The oxidation of substrates (cycloalkanes, cyclohexanol or cyclo-
hexanone) with molecular oxygen catalyzed by porphyrin cobalt (II) or
porphyrin cobalt (II) and anhydrous zinc (II) acetate was conducted in a
stainless steel autoclave reactor (100 mL) possessing a Teflon liner. In
the oxidation operations, porphyrin cobalt (II) (1.2 × 10ꢀ 3%, mol/mol)
or porphyrin cobalt (II) (1.2 × 10ꢀ 3%, mol/mol) and anhydrous zinc (II)
acetate (2.0 %, mol/mol, utilized as purchased with no further treat-
ment) were mixed with substrates (cycloalkanes (200 mmol), cyclo-
hexanol (50 mmol) or cyclohexanone (50 mmol)) through stirring at the
speed of 600 rpm, and then the sealed reactor was stirred and heated to
the desired reaction temperature followed by the feed of O2 slowly. After
stirring for the desired time at the desired temperature and pressure, the
reaction mixture was cooled to room temperature in ice water bath.
Triphenylphosphine (25 mmol) was added to reduce the residual
cycloalkyl hydroperoxides in a small amount to corresponding cyclo-
alkanols quantitatively followed by another 30 min stirring, because the
cycloalkyl hydroperoxides could not be analyzed quantitatively through
GC analyses directly. At last, the obtained reaction mixture was trans-
ferred into a volumetric flask (100 mL) totally with acetone as solvent to
carry out the GC and HPLC analyses to determine the yields of oxy-
genous products. Details could be seen in the Electronic Supplementary
Information.
As demonstrated in Table 1 that, at the reaction temperatures of
110 ◦C, 115 ◦C and 120 ◦C, at which autoxidation of cyclohexane could
be suppressed, the oxygenous products emerged firstly were cyclo-
hexanol, cyclohexanone and cyclohexyl hydroperoxide, no aliphatic
diacid being formed at the beginning of the reaction. With the yields of
cyclohexanol and cyclohexanone increasing, hexanedioic acid appeared
and the yield of hexanedioic acid increased from 0.02 % to 0.40 % as the
reaction time increased from 1.0 h to 6.0 h at 120 ◦C meanwhile the
yields of cyclohexanol and cyclohexanone increased from 0.18 % to 1.50
% and 0.11% to1.96 % respectively. The yield of cyclohexyl hydroper-
oxide stayed at a similar and low level at the reaction temperature
investigated. As for pentanedioic acid, its formation followed the for-
mation of hexanedioic acid. The oxidation of cyclohexane with O2
catalyzed by metalloporphyrins proceeded well in the diluted solution
(0.1 mol/L in acetone and acetonitrile) too (Entry 19 and Entry 20 in
Table 1), with cyclohexanone and cyclohexyl hydroperoxide as the main
products and no hexanedioic acid being detected, because the deep
3. Results and discussion
3.1. The direct source of aliphatic diacids
Based on our previous work [68–73] and others’, hexanedioic acid
and its derivatives such as pentanedioic acid, dicyclohexyl hex-
anedioate, monocyclohexyl hexanedioate and so on are the main
7

H.-M. Shen et al.
Applied Catalysis A, General 609 (2021) 117904
Fig. 4. Effect of oxygen pressure on oxidation of cyclohexane with O2 catalyzed by T(4-Cl)PPCo (a. Cyclohexanol, b. Cyclohexanone, c. Hydroperoxide, d. Hex-
anedioic acid).
Conditions: cyclohexane (200 mmol, 16.83 g), T(4-Cl)PPCo (1.2 × 10ꢀ 3%, mol/mol, 0.0019 g), O2, 8.0 h, 600 rpm.
Fig. 5. Effect of time on oxidation of cyclohexane with O2 catalyzed by T(4-Cl)PPCo.
Conditions: cyclohexane (200 mmol, 16.83 g), T(4-Cl)PPCo (1.2 × 10ꢀ 3%, mol/mol, 0.0019 g), O2 1.40 MPa, 600 rpm, a. 110 ◦C, b. 120 ◦C.
oxidation of the obtained target products was hampered effectively by
the diluted concentration. From the formation sequence of oxygenous
products exhibited in Table 1, it could be found that hexanedioic acid
and pentanedioic acid were not produced at the beginning of the reac-
tion and not come from the conversion of oxidation intermediate
cyclohexyl hydroperoxide directly like cyclohexanol and cyclohexa-
none. The formation of hexanedioic acid following cyclohexanol and
cyclohexanone, might just be the result of their deep oxidations, and
pentanedioic acid was the decarboxylation product of hexanedioic acid
as the residual gas in the autoclave reactor making the clear limewater
becoming turbid. Based on these findings, whether the hexanedioic acid
was come from the oxidation of cyclohexanol or cyclohexanone was
explored deeply at the similar reaction conditions. As illustrated in
Tables 2 and 3, in the oxidation of cyclohexanol, the product formed at
the beginning was just cyclohexanone, no hexanedioic acid being
detected. Following the increase in the yield of cyclohexanone, hex-
anedioic acid appeared, which was followed by the formation of pen-
tanedioic acid. As for the oxidation of cyclohexanone, hexanedioic acid
was produced immediately followed by pentanedioic acid. Therefore, it
could be concluded from the above research that the direct source of
hexanedioic acid in the cyclohexane oxidation employing O2 as oxidant
and metalloporphyrins as catalysts under the present conditions was the
deep oxidation of cyclohexanone, not the transformation of oxidation
intermediate cyclohexyl hydroperoxide and the deep oxidation of
cyclohexanol, and cyclohexanol could be conversed to cyclohexanone,
which could be described briefly in Fig. 1 with some references from the
8

H.-M. Shen et al.
Applied Catalysis A, General 609 (2021) 117904
Fig. 6. Pseudo-first-order kinetic fit for oxida-
tions of cyclohexane (a, b), cyclohexanol (c, d)
and cyclohexanone (e, f).
Conditions: (a, b) Cyclohexane (200 mmol,
16.83 g), T(4-Cl)PPCo (1.2 × 10ꢀ 3%, mol/mol,
0.0019 g), O2 (1.40 MPa), 600 rpm. (c, d)
Cyclohexanol (50 mmol, 5.01 g), T(4-Cl)PPCo
(2.4 × 10-3%,
mol/mol,
0.0010 g),
O2
(1.40 MPa), 600 rpm. (e, f) Cyclohexanone
(50 mmol, 4.91 g), T(4-Cl)PPCo (2.4 × 10ꢀ 3%,
mol/mol, 0.0010 g), O2 (1.40 MPa), 600 rpm.
reported mechanism of cyclohexane oxidation [55,56,79,83–88].
Similar formation sequence of the oxygenous products was also
observed in the oxidation of cyclopentane with O2 catalyzed by metal-
loporphyrins illustrated in Table S1-Table S3 of Electronic Supple-
mentary Information. This formation sequence of the oxygenous
products is a very important information for us to clearly distinguish the
direct source of aliphatic diacids, and has become the theoretical and
experimental foundation for us to adjust the oxidation of cycloalkanes
and increase the selectivity towards cycloalkanols and cycloalkanones
through inhibiting the formation of aliphatic diacids.
Table 4
The kinetic parameters for oxidations of cyclohexane, cyclohexanol and cyclo-
hexanone in pseudo-first-order model.
Entry
Substrates
Temperature (ºC)
k (hꢀ 1
)
R2
Ea (kJ/mol)
1
2
3
4
5
110
115
120
110
115
0.00178
0.00374
0.00659
0.02170
0.09384
0.9189
0.9810
0.9982
0.8521
0.9719
164.02
310.72
71.43
6
120
0.25893
0.9586
7
8
9
70
80
85
0.00646
0.01450
0.01909
0.9536
0.9656
0.9909
3.2. Kinetic study
10
90
0.02558
0.9809
To further investigate the obtained formation sequence of oxygenous
products in oxidation of cycloalkanes and verify the direct source of
aliphatic diacids, the kinetic study was carried out employing cyclo-
hexane, cyclohexanol and cyclohexanone as substrates respectively
(Table S4-Table S6). All the kinetics were performed at the solvent-free
9

H.-M. Shen et al.
Applied Catalysis A, General 609 (2021) 117904
Table 5
The oxidation of cyclohexane with O2 in the presence of T(4-Cl)PPCo and Zn (II)a.
Selectivity (%)b
R1 -OH
Entry
Catalysts
Conversion (%)
R1 =O
R1 -OOH
R2 -COOH
R3 -COOH
KA -oil
1
–
0.36
3.79
1.64
4.24
4.97
4.87
6.20
4.81
4.23
1.88
0.25
2.37
0.28
0.31
N. D.
33.0
23.2
25.5
28.8
32.2
34.7
29.3
30.7
20.7
4.0
22.2
49.1
13.4
35.4
43.8
50.7
51.3
51.7
54.4
23.9
40.0
28.7
35.7
42.0
77.8
1.6
N. D.
14.5
11.6
2.8
N. D.c
> 99.0
83.7
2
T(4-Cl)PPCo
1.8
3
Zn(AcO)2 (1.0 %)
51.8
36.1
24.3
14.8
9.7
N. D.
0.2
88.4
4
T(4-Cl)PPCo & Zn(AcO)2 (0.5 %)
T(4-Cl)PPCo & Zn(AcO)2 (1.0 %)
T(4-Cl)PPCo & Zn(AcO)2 (1.5 %)
T(4-Cl)PPCo & Zn(AcO)2 (2.0 %)
T(4-Cl)PPCo & Zn(AcO)2 (2.5 %)
T(4-Cl)PPCo & Zn(AcO)2 (3.0 %)
T(4-Cl)PPCo & ZnSO4 (2.0 %)
T(4-Cl)PPCo & ZnCl2 (2.0 %)
T(4-Cl)PPCo & NaAcO (2.0 %)
T(4-Cl)PPCo
97.0
5
2.8
0.3
96.9
6
2.3
N. D.
0.9
97.7
7
3.4
95.7
8
18.5
11.6
50.0
56.0
27.4
28.6
9.6
0.5
N. D.
N. D.
N. D.
N. D.
N. D.
N. D.
N. D.
99.5
9
3.3
96.7
10
11
12
13d
14d
5.4
94.6
N. D.
4.7
> 99.0
95.3
39.2
35.7
48.4
N. D.
N. D.
> 99.0
> 99.0
T(4-Cl)PPCo & Zn(AcO)2 (2.0 %)
a
Conditions: cyclohexane (200 mmol, 16.83 g), Zn2+ (mol/mol), O2 (1.00 MPa), metalloporphyrin (1.2 × 10ꢀ 3%, mol/mol, 0.0019 g), 120 ◦C, 8.0 h, 600 rpm.
b
c
d
All the conversions and yields were calculated through GC and HPLC analyses as illustrated in Electronic Supplementary Information.
No obvious product detected.
Without O2.
conditions with O2 as oxidant and T(4-Cl)PPCo as catalyst. Based on
delay the formation of hexanedioic acid and its derivative, and result in
the satisfying selectivity towards KA-oil, although cyclohexanol could be
oxidized to cyclohexanone further. This conception is in well accordance
with our initial consideration of catalytic transformation of cyclohexyl
hydroperoxide through introduction of secondary catalytic center and
boosting its catalytic transformation. The apparent activation energies
(Ea) obtained are another theoretical and experimental foundation for
us to adjust the oxidation of cycloalkanes and increase the selectivity
towards cycloalkanols and cycloalkanones.
some preliminary researches illustrated in Figs. 2–5 and Figs. S1- S4, it
was found that at the temperature range of 100ꢀ 120 ◦C, the oxygen
pressure of 0.80–2.00 MPa and the catalyst loading of 6.0 × 10ꢀ 6
-
3.0 × 10ꢀ 5 (mol/mol), the oxygen pressure and catalyst loading did not
exhibit obvious effect on the yields of oxygenous products in the
oxidation of cyclohexane and cyclopentane at the stirring speed of
600 rpm. And the main factors affecting the yields of oxygenous prod-
ucts were reaction temperature and time. Considering the change in the
concentration of substrates with time might influence the reaction rate,
pseudo-first-order kinetic model was selected to fit the oxidation of
cyclohexane, cyclohexanol and cyclohexanone, which was expressed as
following: - ln(CA / CA0) = kt, where k is the rate constant (h-1), CA0 is the
initial concentration of substrates, and CA is the concentration of sub-
strates at time t. The plots of - ln(CA / CA0) versus t in the oxidation of
cyclohexane and cyclohexanol at 110 ◦C, 115 ◦C, 120 ◦C, and in the
oxidation of cyclohexanone at 70 ◦C, 80 ◦C, 85 ◦C, 90 ◦C were presented
in Fig. 6. The pseudo-first-order rate constant k could be obtained from
the slope of the plots as shown in Table 4. Then the apparent activation
energies (Ea) in oxidations of cyclohexane, cyclohexanol and cyclo-
hexanone could be calculated according to the Arrhenius equation: lnk
= - (Ea / R) × (1 / T) + lnk0 through plotting lnk versus 1/T shown in
Fig. 6.
3.3. Catalytic oxidation of cyclohexane enhanced by Zn (II)
Inspired by the direct source of aliphatic diacids and systematical
kinetic studies, commercially-available Zn (II) was introduced to the
cyclohexane oxidation catalyzed by metalloporphyrins, as secondary
catalytic center to adjust and enhance the transformation of oxidation
intermediate cyclohexyl hydroperoxide based on some preliminary
works [57,70,73]. The primary function of Zn (II) is to enhance the
conversion of cyclohexyl hydroperoxide to cyclohexanol with the
intention to boost the selectivity towards KA-oil through reducing the
formation of cyclohexanone from cyclohexyl hydroperoxide directly and
suppressing the emergence of hexanedioic acid and its derivative.
Available Zn(AcO)2, ZnCl2 and ZnSO4 in commerce were employed as
the source of Zn (II) to verify our conception. As demonstrated in Table 5
that, in the absence of catalyst, no obvious transformation occurred in
the cyclohexane oxidation. Employing metalloporphyrin T(4-Cl)PPCo as
catalyst, the conversion of cyclohexane reached up to 3.79 % with the
selectivity towards KA-oil of 83.7 % (Entry 2 in Table 5), in which the
selectivity of cyclohexyl hydroperoxide in a small quantity was calcu-
lated as a party of KA-oil since the hydroperoxide could be transformed
to KA-oil under alkaline conditions smoothly after reaction. Employing
representative Zn(AcO)2 as sole catalyst, the conversion of cyclohexane
was just 1.64 % with the selectivity towards KA-oil of 88.4 % (Entry 3 in
Table 5). The unsatisfying performance of Zn(AcO)2 in catalytic oxida-
tion of cyclohexane was mainly attributed to its poor ability in activation
of O2 as non-variable-valence metal. But when Zn(AcO)2 was introduced
to adjust the transformation of cyclohexyl hydroperoxide and enhance
the selectivity towards KA-oil in the oxidation of cyclohexane catalyzed
by T(4-Cl)PPCo, not only the selectivity was boosted from 83.7% to
95.7%, but also the conversion was boosted from 3.79 % to 6.20 % in the
As illustrated in Fig. 6 and Table 4, pseudo-first-order kinetics fitted
well the oxidation of cyclohexane, cyclohexanol and cyclohexanone
with high correlation coefficient, and the apparent activation energies
(Ea) were 164.02 kJ/mol, 310.72 kJ/mol and 71.43 kJ/mol in the
oxidation of cyclohexane, cyclohexanol and cyclohexanone respec-
tively. It was very clear that the oxidation of cyclohexanone possessed
the lowest apparent activation energy (Ea), which meant that in the
oxidation of cyclohexane, the formed cyclohexanone had the biggest
trend to be further oxidized and produced by-products. And the oxida-
tion of cyclohexanol was more difficult for the quenching effect of hy-
droxyl in this oxidation system with O2 catalyzed by metalloporphyrins.
Based on the kinetic study and the formation sequence of the oxygenous
products in the oxidation of cyclohexane, with the purpose to increase
the selectivity towards KA-oil, a conception occurred in our researches
to adjust and boost the transformation of oxidation intermediate
cyclohexyl hydroperoxide to cyclohexanol, not from cyclohexyl hydro-
peroxide to cyclohexanone directly, which could have the possibility to
10

H.-M. Shen et al.
Applied Catalysis A, General 609 (2021) 117904
Fig. 7. Scanning electron microscopy (SEM) images of Zn(AcO)2 and the corresponding EDS elemental mapping of C, O, and Zn before (a, c, d, e, f) and after (b, g, h,
i, j) catalytic reaction amplified 200 times.
Zn(AcO)2 loading of 2% (mol/mol), a very appealing level for the
Table 6
oxidation of cyclohexane in industry (Entry 2 and Entry 7 in Table 5).
Due to the enhancement of Zn(AcO)2, the simultaneously increased
conversion and selectivity were achieved, and the increased conversion
did not consume the selectivity towards KA-oil. Compared with Zn
(AcO)2, the oxidation of cyclohexane was nearly suppressed in the
presence of ZnSO4 or ZnCl2 with the conversion of 1.88 % and 0.25 %
respectively. The suppressing phenomenon of ZnSO4 and ZnCl2 might be
the result of the quenching effect of anions on the active species. And
from the poor performance of NaAcO in the enhancement of cyclo-
hexane oxidation, it could be obtained that the enhancing effect was
mainly come from Zn (II), not AcOꢀ . As shown in Entry 13 and Entry 14
in Table 5, without the presence of O2, nearly no oxidative trans-
formation of cyclohexane was observed in the presence of T(4-Cl)PPCo
or T(4-Cl)PPCo and Zn(AcO)2 as catalysts, and the negligible conversion
of cyclohexane was mainly ascribed to the residual air in the stainless
steel autoclave reactor, which meant that O2 was the indispensable
oxidant in these reactions of cyclohexane oxidation in this work. Thus, it
could be concluded that the cyclohexane oxidation with O2 catalyzed by
Transformation of tert-butyl hydroperoxide to tert-butanol enhanced by Zn
a
(AcO)2
.
Entry
Catalysts
Transformation Ratiob (%)
Selectivityc (%)
1
2
3
4
–
9.0
94.2
> 99
> 99
> 99
Zn(AcO)2
T(4-Cl)PPCo
T(4-Cl)PPCo &
Zn(AcO)2
22.4
60.3
86.7
a
Conditions: 70 % Aqueous solution of t-BuOOH (5.0 mmol, 0.6437 g),
cyclohexane (20 mmol, 1.6832 g), catalyst T(4-Cl)PPCo (2.5 × 10ꢀ 3 mmol,
2.0 mg), Zn(AcO)2 (0.05 mmol, 9.2 mg), 80 ◦C, 4.0 h.
b
Calculated by GC analyses based on the amount of O = PPh3 with toluene as
internal standard.
c
Selectivity of tert-butanol.
11

H.-M. Shen et al.
Applied Catalysis A, General 609 (2021) 117904
Fig. 8. The possible mechanism of Zn(AcO)2 in the enhancement of cyclohexane oxidation.
Table 7
a
Enhanced cyclohexane oxidation with O2 in the presence of representative metalloporphyrins and Zn(AcO)2
.
Selectivity (%)b
R1 -OH
Entry
Catalysts
Conversion (%)
R1 =O
R1 -OOH
KA -oil
1
TPPCo
3.89
5.91
3.72
6.12
4.15
6.74
3.79
6.20
3.67
6.76
3.47
6.26
3.57
6.38
4.14
6.47
3.48
3.61
4.08
6.01
4.22
5.49
3.83
6.53
35.5
35.5
34.7
26.1
35.9
29.8
33.0
34.7
33.8
27.5
33.1
27.3
31.9
31.3
34.8
31.5
37.1
23.5
32.9
30.0
32.7
30.4
35.2
32.2
46.8
49.1
41.7
45.4
41.9
50.6
49.1
51.3
49.0
49.6
42.7
42.0
40.6
48.7
42.0
42.7
42.0
16.9
41.3
51.1
41.2
42.8
41.8
53.1
2.0
84.3
95.3
80.4
88.7
84.1
92.1
83.7
95.7
85.3
94.1
79.0
88.8
77.5
92.1
80.4
89.2
82.8
97.2
79.8
92.2
81.2
90.3
80.1
96.9
2
TPPCo & Zn(AcO)2
T(2-Cl)PPCo
10.7
4.0
3
4
T(2-Cl)PPCo & Zn(AcO)2
T(3-Cl)PPCo
17.2
6.3
5
6
T(3-Cl)PPCo & Zn(AcO)2
T(4-Cl)PPCo
11.7
1.6
7
8
T(4-Cl)PPCo & Zn(AcO)2
T(2,6-diCl)PPCo
9.7
9
2.5
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
T(2,6-diCl)PPCo & Zn(AcO)2
T(2,3,6-triCl)PPCo
T(2,3,6-triCl)PPCo & Zn(AcO)2
TPFPPCo
17.0
3.2
19.5
5.0
TPFPPCo & Zn(AcO)2
T(4-F)PPCo
12.1
3.6
T(4-F)PPCo & Zn(AcO)2
T(4-CH3)PPCo
15.0
3.7
T(4-CH3)PPCo & Zn(AcO)2
T(4-OCH3)PPCo
56.8
5.6
T(4-OCH3)PPCo & Zn(AcO)2
T(2-Na.)PCo
11.1
7.3
T(2-Na.)PCo & Zn(AcO)2
T(4-COOCH3)PPCo
T(4-COOCH3)PPCo & Zn(AcO)2
17.1
3.1
11.6
a
Conditions: cyclohexane (200 mmol, 16.83 g), Zn(AcO)2 (2.0 %, mol/mol, 0.7339 g), metalloporphyrins (1.2 × 10ꢀ 3%, mol/mol), O2 (1.00 MPa), 120 ◦C, 8.0 h,
600 rpm.
b
All the conversions and yields were calculated through GC and HPLC analyses as illustrated in Electronic Supplementary Information.
T(4-Cl)PPCo could be enhanced by Zn (II) on the conversion and
selectivity simultaneously, and Zn(AcO)2 was a promising Zn (II) source,
which also could be recovered easily through filtration after the catalytic
reaction. As demonstrated in Fig. 7, the particle size of Zn(AcO)2 became
smaller after the catalytic reactions with the same element distribution
compared with the fresh one, which provided a great potential for Zn
(AcO)2 to be recovered and reused in the following application research.
The simultaneous enhancement on the selectivity and conversion in
oxidation of cyclohexane mainly originated from the adjustment of Zn
(II) on the conversion of cyclohexyl hydroperoxide to cyclohexanol
instead of the non-selective thermal decomposition to the mixture of
cyclohexanol and cyclohexanone, which would reduce the direct for-
mation of cyclohexanone and delay the emergence of hexanedioic acid
and its derivatives. To verify this conception, the adjusting function of
Zn (II) on the transformation of cyclohexyl hydroperoxide in this work
was investigated in detail, and t-BuOOH was utilized as the
representative of cyclohexyl hydroperoxide. As revealed in Table 6, in
the absence of catalyst, the transformation ratio of tert-butyl hydroper-
oxide to tert-butanol was just 9.0 % in the selectivity of 94.2 % with
stirring in cyclohexane at 80 ◦C for 4.0 h. Following the employment of
Zn(AcO)2, T(4-Cl)PPCo or their mixture as catalysts, the transformation
ratio of tert-butyl hydroperoxide to tert-butanol reached up to 22.4 %,
60.3 % and 86.7 % respectively with the selectivity above 99 %, which
implied that both of Zn(AcO)2 and T(4-Cl)PPCo could catalyze the
transformation of cyclohexyl hydroperoxide to cyclohexanol effectively.
The introduction of Zn(AcO)2 as secondary catalytic center boosted the
conversion of cyclohexyl hydroperoxide to cyclohexanol, resulting in
the decrease in the formation of cyclohexanone directly and delay on the
emergence of hexanedioic acid and its derivatives. Therefore, it could be
concluded that, the introduction of secondary catalytic center such as Zn
(II) to the oxidation of cyclohexane could enhance the transformation of
oxidation intermediate cyclohexyl hydroperoxide to cyclohexanol
12

H.-M. Shen et al.
Applied Catalysis A, General 609 (2021) 117904
Table 8
a
Oxidation of cycloalkanes with O2 catalyzed by T(4ꢀ COOCH3)PPCo enhanced by Zn(AcO)2
.
Selectivity (%)b
R1-OH
Entry
Cycloalkanes
Conversion (%)
R1=O
R1-OOH
Total
48.7
1
2
3.39
6.53
5.3
36.0
7.4
32.2
12.3
53.1
65.9
11.6
96.9
98.7
3
4
17.15
18.78
20.5
24.4
31.3
15.8
44.3
51.1
> 99
> 99
5
23.47
33.1
a
Conditions: cycloalkane (200 mmol), T(4ꢀ COOCH3)PPCo (1.2 × 10ꢀ 3%, mol/mol, 0.0022 g), Zn(AcO)2 (2.0 %, mol/mol, 0.7339 g), O2 (1.00 MPa), 120 ◦C, 8.0 h,
600 rpm.
b
All the conversions and yields were calculated through GC and HPLC analyses as illustrated in Electronic Supplementary Information.
effectively, and decrease the direct formation of cyclohexanone which
was the direct source of hexanedioic acid and its derivatives. Conse-
quently, the emergence of hexanedioic acid and its derivatives was
delayed and suppressed, resulting in the satisfying selectivity to KA-oil.
To our best knowledge, it is a very efficient and practical strategy to
realize the simultaneously increased conversion and selectivity in
cycloalkanes oxidation through reducing and delaying the formation of
direct source of aliphatic acids, cycloalkanones, and can act as an effi-
cient and practical reference for other alkanes oxidation too.
(Table S8), and the substrates were extended to a series of cycloalkanes
such as cyclopentane, cycloheptane, cyclooctane and cyclododecane.
The selection of porphyrins ligands was mainly according to the prin-
ciples of representative and simple structures, ready availability, and
easy synthetic routes with high yields, which possessed larger potential
in industrial application. And the determination of Co as central metal
was based on our preliminary exploratory experiments as illustrated in
Table S8 in the “Supplementary Information”, in which central metal Co
was proven to be more efficient in catalytic oxidation of cycloalkanes
with O2 as oxidant than others such as Mn, Fe, Ni, Cu and Zn. As
demonstrated clearly in Table 7 and Table S9 that, for all the repre-
sentative metalloporphyrins involved as catalysts, the conversion and
selectivity could be boosted effectively by Zn(AcO)2 in the oxidation of
cyclohexane with O2, especially for T(4ꢀ COOCH3)PPCo, for which the
selectivity was boosted to 96.9 % from 80.1 % towards KA-oil mean-
while the conversion was boosted to 6.53 % from 3.83 %, an attractive
conversion level with higher selectivity compared with the industrial
process of cyclohexane oxidation. While the enhanced selectivity was
ascribed to the reduced and delayed formation of the direct source of
aliphatic acids (cyclohexanone), the boosted conversion was attributed
to the suppressed non-selective thermal decomposition of cyclohexyl
hydroperoxide, which would benefit metalloporphyrins away from the
attack of free radical species and maintaining stable and active, and the
intensification on the oxidation performance of cyclohexyl hydroper-
oxide by Zn2+. For the substrate tolerance, it could be found in Table 8
that, all the cycloalkanes employed herein could be transformed to
cycloalkanols, cycloalkanones and cycloalkyl hydroperoxides selec-
tively expect for cyclopentane. And the total selectivity reached up to
higher than 96 % in satisfying conversions, especially for cycloheptane
cyclooctane and cyclododecane, the total selectivity of cycloalkanols,
cycloalkanones and cycloalkyl hydroperoxides reached up to nearly 99
% in the conversion of 17.15 %, 18.78 % and 23.47 % respectively. The
formation of aliphatic diacids was inhibited effectively and no other
oxygenous product was detected. And the total selectivity towards al-
cohols, ketones and peroxides increased following the increase in carbon
atoms of cycloalkanes with higher selectivity towards cycloalkanones.
The unsatisfying selectivity for cyclopentane as substrate was mainly
because of the very strong tension of ring with pentanedioic acid as the
main product illustrated in Figs. S1 and S4. Therefore, based on the
satisfying tolerance to metalloporphyrins and the wide universality to
In addition, besides tert-butanol, a little of cyclohexanol and cyclo-
hexanone was detected in the catalytic transformation of t-BuOOH
employing Zn(AcO)2, porphyrin cobalts or their mixtures as catalysts in
the solvent of cyclohexane (Table S7), which indicated that the oxida-
tion of cyclohexane occurred in the transformation of t-BuOOH. It was
also a powerful proof for the satisfying performance of t-BuOOH as
oxidant in the catalytic oxidation of cycloalkanes employing Zn(AcO)2,
porphyrin cobalts or their mixtures as catalysts. Accordingly, it could be
speculated in the oxidation of cyclohexane catalyzed by metal-
loporphyrins and enhanced by Zn(AcO)2, not only the transformation of
cyclohexyl hydroperoxide to cyclohexanol was boosted by Zn2+, but also
some oxidation of cyclohexane by oxidation intermediate cyclohexyl
hydroperoxide might happen with cyclohexanol as the reduction prod-
uct of oxidant, which were summarized and demonstrated in Fig. 8
based on the study in our work and some similar reports [89–93]. Both
of them composed the catalytic transformation of oxidation intermedi-
ate cyclohexyl hydroperoxide to cyclohexanol effectively, and decreased
the direct formation of cyclohexanone. Therefore, for the formation of
the direct source of hexanedioic acid and its derivatives was suppressed
and delayed, and the intensification on the oxidation performance of
cyclohexyl hydroperoxide by Zn2+, simultaneous enhancement on the
selectivity and conversion in cyclohexane oxidation was achieved.
3.4. Scopes of metalloporphyrins and cycloalkanes
As obtained above, in the presence of T(4-Cl)PPCo as catalyst, the
oxidation of cyclohexane with O2 could be enhanced by Zn(AcO)2 on the
conversion and selectivity simultaneously. In order to investigated the
practicability of this strategy, the scope of metalloporphyrins was
extended from T(4-Cl)PPCo to a series of representative porphyrin co-
balts for their high performance in catalytic oxidation of cycloalkanes
13

H.-M. Shen et al.
Applied Catalysis A, General 609 (2021) 117904
Table 9
Table 9 (continued)
Comparison with current systems in cyclohexane oxidation with O2.
Entry
Conditions
Conversion
(%)
Selectivitya
(%)
References
[79]
Entry
1
Conditions
Conversion
(%)
Selectivitya
(%)
References
immobilized onto ZnO as
catalyst
115 ◦C, 0.40 MPa, Acetone
as solvent, Copper
34.5
54.8
89.2
44.4
[94]
22
155 ºC, 1.00 MPa, solvent-
free, D(4-Cl)PPCoCl
immobilized onto ZnO as
catalyst
6.23
89.4
nanoparticles on N-doped
Grapheme, NHPI as catalyst
125 ºC, 1.50 MPa,
2
[95]
23
24
160 ºC, 0.80 MPa, solvent-
free, T(4-COOH)PPMn as
catalyst
21.9
46.1
62.1
46.1
[55]
[55]
Cyclohexanone,
Acetonitrile as solvent,
Partially graphitic carbon
as catalyst
160 ºC, 0.80 MPa, solvent-
free, T(4-COOH)PPMn
immobilized onto ZnS as
catalyst
3
4
150 ◦C, O2 0.50 MPa, scCO2
9.50 MPa as solvent, NHPI/
Co(II)/Fe(II) as catalyst
120 ◦C, 1.00 MPa,
10.2
14.3
94.1
94.2
[96]
[97]
25
26
165 ºC, 0.90 MPa, solvent-
free, T(4-COOH)PPCo as
catalyst
38.9
67.8
51.7
34.2
[55]
[55]
Acetonitrile as solvent,
Porous cobalt silica
165 ºC, 0.90 MPa, solvent-
free, T(4-COOH)PPCo
immobilized onto ZnS as
catalyst
materials as catalyst
130 ◦C, 1.50 MPa, Acetone
as solvent, Annealed carbon
nanotubes as catalyst
150 ◦C, 1.00 MPa, solvent-
free, V16 based MOF as
catalyst
5
6
7
8.57
24.6
8.3
76.2
99.0
85.5
[42]
[98]
[47]
27
28
29
30
31
135 ºC, 0.80 MPa, solvent-
free, Porous polymeric T(4-
Br)PPMnCl as catalyst
150 ◦C, 0.80 MPa, solvent-
free, Porous polymeric T(4-
Br)PPMnCl as catalyst
150 ◦C, 0.80 MPa, solvent-
free, Porous polymeric T(4-
Br)PPFeCl as catalyst
155 ºC, 0.80 MPa, solvent-
free, T(4-SO3H)PPFeCl as
catalyst
12.5
29.9
27.5
29.2
51.4
84.8
72.3
69.8
32.5
55.8
[50]
[50]
[50]
[56]
[56]
150 ◦C, 1.00 MPa, solvent-
free, Cobalt molybdenum
oxide supported on
mesoporous silica as
catalyst
8
9
150 ◦C, 0.60 MPa, solvent-
free, Hydrotalcite-derived
Co-MgAlO as catalyst
150 ◦C, 1.50 MPa air,
solvent-free, Ionic liquid-
modified cobalt ZSM-5
zeolite as catalyst
9.1
9.7
82.0
92.2
[40]
[99]
155 ºC, 0.80 MPa, solvent-
free, T(4-SO3H)PPFeCl
immobilized onto chitosan
as catalyst
10
150 ◦C, 2.00 MPa, solvent-
free, Co-based spinel
nanocrystals in Laponite
cages as catalysts
17.2
95.3
[100]
32
33
34
35
36
37
38
39
40
41
42
120 ◦C, 1.40 MPa, solvent-
free, T(4-Cl)PPCo & T(4-Cl)
PPZn as catalysts
4.29
3.79
6.20
3.67
6.76
3.83
6.53
3.94
6.18
6.48
7.44
> 99
83.7
95.7
85.3
94.1
80.1
96.9
83.6
94.3
73.0
85.6
[73]
120 ◦C, 1.00 MPa, solvent-
free, T(4-Cl)PPCo as
catalyst
This work
This work
This work
This work
This work
This work
This work
This work
This work
This work
11
12
165 ºC, 0.80 MPa, solvent-
free, TPFPPCo as catalyst
165 ºC, 0.80 MPa, solvent-
free, TPFPPCo on
25.7
38.5
72.0
62.8
[43]
[43]
120 ◦C, 1.00 MPa, solvent-
free, T(4-Cl)PPCo & Zn
(AcO)2 as catalysts
nanoporous chitosan as
catalyst
120 ◦C, 1.00 MPa, solvent-
free, T(2,6-diCl)PPCo as
catalyst
13
14
155 ºC, 0.90 MPa, solvent-
free, T(4-COOH)PPMnCl as
catalyst
14.6
14.7
73.5
76.9
[101]
[101]
120 ◦C, 1.00 MPa, solvent-
free, T(2,6-diCl)PPCo & Zn
(AcO)2 as catalysts
155 ºC, 0.90 MPa, solvent-
free, T(4-COOH)PPMnCl
immobilized onto porous
chitosan as catalyst
120 ◦C, 1.00 MPa, solvent-
free, T(4-COOCH3)PPCo as
catalyst
15
16
155 ºC, 0.80 MPa, solvent-
free, T(4-COOH)PPFeCl as
catalyst
16.5
17.3
75.8
75.3
[101]
[101]
120 ◦C, 1.00 MPa, solvent-
free, T(4-COOCH3)PPCo &
Zn(AcO)2 as catalysts
120 ◦C, 1.00 MPa, solvent-
free, cobalt stearate as
catalyst
155 ºC, 0.80 MPa, solvent-
free, T(4-COOH)PPFeCl
immobilized onto porous
chitosan as catalyst
17
18
150 ◦C, 1.00 MPa, solvent-
free, T(4-NO2)PPMn as
catalyst
9.76
7.98
74.7
91.0
[102]
[102]
120 ◦C, 1.00 MPa, solvent-
free, cobalt stearate & Zn
(AcO)2 as catalysts
150 ◦C, 1.00 MPa, solvent-
free, T(4-NO2)PPMn
immobilized onto ZnO as
catalyst
130 ◦C, 1.00 MPa, solvent-
free, T(4-COOCH3)PPCo as
catalyst
130 ◦C, 1.00 MPa, solvent-
free, T(4-COOCH3)PPCo &
Zn(AcO)2 as catalysts
19
160 ºC, 0.80 MPa, solvent-
free, T(4-COOH)PPFeCl
immobilized onto ZnS as
catalyst
64.9
37.6
[54]
a
Selectivity towards KA oil.
20
21
150 ◦C, 0.70 MPa, solvent-
free, TPFPPFeCl as catalyst
150 ◦C, 0.70 MPa, solvent-
free, TPFPPFeCl
23.4
39.8
64.0
56.5
[103]
[103]
14

H.-M. Shen et al.
Applied Catalysis A, General 609 (2021) 117904
substrates, our protocol to suppress the formation of aliphatic diacids
through catalytic transformation of cycloalkyl hydroperoxides to
cycloalkanols which could be oxidized to cycloalkanones further and
delaying the formation of direct source of aliphatic acids (cyclo-
alkanones), is a very efficient, practical and promising strategy to
simultaneously increase the selectivity and conversion in cycloalkanes
oxidation, and could act as a valuable reference to other alkanes
oxidation too.
was boosted to 6.53 % from 3.83 %, a very attractive conversion level
with higher selectivity compared with the current industrial process.
The increased selectivity towards target products did not consume the
conversion, which was a very novel and significant example in the al-
kanes oxidation employing O2. Additionally, our protocol was also very
applicable to a large range of metalloporphyrins and cycloalkanes with
satisfying tolerance to the structures of metalloporphyrins, and wide
universality to substrates. Therefore, the protocol demonstrated in this
work is a very efficient, practical and promising approach to realize the
selective transformation of cycloalkanes to cycloalkanols and cyclo-
alkanones with high conversion employing O2 as oxidant and metal-
loporphyrins as catalysts in the presence of Zn(AcO)2, which is not only
a valuable strategy to solve the problems of low conversion and low
selectivity lying in front of industrial cyclohexane oxidation, but also a
novel reference to other alkanes oxidation. And the research to further
boost the transformation of alkanes to alcohols and ketones with higher
conversion and selectivity is still under way in our group.
3.5. Comparison with current oxidation systems
At last, the protocol developed in this work for cycloalkanes oxida-
tion utilizing metalloporphyrins as catalysts and O2 as oxidant without
any solvent in the presence of Zn(AcO)2 was compared with existing
cycloalkane oxidation systems using cyclohexane as substrate for the
extensive application and high value of its oxidation products. As
illustrated in Table 9, the main advantages of our method were the
higher selectivity towards KA-oil and the lower reaction temperature
with acceptable cyclohexane conversion of 6.53 % in the selectivity of
96.9 %. Although the conversion in our work was not so high and
competitive compared with others’ in Table 9, the higher selectivity
would reduce the formation of by-products and the amount of pollutants
discharged into the environment, which was in complete consistence
with the requirements of green chemistry for “Prevent wastes” and
“Atom economy”, and would be a tremendous promotion not only in the
realization of green chemistry in cycloalkane oxidation, but also in the
reduction of production cost. From the perspective of green chemistry
and effective utilization of resources, it is an advisable and promising
strategy to pursue the high selectivity of target product with acceptable
conversion, not the high conversion with selectivity consumption. In
addition, the cyclohexane conversion of 6.53 % in this work is also a
very acceptable and competitive level from the viewpoint of industrial
oxidation of cyclohexane with higher selectivity of 96.9 % and lower
reaction temperature of 120 ◦C. The cyclohexane conversion of 6.53 %
was also higher than the result of 4.29 % in our previous work [73].
When the industrial catalyst cobalt stearate, and cobalt stearate with Zn
(AcO)2 were employed as catalysts, simultaneously increased conver-
sion and selectivity were obtained too (Entry 39 and Entry 40 in
Table 9), with the conversion being enhanced from 3.94 % to 6.18 %,
and the selectivity being enhanced from 83.6 % to 94.3 %. Although the
conversion of cyclohexane could be boosted by the higher temperature
(130 ◦C) as shown in Entry 37 and Entry 41 (from 3.83 % to 6.48 %),
Entry 38 and Entry 42 (from 6.53 % to 7.44 %) in Table 9, the selec-
tivity to KA oil was consumed by the high conversion from 80.1 %–73.0
% and 96.9 % to 85.6 % respectively. So 120 ◦C was considered as the
suitable temperature for the oxidation of cyclohexane with O2 in this
work catalyzed by metalloporphyrins. Thus, the protocol developed in
this work to oxidize cycloalkanes with molecular oxygen catalyzed by
metalloporphyrins and enhanced by Zn(AcO)2, is a very efficient,
practical and promising strategy and method to realize the green process
for cycloalkanes oxidation possessing high selectivity and acceptable
conversion, which could act as a valuable reference to the industrial
oxidation of cyclohexane, and other alkanes oxidation too.
CRediT authorship contribution statement
Hai-Min Shen: Conceptualization, Methodology, Software, Valida-
tion, Formal analysis, Investigation, Resources, Data curation, Writing -
original draft, Writing - review & editing, Visualization, Project
administration. Xiong Wang: Software, Validation, Formal analysis,
Investigation, Data curation, Writing - review & editing. Lei Ning: Data
curation, Writing - review & editing. A-Bing Guo: Writing - review &
editing, Visualization. Jin-Hui Deng: Data curation, Writing - review &
editing. Yuan-Bin She: Conceptualization, Resources, Supervision,
Project administration, Funding acquisition.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Acknowledgements
This work was supported by the National Natural Science Foundation
of China (Grant No. 21878275, 21476270, 21776259).
Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.apcata.2020.117904.
References
[1] J.T. Grant, J.M. Venegas, W.P. McDermott, I. Hermans, Chem. Rev. 118 (2018)
2769–2815.
[2] H. Sterckx, B. Morel, B.U.W. Maes, Angew. Chem. Int. Edit. 58 (2019)
7946–7970.
[3] S.T. Wu, Y.R. He, C.H. Wang, C.M. Zhu, J. Shi, Z.Y. Chen, Y. Wan, F. Hao,
W. Xiong, P.L. Liu, H.A. Luo, ACS Appl. Mater. Inter. 12 (2020) 26733–26745.
[4] R. Biswas, D. Kanti, S.N. Bhaduri, A. Bhaumik, P. Biswas, ACS Sustain. Chem.
Eng. 8 (2020) 5856–5867.
4. Conclusions
[5] S.L.Y. Tang, R.L. Smith, M. Poliakoff, Green Chem. 7 (2005) 761–762.
[6] S.Y. Tang, R.A. Bourne, M. Poliakoff, R.L. Smith, Green Chem. 10 (2008)
268–269.
A strategy to increase the selectivity and conversion simultaneously
in catalytic oxidation of cycloalkanes to alcohols and ketones with O2
was developed, in which metalloporphyrins were utilized as catalysts
and Zn(AcO)2 was employed to enhance the conversion of oxidation
intermediates cycloalkyl hydroperoxides to cycloalkanols and delay the
emergence of cycloalkanones which were the direct sources of the by-
products in oxidation of cycloalkanes, such as aliphatic diacids and
their derivatives. For the important oxidation of cyclohexane in chem-
ical industry, the selectivity towards cyclohexanol and cyclohexanone
(KA-oil) was boosted to 96.9 % from 80.1 % meanwhile the conversion
[7] R.A. Sheldon, Green Chem. 19 (2017) 18–43.
[8] J.B. Zimmerman, P.T. Anastas, H.C. Erythropel, W. Leitner, Science 367 (2020)
397–400.
[9] A.R. Antonangelo, C.G. Bezzu, N.B. McKeown, S. Nakagaki, J. Catal. 369 (2019)
133–142.
[10] M. Saltarelli, E.H. de Faria, K.J. Ciuffi, E.J. Nassar, R. Trujillano, V. Rives, M.
A. Vicente, Mol. Catal. 462 (2019) 114–125.
[11] O.V. Nesterova, K.V. Kasyanova, V.G. Makhankova, V.N. Kokozay, O.
Y. Vassilyeva, B.W. Skelton, D.S. Nesterov, A.J.L. Pombeiro, Appl. Catal. A-Gen.
560 (2018) 171–184.
[12] R. Singh, G. Ganguly, S.O. Malinkin, S. Demeshko, F. Meyer, E. Nordlander, T.
K. Paine, Inorg. Chem. 58 (2019) 1862–1876.
15

H.-M. Shen et al.
Applied Catalysis A, General 609 (2021) 117904
[13] A. Lebedeva, B.L. Albuquerque, J.B. Domingos, J.F. Lamonier, J.M. Giraudon,
P. Lecante, A. Denicourt-Nowicki, A. Roucoux, Inorg. Chem. 58 (2019)
4141–4151.
[57] H.M. Shen, M.Y. Hu, L. Liu, B. Qi, H.L. Ye, Y.B. She, Appl. Catal. A-Gen. 599
(2020), 117599.
[58] H.M. Shen, L. Liu, B. Qi, M.Y. Hu, H.L. Ye, Y.B. She, Mol. Catal. 493 (2020),
111102.
[14] D. Ottaviani, V. Van-Dunem, A.P. Carvalho, A. Martins, L.M.D.R.S. Martins, Catal.
Today 348 (2020) 37–44.
[59] J. Połtowicz, K. Pamin, J. Haber, J. Mol. Catal. A-Chem. 257 (2006) 154–157.
[60] A. Modak, J. Mondal, A. Bhaumik, Appl. Catal. A-Gen. 459 (2013) 41–51.
[61] S.D. Xu, J. Du, H.X. Li, J.H. Tang, Ind. Eng. Chem. Res. 56 (2017) 15030–15037.
[62] A.A. Alshaheri, M.I.M. Tahir, M.B.A. Rahman, T.B.S.A. Ravoof, T.A. Saleh, Chem.
Eng. J. 327 (2017) 423–430.
[15] S. Yamaguchi, Y. Miyake, K. Takiguchi, D. Ihara, H. Yahiro, Catal. Today 303
(2018) 249–255.
[16] C. Wang, N. Xing, W.J. Feng, S.H. Guo, M.Y. Liu, Y. Xu, Z.L. You, Inorg. Chim.
Acta 486 (2019) 625–635.
[17] S.P. Tang, Z.H. Fu, Y. Li, Y.J. Li, Appl. Catal. A-Gen. 590 (2020), 117342.
[18] D.X. Yang, T.B. Wu, C.J. Chen, W.W. Guo, H.Z. Liu, B.X. Han, Green Chem. 19
(2017) 311–318.
[63] N.M.R. Martins, A.J.L. Pombeiro, L.M.D.R.S. Martins, Catal. Commun. 125 (2019)
15–20.
[64] Y.J. Dou, C. Zhu, M.M. Zhu, Y.J. Fu, H.B. Wang, C.F. Shi, H. Huang, Y. Liu, Z.
H. Kang, Appl. Surf. Sci. 509 (2020), 144706.
[19] H. Tateno, S. Iguchi, Y. Miseki, K. Sayama, Angew. Chem. Int. Edit. 57 (2018)
11238–11241.
[65] K.J. Betsy, C. Nayak, A. Lazar, A. Krishnan, D. Bhattacharyya, S.N. Jha, C.
P. Vinod, ChemCatChem 10 (2018) 3291–3298.
[20] J.L. She, X.F. Lin, Z.H. Fu, J.W. Li, S.P. Tang, M. Lei, X. Zhang, C. Zhang, D.L. Yin,
Catal. Sci. Technol. 9 (2019) 275–285.
[66] S.G. Mncube, M.D. Bala, Polyhedron 157 (2019) 467–473.
[67] D.Z. Zee, T.D. Harris, Chem. Sci. 11 (2020) 5447–5452.
[68] Y.B. She, J.H. Deng, L. Zhang, H.M. Shen, Prog. Chem. 30 (2018) 124–136.
[69] H. Li, Y. She, T. Wang, Front. Chem. Sci. Eng. 6 (2012) 356–368.
[70] H.M. Shen, Y. Wang, J.H. Deng, L. Zhang, Y.B. She, Chinese J. Chem. Eng. 26
(2018) 1064–1070.
[21] J.H. Ji, F. Liu, W.J. Yang, M.Y. Tan, W.P. Luo, S.F. Yin, ChemCatChem 12 (2020)
4331–4338.
[22] D. Paulssen, S. Hardt, P.A. Levkin, ACS Appl. Mater. Inter. 11 (2019)
16130–16138.
[23] H. Watanabe, M. Takahashi, H. Kihara, M. Yoshida, Langmuir 35 (2019)
4534–4539.
[71] T. Wang, Y.B. She, H.Y. Fu, H. Li, Catal. Today 264 (2016) 185–190.
[72] H. Li, Y.B. She, H.Y. Fu, M.J. Cao, J. Wang, T. Wang, Can. J. Chem. 93 (2015)
696–701.
[24] G. Li, Y. Huan, B. Yuan, J. Wang, Q. Jiang, Z. Lin, Z. Shen, H. Huang, Eur. J. Med.
Chem. 124 (2016) 103–116.
[25] M. Guerrero, M. Urbano, E.K. Kim, A.M. Gamo, S. Riley, L. Abgaryan, N. Leaf, L.
J. Van Orden, S.J. Brown, J.Y. Xie, F. Porreca, M.D. Cameron, H. Rosen,
E. Roberts, J. Med. Chem. 62 (2019) 1761–1780.
[73] H.M. Shen, L. Zhang, J.H. Deng, J. Sun, Y.B. She, Catal. Commun. 132 (2019),
105809.
[74] N. Sheng, B. Gu, B.X. Ren, J. Zhang, Y.Y. Wang, J.X. Wang, J.Q. Sha, Dyes Pigm.
142 (2017) 116–120.
[26] D.D. Chen, B.Y. Zhang, X.X. Liu, X.Q. Li, X.J. Yang, L. Zhou, Bioorg. Med. Chem.
Lett. 28 (2018) 1149–1153.
[75] D.W. Feng, Z.Y. Gu, J.R. Li, H.L. Jiang, Z.W. Wei, H.C. Zhou, Angew. Chem. Int.
Edit. 51 (2012) 10307–10310.
[27] X.M. Zhao, X. Xi, Z. Hu, W.J. Wu, J.W. Zhang, J. Agr. Food Chem. 64 (2016)
1503–1508.
[76] Z. Wang, J.H. Zhang, J.J. Jiang, H.P. Wang, Z.W. Wei, X.J. Zhu, M. Pan, C.Y. Su,
J. Mater. Chem. A 6 (2018) 17698–17705.
[28] A. Saeed, G. Shabir, M. Arshad, J. Fluoresc. 25 (2015) 1045–1053.
[29] P.V. Santhini, V. Jayadev, S.C. Pradhan, S. Lingamoorthy, P.R. Nitha, M.
V. Chaithanya, R.K. Mishra, K.N.N. Unni, J. John, S. Soman, New J. Chem. 43
(2019) 862–873.
[77] M. Tanasova, B. Borhan, Eur. J. Org. Chem. (2012) 3261–3269.
[78] N. Huang, K.C. Wang, H. Drake, P.Y. Cai, J.D. Pang, J.L. Li, S. Che, L. Huang,
Q. Wang, H.C. Zhou, J. Am. Chem. Soc. 140 (2018) 6383–6390.
[79] Y.J. Xie, F.Y. Zhang, P.L. Liu, F. Hao, H.A. Luo, Ind. Eng. Chem. Res. 54 (2015)
2425–2430.
[30] B.C. Chen, B.Y. Yu, Y.L. Lin, H.P. Huang, I.L. Chien, Ind. Eng. Chem. Res. 53
(2014) 7079–7086.
[31] Z.Z. Wei, Y. Li, J. Wang, H.R. Li, Y. Wang, Chin. Chem. Lett. 29 (2018) 815–818.
[32] Y.L. Wan, Q. Guo, K. Wang, X.T. Wang, Chem. Eng. Sci. 203 (2019) 163–172.
[33] D. Contreras, V. Melin, K. Marquez, G. Perez-Gonzalez, H.D. Mansilla, G. Pecchi,
A. Henriquez, Appl. Catal. B-Environ. 251 (2019) 17–24.
[34] L.P. Xiang, J.J. Fan, W.Z. Zhong, L.Q. Mao, K.Y. You, D.L. Yin, Appl. Catal. A-Gen.
575 (2019) 120–131.
[80] X. Jiang, F.L. Gou, H.W. Jing, J. Catal. 313 (2014) 159–167.
[81] N. Huang, S. Yuan, H. Drake, X.Y. Yang, J.D. Pang, J.S. Qin, J.L. Li, Y.M. Zhang,
Q. Wang, D.L. Jiang, H.C. Zhou, J. Am. Chem. Soc. 139 (2017) 18590–18597.
[82] Q. Jiang, W.B. Sheng, X.D. Guo, J. Tang, C.C. Guo, J. Mol. Catal. A-Chem. 373
(2013) 121–126.
[83] G.Q. Zou, W.Z. Zhong, Q. Xu, J.F. Xiao, C. Liu, Y.Q. Li, L.Q. Mao, S. Kirk, D.L. Yin,
Catal. Commun. 58 (2015) 46–52.
[35] P.A. Payard, Y.T. Zheng, W.J. Zhou, L. Khrouz, L. Bonneviot, R. Wischert,
L. Grimaud, M. Pera-Titus, Eur. J. Org. Chem. (2020) 3552–3559.
[36] A. Shahzeydi, M. Ghiaci, H. Farrokhpour, A. Shahvar, M.X. Sun, M. Saraji, Chem.
Eng. J. 370 (2019) 1310–1321.
[84] H. Noack, V. Georgiev, M.R.A. Blomberg, P.E.M. Siegbahn, A.J. Johansson, Inorg.
Chem. 50 (2011) 1194–1202.
[85] K.B. Cho, X. Wu, Y.M. Lee, Y.H. Kwon, S. Shaik, W. Nam, J. Am. Chem. Soc. 134
(2012) 20222–20225.
[37] B. Yang, Z.H. Fu, A.Q. Su, J.L. She, M.K. Chen, S.P. Tang, W.W. Hu, C. Zhang, Y.
C. Liu, Appl. Catal. B-Environ. 242 (2019) 249–257.
[86] S.A. Wilson, J. Chen, S. Hong, Y.M. Lee, M. Clemancey, R. Garcia-Serres,
T. Nomura, T. Ogura, J.M. Latour, B. Hedman, K.O. Hodgson, W. Nam, E.
I. Solomon, J. Am. Chem. Soc. 134 (2012) 11791–11806.
[87] K. Ray, F.F. Pfaff, B. Wang, W. Nam, J. Am. Chem. Soc. 136 (2014) 13942–13958.
[88] J. Rittle, M.T. Green, Science 330 (2010) 933–937.
[89] P.H. Li, Y.Y. Wang, X. Wang, Y. Wang, Y. Liu, K.K. Huang, J. Hu, L.M. Duan, C.
W. Hu, J.H. Liu, J. Org. Chem. 85 (2020) 3101–3109.
[38] K. Pamin, E. Tabor, S. Gorecka, W.W. Kubiak, D. Rutkowska-Zbik, J. Poltowicz,
ChemSusChem 12 (2019) 684–691.
[39] X.F. Huang, G.P. Yuan, G. Huang, S.J. Wei, J. Ind. Eng. Chem. 77 (2019)
135–145.
[40] P. Liu, K.Y. You, R.J. Deng, Z.P. Chen, J. Jian, F.F. Zhao, P.L. Liu, Q.H. Ai, H.
A. Luo, Mol. Catal. 466 (2019) 130–137.
[41] I. Graca, D. Chadwick, Microporous Mesoporous Mater. 294 (2020), 109873.
[42] Z. Wang, Y. Wu, C. Wu, J. Xie, X. Gu, P. Yu, M. Zong, I.D. Gates, H. Liu, J. Rong,
Catal. Sci. Technol. 10 (2020) 332–336.
[90] Y.M. So, K.L. Wong, H.H.Y. Sung, I.D. Williams, W.H. Leung, Eur. J. Inorg. Chem.
(2019) 2368–2374.
[91] A. Dobrov, D. Darvasiova, M. Zalibera, L. Bucinsky, I. Puskarova, P. Rapta,
S. Shova, D. Dumitrescu, L.M.D.R.S. Martins, A.J.L. Pombeiro, V.B. Arion, Inorg.
Chem. 58 (2019) 11133–11145.
[43] L.Q. Mo, X.F. Huang, G. Huang, G.P. Yuan, S.J. Wei, ChemistryOpen 8 (2019)
104–113.
[44] A. Pokutsa, S. Tkach, A. Zaborovsky, P. Bloniarz, T. Paczesniak, J. Muzart, ACS
Omega 5 (2020) 7613–7626.
[92] M. Sutradhar, T.R. Barman, A.J.L. Pombeiro, L.M.D.R.S. Martins, Molecules 24
(2019) 47.
[45] L.F. Chen, Y.Y. Zhou, Z.Y. Gui, H.Y. Cheng, Z.W. Qi, J. Mater. Sci. 52 (2017)
7186–7198.
[93] C.B. Bo, Q.Q. Bu, X. Li, G. Ma, D.H. Wei, C. Guo, B. Dai, N. Liu, J. Org. Chem. 85
(2020) 4324–4334.
[46] X. Liu, M. Conte, Q. He, D.W. Knight, D.M. Murphy, S.H. Taylor, K. Whiston, C.
J. Kiely, G.J. Hutchings, Chem. Eur. J. 23 (2017) 11834–11842.
[47] A.P. Unnarkat, T. Sridhar, H.T. Wang, S.M. Mahajani, A.K. Suresh, Catal. Today
310 (2018) 116–129.
[94] W. Sun, L.F. Gao, X. Feng, X. Sun, G.X. Zheng, Eur. J. Org. Chem. (2018)
1121–1129.
[95] Y. Guo, T. Ying, X.H. Liu, B.F. Shi, Y.Q. Wang, Mol. Catal. 479 (2019) 170–175.
[96] D. Lisicki, B. Orlinska, Chem. Pap. 74 (2020) 711–716.
[97] J.H. Ye, J.J. Tang, Y.J. Zhao, C.D. Wu, Inorg. Chem. 59 (2020) 767–776.
[98] S. Wang, Z.X. Sun, X.Y. Zou, Z.J. Zhang, G.Y. Fu, L. Li, X. Zhang, F. Luo, New J.
Chem. 43 (2019) 14527–14535.
[48] X.K. Guo, M.X. Xu, M.Y. She, Y. Zhu, T.T. Shi, Z.X. Chen, L.M. Peng, X.F. Guo,
M. Lin, W.P. Ding, Angew. Chem. Int. Edit. 59 (2020) 2606–2611.
[49] X.X. Yang, Y.H. Cao, H. Yu, H.Y. Huang, H.J. Wang, F. Peng, Catal. Sci. Technol. 7
(2017) 4431–4436.
[99] Y. Hong, Y.X. Fang, X.T. Zhou, G. Du, J.J. Mai, D.L. Sun, Z.P. Shao, Ind. Eng.
Chem. Res. 58 (2019) 19832–19838.
[50] Y.J. Li, C.R. Liu, W.J. Yang, New J. Chem. 41 (2017) 8214–8221.
[51] X. Guo, D.H. Shen, Y.Y. Li, M. Tian, Q. Liu, C.C. Guo and, Z.G. Liu,, J. Mol. Catal.
A-Chem. 351 (2011) 174–178.
[100] P. Zhang, J. Wang, Y. Jia, W.Q. Li, X.L. Tan, D. Zhang, S.N. Xu, P.P. Zhang, C.
D. Wei, S.D. Miao, Appl. Clay Sci. 181 (2019), 105226.
[101] G. Huang, P. Wang, L. Shen, Y.X. Wei, K. Zeng, S.J. Wei, Mat. Sci. Eng. C-Mater.
49 (2015) 844–850.
[52] G. Huang, Z.C. Luo, Y.D. Hu, Y.A. Guo, Y.X. Jiang, S.J. Wei, Chem. Eng. J. 195
(2012) 165–172.
[53] C.G. Sun, B.C. Hu, D.H. Zhao, Z.L. Liu, J. Appl. Polym. Sci. 125 (2012) E79–E87.
[54] Y.X. Jiang, T.M. Su, Z.Z. Qin, G. Huang, RSC Adv. 5 (2015) 24788–24794.
[55] G. Huang, W.L. Wang, X.X. Ning, Y. Liu, S.K. Zhao, Y.A. Guo, S.J. Wei, H. Zhou,
Ind. Eng. Chem. Res. 55 (2016) 2959–2969.
[102] Z. Feng, Y.J. Xie, F. Hao, P.L. Liu, H.A. Luo, J. Mol. Catal. A-Chem. 410 (2015)
221–225.
[103] G. Huang, L.Q. Mo, J.L. Cai, X. Cao, Y. Peng, Y.A. Guo, S.J. Wei, Appl. Catal. B.-
Environ. 162 (2015) 364–371.
[56] G. Huang, Y. Liu, J.L. Cai, X.F. Chen, S.K. Zhao, Y.A. Guo, S.J. Wei, X. Li, Appl.
Surf. Sci. 402 (2017) 436–443.
16