Aliphatic amines modified CoO nanoparticles for catalytic oxidation of aromatic hydrocarbon with molecular oxygen

Article abstract of DOI:10.1016/S1872-2067(19)63413-3

The surface modification of metal oxides using organic modifiers is a potential strategy for enhancing their catalytic performances. In this study, a hydrophobic surface amine-modified CoO catalyst with a water contact angle of 143° was fabricated. The catalyst was characterized by XRD, TGA, FT-IR, HR-TEM, and XPS. The results showed that the fabricated catalyst performed better than the hydrophilic commercial CoO nanoparticle in the process of aromatic hydrocarbon oxidation. After the amines modification, commercial CoO also became hydrophobic and improved conversion of ethylbenzene was achieved. The surface modification of CoO with amines induced the hydrophobicity property, which could serve as a reference for the design of other hydrophobic catalysts.

Full text of DOI:10.1016/S1872-2067(19)63413-3

Chinese Journal of Catalysis 40 (2019) 1488–1493
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
Communication
Aliphatic amines modified CoO nanoparticles for catalytic oxidation
of aromatic hydrocarbon with molecular oxygen
a,b
a,#
a,b
a,c
a
a,
Meng Liu , Song Shi , Li Zhao , Chen Chen , Jin Gao , Jie Xu *
a
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian National Laboratory for Clean Energy,
Dalian 116023, Liaoning, China
University of Chinese Academy of Sciences, Beijing 100049, China
School of Materials Science & Chemical Engineering, Ningbo University, Ningbo 315211, Zhejiang, China
b
c
A R T I C L E I N F O
A B S T R A C T
Article history:
The surface modification of metal oxides using organic modifiers is a potential strategy for enhanc-
ing their catalytic performances. In this study, a hydrophobic surface amine-modified CoO catalyst
with a water contact angle of 143° was fabricated. The catalyst was characterized by XRD, TGA,
FT-IR, HR-TEM, and XPS. The results showed that the fabricated catalyst performed better than the
hydrophilic commercial CoO nanoparticle in the process of aromatic hydrocarbon oxidation. After
the amines modification, commercial CoO also became hydrophobic and improved conversion of
ethylbenzene was achieved. The surface modification of CoO with amines induced the hydrophobi-
city property, which could serve as a reference for the design of other hydrophobic catalysts.
Received 28 June 2019
Accepted 19 July 2019
Published 5 October 2019
Keywords:
Hydrocarbon oxidation
Hydrophobic modification
Amines coating
©
2019, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
Cobalt oxide
Surface modification
The selective oxidation of hydrocarbons to oxy-
gen-containing compounds with dioxygen is an important pro-
cess in both academic research and industrial production [1–3].
The difficulties in this process lie in the activation of the inert
C–H bond and the selectivity toward the alcohols and ketones,
which are more active than the hydrocarbons [4,5]. Metal ox-
ides nanoparticles are efficient catalysts for hydrocarbon oxi-
dation. Several metal oxides have been developed to improve
reaction exist, such as the electronic state [13] and the micro-
environment [14]. The surface hydrophobicity of the catalyst
was advantageous to the hydrocarbon oxidation owing to the
nature of the process [15–19]. The CoO nanoparticles exhibit-
x
ed hydrophilic properties toward the polar hydroxyl groups on
the surface. In our previous report [15,17], silica served as the
co-component, and a common strategy of organosilane modifi-
cation was applied to make the surface hydrophobic. The direct
the efficiency of this process, including Mn
CuO [8,9]. Among these catalyst systems, CoO
cellent performance, particularly the nano-sized particles. The
porosity [10], particle size [11], and co-component [12] of CoO
nanoparticles have been investigated. Many other factors that
could enhance the reaction rate of a heterogeneous catalysis
3
O
4
[6], CoO
x
[7], and
hydrophobic modification of CoO nanoparticles, which acted
x
x
x
exhibited ex-
as active sites, has rarely been studied. The direct modification
of nanoparticles to have a hydrophobic surface is challenging.
Organic modification is an important strategy for modifying
the surface of catalysts [20,21]. Several researchers have re-
ported the application of the modification method to improve
x
*
#
Corresponding author. Tel/Fax: +86-411-84379245; E-mail: xujie@dicp.ac.cn
Corresponding author. Tel/Fax: +86-411-84379277; E-mail: shisong@dicp.ac.cn
This work was supported by the National Natural Science Foundation of China (21790331, 21603218) and the Strategic Priority Research Program of
Chinese Academy of Sciences (XDA21030400, XDB17020300).
DOI: S1872-2067(19)63413-3 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 40, No. 10, October 2019

Meng Liu et al. / Chinese Journal of Catalysis 40 (2019) 1488–1493
1489
the selectivity of certain reactions. In particular, when organic
modifiers, including organophosphonic acids [22], carboxylates
126° (c)
143°
(
a)
1°
(b)
1
[
23], and 2-cyanopyridine [24], were employed, metal oxides
such as CeO , TiO , and MnO were promoted to achieve en-
hanced reaction performance. Our team has previously re-
ported the green modification of the MnO surface with car-
boxylates to adjust the selectivity of the desired product [23].
2
2
2
2
However, little attention was paid to the modification of CoO
x
(d)
(e)
(f)
with aliphatic amines for aromatic hydrocarbon oxidation.
Here, amine-modified CoO nanoparticles were synthesized
through the solvothermal approach to decompose a co-
balt-oleate complex in 2-octanol solvent and amines system.
The amines, which acted as organic modifiers, were in-situ in-
troduced to the CoO during the synthesis process; the CoO na-
noparticle exhibited hydrophobic characteristics and showed
good performance in the aromatic hydrocarbon oxidation pro-
cess. Two similar CoO nanoparticles, surface-coated with bu-
tylamine (BA) and dodecylamine (DA), were obtained and were
denoted as BA-CoO and DA-CoO, respectively.
The X-ray diffraction (XRD) patterns in Fig. 1 show the bulk
phase of the as-synthesized nanoparticles. Both BA-CoO and
DA-CoO display main peaks at the (111), (200), and (220)
planes of cubic CoO with a rock salt structure as the commer-
cial CoO, confirming that the nanoparticles were in the CoO
phase. This was also confirmed by the high resolution trans-
mission electron microscopy (HR-TEM) (Fig. 2(d)) results,
which exhibited a d-spacing value of 0.25 nm corresponding to
the CoO (111) plane. The peak intensity of DA-CoO was weaker
than those of BA-CoO and commercial CoO, which was at-
tributed to the smaller particle size of DA-CoO, in agreement
with the TEM results shown in Fig. 2.
Fig. 2. TEM images of the commercial CoO (a), BA-CoO (b), and DA-CoO
(
(
c); (d) HRTEM of BA-CoO; SEM images of BA-CoO (e) and DA-CoO (f)
Insets are the images of sessile water droplets on the material film).
er size and broad distribution of BA-CoO. The commercial CoO
has an average size of 49 nm, similar to that of BA-CoO (Fig. S3).
This excludes the size effect on the reaction (vide infra). The
hydrophobicity of the catalyst was characterized by water
droplet contact angle measurements (WCA). The insets in Fig. 2
are the images of sessile water droplets on the material film.
The commercial CoO is hydrophilic, and it has a WCA value
below 20°. In contrast, BA-CoO has a WCA value of 126° and
DA-CoO has a WCA value of 143°. This may be explained by the
catalytic difference (vide infra). The difference in the WCA val-
ues also suggested that the surface of the as-synthesized CoO
was coated by amines.
The existence of amines on the surface of the as-synthesized
CoO was determined by Fourier transform infrared spectros-
copy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The
nanoparticles were washed with hexane and ethanol until the
FT-IR spectra remained unchanged to remove the organic
compounds adsorbed (Figs. S4 and S5). The three samples
presented broad absorption peaks at 3440 and 1630 cm–1,
which was attributed to the O–H stretching vibration and
bending mode of the adsorbed water [25], respectively. The
peaks at 2854 and 2926 cm–1 in the FT-IR spectrum of DA-CoO
are attributed to the C–H band vibration absorption. The peak
at approximately 1040 cm–1 could be ascribed to the stretching
vibrations of the C–N bonds [26,27], and the peaks between
The morphology of the particle and distribution of the parti-
cle size could be directly observed through TEM characteriza-
tion. As can be seen in Figs. 2(c) and 2(f), the DA-CoO nanopar-
ticles have a nano-cubic morphology and an average size of
~
25 nm (Fig. S1). Similarly, the BA-CoO nanoparticles exhibit a
nano-cubic morphology, although the size distribution is broad
Fig. S2). This difference may be owing to the stronger basicity
(
of butylamine compared to that of dodecylamine, which accel-
erated the decomposition of Co-oleate and resulted in the larg-
(
200)
(
111)
1
300 and 1600 cm–1 could be due to the –NH
group [28],
2
(220)
which confirmed the existence of the amines on the surface
(Fig. 3(c)). In contrast, no peaks attributed to the C–H band
vibration absorption in the commercial CoO were observed. In
comparison with that of DA-CoO, a weaker absorption peak
appeared in the BA-CoO spectrum, which was attributed to the
shorter length of butylamine compared to that of dodecyla-
mine. Comparing BA-CoO with DA-CoO, the increase in the
WCA could also be attributed to the longer length of dodecyla-
mine (vide supra).
(311) (222)
(
c)
(
b)
(
a)
The XPS measurements confirmed that the amines existed
on the surface of the nanoparticles based on the presence of N
1
0
20
30
40
50
60
70
80
o
2
/( )
1
s peak (Figs. S7 and S8). The compositions of the samples are
presented in Table S1. The N content in each sample is less than
%, which is consistent with the TGA results (Fig. S9). The TGA
Fig. 1. XRD patterns of the commercial CoO (a), BA-CoO (b), and
DA-CoO (c).
1

1490
Meng Liu et al. / Chinese Journal of Catalysis 40 (2019) 1488–1493
small amounts of Co(III) [25]. The two bands observed at 653
and 561 cm–1 were the characteristic vibrations of Co(II)–O and
Co(III)–O bonds in Co [25,32], respectively, which implied
(c)
O
3 4
the existence of Co(III) in the commercial CoO. The existence of
Co(III) might favor the hydrocarbon oxidation [31], which can
also be a factor for the enhancement of the catalytic perfor-
mance.
1040
2
926 2854
(
b)
(
a)
The selective oxidation of ethylbenzene was conducted as
the model reaction with the above materials as catalysts (Table
1). A remarkable difference was observed between the hydro-
philic and hydrophobic catalysts. With the commercial hydro-
philic CoO particles, the conversion was only 18% (Table 1,
entry 3); in contrast, the hydrophobic DA-CoO exhibited a high
conversion of 53% (Table 1, entry 2), which is almost twofold
higher than that of commercial CoO particles. In addition, the
selectivity of acetophenone increased from 69% to 78%. In the
selective oxidation of hydrocarbons, alcohol is one of the pri-
mary oxidation products, which can be further oxidized to ke-
tone. Higher selectivity towards ketones means that the hy-
drophobic DA-CoO has stronger oxidation ability. To investi-
gate the vital factors for the catalytic differences between the
commercial CoO and DA-CoO toward the selective oxidation of
ethylbenzene, a few contrast experiments were conducted.
First, a reaction was designed with the commercial CoO and
additional DA as a catalyst to exclude the impact of dissociative
DA. From the results, with a conversion of 17%, it can be de-
duced that the dissociative DA had no vital effect on the reac-
tion (Table 1, entry 4). Subsequently, the hydrophilic and hy-
drophobic properties of CoO for the reaction were researched.
When the commercial CoO was impregnated with 2-octanol
and DA under stirring at room temperature for 5 h, it still had a
hydrophilic surface with a WCA of 12° (Fig. S11), and the cata-
lytic conversion was 20% (Table 1, entry 5). However, when
the commercial CoO was impregnated with 2-octanol and DA at
4
000
3500
3000
1500
1000
500
-1
Wavenumber (cm )
Fig. 3. FT-IR spectra of the commercial CoO (a), BA-CoO (b), and
DA-CoO (c).
results showed a weight loss of 7% for DA-CoO and nearly no
weight loss for the commercial CoO. For DA-CoO, there was an
obvious weight loss at 410 °C, which was much higher than the
boiling temperatures of 2-octanol (178 °C) and dodecylamine
(
259 °C). Furthermore, both the TGA results of 2-octanol and
dodecylamine indicated a rapid weight loss at temperatures
below 200 °C (Fig. S10). This confirmed the interaction be-
tween the amines and CoO nanoparticles to some extent. Alt-
hough the XRD results confirmed that the nanoparticles are in
the CoO phase, in the XPS measurement, Co(III) was detected.
The Co 2p XPS spectra, as illustrated in Fig. 4, exhibited two
main peaks at approximately 780.0 and 796.5 eV, assigned to
Co 2p3/2 and Co 2p1/2, respectively. Fitting the curves according
to the characteristics of the cobalt oxides [29–31], the
Co(III)/Co(II) ratio of the two samples are depicted in Table S1.
Co(III) existed on the surface of the samples, which implied that
a section of the surface of the CoO nanoparticle bore high va-
lence Co(III). Using the FT-IR spectra to analyze the Co species,
the peak located at 460 cm–1 was attributed to the stretching
vibration of the Co–O bond in CoO with a rock-salt structure,
and the peak at 522 cm–1 was attributed to the existence of
250 °C for 5 h, the WCA reached 143°, which indicated the hy-
drophobic property of the amine treated commercial CoO (Fig.
S12). With this hydrophobic catalyst, the conversion of
ethylbenzene increased from 18% to 45%, and the selectivity
of acetophenone increased from 69% to 81% (Table 1, entry 6).
Besides, as shown in Fig. 5, the mass–specific activity for CoO
was 92 mmol gcat h–1 after DA impregnation, which increased
–1
Co 2p3/2
b
Co 2p1/2
Table 1
3
+
2
+
Co 780.2 eV
Co 782.1 eV
Selective oxidation of ethylbenzene with different catalysts.
Conversion
Distribution of products (%)
Entry Catalyst
Co 2p3/2
3
+
(%)
50
53
18
17
20
45
1b
16
13
27
27
27
14
1c
79
78
69
64
66
81
1d
4
7
–
–
1e
1
1
1
2
1f
0
1
3
7
5
2
a
Co 780.2 eV
Co 2p1/2
2+
Co 782.2 eV
1
2
3
4
5
6
BA-CoO
DA-CoO
CoO
CoO
CoO
a
b
c
1
1
1
2
CoO
Reaction conditions: catalyst (20 mg), ethylbenzene (80 mmol), 1.0
810
805
800
795
790
785
780
775
770
MPa O
1
2
, TBHP (80 mg) as initiator.
Binding energy (eV)
a
.6 mg DA was added; b the CoO was impregnated with DA at room
Fig. 4. Co 2p XPS spectra of DA-CoO (a) and BA-CoO (b).
temperature; the CoO was impregnated with DA at 250 °C.
c

Meng Liu et al. / Chinese Journal of Catalysis 40 (2019) 1488–1493
1491
Table 2
320
300
280
260
240
220
200
180
160
140
120
100
Comparative selective oxidation of tetralin and mesitylene using differ-
ent catalysts.
160
1
40
20
1
100
8
0
0
Distribution of products
Mass–specific
Conversion
(%)
6
Entry Catalyst
activity (mmol
(%)
–
1
–1
2b
2c
Others
g
cat h )
40
1
2
CoO
32
63
37
32
57
56
6
12
256
503
20
DA-CoO
0
CoO
DA+CoO
BA-CoO
DA-CoO
–1
h–1) of CoO, and
Fig. 5. Mass-specific activity (mmol
g
cat
amines-modified CoO toward ethylbenzene oxidation with the variable
WCA.
Distribution of products Mass–specific
Conversion
Entry Catalyst
(%)
activity (mmol
(%)
–
1
–1
3b
3c 3d Others
g
cat h )
to 271 mmol gcat h−1 for DA-CoO, along with an increase in
WCA from 11° to 143°. In summary, these contrasted results
can verify that the hydrophobic surface is important for en-
hanced catalytic activity. Furthermore, the reusability of the
DA-CoO was investigated by recycling experiments. The cata-
lyst was regenerated after the reaction through impregnation
with 2-octanol and DA at 250 °C. After the regeneration pro-
cess, the catalyst could be reused for four runs.
−1
1
2
CoO
DA-CoO
25
52
34
15
35 29
17 55
2
13
306
637
Reaction conditions: catalyst (20 mg), reactant (74 mmol), TBHP as
initiator (80 mg), O as oxidant.
2
same conditions; the conversion of tetralin and mesitylene
increased from 32% to 63% and 25% to 52%, respectively. In
addition, the selectivity of deep oxidation products also in-
creased, in accordance with the ethylbenzene oxidation.
In summary, through surface modification, a new hydro-
phobic CoO nanoparticle coating by amines was synthesized,
which showed high activity towards the selective oxidation of
aromatic hydrocarbons. The surface-amines coated CoO nano-
particles exhibited hydrophobic properties, with a WCA of
In the distribution test, it could be observed that the hydro-
phobic DA-CoO remained in a highly distributed state in the
organic phase (Fig. S14), while the commercial hydrophilic CoO
nanoparticle was distributed in the water phase. This experi-
ment was in accordance with the WCA test, confirming the high
affinity towards the organic molecule and the strong water
repellent ability. This property could hinder the inevitable ad-
sorption of water on the active site, and uniform dispersal dur-
ing the reaction could be achieved, as was the case in our pre-
vious report. Accordingly, excellent catalytic performance was
achieved with the hydrophobic catalyst.
1
43°. It is believed that the hydrophobic property of the CoO
surface is an important factor for high catalytic performance.
References
The hydrophobic DA-CoO catalyst was not only active for
ethylbenzene oxidation, but also for the selective oxidation of
tetralin and mesitylene (Table 2). The hydrophobic and hy-
drophilic DA-CoO catalyst exhibited similar effects under the
[
1] A. K. Suresh, M. M. Sharma, T. Sridhar, Ind. Eng. Chem. Res., 2000,
39, 3958–3997.
[2] J. M. Thomas, R. Raja, G. Sankar, R. G. Bell, Nature, 1999, 398,
227–230.
[
[
[
[
[
[
[
3] T. Punniyamurthy, S. Velusamy, J. Iqbal, Chem. Rev., 2005, 105,
2329–2363.
4] M. S. Hamdy, A. Ramanathan, T. Maschmeyer, U. Hanefeld, J. C.
Jansen, Chem. -Eur. J., 2006, 12, 1782–1789.
5] C. Chen, J. Xu, Q. Zhang, Y. Ma, L. Zhou, M. Wang, Chem. Commun.,
6
4
2
0
0
0
0
2
011, 47, 1336–1338.
6] X. Li, L. Zhou, J. Gao, H. Miao, H. Zhang, J. Xu, Powder Technol.,
009, 190, 324–326.
2
7] G. Zhang, D. E. Wang, P. Feng, S. Shi, C. Wang, A. Zheng, G. Lü, Z.
Tian, Chin. J. Catal., 2017, 38, 1207–1215.
8] M. Y. Zhang, L. F. Wang, H. B. Ji, B. Wu, X. P. Zeng, J. Nat. Gas Chem.,
2007, 16, 393–398.
9] C. Zhang, Y. Bai, Y. Yin, J. Gu, Y. Sun, Korean J. Chem. Eng., 2011, 28,
602–607.
1
2
3
4
[
10] D. N. Srivastava, N. Perkas, G. A. Seisenbaeva, Y. Koltypin, V. G.
Kessler, A. Gedanken, Ultrason. Sonochem., 2003, 10, 1–9.
11] L. Zhou, J. Xu, H. Miao, F. Wang, X. Li, Appl. Catal. A, 2005, 292,
223–228.
Fig. 6. Cycle tests on DA-CoO. Reaction conditions: ethylbenzene (80
mmol), catalyst (20 mg), 1.0 MPa O
and 8 h.
[
2
, TBHP (80 mg) as initiator, 120 °C,

1492
Meng Liu et al. / Chinese Journal of Catalysis 40 (2019) 1488–1493
Graphical Abstract
Chin. J. Catal., 2019, 40: 1488–1493 doi: S1872-2067(19)63413-3
Aliphatic amines modified CoO nanoparticles for catalytic oxidation of
aromatic hydrocarbon with molecular oxygen
WCA 143
o
Meng Liu, Song Shi *, Li Zhao, Chen Chen, Jin Gao, Jie Xu *
Dalian Institute of Chemical Physics, Chinese Academy of Sciences;
University of Chinese Academy of Sciences; Ningbo University
N-R
WCA 11
o
The amines-modified CoO nanoparticles exhibited hydrophobic properties
with a water contact angle of 143°, which was accompanied by better per-
formance in the hydrocarbon oxidation process compared to that of the
hydrophilic commercial CoO nanoparticles.
[12] T. Liu, H. Cheng, L. Sun, F. Liang, C. Zhang, Z. Ying, W. Lin, F. Zhao,
lin, ACS Catal., 2017, 7, 8351–8357.
Appl. Catal. A, 2016, 512, 9–14.
[23] X. Jia, J. Ma, F. Xia, Y. Xu, J. Gao, J. Xu, Nat. Commun., 2018, 9, 933.
[24] M. Tamura, R. Kishi, Y. Nakagawa, K. Tomishige, Nat. Commun.,
2015, 6, 8580.
[25] L. Li, X. Sun, X. Qiu, J. Xu, G. Li, Inorg. Chem., 2008, 47, 8839–8846.
[26] X. Liu, M. Atwater, J. Wang, Q. Dai, J. Zou, J. P. Brennan, Q. Huo, J.
Nanosci. Nanotechnol., 2007, 7, 3126–3133.
[
13] H. Li, L. Li, Y. Li, Nanotechnol. Rev., 2013, 2, 515–518.
14] W. Shi, L. Cao, H. Zhang, X. Zhou, B. An, Z. Lin, R. Dai, J. Li, C. Wang,
W. Lin, Angew. Chem. Int. Ed., 2017, 56, 9704–9709.
[
[
[
[
15] C. Chen, J. Xu, Q. Zhang, H. Ma, H. Miao, L. Zhou, J. Phys. Chem. C,
2009, 113, 2855–2860.
16] M. Wang, C. Chen, Q. Zhang, Z. Du, Z. Zhang, J. Gao, J. Xu, J. Chem.
Technol. Biotechnol., 2010, 85, 283–287.
17] C. Chen, S. Shi, M. Wang, H. Ma, L. Zhou, J. Xu, J. Mater. Chem. A,
[27] Y. Tian, B. Yu, X. Li, K. Li, J. Mater. Chem., 2011, 21, 2476–2481.
[28] Z. Xu, C. Shen, Y. Hou, H. Gao, S. Sun, Chem. Mater., 2009, 21,
1778–1780.
2
014, 2, 8126–8134.
[29] B. Ernst, S. Libs, P. Chaumette, A. Kiennemann, Appl. Catal. A,
1999, 186, 145–168.
[30] T. Garcia, S. Agouram, J. F. Sánchez-Royo, R. Murillo, A. M. Mastral,
A. Aranda, I. Vázquez, A. Dejoz, B. Solsona, Appl. Catal. A, 2010,
386, 16–27.
[
18] L. Wang, F.-S. Xiao, ChemCatChem, 2014, 6, 3048–3052.
19] T. Li, J. Wang, F. Wang, L. Zhang, Y. Jiang, H. Arandiyan, H. Li,
ChemCatChem, 2019, 11, 1576–1586.
[
[
[
[
20] J. Zhang, X. Liu, R. Blume, A. Zhang, R. Schlögl, D. S. Su, Science,
2
008, 322, 73–77.
[31] Y. Chen, S. Zhao, Z. Liu, Phys. Chem. Chem. Phys., 2015, 17,
14012–14020.
[32] K. B. Klepper, O. Nilsen, H. Fjellvåg, Thin Solid Films, 2007, 515,
7772–7781.
21] F. Studt, F. Abild-Pedersen, T. Bligaard, R. Z. Sorensen, C. H. Chris-
tensen, J. K. Norskov, Angew. Chem. Int. Ed., 2008, 47, 9299–9302.
22] L. D. Ellis, R. M. Trottier, C. B. Musgrave, D. K. Schwartz, J. W. Med-
脂肪胺修饰的CoO纳米粒子催化分子氧选择氧化芳香烃
a,b
a,#
a,b
a,c
a
a,*
刘 梦 , 石 松 , 赵 丽 , 陈 晨 , 高 进 , 徐 杰
a
中国科学院大连化学物理研究所催化基础国家重点实验室, 洁净能源国家实验室(筹), 辽宁大连116023
b
中国科学院大学, 北京 100049
c
宁波大学材料科学与化学工程学院, 浙江宁波 315211
摘要: 以分子氧为氧化剂实现烃类的选择氧化在学术研究和工业应用中均具有重要的意义. 钴氧化物(CoO
催化烃类选择氧化过程中具有较高的催化活性, 其粒径、孔结构以及组分等因素均对催化活性有着重要的影响. 由于烃类
氧化反应过程中生成的产物分子极性大于底物分子, 使得疏水的催化剂对该类反应有利. 而CoO 由于自身表面羟基的存
在呈亲水性质, 因此可以通过疏水修饰进一步提升CoO 的催化活性. 我们课题组报道了通过有机硅烷的修饰方法制备了
x
)纳米粒子在
x
x
疏水钴基二氧化硅材料, 该过程是通过对载体的间接修饰而达到调控催化剂亲疏水微环境的目的. 然而, 关于CoO
位点的直接疏水修饰较少报道, 对于CoO 进行修饰制备疏水纳米粒子是一个具有挑战性的工作.
本文利用有机胺对CoO 纳米粒子进行有机修饰, 得到了丁胺(BA)修饰的BA-CoO和十二胺(DA)修饰的DA-CoO催化
x
活性
x
x
o
o
剂, 静态水滴接触角分别为126 和143 , 证明了其表面呈疏水性质,并且二者疏水角度具有一定的差异. 通过X射线粉末衍

Meng Liu et al. / Chinese Journal of Catalysis 40 (2019) 1488–1493
1493
射测定了催化剂的晶型为立方相CoO, 从高分辨透射电镜结果也观察到了CoO(111)晶面的晶格条纹, 晶面间距为0.25 nm.
通过透射电镜表征方法, 对纳米粒子的形貌和粒径大小进行分析, BA-CoO和DA-CoO均为纳米立方体的形貌, 其中
DA-CoO的纳米粒子相对均匀并且粒径更小, 这可能是由于DA的碱性相对于BA较弱, 从而使得前驱体分解更慢导致. 进
一步通过红外光谱和X射线光电子能谱证明了纳米粒子中有机胺的存在.
在催化芳香烃类分子氧氧化反应中, 疏水性的DA-CoO和BA-CoO均表现出比亲水性的CoO更高的催化活性, 其中
DA-CoO催化乙苯转化率为53%, 苯乙酮选择性为78%; 而亲水的CoO对应的转化率和选择性分别为18%和69%. 通过利用
o
o
DA和2-辛醇体系对商品化的CoO进行修饰, 经过250 C处理5 h得到了疏水的CoO, 水滴接触角为143 . 将该催化剂应用在
乙苯氧化中, 对比处理前后的催化剂活性, 转化率从18%提高到45%, 这说明疏水性质是影响CoO催化乙苯氧化活性的重
要因素. 有机胺修饰的CoO纳米粒子在烃类催化氧化中的活性增加, 这种有机胺修饰的方法为其它金属氧化物的疏水性
修饰提供了参考.
关键词: 烃氧化; 疏水修饰; 有机胺修饰; 钴氧化物; 表面修饰
收稿日期: 2019-06-28. 接受日期: 2019-07-19. 出版日期: 2019-10-05.
*
通讯联系人. 电话/传真: (0411)84379245; 电子信箱: xujie@dicp.ac.cn
#
通讯联系人. 电话/传真: (0411)84379277; 电子信箱: shisong@dicp.ac.cn
基金来源: 国家自然科学基金(21790331, 21603218); 中国科学院战略性先导科技专项(XDA21030400, XDB17020300).
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).