A boron-doped carbon aerogel-supported Cu catalyst for the selective hydrogenation of dimethyl oxalate

Article abstract of DOI:10.1039/c9nj05956c

Carbon aerogels (CA) were applied in the synthesis of Cu/CA catalysts by the impregnation method and the catalysts with boron-doped CA supports were systematically characterized and evaluated in the hydrogenation of dimethyl oxalate (DMO). The Cu/xB-CA catalyst with 25 wt% copper showed 100% DMO conversion and the highest ethylene glycol (EG) or methyl glycolate (MG) selectivity of 70% at 230 °C as well as a lifetime of over 150 h. The characterization results disclosed the reason the performance of the catalysts could be tuned facilely by changing the amount of boron doping, which effectively influenced the interrelation between copper and CA, acidity and alkalinity of catalysts and Cu dispersion. Both the original carbon aerogels and that promoted with little B could provide larger surface areas and high dispersion of the metal. The species, size of copper particles and the ratio of Cu⁺/(Cu⁺ + Cu⁰) could be regulated by boron doping, thus adjusting the type of hydrogenation products.

Full text of DOI:10.1039/c9nj05956c

View Article Online
View Journal
NJC
New Journal of Chemistry
Accepted Manuscript
A journal for new directions in chemistry
This article can be cited before page numbers have been issued, to do this please use: X. Lu, G. Wang, X.
Kong, Y. Yu and J. Chen, New J. Chem., 2020, DOI: 10.1039/C9NJ05956C.
Volume 42
This is an Accepted Manuscript, which has been through the
Number
6
21 March 2018
Pages 3963-4776
Royal Society of Chemistry peer review process and has been
accepted for publication.
NJC
New Journal of Chemistry
rsc.li/njc
A journal for new directions in chemistry
Accepted Manuscripts are published online shortly after acceptance,
before technical editing, formatting and proof reading. Using this free
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
shall the Royal Society of Chemistry be held responsible for any errors
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
ISSN 1144-2546
PAPER
Chechia Hu, Tzu-Jen Lin et al.
Yellowish and blue luminescent graphene oxide quantum dots
prepared via a microwave-assisted hydrothermal route using
H2O2 and KMnO4 as oxidizing agents
rsc.li/njc

Page 1 of 16
New Journal of Chemistry
1
2
3
View Article Online
DOI: 10.1039/C9NJ05956C
4
5
6
7
8
Boron-doped Carbon aerogels supported Cu catalyst for
selective hydrogenation of dimethyl oxalate
9
Xiaodong Lua,b
,
Guofu Wanga, Yu Yanga, Xiangpeng Kongc, Jiangang Chen*a
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
aState Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, 030001 Shanxi,
PR China
bUniversity of Chinese Academy of Sciences, Beijing 100049, PR China
cTaiyuan Institute of Technology, Taiyuan, 030008 shanxi, PR China
Abstract
The Carbon aerogels (CA) was applied to synthesize Cu/CA catalysts by the impregnation method and the catalysts with
boron-doped CA supports were systematically characterized and evaluated in the hydrogenation of dimethyl oxalate (DMO).
The Cu/xB-CA catalyst with 25wt% copper showed 100% DMO conversion and the highest ethylene glycol(EG) or methyl
glycolate(MG) selectivity of 70 % at 230°C, as well a lifetime of over 150h. The characterization results disclosed the reason
why the performance of catalysts could be tuned facilely by changing the amount of boron doping, which effectively influenced
the interrelation between copper and CA, the acidity and alkalinity of catalysts and the Cu dispersion. Both the original carbon
aerogels and that promoted with little B could provide larger surface area and high dispersion of metal. The species, size of
copper particle and the ratio of Cu+/(Cu++Cu0) could be regulated by boron doping, thus adjust the type of hydrogenation
products.
Keywords:
Carbon aerogels; boron doping; DMO hydrogenation; copper; ethylene glycol; methyl glycolate
1. Introduction
Ethylene glycol (EG) is an important chemical product that has a wide range of applications in the industry, such as the
manufacturing of polyester, lubricant, antifreeze additives and solvent1, 2. Currently, in industrial production the most common
method of synthesizing ethylene glycol is direct hydration of ethylene oxide, which is usually produced from petroleum-derived
ethylene. Due to the shrinking of crude oil resources, the conventional ethylene oxidative hydrolysis process, which relies on the
petrochemical industry to synthesize ethylene glycol, confront enormous challenges3. Owning to the reduction of crude oil
resources as well the increase in demand for ethylene glycol, the synthesis of ethylene glycol from coal has attracted a lot of
interests and commercialized in China to reduce the dependence on petroleum resource4-7. Methyl glycolate (MG) is an
important platform material and chemical intermediate, and has been widely used in the synthesis of value-added products in the
pharmaceutical, fine chemical, and perfume industries1. At present, several methods for synthesizing MG have been developed,
such as carbonylation of formaldehyde with carbon monoxide, coupling of methyl formate with formaldehyde under strong acid

New Journal of Chemistry
Page 2 of 16
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ05956C
catalysis, and high pressure esterification1-3. The main disadvantages of these processes are limited source of raw materials,
harsh reaction conditions, complex separation techniques, severe reactor corrosion, and low yields of target products4-7. Now,
the new route of synthesizing EG/MG under mild conditions with cheap syngas as raw material has become a research highlight,
mainly including two steps: coupling carbon monoxide with nitrite ester to synthesize dimethyl oxalate (DMO), then catalytic
hydrogenation of DMO to EG/MG3, 8. Although the silica supported copper catalysts have been extensively investigated for
hydrogenation of DMO as a result of their high catalytic activity for DMO hydrogenation9, the usage of silica support could be a
fatal flaw in the DMO hydrogenation process because of the leaching of the silica under the gas phase reaction condition
containing methanol10. The development of other support material is important for obtaining highly active and stable Cu-based
catalyst for DMO hydrogenation from commercial application prospect. Noritatsu Tsubaki11 et al. Reported that boron doped
carbon nanotubes was used as the support of copper based catalyst for DMO hydrogenation to ethanol, and the ethanol
selectivity was 78% (300℃,2.5 MPa, H2/DMO =200). Ren12 et al. Reported that the activated carbon aerogel supported copper
catalyst was applied to the hydrogenation of DMO to ethanol, and its selectivity of ethanol was 62% (2.0 MPa, 330℃, H2/DMO
= 60). Carbon aerogels are widely used in catalyst supports, capacitors, fuel cells, adsorber/separator and other fields because of
their superior porosity, high specific surface area, low density and excellent electrochemical performance13-17. Therefore, the
boron-doped Carbon aerogels was adopted as a support for Cu catalyst to carry out the DMO hydrogenation. By doping
different proportion of boron to CA, the interaction between copper and support and the species of rare copper were also
affected, thus different hydrogenation products(EG/MG) were obtained. All along, the types of DMO hydrogenated products are
mainly controlled by temperature. We found that the addition of different amounts of boron in the carbon aerogel could achieve
the hydrogenation product deployment, which reduced energy consumption in industry. In this work, various Cu/xB-CA
catalysts were prepared by thermal treating CA in the presence of boric acid followed by impregnation with Cu species, and
their catalytic performances were evaluated in the hydrogenation of DMO. On basis of systematic characterizations, the effect of
boron doping on the size of copper nanoparticles, interaction between Cu species and CA support, Cu0 and Cu+ distribution,
along with surface acidity of Cu/CA catalysts were elucidated. Thus, the catalytic performance could be controlled and
hydrogenation products were modulated. Our results may encourage readers to design and investigate other related carbon
materialbased catalysts with favorable performances for the hydrogenation of DMO.
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2. Experiment
2.1. Catalyst preparation
Carbon aerogels：Resorcinol and formaldehyde (molar ratio) were mixed in a ratio of 1:2. Sodium carbonate was added as
catalyst and stirred in inert gas atmosphere for 30 minutes. Subsequently, refined constant temperature for 7 days, followed by
acidification with 3% acetic acid for 1 day, then replacement with tert-butanol for 3 days, freeze-drying. After 800℃（ramping
rate: 5℃/min） hours of carbonization in a high temperature tubular furnace for three hours, carbon aerogels were obtained18.
xB-CA supports: the boron-doped CA supports were prepared by thermal annealing of a mixture of CA and boric acid. CA and
boric acid were mixed with different weight ratio (boric acid: CA = 0.1: 1, 0.3:1, 0.5:1, 1: 1, respectively) and the uniform
mixture were obtained by grinding for about 30 minutes. Then, the mixture was calcined at 1000℃ for 4 hours in argon
atmosphere and cooled to room temperature. Finally, the collected sample was washed with deionized water before drying at
90℃ in vacuum. The corresponding supports were denoted as 0.1B-CA, 0.3B-CA, 0.5B-CA, 1B-CA , respectively.
Cu/xB-CA catalysts: Cu/xB-CA catalysts were prepared by sonication-assisted impregnation method, in which the loading of Cu
was 25 wt%. Quantitative Cu(NO3)2•3H2O was dissolved in deionized water, then dripped into xB-CA supports, and stirred for
30 minutes before ultrasonic treatment. All of these operations were carried out at room temperature. The resulting solid was

Page 3 of 16
New Journal of Chemistry
1
2
3
4
5
View Article Online
dried for 12h at 90℃ in vacuum and then calcined at 500 ℃ (ramping rate: 3℃/min) under argon atmosphere for 3 h. Cu/CA
DOI: 10.1039/C9NJ05956C
catalyst preparation method was the same as above.
6
7
8
9
2.2. Catalyst test
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Catalytic test of DMO hydrogenation was conducted in a continuous flow mode using a fixed bed reactor. Calcined catalyst
mixed with quartz sand was placed in the middle of the reactor, and quartz wool was filled on both sides of the catalyst bed.
Then, the system was heated to reduction temperature (300℃), and the system pressure was precisely controlled at 2.4 MPa, and
the reaction temperature is 230℃. Then, a 30 wt% DMO solution with methanol as solvent was continuously pumped into the
reactor with co-feeding H2 at a H2/DMO molar ratio of 180. Finally, the products were condensed in a cold trap and analyzed by
using a gas chromatography instrument equipped.
2.3. Catalyst characterization
Copper loading was determined by inductively coupled plasma emission spectroscopy (ICP-OES). The
Brunauer–Emmett–Teller (BET) surface area (SBET), pore volume (Vp) were tested via N2 physical adsorption at −196℃. All
samples were degassed under vacuum at 90℃ for 1 h before measurement and then degassed at 350℃ for 8 h. The metallic Cu
surface area and copper dispersion was the adsorption and decomposition of N2O with the pulse titration method. The acidic
strength of the catalyst surface was titrated by NH3-TPD. The calcined catalyst of 30 mg was degassed at 350℃ for 1 h under Ar.
Then the temperature was cooled to room temperature and NH3 was adsorbed (30ml/min, 0.5h). Finally, the desorption signal of
NH3 was recorded by mass spectrometry after blowing with Ar for 1 h, then rising to 600℃ with 15℃/min. The defect level in
catalysts was evaluated by Raman spectra, and the experiments that the excitation wavelength was 532nm and power was12mW
were operated on a HORIBA evolution equipment at room temperature. X-ray diffraction (XRD) was carried out with a
D/max-RA X-ray diffractometer, and the patterns were acquired from 5℃to 85℃ with a rate of 10℃/min. For the reduced
samples, catalysts were reduced at 300℃ for 4 h, then cooled to room temperature and sealed in a centrifuge tube to avoid
oxidation. Temperature-programmed reduction(TPR) was conducted in an atmospheric quartz reactor(5 mm i.d.). The calcined
catalyst of 25 mg was gasified for 1 h at 100℃ under Ar. After cooling to room temperature under Ar, the gas was switched to
5% H2/Ar, and the sample was heated to 800℃ at a heating rate of 10℃/min. Thermal conductivity detector (TCD) was used to
monitor the consumption of H2. Copper on the surface of reduction catalyst was determined by X-ray photoelectron
spectroscopy (XPS) and Auger electron spectroscopy (XAES) at Perkin Elmer Phi 1600 ESCA.
3. Results and discussion
3.1. Properties of Cu/xB-CA

New Journal of Chemistry
Page 4 of 16
1
2
3
View Article Online
DOI: 10.1039/C9NJ05956C
4
5
Table 1.Physicochemical properties of Cu/CA and Cu/xB-CA catalysts.
6
7
8
9
Cu loading
(wt%)[a]
Cu+/(Cu0+Cu+)
acid amount
Catalyst
Cu/CA
SBET (m2/g)[b] Vp(cm3/g)[b] dCu0(nm)[c] SCu (m2 /g)[c]
DCu (%)[c]
SCu+ (m2 /g)[d]
(%)[e]
(mmol/g cat)[f]
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
25.1
399.03
0.22
2.4
72.1
42.6
32.9
31.3
0.019
Cu/0.1B-CA
Cu/0.3B-CA
Cu/0.5B-CA
Cu/1.0B-CA
24.9
25.5
25.7
25.3
299.36
284.20
9.69
0.19
0.16
0.02
0.01
2.3
4.1
73.6
40.9
22.0
16.6
43.5
24.2
13.0
9.5
43.8
35.1
20.1
21.0
37.3
46.2
47.7
55.9
0.037
0.028
0.021
0.023
7.7
6.51
10.2
[a] Cu loading determined by ICP-OES analysis. [b] Determined by N2 isotherm adsorption.. [c] Determined by the N2O titration
method.. [d] Calculated SCu+by N2O titration and Cu LMM XAES spectra. [e] Peak area ratio between Cu+ and (Cu++Cu0 ) by
deconvolution of Cu LMM XAES spectra. [f] Amount of acid sites estimated by NH3-TPD.
The copper loading of calcined Cu/xB-CA catalysts were detected by ICP-OES and summarized in Table 1. The Cu amount of
those catalysts were similar. The texture characteristics and the dispersion of copper was also listed in Table 1. The BET surface
area values and the pore volume of Cu/xB-CA catalysts varied upon the boron doping . With the increment of boron doping ratio
from 0 to 1, the BET surface area decreased from 399 m2/g to 6.51 m2/g. Meanwhile, the pore volume decreased from 0.22
cm3/g to 0.01 cm3/g. The decrease of BET surface area may be attributed to that collapse of porous carbon matrix as more B
substituted carbon atoms. N2 adsorption-desorption isotherms of calcined Cu/xB-CA catalysts were shown in Figure 1. All the
N2 adsorption-desorption isotherms of Cu/xB-CA presented typical type IV Langmuir isotherms with a H4-type hysteresis loops,
indicating that the pore were mainly composed of mesoporous and microporous one. The XPS characterization was
implemented to confirm the presence of the doped boron. The XPS survey spectra of Cu/CA and Cu/xB-CA were illustrated in
Figure 2. For Cu/CA, no B1s peak was detected due to the absence of boron source. In addition to the C1s peak, a small B 1s
peak was detected in the spectrum of xB-CA, which proved the successful doping of boron. The use of Raman spectra as a
method for the characterization of graphite was first reported by Tuinstra19. Those catalyst were subjected to Raman
characterization and shown in Figure 3, The band near 1350 cm-1 (d-band) is associated with disorder induced scattering due to
defects in the carbon structure or loss of hexagonal symmetry20, 21. In Figure 3, as the doping amount of boron increases, the D
band shifted to the left and the G band did not shift substantially which indicated that the addition of boron can enhance the
carbon aerogel structure to be more ordered. The NH3-TPD measurement was taken to evaluate the strength and quantity of
acidic sites on Cu/xB-CA catalysts and the obtained profiles were compared in Figure 5 and Table 1. The acidity of the catalyst
and its contribution were not entirely dependent on boron. The addition of boron first increased the acidity to a certain extent,
and then the acidity decreased as the boron content increases furthermore. Boron doping could improve the acidity of catalyst,
because boron played the role of electron acceptor Lewis acid in catalyst. As shown in Figure 6, it could be clearly seen that the
amount of boron doping was different, the existence form of the metal in the catalyst was different, and its acidity was also
different. Cu/0.1B-CA catalyst had the strongest acidity because of the contribution of boron and the existence of Cu2+ on its
surface, which had a stronger ability to accept electrons. For DMO hydrogenation, the metallic Cu catalyzes the conversion of
C=O bonds and C−O bonds in DMO to MG and EG step-by-step with the assistance of acid sites in activating these bonds22.
Therefore, when the acidity was strong (Fig. 4 (b)), this was conducive to the conversion of DMO and the formation of EG. To
clarify the morphology of the Cu/CA and Cu/xB-CA catalysts, the TEM image of the calcined catalysts was shown in Figure 4.
With the increase of boron doping ratio, it can be seen that the copper particles tend to form regular patterns. The Cu particle
size became smaller upon B modification, then increased monotonously with B amount, which was consistent with the results of
Table1. It can also be seen that the support structure of the catalyst would be destroyed with excessive boron doping, and the

Page 5 of 16
New Journal of Chemistry
1
2
3
4
View Article Online
support structure would change from amorphous matrix to sheet-like one, which was consistent with the variation of specific
DOI: 10.1039/C9NJ05956C
surface area in Table 1. The N2O titration was taken to evaluate the particle size, dispersion and Cu exposed surface area. As
shown in Table 1, the dispersion of copper nanoparticles followed the order of Cu/0.1B-CA > Cu/CA > Cu/0.3B-CA >
Cu/0.5B-CA > Cu/1B-CA, and the TEM images also displayed the similar result. As shown in Table 1, both the Cu0 surface
area and Cu+ surface area increased then decreased with increased boron content. This phenomenon could be attributed to the
following reasons:1) The dispersion of supported Cu species could be improved by boron doping into the CA, resulted in large
Cu exposed surface area. However, when boron was excessive, the structure of CA would be destroyed and the surface of Cu0
was decreased. 2) the doped boron could interact strongly with positive-valence Cu species, keeping highly dispersed Cu+ sites
simultaneously. The surface area of Cu+ decreased when the structure was destroyed.
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 1. Adsorption isotherms of catalyst: (a) Cu/CA, (b) Cu/0.1B-CA, (c) Cu/0.3B-CA, (d) Cu/0.5B-CA, (e) Cu/1B-CA.
Figure 2. XPS part of survey spectra of catalyst: (a) Cu/CA, (b) Cu/0.1B-CA, (c) Cu/0.3B-CA, (d) Cu/0.5B-CA, (e) Cu/1B-CA.

New Journal of Chemistry
Page 6 of 16
1
2
3
View Article Online
DOI: 10.1039/C9NJ05956C
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 3. Raman spectra of survey spectra of catalyst: (a) Cu/CA, (b) Cu/0.1B-CA, (c) Cu/0.3B-CA, (d) Cu/0.5B-CA, (e) Cu/1B-CA.

Page 7 of 16
New Journal of Chemistry
1
2
3
View Article Online
DOI: 10.1039/C9NJ05956C
4
5
b
a
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
d
c
e
Figure 4. TEM images of calcined catalysts: (a) Cu/CA, (b) Cu/0.1B-CA, (c) Cu/0.3B-CA , (d) Cu/0.5B-CA, (e) Cu/1B-CA.

New Journal of Chemistry
Page 8 of 16
1
2
3
View Article Online
DOI: 10.1039/C9NJ05956C
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 5. NH3-TPD of calcined catalyst: (a) Cu/CA, (b) Cu/0.1B-CA, (c) Cu/0.3B-CA , (d) Cu/0.5B-CA, (e) Cu/1B-CA.
3.2. XRD profiles
Figure 6. XRD patterns of calcined catalyst: (a) Cu/CA, (b) Cu/0.1B-CA, (c) Cu/0.3B-CA, (d) Cu/0.5B-CA, (e) Cu/1B-CA.
X-ray diffraction patterns of calcined Cu/xB-CA catalysts are shown in Figure 6. The Cu2O and metallic Cu peaks indicated that
the facile reduction of copper species by CA support took place even in the absence of hydrogen23, 24. Compared with Fig. 6 (b)
and (c), when the amount of boron added was relatively small, the peaks of CuO (2theta = 35.4 and 38.6(JCPDS05-0661)) of (b)
and (c) were more obvious than that of a, probably because the boron doping in CA enhanced the interaction between Cu2 + and
CA. With increasing amount of doped boron, the peak of Cu2O(JCPDS05-0667) appeared first, then decreased, and the peak of
Cu (JCPDS04-0836) increases continuously. This indicated that the addition of boron could hinder the further transformation
from Cu2+ to Cu+ and Cu11. However, as the amount of boron was increased excessivly (Figure 6 (d) (e) (f)), it would promote
the transformation of Cu+ to Cu. Therefore, from XRD results, it is reasonable to conclude that boron doping could affect the
reduction of Cu species. The influence of boron doping on the interaction of Cu species with CA support could be further
investigated by H2-TPR as shown in Figure 8.

Page 9 of 16
New Journal of Chemistry
1
2
3
View Article Online
DOI: 10.1039/C9NJ05956C
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 7. XRD patterns and part of XRD patterns of reduced catalyst: (a) Cu/CA, (b) Cu/0.1B-CA, (c) Cu/0.3B-CA, (d) Cu/0.5B-CA, (e)
Cu/1B-CA.
X-ray diffraction patterns of reduced Cu/xB-CA catalysts are shown in Figure 7, After hydrogen reduction, Cu2+ are transformed
into Cu0. However, due to the appropriate amount of boron doping, the degree of crystallization and particle size of Cu0 were
changed. This may be due to the addition of appropriate boron, the relationship between Cu0 and CA was strengthened, and the
growth of copper nanoparticles is limited, but when the amount of boron increases, the limiting effect will be weakened. There
was a distinct asymmetric peak in Figure 10, indicating the presence of Cu2O, but there was no significant Cu2O peak in Figure
7. This was due to that the Cu2O particles were too small and were present only on the surface of the catalyst, resulting in poor
crystallization.
3.3. TPR profiles
Figure 8. TPR patterns of calcined catalyst: (a) Cu/CA, (b) Cu/0.1B-CA, (c) Cu/0.3B-CA, (d) Cu/0.5B-CA, (e) Cu/1B-CA.
The TPR measurements(Figure 8) were preformed to investigate the interaction between Cu species and CA support and
reducibility of Cu/xB-CA catalysts with different amount of boron. The Cu/xB-CA catalysts with boron doping showed much
higher reduction temperature and the reduction peak gradually shifted to higher temperature with increased boron amount. As an

New Journal of Chemistry
Page 10 of 16
1
2
3
4
5
6
7
8
9
View Article Online
electron-deficient element, boron doped in the graphitic structure of CA could strengthen the interaction of positive-valence Cu
DOI: 10.1039/C9NJ05956C
species with CA support25. Therefore, boron doping hindered the transformation of the positive-valence Cu species to metallic
Cu to some extent11. However, when the ratio of boron to CA exceeds 0.5:1, the reduction temperature remains basically
unchanged, which may be due to the limited amount of boron entering CA support and the limited interaction between Cu and
CA support. When the ratio of boron to CA is less than 0.3:1, the small shoulder peak may be caused by different copper
species26. When the ratio is greater than 0.5:1, the small shoulder peak may be affected by different Cu+ states. In addition, due
to the reduction of hydrogen at high temperature, the oxygen-containing functional groups on the surface of CA support are
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
gasified, resulting in the peak of hydrogen consumption at about 600℃27, 28
.
3.4. XPS
Figure 9. XPS patterns of calcined catalyst: (a) Cu/CA, (b) Cu/0.1B-CA, (c) Cu/0.3B-CA, (d) Cu/0.5B-CA, (e) Cu/1B-CA.

Page 11 of 16
New Journal of Chemistry
1
2
3
View Article Online
DOI: 10.1039/C9NJ05956C
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 10. Cu LMM Auger spectra of reduced Cu/XB-CA catalysts: (a) Cu/CA, (b) Cu/0.1B-CA, (c) Cu/0.3B-CA, (d) Cu/0.5B-CA, (e)
Cu/1B-CA.
The surface chemistry of the Cu/xB-CA and reduced Cu/xB-CA catalyst was detected by XPS and X-ray induced Auger
spectroscopy (XAES) measurements. As shown in Figure 9, the intensive photoelectron peaks of samples at 933.1 eV and 952.8
eV were assigned to the binging energy (BE) of Cu 2p3/2 and Cu 2p1/2, respectively29. Meanwhile, there were some peaks(Fig 8 a
b c) between 942 and 944 eV ,which be ascribed to Cu+ implying incomplete reduction of Cu2+ to Cu0 .This phenomenon
corresponds to the XRD spectrum (a b c). As shown in Figure 10, all the Cu LMM spectra of reduced catalysts presented an
asymmetrical and broad peak, suggesting the stable coexistence of Cu+ and Cu0 on the surface of these catalysts. The
concentration of Cu+ and Cu0 on the surface can be determined by the ratio between their band intensities in the Cu LMM XAES
31
spectra30, . The distributions of Cu+ and Cu0 species showed distinct changes with the boron doping32. The ratio of Cu+
/(Cu++Cu0) of (a) Cu/CA, (b) Cu/0.1B-CA, (c) Cu/0.3B-CA , (d) Cu/0.5B-CA and (e) Cu/1B-CA were 31.3%, 37.3%, 46.2%,
47.7% and 55.9%, respectively. The ratio of Cu+ /(Cu++Cu0) increases as the boron content increases, which also indicates that
boron doping hinder the reduction of copper species. Comparing with Figure 7, the presence of asymmetric peaks indicates the
coexistence of Cu+ and Cu0, while there were only obvious peaks of Cu0 in Figure 7, probably due to the better dispersion of Cu
on the catalyst surface and poor crystallinity.
3.5. Catalytic performance
The catalytic performance of Cu/xB-CA catalyst prepared by impregnation method was studied in a fixed-bed reactor by DMO
gas-phase hydrogenation. The reaction was carried out at the temperature of 230℃, the total system pressure was maintained at
2.4 MPa and the molar ratio of H2/DMO was 180. The LHSV of DMO was 1h-1. It is know that the hydrogenation reaction of
DMO involves several steps of reactions:
(1)CH3OOCCOOCH3  2H2  HOCH2OOCH3  CH3OH
(2)HOCH2OOCH3  2H2  HOCH2CH2OH  CH3OH
(3)HOCH2CH2OH  2H2 C2H5OH  H2O

New Journal of Chemistry
Page 12 of 16
1
2
3
View Article Online
DOI: 10.1039/C9NJ05956C
Table 2. DMO hydrogenation to EG over Cu/CA and Cu/xB-CA catalysts.
4
5
6
7
SEL(60h)(%)[b][c]
SEL(130h)(%)[b][d]
[c]
[d]
CONV(60h)
CONV(130h)
Catalyst[a]
T(℃)
(%)
(%)
EG
MG Ethanol Other
EG
MG
Ethanol Other
8
9
Cu/CA
230
230
230
230
230
100.0
100.0
84.6
71.0 13.0
68.4 14.8
45.2 37.3
41.7 37.2
1.4
5.2
1.3
3.0
3.3
14.6
11.2
16.2
18.1
21.4
100.0
96.4
48.9
42.2
64.9
60.2
67.4
30.2
17.4
11.2
22.9
21.6
50.0
50.7
55.4
4.4
2.8
3.1
3.0
2.1
12.5
8.2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Cu/0.1B-CA
Cu/0.3B-CA
Cu/0.5B-CA
Cu/1.0B-CA
16.7
28.9
31.3
73.8
73.4
9.4
65.9
[a]Reaction conditions: 230℃, 2.4 MPa, LHSV =1 h−1, H2/DMO=180, reaction time=12h, 30wt% DMO/methanol as feed. [b] MG:
methyl glycolate, EG: ethylene glycol, Others mainly consist of H2O, methyl methoxyacetate, methyl acetate. [c] 60h: the reaction time
was 60 hours. [d] 130h: the reaction time was 130 hours.
The DMO hydrogenation reaction catalyzed by boron-free and boron-doped catalysts was executed under the same reaction
conditions, which study the effect of boron doping on the catalytic performance. The conversion of DMO and selectivity of
product were listed in Table 2(detailed data are shown in Table S1 S2 and S3). The conversion of DMO and the selectivity of
EG and MG showed significant regular changes.
Figure 11. Spectra of Catalytic activity
Reaction conditions: 300℃, 2.4 MPa, LHSV = 1 h−1, H2/DMO = 180, 30wt% DMO/methanol as feed.
The DMO conversion of Cu/CA and Cu/0.1B-CA was close to 100%, while the other catalysts are low initially and are rising
along the time on stream. After about 50 h, there was a downward trend. An optimum EG selectivity of about 70% was obtained
on Cu/CA and Cu/0.1b-CA catalysts. Combining with the characterization results, the Cu/CA catalyst with the best activity
showed the highest specific surface area (as shown in Table 1). For instance, the specific surface area of the catalyst followed
the order of Cu/CA > Cu/0.1B-CA > Cu/0.3B-CA > Cu/0.5B-CA > Cu/1B-CA, which is in accordance with activity sequence.
The DMO conversion of Cu/0.3B-CA, Cu/0.5B-CA and Cu/1B-CA catalysts was relatively low, mainly due to the excessive
boron addition, which caused the structure of the catalyst to be destroyed to varying degrees (as shown in Table 1). With regards

Page 13 of 16
New Journal of Chemistry
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ05956C
to the size of copper nanoparticles and Cu+/(Cu0+Cu+), they are correlated with the selectivity of the catalyst. As shown in Table
1, the dispersion of copper nanoparticles followed the order of Cu/0.1B-CA > Cu/CA > Cu/0.3B-CA > Cu/0.5B-CA >
Cu/1B-CA, which comply with the EG selectivity order. Compared with EG, the selectivity of MG of Cu/0.3B-CA, Cu/0.5B-CA
and Cu/1B-CA catalysts was higher, which was related to the interaction between Cu and CA after mass boron addition (as
shown in Figure 7), thus the specific surface area and ratio of Cu+and Cu0 changed dramatically (as shown in Table 1), thereby
the progress of reaction 2 was suppressed. That is to say, when the ratio of Cu+/(Cu++Cu0) reached a suitable value, the
dispersion of copper was optimized, the selectivity of EG reached maximum value and the catalyst became more stable. Cu0
activates H2 and Cu+ adsorbs carbonyl groups, the reaction proceed smoothly according to the supposed reaction mechanism33.
As can be seen from Table 1, only when Cu0 and Cu+ cooperate, can EG selectivity be maximized. When the amount of Cu0 was
small, less hydrogen was activated in comparison with activated carbonyl, so that reaction 2 was restricted, thus produced more
MG.
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Fig. 11 also shown the stability of Cu/0.1B-CA catalyst in comparison with that of Cu/CA catalyst. The Cu/0.1B-CA catalyst
was more stable after 120h. The improved stability was attributed to the enhanced interaction between Cu species and CA
support by the doped boron, which might reduce the sintering of Cu to some extent. However, the amount of boron should not
be too much, otherwise the structure of catalyst will be destroyed (see Table 1), and the stability of catalyst would be reduced.
4. Discussion
As shown in Table 2, Cu/0.1B-CA catalyst shows the best catalytic activity in DMO hydrogenation. Generally speaking, the
catalytic performance of copper catalyst was related to the dispersion of copper and the (Cu+ + Cu0) ratio of copper34. In this
work, carbon aerogels with abundant micropores and high specific surface areas were obtained. The highest BET specific
surface area was 399m2/g, which made the dispersion of copper nanoparticles very high, thus further improved the catalytic
performance. In addition, as the anchor point, the occurrence of micropores in the carrier greatly enhanced the dispersion of
copper particles35, which was verified by TEM analysis (Fig. 4) and N2O titration (Table 1). It had been reported that the
synergistic effect of Cu0 and Cu+ was very important for the catalytic activity of ester hydrogenation36, 37. As shown in Table 1
and table 2, the activity of Cu catalyst increases with the increase of Cu0 content. In Cu/0.1B-CA, the highest DMO conversion
and EG selectivity were achieved when the ratio of Cu+/(Cu++ Cu0) was 37.3%. The analysis is as follows: only when Cu0 and
Cu+ cooperate, can EG selectivity be maximized. When the amount of Cu0 was small, less hydrogen was activated in
comparison with activated carbonyl, so that reaction 2 was restricted, thus produced more MG.
5. Conclusion
In summary, the doping of boron to CA support will change the Cu catalysts structure greatly as well as the performance in
DMO hydrogenation. The pore size has little change, but the specific surface area change obviously. The Cu+ and Cu0 specific
surface area increased upon B addition, then decreased monotonously with more B content. Both the Cu dispersion and acidity
maximized at Cu/0.1B-CA catalyst. Acid-base and the interaction of copper with CA are changed by boron doping, so that the
copper particle size of the catalyst, Cu dispersion and the ratio of Cu+/(Cu++ Cu0) were changed. The Cu/0.1B-CA catalyst
exhibited superior catalytic performance in the hydrogenation of DMO to EG, achieved the highest EG selectivity and DMO

New Journal of Chemistry
Page 14 of 16
1
2
3
4
5
6
7
View Article Online
conversion, which could be attributed to small copper particle size, high copper dispersion, matchable interaction strength
DOI: 10.1039/C9NJ05956C
between suitable Cu substances and CA support, appropriate Cu0 and Cu+ distribution and suitable surface acidity. Therefore,
boron doping is an effective method to improve the catalytic performance of CA-based catalysts and to guide the direction of
hydrogenation scheme for DMO hydrogenation.
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Acknowledgement
This work was supported by the Chinese Academy of Sciences Strategic Pilot Science and Technology Special (Class A)
(XDA21020000), the National Natural Science Foundation of China (21673272), the autonomous research project of State Key
Laboratory of Coal Conversion (SKLCC 2018BWZ001).
Graphical Abstract
The modification of B in carbon support can modulate the hydrogenation selectivity.
References
1.
G. H. Xu, Y. C. Li, Z. H. Li and H. J. Wang, Industrial & Engineering Chemistry Research, 1995,
34, 2371-2378.
2.
3.
H. Yue, Y. Zhao, X. Ma and J. Gong, Cheminform, 2012, 41, 4218-4244.
L. Chen, P. Guo, M. Qiao, S. Yan, H. Li, S. Wei, H. Xu and K. Fan, Journal of Catalysis, 2008, 257,
172-180.
4.
F. E. Celik, H. Lawrence and A. T. Bell, Journal of Molecular Catalysis A Chemical, 2008, 288,
87-96.
5.
6.
H. Liu, Z. Huang, C. Xia, Y. Jia, J. Chen and H. Liu, Chemcatchem, 2015, 6, 2918-2928.
J. Pang, M. Zheng, A. Wang and T. Zhang, Industrial & Engineering Chemistry Research, 2011,
50, 6601-6608.

Page 15 of 16
New Journal of Chemistry
1
2
3
4
5
View Article Online
7.
H. Yue, Y. Zhao, L. Zhao, J. Lv, S. Wang, J. Gong and X. Ma, Aiche Journal, 2012, 58,
DOI: 10.1039/C9NJ05956C
2798-2809.
8.
Pruett and R. L., Science, 1981, 211, 11-16.
6
7
8
9
9.
A. Yin, C. Wen, X. Guo, W.-L. Dai and K. Fan, Journal of Catalysis, 2011, 280, 77-88.
C. Wen, Y. Cui, W.-L. Dai, S. Xie and K. Fan, Chemical Communications, 2013, 49, 5195-5197.
P. Ai, M. Tan, N. Yamane, G. Liu, R. Fan, G. Yang, Y. Yoneyama, R. Yang and N. Tsubaki,
Chemistry - A European Journal, 2017, 23.
10.
11.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
12.
13.
14.
15.
16.
X. H, J. Z, J. L, Y. H, Y. P, J. R, New Journal of Chemistry, 2019, 43.
C. Liang, G. Sha and S. Guo, Journal of Non-Crystalline Solids, 2000, 271, 167-170.
F. J. Maldonado-Hódar, J. Rivera-Utrilla and C. Moreno-Castilla, Carbon, 1999, 37, 1199-1205.
C. Moreno-Castilla and F. J. Maldonado-Hódar, Carbon, 2005, 43, 455-465.
R. Saliger, U. Fischer, C. Herta and J. Fricke, Journal of Non-Crystalline Solids, 1998, 225,
81-85.
17.
18.
19.
20.
21.
22.
23.
D. Wu, R. Fu, S. Zhang, M. S. Dresselhaus and G. Dresselhaus, Carbon, 2004, 42, 2033-2039.
Z. Guo, H. Zhu and X. Zhang, Journal of Beijing Jiaotong University, 2010, 34, 103-106.
F. Tuinstra and J. L. Koenig, Journal of Chemical Physics, 1970, 53, 1126-1130.
K. Nakamura, Carbon, 1998, 36, 1693-1696.
Z. Wang, Z. Lu, X. Huang, R. Xue and L. Chen, Carbon, 1998, 36, 51-59.
A. Yin, X. Guo, W.-L. Dai and K. Fan, J.phys.chem.c, 2009, 113, 11003-11013.
P. Ai, M. Tan, Y. Ishikuro, Y. Hosoi, G. Yang, Y. Yoneyama and N. Tsubaki, Chemcatchem, 2017,
9, 307--315.
24.
D. Wang, G. Yang, Q. Ma, M. Wu, Y. Tan, Y. Yoneyama and N. Tsubaki, Acs Catalysis, 2012, 2,
1958–1966.
25.
26.
27.
M. Enterría, M. F. R. Pereira, J. I. Martins and J. L. Figueiredo, Carbon, 2015, 95, 72-83.
H. Zhe, H. Lin, H. Ping and Y. Yuan, Journal of Catalysis, 2011, 277, 54-63.
H. Zhang, Y. A. Alhamed, W. Chu, Z. Ye, A. AlZahrani and L. Petrov, Applied Catalysis A General,
2013, 464, 156-164.
28.
29.
H. Zhang, C. Lancelot, W. Chu, J. P. Hong, A. Y. Khodakov, P. A. Chernavskii, J. Zheng and D. G.
Tong, J. Mater. Chem., 2009, 19, 9241-9249.
L. He, X. Li, W. Lin, W. Li, H. Cheng, Y. Yu, S.-i. Fujita, M. Arai and F. Zhao, Journal of Molecular
Catalysis A Chemical, 2014, 392, 143-149.
30.
31.
32.
A. Yin, X. Guo, W.-L. Dai, H. Li and K. Fan, Applied Catalysis A General, 2008, 349, 91-99.
A. Yin, X. Guo, K. Fan and W. L. Dai, Applied Catalysis A General, 2010, 377, 128-133.
Y. Zhao, S. Li, Y. Wang, B. Shan, J. Zhang, S. Wang and X. Ma, Chemical Engineering Journal,
2017, 313, 759-768.
33.
34.
E. K. Poels and D. S. Brands, Applied Catalysis A General, 2010, 31, no-no.
S. G. Popa, B. S. Ungureanu, I. A. Gheonea, A. Mitrea and A. Săftoiu, Rom J Morphol Embryol,
2015, 56, 1495-1502.
35.
36.
37.
B. Lin, K. Wei, J. Ni and J. Lin, Chemcatchem, 5, 1941-1947.
K. Sun, W. Lu, F. Qiu, S. Liu and X. Xu, 2003, 252, 243-249.
H. Ying, H. Ariga, X. Zheng, X. Duan and Y. Yuan, Journal of Catalysis, 2013, 307, 74-83.

New Journal of Chemistry
Page 16 of 16
1
2
3
4
View Article Online
DOI: 10.1039/C9NJ05956C
5
6
7
8
Graphical Abstract
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The modification of B in carbon support can modulate the hydrogenation selectivity.