Heterogeneous selective hydrogenation of ethylene carbonate to methanol and ethylene glycol over a copper chromite nanocatalyst

Article abstract of DOI:10.1039/c4cc08247h

Heterogeneous selective hydrogenation of ethylene carbonate (EC), a key step in indirect conversion of CO₂, was realized over a copper chromite nanocatalyst prepared via a hydrothermal method followed by calcination. The selectivities towards methanol (60%) and ethylene glycol (93%) were higher than those achieved over other usual hydrogenation catalysts.

Full text of DOI:10.1039/c4cc08247h

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Heterogeneous selective hydrogenation of
ethylene carbonate to methanol and ethylene
Cite this:DOI: 10.1039/c4cc08247h
glycol over a copper chromite nanocatalyst†
Received 18th October 2014,
Accepted 25th November 2014
Chao Lian,a Fumin Ren,b Yuxi Liu,a Guofeng Zhao,a Yongjun Ji,a Hongpan Rong,a
Wei Jia,a Lei Ma,a Haiyuan Lu,b Dingsheng Wanga and Yadong Li*a
DOI: 10.1039/c4cc08247h
www.rsc.org/chemcomm
Heterogeneous selective hydrogenation of ethylene carbonate hydrogenation of EC over a homogeneous pincer-type RuII
(EC), a key step in indirect conversion of CO2, was realized over a complex catalyst.7,8 The green and efficient indirect conversion
copper chromite nanocatalyst prepared via a hydrothermal method process has an atom economy of 100%, which prompted us to
followed by calcination. The selectivities towards methanol (60%) develop an industrial preferred heterogeneous catalysis system.
and ethylene glycol (93%) were higher than those achieved over Although no heterogeneous hydrogenation of EC has been
other usual hydrogenation catalysts.
reported until now, some studies on the heterogeneous hydro-
genation of carboxylate esters have revealed that copper chromite is
The synthesis of chemicals using CO2 as a C1 building block an excellent catalyst for the hydrogenation of esters, which provided
has attracted much attention in recent decades because of the us with a clue for the heterogeneous selective hydrogenation of EC.9
potential economic outlook and growing concern over environ- Herein, we report our preliminary results on heterogeneous
mental protection.1 Great efforts have been made to convert selective hydrogenation of EC to methanol and EG. High selectivities
CO2 to methanol, a sustainable source of liquid fuels and one towards EG (93%) and methanol (60%), which are much higher than
of the most useful organic chemicals.1–5 However, due to the those achieved over the hydrogenation catalysts in common use,
high activation energy for cleavage of the CQO bonds of CO2, were obtained over a copper chromite nanocatalyst. It was proved
the direct hydrogenation of CO2 to methanol is usually carried that the metallic Cu species formed in pretreatment possessed high
out under harsh conditions (220–300 1C, 50–100 atm), which catalytic selectivity for the selective hydrogenation of EC to methanol
hinders its industrial application.1,6 Ding and coworkers have and EG.
developed a novel CO2 indirect conversion process by coupling
the shell omega process and selective hydrogenation of ethylene via a hydrothermal method followed by calcination (see ESI†).
carbonate (EC) to obtain methanol and ethylene glycol (EG) at The prepared catalyst has a specific surface area of 19 m2 gÀ1
The copper chromite catalyst used in this work was prepared
.
the same time (Scheme 1), and have achieved the selective As shown in the SEM image (Fig. 1a), the copper chromite
powder was an association of nanoparticles. The XRD pattern
(Fig. 1b) of the prepared oxide matched well with that of a
tetragonal spinel CuCr2O4 (ref. 10) and the grain size, calcu-
lated from the half width of the diffraction line (101) by using
the Scherrer equation, was 15 nm. The characteristic absorp-
tion bands of CuCr2O4 at 608 and 517 cmÀ1 could be observed
in the FTIR spectrum of the copper chromite catalyst (Fig. S1,
ESI†).11 Elemental compositions of the prepared catalyst mea-
sured by various compositional analysis techniques (Table S1,
Scheme 1 Indirect conversion of CO2 to methanol by coupling the shell
omega process and hydrogenation of EC.
ESI†) corresponded well with the theoretical composition of
a Department of Chemistry & Collaborative Innovation Center for Nanomaterial
Science and Engineering, Tsinghua University, Beijing 100084, China.
E-mail: ydli@tsinghua.edu.cn; Fax: +86 10 6278 8765; Tel: +86 10 6277 2350
b Department of Municipal and Environment Engineering, Beijing Jiaotong
University, Beijing 100044, China
CuCr2O4. Therefore, it was confirmed that the prepared copper
chromite catalyst was a stoichiometric CuCr2O4 nanocrystal
with a tetragonal spinel structure. The redox properties of the
as-prepared copper chromite catalyst were studied by the hydro-
gen temperature-programmed reduction (H2-TPR) experiment.
As shown in Fig. S2 (see ESI†), a reduction peak in the tempera-
ture range of 170–300 1C can be attributed to the reduction of
† Electronic supplementary information (ESI) available: Experimental details,
characterization of the prepared copper chromite catalyst and recycle test results.
See DOI: 10.1039/c4cc08247h
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Fig. 1 SEM image (a) and the XRD pattern (b) of the prepared copper chromite catalyst.
surface Cu2+ and Cu+ species in different local coordination proved this speculation. Over the prepared copper chromite
environments, whereas those in the high temperature region catalyst, the side-reactions mentioned above were greatly sup-
were due to the reduction of bulk CuCr2O4 and Cr2O3.12–14 In pressed and the selectivities towards methanol and EG reached
order to make the catalyst structure in the hydrogenation system 60% and 93%, respectively (Table 1, entry 2). By prolonging the
clear, the copper chromite catalyst was pretreated with H2 at reaction time, EC could be converted completely while the
300 1C before catalysis tests.
selectivities remained unchanged (Table 1, entries 3 and 4). To
The catalytic properties of the prepared copper chromite investigate the reusability of copper chromite, the catalyst was
catalyst and some usual hydrogenation catalysts employed for filtered after the reaction and then used for a new hydrogenation
the hydrogenation of EC were studied, and the results are listed test. As shown in Fig. S3 (ESI†), the prepared catalyst could be
in Table 1. It was obvious that no acceptable selectivity towards repeatedly used without significant loss of catalytic efficiency.
methanol and EG can be obtained over usual hydrogenation This cheap and recoverable Cu-based catalyst was found to have
catalysts (Table 1, entries 6–11). The gas in the autoclave was great potential for practical industrial application.
collected for analysis after the reaction, and CH4, CO, and CO2
X-ray photoelectron spectroscopy (XPS) characterization
could be detected, which illustrated that there were methanation, (Fig. 2) illustrated that some Cu species in the low valence
decarbonylation and decomposition side-reactions occurring states were generated after the H2 pretreatment. As shown in
under the hydrogenation conditions and these side-reactions XRD patterns (Fig. 3), the tetragonal spinel CuCr2O4 trans-
could decrease the methanol selectivity. Furthermore, some formed to a cubic spinel structure19 with metallic Cu crystals20
research on the hydrogenation of glycerol showed that there is after the pretreatment. These results were in accordance with
excessive hydrogenolysis of EG occurring under the hydrogena- those obtained from the H2-TPR experiment mentioned above.
tion conditions.15–18 This subsequent reaction could affect the It has been reported that the specific structure formed in the
selectivity of EG and the ethanol detected in the reaction solution
Table 1 Catalytic properties of various catalysts for the hydrogenation of ECa
Selectivity (%)
Reaction
time (h)
Conversion
(%)
Entry
Catalyst
Blank
MeOH
EG
1
3
3
6
12
3
3
3
3
3
3
0
75
81
100
27
100
100
100
66
—
60
60
60
2
12
8
13
0
0
—
93
89
92
63
48
16
64
43
48
99
b
2
3
4
5
6
7
8
9
CuCr2O4b
CuCr2O4b
CuCr2O4
CuCr2O4-Wc
Raney Cu
Raney Ni
Ru/C (5%)
Pt/C (5%)
Pd/C (5%)
Rh/C (5%)
10
11
38
18
3
2
a
Reaction conditions: catalyst, 0.5 g; EC, 10 mmol; THF, 20 mL;
b
temperature, 180 1C; initial hydrogen pressure, 5 MPa. CuCr2O4 was
used after pretreatment with H2 at 300 1C for 2 h. The pretreated
c
Fig. 2 XPS spectra of Cu 2p3/2 for CuCr2O4 pretreated with H2 at 300 1C
CuCr2O4 catalyst was washed with an aqueous solution of FeCl3 (1 M). for 2 h (a), fresh CuCr2O4 (b), and CuCr2O4-W (c).
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CO2 conversion, the hydrogenation system needs to be further
optimized to improve the catalysis efficiency and a chromium-
free catalyst should also be developed. In fact, the relevant work
is currently underway in our laboratory.
This work was supported by the State Key Project of Funda-
mental Research for Nanoscience and Nanotechnology
(2011CB932401, 2011CBA00500, and 2012CB224802), and the
National Natural Science Foundation of China (21221062,
21131004, and 21390393).
Notes and references
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