Effective production of Γ-valerolactone from biomass-derived methyl levulinate over CuOx-CaCO3 catalyst

Article abstract of DOI:10.1016/S1872-2067(19)63270-5

The production of γ-valerolactone (GVL) from lignocellulosic biomass has become a focus of research owing to its potential applications in fuels and chemicals. In this study, (n)CuO_x-CaCO₃ (where n is the molar ratio of Cu to Ca) compounds were prepared for the first time and shown to function as efficient bifunctional catalysts for the conversion of biomass-derived methyl levulinate (ML) into GVL, using methanol as the in-situ hydrogen source. Among the catalysts with varied Cu/Ca molar ratios, (3/2)CuO_x-CaCO₃ provided the highest GVL yield of 95.6% from ML. The incorporation of CaCO₃ with CuO resulted in the formation of Cu⁺ species in a CuO_x-CaCO₃ catalyst, which greatly facilitated the hydrogenation of ML. Notably, CuO_x-CaCO₃ also displayed excellent catalytic performance in the methanolysis products of cellulose, even in the presence of humins. Therefore, a facile two-step strategy for the production of GVL from cellulose could be developed over this robust and inexpensive catalyst, through the integration of cellulose methanolysis catalyzed by sulfuric acid, methanol reforming, and ML hydrogenation in methanol medium.

Full text of DOI:10.1016/S1872-2067(19)63270-5

Chinese Journal of Catalysis 40 (2019) 192–203
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c h n j c
Article
Effective production of γ-valerolactone from biomass-derived
methyl levulinate over CuO -CaCO catalyst
x
3
a
a
a
a,b,
a,b
a,b
c
Xuejuan Cao , Huai Liu , Junnan Wei , Xing Tang *, Xianhai Zeng , Yong Sun , Tingzhou Lei ,
d
a,b,#
Geng Zhao , Lu Lin
a
Xiamen Key Laboratory of Clean and High-valued Utilization for Biomass, College of Energy, Xiamen University, Xiamen 361102, Fujian, China
Fujian Engineering and Research Center of Clean and High-valued Technologies for Biomass, Xiamen 361005, Fujian, China
Henan Key Lab of Biomass Energy, Zhengzhou 450008, Henan, China
b
c
d
College of Chemistry and Chemical Engineering, Xinyang Normal University, Xinyang 464000, Henan, China
A R T I C L E I N F O
A B S T R A C T
Article history:
The production of -valerolactone (GVL) from lignocellulosic biomass has become a focus of re-
Received 25 October 2018
Accepted 26 November 2018
Published 5 February 2019
search owing to its potential applications in fuels and chemicals. In this study, (n)CuO
(where n is the molar ratio of Cu to Ca) compounds were prepared for the first time and shown to
function as efficient bifunctional catalysts for the conversion of biomass-derived methyl levulinate
x
-CaCO
3
(ML) into GVL, using methanol as the in-situ hydrogen source. Among the catalysts with varied
Cu/Ca molar ratios, (3/2)CuO
poration of CaCO
greatly facilitated the hydrogenation of ML. Notably, CuO
performance in the methanolysis products of cellulose, even in the presence of humins. Therefore, a
facile two-step strategy for the production of GVL from cellulose could be developed over this ro-
bust and inexpensive catalyst, through the integration of cellulose methanolysis catalyzed by sulfu-
ric acid, methanol reforming, and ML hydrogenation in methanol medium.
x
-CaCO
3
provided the highest GVL yield of 95.6% from ML. The incor-
Keywords:
+
3
with CuO resulted in the formation of Cu species in a CuO
x
-CaCO
3
catalyst, which
γ-Valerolactone
Methyl levulinate
Hydrocyclization
Methanol reforming
Cellulose methanolysis
x
-CaCO
3
also displayed excellent catalytic
©
2019, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1
.
Introduction
has great potential to partially replace fossil resources [2–7].
For example, γ-valerolactone (GVL) derived from inedible lig-
nocellulose can serve as a flexible building block to manufac-
ture various value-added chemicals and biofuels, including
pentenoic acid, butane, 5-nonanone, 1,4-pentanediol, and aro-
matics [8,9]. Previous work has shown C8–C18
branched/straight-chain hydrocarbons fuels from GVL can be
synthesized by sequential condensation and hydrodeoxygena-
tion [10]. In addition, the application of GVL as a novel and
There has been a surge in demand for carbon resources for
production of transportation fuels, commodity chemicals, and
polymeric materials [1]. However, traditional fossil resources
are being increasingly exhausted, with associated problems
including excessive emissions of greenhouse gases and other
environmental pollution. As a renewable carbon source, bio-
mass can be regenerated in a relatively short span of time and
*
#
Corresponding author. Tel/Fax: +86-592-5952786; E-mail: x.tang@xmu.edu.cn
Corresponding author. Tel/Fax: +86-592-5952786; E-mail: lulin@xmu.edu.cn
This work was supported by the National Natural Science Foundation of China (21676223, 21706223, 21776234, 21606188), the Fundamental Re-
search Funds for the Central Universities (20720180084), the Natural Science Foundation of Fujian Province of China (2018J01017), the Education
Department of Fujian Province (JZ160398) and the Energy development Foundation of Energy College, Xiamen University (2017NYFZ02).
DOI: S1872-2067(19)63270-5 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 40, No. 2, February 2019

Xuejuan Cao et al. / Chinese Journal of Catalysis 40 (2019) 192–203
193
green solvent in biomass conversion has recently received
widespread attention [11–13].
methanolysis of cellulose, MeOH reforming, and ML hydrocy-
clization in MeOH medium.
A large number of studies have been devoted to GVL pro-
duction by the hydrogenation of levulinic acid (LA) and its es-
ters, which can be readily formed by the acid-catalyzed hydrol-
ysis or alcoholysis of biomass-derived carbohydrates [14–16].
Several review articles have provided comprehensive over-
views of the hydrogenation of LA and its esters to GVL in terms
of the diversity of hydrogen sources, which mainly include mo-
2. Experimental
2.1. Chemicals
MeOH, ethanol, oxalic acid, and all metallic nitrates, includ-
3 2 2
ing Cu(NO ) ·3H O, Ca(NO
3 2
) ·4H
2
O, Mg(NO
) ·6H O, Ba(NO ) ,
3 2 2 3 2
lecular H
2
, alcohols, formic acid, and water [17]. For instance,
Ni(NO ·6H
3
)
2
2 3 2 2 3 3 2
O, Zn(NO ) ·6H O, and Al(NO ) ·9H O, were pur-
various supported noble metals (Ru, Pt, Ir, and Au) have proved
to be effective catalysts for the hydrogenation of LA and its
chased from Sinopharm Chemical Reagent Co. Ltd. GVL (98%)
and ML (99%) were supplied by Aladdin Reagent Co. Ltd.
(Shanghai, China) and TCI (Shanghai) Development Co. Ltd.
(Shanghai, China), respectively. All the chemicals were analyti-
cal reagents and used without further purification.
esters to GVL, using external molecular H
the high costs of noble catalysts set limits on their applications
17,19,21–24]. In this light, inexpensive non-noble catalysts
such as Cu, Mo C, Ni, Co, and Zr are desirable alternatives
25–30]; nevertheless, relatively harsh reaction conditions are
2
[18–20]. However,
[
2
[
2.2. Catalyst preparation
required to obtain GVL yields comparable to those in the case
of noble catalysts. Recently, the use of alcohols, such as ethanol
and isopropanol, as the solvent and hydrogen source for GVL
production is gaining momentum, because the management
CuO
x
-CaCO with varied Cu/Ca molar ratios and other
3
Cu-based bimetallic catalysts were prepared by an oxalate
gel-coprecipitation method. For preparation of the
and use of alcohols are convenient compared with those of H
2
.
x 3 3 2 2
(3/2)CuO -CaCO , the desired amounts of Cu(NO ) ·3H O and
For example, Meerwein-Ponndorf-Verley (MPV) reduction of
levulinate esters to GVL can be achieved over various Zr-based
catalysts by using ethanol or isopropanol as the in-situ hydro-
gen source [16,31].
Ca(NO ·4H
3
)
2
2
O (Cu and Ca precursors) were dissolved into
absolute ethanol (0.1 M of the total nitrates) under vigorous
magnetic stirring (1000 rpm) at room temperature. Then, the
saturated oxalic acid/ethanol solution (oxalic acid/(Cu2+ + Ca2+)
molar ratio = 1.5) was rapidly added into the prepared metal
precursor solution. The resultant gel-like precipitates were
formed within several seconds. The gel-like precipitates were
aged at room temperature for 30 min and separated by cen-
trifugation to give the catalyst precursor, which was dried at
110 °C overnight. The dried gel was ground to pass through
100 mesh and calcined at 500 °C for 5 h in air atmosphere to
Methanol (MeOH) is also an appealing hydrogen source that
can be catalytically reformed to H
2
and CO /CO [32]. For in-
2
stance, Barta et al. [33,34] reported a one-pot conversion of
woody biomass to aromatics and/or liquid fuels in supercritical
MeOH in the presence of a Cu-based catalyst. The advantages of
employing Methanol (MeOH) as the hydrogen source for the
GVL production include the fact that methyl levulinate (ML) can
be easily produced by the methanolysis of carbohydrates in
MeOH catalyzed by sulfuric acid [35]. Therefore, a facile
two-step strategy for GVL production from biomass can be
developed in MeOH by the integration of acid-catalyzed meth-
anolysis of biomass to ML and the subsequent reduction of ML
to GVL. In this respect, we previously reported that CuO could
serve as a bi-functional catalyst for MeOH reforming and ML
hydrogenation, giving a nearly complete ML conversion and a
GVL selectivity up to 87.6% at 240 °C in 1 h. However, the CuO
could be completely reduced to metallic Cu, losing its activity
for MeOH reforming. Hence, it is highly desirable to prepare
robust catalysts for GVL production using MeOH as the in-situ
hydrogen source.
give the target (3/2)CuO
CaCO were also prepared by the same oxalate
gel-coprecipitation method. CaO was obtained by the calcina-
tion of CaCO at 900 °C for 5 h.
x
-CaCO
3
catalyst [36–38]. CuO and
3
3
2.3. Catalyst characterization
Chemical compositions of the fresh and spent catalysts and
possible elemental leaching in the reaction filtrates were
measured using inductively coupled plasma optical emission
spectrometry (ICP-OES, Agilent Technologies 7700X) after di-
gestion in concentrated HNO
terns of the catalysts were obtained using a Rigaku Ultima IV
diffractometer with a Cu K radiation source and the following
3
. The X-ray diffraction (XRD) pat-
In this work, (n)CuO
x
-CaCO
3
(where n is the molar ratio of
α
Cu to Ca) compounds were prepared by an oxalate
gel-coprecipitation method and were verified as effective and
parameters: 40 kV, 30 mA, 2θ from 10° to 80°, at a scanning
speed of 10°/min. The specific surface areas of the catalysts
robust catalysts for H
and ML hydrocyclization to GVL. Incorporation of the CaCO
with CuO resulted in the formation of Cu+ species in the
CuO -CaCO catalyst, which greatly promoted the hydrogena-
tion of ML to GVL, even in the methanolysis products of cellu-
lose. Hence, a facile two-step strategy for the production of GVL
from cellulose could be developed over the effective and robust
2
production through MeOH reforming
were determined by N adsorption-desorption analysis at –196
2
3
°C on a Micromeritics ASAP 2020 HD88. Degassing was per-
formed before sorption measurements for all samples. Scan-
ning electron microscopy (SEM) images were obtained using a
Hitachi S-4800 microscope with an accelerating voltage of 15
kV. Energy dispersive X-ray spectrometry (EDS) and ener-
gy-dispersive X-ray (EDX) element mapping images were ob-
tained using a ZEISS SUPRA 55 SAPPHIRE field emission scan-
x
3
CuO
x
-CaCO catalyst, through the integration of acid-catalyzed
3

194
Xuejuan Cao et al. / Chinese Journal of Catalysis 40 (2019) 192–203
ning electron microscope. X-ray photoelectron spectroscopy
XPS) spectra were recorded with a Thermo Scientific ESCALAB
50Xi electron spectrometer under a base pressure <2 × 10−9
mbar. A monochromatic Al K (hν = 1486.6 eV) excitation en-
ergy source was used. NH temperature-programmed desorp-
tion (NH -TPD) and H temperature-programmed reduction
-TPR) were performed on a Micromeritics AutoChem II
920, equipped with a thermal conductivity detector (TCD).
For NH -TPD, after loading into the quartz tube, a sample (40
cellulose, the weight yield of ML was 32.4% (44.8% molar
yield), and the resulting liquid products contained around 3.7
wt% ML.
Next, 13.9 g of the methanolysis product (containing around
4 mmol ML) and 0.25 g catalyst were placed in the Parr reactor
as described above. The subsequent procedure for the GVL
production was the same as that detailed in Section 2.4.1.
(
2
α
3
3
2
(H
2
2
3
2.5. Liquid and gaseous products analysis
mg) was first pretreated at a rate of 20 C/min up to 550 C in
He gas flow for 1 h to remove adsorbed species on its surface.
Then, the temperature was reduced to 120 C at a rate of 50
The analysis for gaseous products was performed on a Shi-
madzu GC-2010 Plus analyzer equipped with an Agilent
CP-7429 column and a TCD. GC analysis for liquid samples was
conducted on an Agilent 7890 series equipped with a
DB-Waxetr column (30.0 m × 0.25 mm × 0.25 μm) and a flame

C·min−1 and the sample was treated with 10% NH
mixture for 0.5 h. After NH adsorption, the remaining or
weakly adsorbed NH was purged by high-purity He for 1 h at
20 C. TPD was performed in He flow by raising the tempera-
ture to 800 C at a rate of 20 C/min and then holding at 800 C
for 0.5 h. H -TPR was performed using a similar procedure
under 10% H /Ar. Elemental analysis for C and H was con-
3
-He (vol%)
3
3
1
ionization detector operated at 270 °C. The carrier gas (N
) had
2
a flow rate of 1.0 mL/min. Temperatures were programmed as
follows: 40 °C (4 min), 15 °C/min, 250 °C (5 min). The qualita-
tive analysis of products after reaction was conducted using a
Thermofisher Trace 1300 & ISQ LT GC-MS instrument with a
TR-5MS column (15.0 m  0.25 mm  0.25 μm). Temperatures
were programmed as follows: 40 °C (2 min), 150 °C/min, 280
2
2
ducted with an Elementar Vario EL III (Elementar Analysen-
systeme GmbH, Germany), and all samples were measured
twice for averaging.
°C (2 min). The flow rate was 1.2 mL/min and the split ratio
2
.4. Catalytic reaction
was 1:50 for the carrier gas (He). The mass spectra were ob-
tained by electron impact ionization (EI) at an electron energy
of 70 eV and with a 25 μA emission current. The operating pa-
rameters for the GC-MS analysis were consistent with those of
the GC analysis. Note that the quantitative analysis of the
by-products (hydrocarboxylation products and ring-opening
products) was performed according to the standard curve of
GVL, because these by-products were not commercially availa-
ble. ML conversion (XML, %), GVL selectivity (SGVL, %), and
MeOH loss (LMeOH, wt%) before and after the reaction were
calculated by the following equations:
2.4.1. Conversion of ML to GVL in MeOH
All experiments were carried out in a 100-mL stainless steel
high-pressure reactor (PARR, USA). After loading of ML (4
mmol), MeOH (19.5 g), and catalyst (0.25 g), the reactor was
weighed, and then purged five times with N before being
2
sealed and heated to the target temperature with stirring (500
rpm). The reactor was naturally cooled to room temperature
after the reaction, and the pressure was recorded before the
collection of gaseous products. Gaseous products were ana-
lyzed by gas chromatography (GC) methods. The reactor was
weighed again upon opening, and the weight loss compared
with before the reaction was calculated. The weight loss in the
present study was ascribed to the consumption of MeOH by
reforming. The used catalyst was recovered by vacuum filtra-
tion, and washed with MeOH and ethanol before being dried at
ML  (1  mol
of ML in products
(1)
X

 100%
initial mol of ML
mol of GVL in products
S
GVL  (initial

 100%
mol of ML  mol of ML in products
(2)
total mass of products
L
MeOH  (1 

 100%
6
6
0 °C for 2 h. Liquid products were centrifuged at 8000 rpm for
min before analysis by GC-mass spectrometry (GC-MS) and
(3)
total mass of initial input
GC methods, respectively.
3
. Results and discussion
2
.4.2. Methanolysis of cellulose to ML and hydrogenation of ML
to GVL
About 16 g microcrystalline cellulose (MCC) (90 μm) was
3.1. Catalyst characterization
added into a 400 mL Hastelloy-C high pressure reactor (Da-
lian-controlled plant), followed by 200 g MeOH solution with a
3
.1.1. Crystallinity
In this study, CuO, CaCO
3
, and CuO
x
-CaCO catalysts were
3
H
2
SO concentration of 0.01 mol/L. The autoclave was heated
4
prepared by an oxalate gel-coprecipitation method, followed by
calcination at 500 °C (Figs. 1 and S1). When the calcination
to 200 °C and maintained at that temperature for 4 h under
vigorous stirring (500 rpm). The reactor was cooled to room
temperature after the reaction, and only a small quantity of
temperature increased to 900 °C, CaCO
to afford CaO (Figure S1). As shown in Fig. 1, all the CuO
catalysts displayed characteristic peaks of CuO (2 = 35.5 and
8.7) and CaCO (2 = 29.3). The Cu/Ca molar ratio had a
3
was further degraded
x
-CaCO
3
insoluble humins was observed. Excess CaCO
3
was added to
neutralize H SO , and the resulting CaSO was separated by
2
4
4
3
3
vacuum filtration. The resultant filtrate was also centrifuged
and analyzed by the GC method. Based on the glucose units in
significant influence on the degree of ordering and crystallite
size of CuO in these catalysts. As shown in Fig. 1 and Table 1,

Xuejuan Cao et al. / Chinese Journal of Catalysis 40 (2019) 192–203
195
2
(
4)CuO
x
-CaCO
3
had a specific surface area of only 7.0 m /g with
a total pore volume of 106.3 × 10−3 cm /g.
3

CaCO ; .Cu O; CuO


3
2




3.1.3.
The reduction behavior of Cu-based catalysts and its coun-
terparts was studied using H -TPR. All the CuO -CaCO catalysts
exhibited broad bands for H consumption; CuO showed a sin-
H
2
-TPR analysis

a


2
x
3
.
.

b
2






gle peak at about 220 °C, which was attributed to one-step re-
duction of Cu2+ to Cu [39]. No obvious peaks were observed in
the pure CaO, whereas a notable peak at around 740 °C ap-

c
0


peared in the H
known that Ca2+ species cannot be reduced in an H
phere; thus, the peak at around 740 °C was attributed to CO
formed by the degradation of CaCO at elevated temperatures.
This was verified by TG analysis for the CaCO and
3/2)CuO -CaCO catalysts, as shown in Fig. S2. On the other
hand, the reduction peak for Cu2+ species in CuO
-CaCO cata-
-TPR profile of CaCO
(Fig. 2(f) and (g). It is
.
2
3
d
2
atmos-
2
1
0
20
30
40
50
60
70
80
o
2
/( )
3
3
Fig. 1. XRD patterns of (4)CuO
x
-CaCO
-CaCO
3
(a), (3/2)CuO
(d).
x
-CaCO (b),
3
(
x
3
(
2/3)CuO -CaCO (c), and (1/4)CuO
x
3
x
3
x
3
Table 1
Specific surface area (SBET), total pore volume (V
(
lysts was slightly shifted to a lower-temperature region, proba-
bly owing to an interaction between Cu and Ca species [40].
p
), mean pore radius
r–), and crystallite size (D) of various catalysts.
Overlapping shoulders in (4)CuO
x
-CaCO were observed in the
3
a
a
r−a
Db
S
BET
V
p
temperature range of 150–250 °C, indicating the existence of
two types of Cu species in the oxidation state. This finding was
in line with the characterization of XRD (Fig. 1).
Catalyst
2
(10−3 cm /g)
3
(
m /g)
10.3
8.1
(nm)
44.6
39.4
(nm)
CuO
CaO
120.3
102.7
11.5
37.6
1.0
(
(
(
(
1/4)CuO
2/3)CuO
3/2)CuO
x
x
x
-CaCO
-CaCO
-CaCO
3
3
3
2.6
4.6
6.3
7.0
6.5
6.1
15.9
102.1
106.3
82.4
9.5
13.8
64. 9
68. 3
34.9
3
3.1.4. NH -TPD analysis
1.4
Acidic sites on the catalysts are conducive to the intramo-
lecular cyclization of intermediates to form GVL during hydro-
genation [41]. However, no peaks and an almost straight line
13.7
11.7
77.6
x
4)CuO -CaCO
3
CaCO
3
were observed in the NH -TPD profile of CuO over the full
3
a
Determined by BET analysis of N
2
adsorption isotherms.
The crystallite size was calculated using Scherrer equation, and the
crystallite size of CuO phase was calculated for CuO -CaCO catalysts.
b
range of test temperatures, indicating that there were no active
acidic sites on the surface of CuO (Fig. 3(a)). Only a small peak
representative of a moderate acidic site for pure CaO was ob-
served. Notably, a broad peak in the range of 650–750 °C was
x
3
the intensity of diffraction peaks and crystallite size of CuO
decreased with the increase of CaCO content. Notably, all the
catalysts (except for (4)CuO -CaCO ) gave an apparent diffrac-
tion peak of Cu O at around 2 = 42.1, which became more
visible with increasing CaCO content (Fig. 1), indicating that
the incorporation of CaCO is conducive to the formation of
Cu O even after the calcination of catalyst precursor at 500 °C.
Moreover, XPS analysis of (3/2)CuO -CaCO further consoli-
dated the above observation, as will be discussed later (Fig. 4).
observed in the CaCO
CO resulting from the decomposition of CaCO
atures, according to the TPD test, which was conducted under
the same conditions but without NH during the adsorption
process (Fig. S2(c)). TG analysis of CaCO and (3/2)CuO -CaCO
gave the same results (Fig. S2(a) and (b)). Therefore, no acidic
3
. This peak was ascribed to the release of
3
2
3
at high temper-
x
3
2
3
3
3
x
3
3
2
sites were detected on the surface of CuO
x
-CaCO . Interestingly,
3
x
3
3.1.2. Surface area and porosity
a
The textural properties of catalysts prepared by an oxalate
b
gel-coprecipitation method were measured by N adsorp-
2
c
tion-desorption isotherms. As shown in Table 1, CuO had the
2
highest specific surface area (10.3 m /g) among all these cata-
d
lysts, with a total pore volume of 120.3 × 10−3 cm /g and a
3
e
f
mean pore radius of 44.6 nm (Table 1, entry 1). Both CaO and
CaCO had relatively lower specific surface areas, smaller pore
3
volume, and mean pore radius compared with CuO (entries 2
and 7, Table 1). The specific surface area, pore volume, and
g
mean pore radius of (n)CuO
creased with increasing CuO content. For example,
x
-CaCO
3
catalysts gradually in-
100
200
300
400
500
600
700
800
o
T ( C)
-TPR profiles of CuO (a), (4)CuO
(c), (2/3)CuO -CaCO (d), (1/4)CuO -CaCO
2
(
1/4)CuO
x
-CaCO
3
had a specific surface area of only 2.6 m /g
Fig. 2. H
2
x
-CaCO
(e), CaCO
3
(b), (3/2)CuO
x
-CaCO
3
with a total pore volume of 6.1 × 10−3 cm/g, whereas
x
3
x
3
3
(f), and CaO (g).

196
Xuejuan Cao et al. / Chinese Journal of Catalysis 40 (2019) 192–203
x 3
Cu 2p1/2 of (3/2)CuO -CaCO , respectively (Fig. 4(b)). Each Cu
2
p emission line could be fitted by using two Gaussian compo-
nents, which were representative of Cu2+ and Cu /Cu species,
0
+
a
respectively. Compared with CuO (954.2 eV for Cu 2p1/2), the
b
c
Cu 2p1/2 spectrum of (3/2)CuO
x
-CaCO showed a drift toward
3
lower binding energies, confirming the interaction between Ca
and Cu [42]. Specifically, partial electrons probably transferred
d
e
from Ca to Cu species in CuO
x
-CaCO , owing to the stronger
3
electronegativity of Cu (1.9) compared with that of Ca (1.0)
f
0
+
[
43,44]. A higher proportion of Cu /Cu species was observed
in the high-resolution spectrum of Cu 2p of (3/2)CuO -CaCO
Fig. 4(b)), indicating that CaCO has a crucial role in stabilizing
g
x
3
(
3
100
200
300
400
T ( C)
500
600
700
800
0
+
o
Cu /Cu species. There were known to be defects on the surface
of metal oxides, which could result in local charge imbalance of
the surface species; therefore, Cu species were detected on the
Fig. 3. NH
3
-TPD profiles of CuO (a), (4)CuO
-CaCO (c), (2/3)CuO -CaCO (d), (1/4)CuO -CaCO
f), and CaO (g).
x
-CaCO
3
(b),
3
+
(
(
3/2)CuO
x
3
x
3
x
3
(e), CaCO
+
surface of CuO by XPS. However, trace amounts of Cu species
cannot be detected by XRD.
the decomposition temperature of CaCO
presence of Cu species (Fig. 3(b)–(f)), which could be regarded
as evidence of an interaction between Cu species and CaCO
3
was lower in the
3.1.6. Surface morphology
The SEM images showed that the CuO mainly consisted of
secondary particles with diameter of around 50 nm, and the
particles were relatively uniform (Fig. 5(a)). In the case of
3
.
3
.1.5. XPS analysis
As expected, Cu, Ca and O were detected in the survey scan
of (3/2)CuO -CaCO (Fig. 4(a)). Binding energy (BE) values
centered at 934.2 and 954.0 eV were attributed to Cu 2p3/2 and
(3/2)CuO
x
-CaCO , the distribution of the particle size was
3
non-uniform, and particles with a diameter greater than 100
nm were clearly present (Fig. 5(b)). Similar phenomena were
observed for other CuO
x
3
x
-CaCO catalysts (Fig. S3). To gain more
3
Fig. 4. XPS spectra of survey scan of (3/2)CuO
x
-CaCO
3
(a), Cu 2p high-resolution spectra of (3/2)CuO
x
-CaCO (b), survey scan of CuO (c), and Cu 2p
3
high-resolution spectrum of CuO (d).

Xuejuan Cao et al. / Chinese Journal of Catalysis 40 (2019) 192–203
197
MeOH to produce H
ML to GVL are both catalyzed by CuO
2
and the subsequent hydrocyclization of
-CaCO . A plausible reac-
x
3
tion pathway can be elucidated as in Scheme 1, based on the
identification of products via GC-MS. It can be seen that methyl
4-hydroxypentanoate (MHP) occurs as an intermediate, alt-
hough it is undetectable by GC-MS, indicating that the hydro-
genation of ML to MHP is the rate-limiting step, while the ring
closing of MHP to GVL is a fast step under the conditions used
in this study [45,46]. As well as the main product GVL, small
amounts of by-products are formed through the hydrocarbox-
ylation/alkoxycarbonylation of GVL followed by hydrogenation
2
00 nm
200 nm
Fig. 5. SEM images of CuO (a) and (3/2)CuO
x
-CaCO (b).
3
a
c
b
(Scheme 1) [47].
3.3. Catalytic activity evaluation
3.3.1. Catalyst screening
In this study, both the gaseous and liquid products were
d
collected for analysis. Gaseous products contained H
and/or CO ; no methyl ether was detected (Fig. S5). As shown
in Table 2, the CuO could provide a ML conversion (XML) of
1.5% with a GVL selectivity (SGVL) of 82.2% at 240 °C in 1 h
Table 2, entry 6). Some by-products (SROP of 7.3%, SHCP of
.3%) derived from the hydrocarboxylation and ring-opening
of GVL were also detected. However, a low LMeOH with negligible
2
, CO,
2
9
(
6
X
7
ML and YGVL was obtained over CaO or CaCO
and 8), indicating the poor catalytic performance of CaO or
in H production and ML hydrogenation. Interestingly,
an XML of 96.8% with a SGVL up to 88.9% was achieved over
(3/2)CuO -CaCO under the same reaction conditions (Table 2,
3
(Table 2, entries
Fig. 6. SEM images (a), O (b), Cu (c), and Ca (d) elemental mappings of
3/2)CuO -CaCO
(
x
3
.
CaCO
3
2
insight into the elemental distribution on the surface of
CuO -CaCO catalysts, EDX elemental mapping for these cata-
lysts was carried out. As shown in Figs. 6 and S4, both Cu and
Ca, in all the CuO -CaCO , were evenly connected and dispersed
with O, respectively, in all regions.
x
3
x
3
entry 3); SHCP decreased to only 3.2% and YGVL increased to
86.1% in this case. The above observation clearly indicates that
(3/2)CuO
To determine the role of CaCO
of (3/2)CuO -CaCO , several blank experiments were carried
out. When a physical mixture of CuO and CaCO was used as the
x
3
x
-CaCO
3
is highly active for ML hydrogenation to GVL.
3
in the catalytic performance
x
3
3.2. Reaction pathway for ML hydrogenation to GVL in MeOH
3
catalyst, XML was reduced to 71.7% while the hydrocarboxyla-
tion by-product increased dramatically to 16.2%, but selectivity
towards ring-opening by-product declined compared with CuO
MeOH acts as both a solvent and an in-situ H-donor for the
conversion of ML to GVL in all experiments. The reforming of
Scheme 1. The reaction pathway of the conversion of ML to GVL, as well as by-products, using MeOH as in-situ hydrogen source over CuO
x
-CaCO .
3

198
Xuejuan Cao et al. / Chinese Journal of Catalysis 40 (2019) 192–203
Table 2
Table 3
Catalytic performance of CuO, CaO, CaCO
catalysts.
3
, CuO-CaO and CuO
x
-CaCO
3
Conversion of ML into GVL in MeOH.
T
Time ML
X
ML
S
GVL
S
HCP
S
ROP
Y
GVL
L
MeOH
Entry
X
ML
S
(%)
GVL
S
ROP
S
HCP
Y
GVL
L
MeOH
(°C) (h) (mmol) (%) (%) (%) (%) (%) (%)
Entry
Catalyst
(%)
(%) (%) (%) (%)
1
2
3
4
5
6
7
8
200
220
240
260
280
240
240
240
1
1
1
1
1
2
3
4
4
4
4
4
4
4
4
4
76.1 92.3 3.5
91.3 90.8 8.2
96.8 88.9 7.6
99.1 84.7 9.9
1.8 70.3 4.1
0.0 82.8 4.8
3.2 86.1 6.0
1.5 83.9 6.1
1
2
3
4
5
6
7
8
9
(1/4)CuO
(2/3)CuO
(3/2)CuO
x
x
x
-CaCO
-CaCO
-CaCO
3
3
3
44.4
73.0
96.8
93.2
67.3
91.5
2.9
57.4 27.5 10.1 25.5
73.4 16.7
3.6
4.6
6.0
6.3
5.4
6.5
2.5
3.1
5.2
3.9
5.1
9.0 53.6
3.2 86.1
4.4 80.2
88.9
86.1
79.8
82.2
59.8
89.4
83.6
7.6
7.6
x
(4)CuO -CaCO
3
99.4 70.3 17.8 8.1 69.9 7.9
(3/2)CuO-CaO a
3.7 16.2 53.7
7.3 6.3 75.2
2.1 35.2
97.8 90.6 7.8
99.5 96.1 3.0
100.0 89.4 3.2
1.7 88.5 6.5
0.0 95.6 6.6
2.9 89.4 6.9
CuO
CaO
1.7
4.7
4.1 59.9
CaCO
(3/2)CuO-CaCO
(3/2)CuO
-CaCO c
3
5.3
4.3
2.8
–
Reaction conditions: 19.5 g MeOH, 0.25 g catalyst, 500 rpm.
b
3
71.7
49.6
70.2
10
1
x
3
43.3 29.8 19.2 21.5
79.6 3.4 12.9 55.9
(3/2)CuO-CaO d
hydrogenation. An excess of gaseous products containing H ,
2
1
CO, and CO formed by MeOH reforming could further promote
2
Reaction conditions: 4 mmol ML, 19.5 g MeOH, 0.25 g catalyst, 1 h, 500
rpm, 240 °C.
the hydrocarboxylation of GVL (Scheme 1). Elevation of the
temperature to 280 °C resulted in complete reduction of CuO
a
Physical mixture of CuO and CaO with a Cu/Ca molar ratio of 3:2.
b
Physical mixture of CuO and CaCO
3
with a Cu/Ca molar ratio of 3:2.
at 300 °C for 2 h.
3/2)CuO-CaO was prepared by the same method with the calculation
2
and Cu O to Cu in (3/2)CuO-CaCO
3
(Fig. S6), and the side reac-
c
Pre-reduced (3/2)CuO
x
-CaCO
3
+
tion was greatly promoted because of the inadequate Cu spe-
d
(
+
cies, revealing that Cu species are conducive to suppressing
temperature at 900 °C for 5 h.
the side reaction. When pre-reduced (3/2)CuO-CaCO was used
3
as the catalyst, an ML conversion of only 49.6% was obtained,
along with a poor GVL selectivity (43.3%), at 220 °C in 1 h (Ta-
ble 2, entry 10); this is specific evidence for the suppression of
side reactions by Cu+.
(
Table 2, entries 6 and 9). This indicates that a simple physical
mixture of CaCO with CuO not only harms the catalytic activity
of CuO for ML conversion, but also favors the side reaction of
GVL hydrocarboxylation. Therefore, there are probably strong
3
The influence of reaction time was investigated at 240 °C.
When the reaction time was prolonged from 1 to 4 h, XML grad-
ually increased from 96.8% to 100%, whereas SGVL continuous-
ly increased to 96.1% in 3 h and then decreased 89.4% in 4 h
interactions between Cu species and CaCO
3/2)CuO -CaCO , which may be responsible for the outstand-
ing catalytic performance. (3/2)CuO-CaO was obtained by the
calcination of (3/2)CuO -CaCO at 900 °C for 5 h; its catalytic
performance was inferior to that of (3/2)CuO -CaCO , which
confirmed the importance of CaCO during the hydrogenation
3
in the
(
x
3
x
3
(
Table 3, entry 3 and entries 6–8). Further prolonging the reac-
tion time to 4 h would result in more ring-opening of GVL at the
cost of SGVL
x
3
3
.
of ML to GVL with MeOH as the in-situ H-source.
In addition, XML and SGVL gradually increased as the molar
3
.3.3. Catalytic performance of (3/2)CuO
methanolysis product of cellulose
In view of the excellent catalytic performance of
3/2)CuO -CaCO in neat ML/methanol solution, it was highly
desirable to test the catalytic activity of (3/2)CuO -CaCO in the
x
-CaCO
3
in the
ratio of Cu to Ca increased (from 1/4 to 3/2 CuO
then decreased with a further increase of the molar ratio of Cu
to Ca to 4 (Table 2, entries 1–4). Notably, the (3/2)CuO-CaCO
x 3
-CaCO ), and
3
(
x
3
catalyst also outperformed other Cu-based bimetallic catalysts
for ML hydrogenation in MeOH (Table S1).
x
3
methanolysis product of carbohydrates. A detailed procedure is
given in Section 2.4.2. The biggest challenge for the hydrogena-
tion of ML to GVL in methanolysis products is the presence of
humins, which are inevitable and complicated by-products that
are formed during acid-catalyzed degradation of carbohydrates
3
.3.2. Effect of reaction temperature, time and the ML dosage
Given the outstanding performance of (3/2)CuO-CaCO , the
3
effects of reaction temperature and time on the hydrogenation
of ML to GVL were investigated. When the reaction was con-
ducted at 200 °C for 1 h, an XML of only 76.1% with an SGVL of
[
49]. Humins can be easily adsorbed onto solid catalysts, lead-
ing to their deactivation. As shown in Table 4, an XML of 72.9%
was obtained over (3/2)CuO -CaCO at 240 °C in 1 h in the
9
2.3% was obtained (Table 3, entry 1). The low XML was mainly
ascribed to the poor catalytic activity of the catalyst for ML
hydrogenation at a relatively low temperature [48]. Moreover,
only a small number of by-products were detected in this case.
Notably, an increase in the reaction temperature to 240 °C
brought about a significant improvement of XML to 96.8%, with
a small decline in SGVL compared with the case at 200 °C (Table
x
3
methanolysis product (Table 4, entry 1), while SHCP sharply
increased to 17.6% at the cost of SGVL, compared with the case
of neat ML/MeOH feedstock (Table 3, entry 3). The above ob-
servations clearly reveal that the presence of humins facilitates
side reactions over (3/2)CuO
reaction time to 4 h, both XML and SGVL gradually increased to
6.5% and 82.4%, respectively (Table 4, entries 2–4). In the
x
-CaCO . With extension of the
3
3
, entries 1–3). Further increasing the temperature to 260 °C
resulted in the gradual decrease of SGVL to 84.7%, although the
ML reached 99.1% (Table 3, entry 4). It appears that elevated
8
methanolysis of MCC, the formation of humins is inevitable. We
assumed that the adsorption of humins on the catalysts led to
the indirect adsorption of ML, as the humins coated the cata-
X
temperatures greatly favor side reactions, indicating that these
side reactions have higher activation energies than that of ML

Xuejuan Cao et al. / Chinese Journal of Catalysis 40 (2019) 192–203
199
Table 4
Production of GVL from ML in methanolysis product of MCC.
1
00
Time (h)
X
ML (%)
72.9
77.5
83.7
86.5
89.2
92.5
S
GVL (%)
61.0
69.7
75.8
82.4
87.8
85.6
SHCP (%) SROP (%) YGVL (%) LMeOH (%)
1
2
3
4
6
8
17.6
11.6
10.0
8.9
13.8
10.2
4.1
44.5
54.0
63.4
71.3
78.3
79.2
4.9
5.1
5.4
5.6
6.1
6.4
98
9
9
9
6
4
2
5.1
7.2
4.4
7.9
4.8
90
Reaction conditions: 13.9 g methanolysis product of MCC (containing
about 4 mmol ML), 0.25 g catalyst, 500 rpm, 240 °C.
8
8
8
8
6
4

Selectivity of GVL
Conversion of ML

-
----- Leaching test (without catalyst)
lysts with a loose structure and improved their overall specific
surface area. This would have resulted in a reduced amount of
ML in the solution. The adsorbed ML would not have been
converted into GVL; thus, the XML values (Table 4) for the first
several hours were inevitably higher than the real ones, while
the opposite was true for SGVL. A desorption experiment was
conducted to verify the above assumption. After the reaction
had proceeded for 1 h in methanolysis product, the catalyst was
separated by centrifugation and washed by methanol with ul-
trasonic cleaning. About 7.1 wt% ML was washed out (based on
1.0 1.5 2.0 2.5 3.0
3.5
4.0
Reaction time (h)
Fig. 7. Leaching test of (3/2)CuO -CaCO for hydrogenation of ML to
GVL using MeOH as the in-situ H-source. Reaction conditions: 19.5 g
MeOH, 4 mmol ML, 0.25 g catalyst, 240 °C, 500 rpm.
x
3
catalyst was negligible during the reaction. The possible leach-
ing of active metals during the reusability tests was also inves-
tigated; the results are provided in Table S2. The Cu and Ca
contents of the filtrate did not increase during the recycling
the initial ML dosage). The overall selectivity (SGVL+SHCP+SROP
)
test, which clearly indicates that CuO
x
-CaCO is a robust cata-
3
did not reach 100%, and the hydrocarboxylation and
alkoxycarbonylation of GVL were reversible. Some
by-products/intermediates were eventually converted into
GVL when the reaction time was prolonged.
Notably, the initial black methanolysis product changed to a
canary yellow and transparent liquid product after the reaction
lyst.
A recyclability test was also conducted to evaluate the cata-
lytic stability of (3/2)CuO -CaCO in both the neat ML/MeOH
x
3
solution and the methanolysis solution. In a typical reusability
test, the used catalyst was separated by vacuum filtration and
then directly reused in the next run. Unexpectedly, only negli-
gible decreases in XML and SGVL were observed with the recy-
cling tests in both neat ML methanol solution and methanolysis
product of cellulose (Tables 5 and S3); this was ascribed to the
limited carbon deposition on the surface of the catalysts. This
insignificant reduction in the catalytic ability of
3/2)CuO
the used catalyst at 500 °C (Table 5, entries 8; Table S3, entry
).
In view of the catalytic performance of (3/2)CuO
the spent catalysts were further characterized for neat
in the presence of (3/2)CuO
x
-CaCO (Fig. S7), suggesting that
3
most humins in the methanolysis product were adsorbed onto
the catalyst during the reaction, along with the ML. The carbon
content of the used (3/2)CuO
was measured as 6.5 wt% by elemental analysis after the reac-
tion. According to NH -TPD analysis, the adsorption of humins
conferred a number of acid sites on the spent (3/2)CuO -CaCO
x
-CaCO in methanolysis product
3
3
(
x
-CaCO could be easily recovered by calcination of
3
x
3
catalyst (Fig. S8), which were thought to be responsible for the
improvement in the selectivity of by-products compared with
that in the neat ML/MeOH group [47].
7
x
-CaCO ,
3
ML/MeOH solution and methanolysis solution. As shown in Fig.
3.4. Leaching and reusability tests
+
8, the characteristic diffraction peaks for Cu species of the
Leaching tests were performed to investigate the stability of
Table 5
Recycling test of (3/2)CuO
x
-CaCO
3
in neat ML/MeOH solution.
the CuO
x
-CaCO
3
catalyst. Hydrogenation of ML in both
S
ROP (%)
YGVL (%) LMeOH (%)
ML/MeOH solution and the methanolysis solution were con-
ducted at 240 °C in 1 h, after which the reaction was stopped
and the solid catalyst was separated from the reaction mixture
by centrifugation. The resulting filtrate was reloaded into the
reactor and then reacted at 240 °C for another 3 h. As shown in
Figs. 7 and S9, only negligible fluctuation was observed, indi-
cating that no soluble catalytic active species leached into the
resulting filtrates. Element leaching (Cu and/or Ca species) was
also verified by ICP-OES. The Cu and Ca contents in the reaction
mixture were measured as 3.92 and 6.01 ppm for neat
ML/MeOH solution, while there was almost no leaching of Cu
and Ca species in the methanolysis solution (0.48 and 0.85
ppm, respectively) (Table S2). Therefore, the leaching of the
Cycle
Fresh
1st
2nd
3rd
4th a
5th
6th
7th
X
ML (%)
99.5
96.5
95.2
94.3
97.4
97.1
95.8
94.2
98.9
S
GVL (%)
96.1
94.0
92.1
90.3
96.6
95.3
94.5
92.8
95.7
S
HCP (%)
3.0
4.5
0.0
1.5
1.3
2.0
95.6
90.7
87.6
85.1
94.1
92.5
90.5
87.4
94.6
6.6
6.4
6.4
6.3
6.5
6.6
6.4
6.4
6.7
6.6
7.1
1.9
1.0
2.9
4.2
5.1
2.1
1.2
0.0
1.7
1.3
8th a
Reaction conditions: 19.5 g MeOH, 0.25 g catalyst, 3 h, 500 rpm, 240 °C,
4
a
mmol ML.
Spent catalyst was regenerated by calcination at 500 °C before reac-
tion.

200
Xuejuan Cao et al. / Chinese Journal of Catalysis 40 (2019) 192–203
Fig. 8. XRD patterns of the fresh (a) and the spent (3/2)CuO
methanolysis solution (d), the spent (1/4)CuO -CaCO after first cycle (e), the spent (2/3)CuO
x
-CaCO
3
after first (b) and 8th cycle (c), the spent (3/2)CuO
-CaCO after first cycle (f), the spent (4)CuO
x
-CaCO
3
after first cycle in
-CaCO
x
3
x
3
x
3
after first cycle (g), and the spent CuO after first cycle (h). Reaction conditions: 19.5 g MeOH, 4 mmol ML, 0.25 g catalyst, 240 °C, 3 h, 500 rpm; all the
spent catalysts were recycled from neat ML/MeOH solution, except for sample (d).
spent (3/2)CuO
x
-CaCO
3
in both neat ML/MeOH solution and
lines clearly indicates that both metallic and oxidized Cu crys-
methanolysis solution were markedly intensified after the re-
action compared with those of the fresh catalyst (Figure 1).
Note that the majority of Cu species in the used
tallite species were present in the spent (3/2)CuO
ilar to the fresh one (Fig. 4(b)). The proportion of Cu /Cu spe-
cies in Cu 2p3/2 drastically increased in the spent
x
-CaCO
3
, sim-
0
+
+
0
2+
-CaCO
(Fig. 9(b)), indicating that more Cu2+ species
(
3/2)CuO
x
-CaCO
3
existed in the form of Cu /Cu instead of Cu
(3/2)CuO
x
3
0
+
(
Fig. 8(b)–(d)). However, the intensity of diffraction peaks for
were reduced to Cu /Cu species after the reaction. Notably, no
satellite peak for Cu2+ species of spent CuO was observed
alongside the Cu 2p3/2 and 2p1/2 peaks (Fig. 9(d)). These ob-
servations agree well with the XRD analysis of the spent cata-
lysts (Fig. 8), according to which the oxidation state species of
Cu in the spent CuO catalyst were almost entirely reduced into
+
0
Cu or Cu species remained almost unchanged even after the
eighth recycling test (Fig. 8(c)). On the contrary, CuO was com-
pletely reduced to metallic Cu after the first run under the same
conditions (Fig. 8(h)). Interestingly, the Ca proportions in the
catalysts greatly influenced the state of copper species after the
reaction. Based on XRD patterns, there was no Cu phase for
metallic copper. This confirms the promotion of Ca species in
+
(
1/4)CuO
x
-CaCO
3
and (2/3)CuO
x
-CaCO
3
(Fig. 8(e)–(f)); howev-
stabilizing Cu species in (3/2)CuO
x
-CaCO
3
. On the other hand,
-CaCO obviously
shifted to higher values compared with the fresh
(3/2)CuO -CaCO or CaO (Fig. S10), suggesting an elusory in-
+
er, apparent peaks for Cu around 2 = 36.2 were observed for
BE signals of Ca 2p in the spent (3/2)CuO
x
3
all the catalysts, with relatively moderate Ca percentages (Fig.
8
(b)–(d), g), especially in the case of (3/2)CuO
x
-CaCO
3
, whose
x
3
+
Cu proportion was the highest among the three catalysts. The
above observations reveal that the incorporation of moderate
Ca by an oxalate gel-coprecipitation method effectively pre-
vents the reduction of CuO to Cu in a reducing atmosphere, and
greatly favors the stabilization of Cu species. Note that Cu2+
species were observed in the XPS spectra for the spent
teraction between Ca species and Cu species.
To further probe the deactivation of CuO
x
-CaCO catalysts,
3
the carbon content of the spent catalysts was measured by el-
emental analysis. The C content of the spent (3/2)CuO -CaCO
was only 0.514 wt% after the first cycle, and only slightly in-
creased to 1.119 wt% after the 7th cycle in neat ML/MeOH
x
3
+
(
3/2)CuO
x
-CaCO
3
catalysts, probably owing to the difference in
solution. SEM images showed that the spent (3/2)CuO
x
-CaCO
3
limit of detection between XPS and XRD analysis. This result
also indicates that there was a small quantity of Cu2+ species
dispersed on the catalyst surface, and that the particle size of
the CuO in the spent catalysts was too small to be detected by
XRD.
after the first cycle in ML/MeOH solution was composed of
irregular particles with a similar diameter to those in the fresh
catalyst (Figs. 5(b) and S11(a)). Cu and Ca in the spent
(3/2)CuO
x
-CaCO after the fourth and eighth cycles were evenly
3
connected and dispersed with O in all regions, as before (Fig.
S12(a)–(h)). Agglomeration of the spent catalyst was negligible
As shown in Fig. 9(b), the deconvolution of Cu 2p emission

Xuejuan Cao et al. / Chinese Journal of Catalysis 40 (2019) 192–203
201
Fig. 9. (a) XPS survey scan of the spent (3/2)CuO
x
-CaCO
3
; high-resolution spectra of Cu 2p (b), O 1s (c) and Ca 2p (d) of the spent (3/2)CuO
x
-CaCO
3
after the first cycle; survey scan (e) and Cu 2p high-resolution spectra (f) of the spent CuO after the first cycle.
with the recycling of the catalyst, which was probably a major
contributor to the excellent catalytic performance of
effectively catalyze both the in-situ production of H
reforming and the simultaneous hydrogenation of ML to GVL.
(3/2)CuO -CaCO achieved GVL yield up to 95.6% at 240 °C in 3
2
by MeOH
(
3/2)CuO
x
-CaCO
3
in ML/MeOH solution. However, severe car-
x
3
bon deposition of the catalyst occurred in the methanolysis
product of cellulose. In these cases, the C content of the catalyst
was 6.455 wt% after the first cycle, dramatically increasing to
h. Incorporation of CaCO
3
with CuO resulted in the formation of
catalyst, which greatly facilitated
-CaCO could
+
x
Cu species in the CuO -CaCO
3
the hydrogenation of ML. In addition, (3/2)CuO
x
3
3
8.14 wt% after the fifth cycle (Table S4). The deactivation of
be reused for at least eight consecutive reaction cycles without
significant loss of its catalytic activity. Notably, the presence of
humins in methanolysis products has an inconspicuous influ-
ence on its catalytic performance. Therefore, it is possible to
develop a facile two-step strategy for GVL production from
cellulose through the integration of ML production, by meth-
solid catalysts is strongly associated with the carbon deposition
of the catalyst in organic solvents. Fortunately, the carbon de-
posits could be readily removed by calcination at 500 °C.
Leaching and reusability tests of the CuO prepared by the
same method were also conducted, as described in the sup-
porting information (experimental section). The leaching of Cu
species was much more severe for CuO than for the
anolysis of cellulose, H formation by MeOH reforming, and ML
2
hydrogenation in an MeOH system.
(
3/2)CuO
x
-CaCO catalyst. According to the XRD pattern and
3
XPS spectra for the spent CuO (Figs. 8(h) and 9(f)), the CuO was
completely reduced to metallic Cu after the first run (Fig. 8(h)),
with significant drops for the both the XML and YGVL compared
References
[1] D. Tilman, R. Socolow, J. A. Foley, J. Hill, E. Larson, L. Lynd, S. Pa-
cala, J. Reilly, T. Searchinger, C. Somerville, Science, 2009, 325,
270–271.
with the first cycle (Table S5). This was in marked contrast to
+
the (3/2)CuO
x
-CaCO
3
, whose Cu species were retained for at
least eight continuous recycling runs (Table 5, Figs. 8 and 9).
These results reaffirm the superior stability and reusability of
[2] L. S. Ribeiro, J. J. Delgado, J. J. M. Órfão, M. F. R. Pereira, Appl. Catal.
B, 2017, 217, 265–274.
the (3/2)CuO
x
-CaCO
3
catalyst, due to the incorporation of Ca-
[3] T. Chen, L. C. Peng, X. Yu, L. He, Fuel, 2018, 219, 344–352.
[4] Z. Yuan, Z. Zhang, J. Zheng, J. Lin, Fuel, 2015, 150, 236–242.
3
CO .
[5] C. G. Yoo, N. Li, M. Swannell, X. Pan, Green Chem., 2017, 19,
4402–4411.
4. Conclusions
[6] C. G. Yoo, S. Zhang, X. Pan, RSC Adv., 2017, 7, 300–308.
The
gel-coprecipitation method resulted in a robust dual-functional
3/2)CuO -CaCO catalyst. This dual-functional catalyst could
incorporation
of
CaCO
3
by
an
oxalate
[7] D. F. Li, W. X. Ni, Z. S. Hou, Chin. J. Catal., 2017, 38, 1784–1793.
[8] K. Yan, Y. Y. Yang, J. J. Chai, Y. Lu, Appl. Catal. B, 2015, 179,
292–304.
(
x
3

202
Xuejuan Cao et al. / Chinese Journal of Catalysis 40 (2019) 192–203
Graphical Abstract
Chin. J. Catal., 2019, 40: 192–203 doi: S1872-2067(19)63270-5
Effective production of γ-valerolactone from biomass-derived methyl levulinate over CuO
x
-CaCO catalyst
3
Xuejuan Cao, Huai Liu, Junnan Wei, Xing Tang *, Xianhai Zeng, Yong Sun, Tingzhou Lei, Geng Zhao, Lu Lin *
Xiamen University; Fujian Engineering and Research Center of Clean and High-valued Technologies for Biomass;
Henan Key Lab of Biomass Energy; Xinyang Normal University
+
Incorporation of CaCO
3
greatly stabilized Cu species. The robust and stable CuO
x
-CaCO catalyst could contribute to the development of a
3
facile two-step strategy for the production of GVL from cellulose with methanol as the in-situ hydrogen source.
[
9] X. L. Du, Q. Y. Bi, Y. M. Liu, Y. Cao, H. Y. He, K. N. Fan, Green Chem.,
012, 14, 935–939.
10] J. Q. Bond, D. M. Alonso, D. Wang, R. M. West, J. A. Dumesic, Science,
010, 327, 1110–1114.
Grunwaldt, Appl. Catal. A, 2015, 502, 18–26.
[27] X. Long, P. Sun, Z. Li, R. Lang, C. Xia, F. Li, Chin. J. Catal., 2015, 36,
1512–1518.
[28] E. F. Mai, M. A. Machado, T. E. Davies, J. A. Lopez-Sanchez, V.
Teixeira da Silva, Green Chem., 2014, 16, 4092–4097.
[29] I. Obregón, E. Corro, U. Izquierdo, J. Requies, P. L. Arias, Chin. J.
Catal., 2014, 35, 656–662.
[30] K. Yan, A. Chen, Energy, 2013, 58, 357–363.
[31] X. Tang, L. Hu, Y. Sun, G. Zhao, W. Hao, L. Lin, RSC Adv., 2013, 3,
10277–10284.
2
[
[
[
[
2
11] S. G. Wettstein, D. M. Alonso, Y. Chong, J. A. Dumesic, Energy Envi-
ron. Sci., 2012, 5, 8199–8203.
12] E. I. Gurbuz, J. M. R. Gallo, D. M. Alonso, S. G. Wettstein, W. Y. Lim, J.
A. Dumesic, Angew. Chem. Int. Ed., 2013, 52, 1270–1274.
13] J. S. Luterbacher, J. M. Rand, D. M. Alonso, J. Han, J. T. Youngquist, C.
T. Maravelias, B. F. Pfleger, J. A. Dumesic, Science, 2014, 343,
2
77–280.
[32] S. T. Yong, C. W. Ooi, S. P. Chai, X. S. Wu, Int. J. Hydrogen Energy,
2013, 38, 9541–9552.
[
14] M. Al-Naji, A. Yepez, A. M. Balu, A. A. Romero, Z. Chen, N. Wilde, H.
Li, K. Shih, R. Gläser, R. Luqueb, J. Mol. Catal. A, 2016, 417,
[33] Z. H. Sun, G. Bottari, A. Afanasenko, M. C. A. Stuart, P. J. Deuss, B.
Fridrich, K. Barta, Nat. Catal., 2018, 1, 82–92.
[34] T. D. Matson, K. Barta, A. V. Iretskii, P. C. Ford, J. Am. Chem. Soc.,
2011, 133, 14090–14097.
1
45–152.
15] X. Tang, L. Hu, Y. Sun, G. Zhao, W. Hao, L. Lin, RSC Adv., 2013, 3,
0277–10284.
[
[
[
[
[
[
[
1
16] X. Tang, H. Chen, L. Hu, W. Hao, Y. Sun, X. Zeng, L. Lin, S. Liu, Appl.
Catal. B, 2014, 147, 827–834.
17] X. Tang, X. Zeng, Z. Li, L. Hu, Y. Sun, S. Liu, T. Lei, L. Lin, Renewable
Sustainable Energy Rev., 2014, 40, 608–620.
[35] L. Peng, L. Lin, H. Li, Ind. Crop. Prod., 2012, 40, 136–144.
[36] X. Tang, Z. Li, X. Zeng, Y. Jiang, S. Liu, T. Lei, Y. Sun, L. Lin,
ChemSusChem, 2015, 8, 1601–1607.
[37] N. Habibi, H. Arandiyan, M. Rezaei, RSC Adv., 2016, 6,
29576–29585.
[38] L. C. Wang, Q. Liu, M. Chen, Y. M. Liu, Y. Cao, H. Y. He, K. N. Fan, J.
Phys. Chem. C, 2007, 111, 16549–16557.
[39] E. D. Guerreiro, O. F. Gorriz, J. B. Rivarola, L. A. Arrúa, Appl. Catal. A,
1997, 165, 259–271.
[40] G. Geng, R. Wei, T. Liang, M. Zhou, G. Xiao, React. Kinet. Mech. Catal.,
2016, 117, 239–251.
[41] J. Geboers, X. Y. Wang, A. B. de Carvalho, R. Rinaldi, J. Mol. Catal. A,
2014, 388, 106–115.
[42] J. Wu, Y. Shen, C. Liu, H. Wang, C. Geng, Z. Zhang, Catal. Commun.,
2005, 6, 633–637.
18] E. I. Gürbüz, D. M. Alonso, J. Q. Bond, J. A. Dumesic, ChemSusChem,
2011, 4, 357–361.
19] J. A. Melero, G. Morales, J. Iglesias, M. Paniagua, C. Lópezaguado, K.
Wilson, A. Osatiashtiani, Green Chem., 2017, 19, 5114–5121.
20] L. Landenna, A. Villa, R. Zanella, C. Evangelisti, L. Prati, Chin. J.
Catal., 2016, 37, 1771–1775.
21] S. G. Wettstein, J. Q. Bond, D. M. Alonso, H. N. Pham, A. K. Datye, J. A.
Dumesic, Appl. Catal. B, 2012, 117–118, 321–329.
[
22] Z. P. Yan, L. Lin, S. Liu, Energy Fuels, 2009, 23, 3853–3858.
23] C. B. Chen, M. Y. Chen, B. Zada, Y. J. Ma, L. Yan, Q. Xu, W. Z. Li, Q. X.
Guo, Y. Fu, RSC Adv., 2016, 6, 112477–112485.
[
[
[
[
24] Z. Gao, C. Y. Li, G. L. Fan, L. Yang, F. Li, Appl. Catal. B, 2018, 226,
[43] F. Yang, X. Bi, J. Magn. Magn. Mater., 2017, 312, 324–327.
[44] P. Anguita, J. M. García-Vargas, F. Gaillard, E. Iojoiu, S. Gil, A.
Giroir-Fendler, Chem. Eng. J., 2018, 352, 333–342.
[45] N. Scotti, M. Dangate, A. Gervasini, C. Evangelisti, N. Ravasio, F.
Zaccheria, ACS Catal., 2014, 4, 2818−2826.
5
23–533.
25] Z. Li, M. Zuo, Y. Jiang, X. Tang, X. Zeng, Y. Sun, T. Lei, L. Lin, Fuel,
016, 175, 232–239.
26] K. Hengst, M. Schubert, H. W. P. Carvalho, C. Lu, W. Kleist, J. D.
2

Xuejuan Cao et al. / Chinese Journal of Catalysis 40 (2019) 192–203
203
[
46] C. E. Chan-Thaw, M. Marelli, R. Psaro, N. Ravasio, F. Zaccheria, RSC
Adv., 2013, 3, 1302–1306.
[48] J. Zhu, Y. Tang, K. Tang, RSC Adv., 2016, 6, 87294–87298.
[49] I. van Zandvoort, Y. Wang, C. B. Rasrendra, E. R. H. van Eck, P. C. A.
Bruijnincx, H. J. Heeres, B. M. Weckhuysen, ChemSusChem, 2013,
6, 1745–1758.
[47] X. Tang, X. Zeng, Z. Li, W. Li, Y. Jiang, L. Hu, S. Liu, Y. Sun, L. Lin,
ChemCatChem, 2015, 7, 1372–1379.
CuO -CaCO 催化剂高效催化生物质乙酰丙酸甲酯制备γ-戊内酯
x
3
a
a
a
a,b,*
a,b
a,b
c
d
a,b,#
曹雪娟 , 刘 淮 , 魏珺楠 , 唐 兴 , 曾宪海 , 孙 勇 , 雷霆宙 , 赵 耿 , 林 鹿
a
厦门大学能源学院, 生物质清洁高值化利用厦门市重点实验室, 福建厦门361102
b
福建省生物质清洁高值化技术工程研究中心, 福建厦门361005
c
河南省生物质能源重点实验室, 河南郑州450008
d
信阳师范学院化学化工学院, 河南信阳464000
摘要: γ-戊内酯(GVL)在燃料和化学品上有着巨大的潜在利用价值, 如何从生物质木质纤维素出发经济地制备GVL广受关
注. 目前已有大量的研究致力于利用不同氢源从乙酰丙酸及其酯类催化加氢制备GVL的催化体系. 过去的数年里, 外加氢
气条件下的乙酰丙酸及其酯类加氢制备GVL已经得到了广泛的研究. 考虑到液体醇使用和管理相比于氢气更为安全便捷,
而且醇类如甲醇、乙醇都是可以从生物质制备的绿色环保的溶剂, 利用醇类通过Meerwein-Ponndorf-Verley (MPV)还原作
为生物质催化加氢过程中的的溶剂和氢供体已经引起了人们的浓厚兴趣. 在脂肪醇中, 甲醇的还原势能最高, 在MPV还原
里的效果不如其他醇, 但可以通过甲醇重整制氢的方式来供氢. 此外, 乙酰丙酸甲酯(ML)可以通过甲醇中酸催化醇解碳水
化合物制得, 因此可以尝试将碳水化合物醇解制备ML; 甲醇重整制氢以及ML加氢结合起来, 从而省去繁琐且能耗较大的
ML分离步骤. 腐殖质的存在和固体催化剂在甲醇中的稳定性是上述两步法策略的最大挑战.
x 3
本文通过草酸凝胶共沉淀法首次制备了(n)CuO -CaCO (n为Cu/Ca摩尔比)双功能催化剂, 用于以甲醇为原位氢源, 从
生物质ML一锅制备GVL反应中. 经筛选, (3/2)CuO -CaCO 催化制备GVL的得率高达95.6%. 利用各种表征手段分析了催
x
3
+
化剂使用前后的组成和结构变化. 结果显示, 新制的CuO
x
3 3
-CaCO 催化剂中即可检测到Cu 的存在, 且在使用过程中CaCO
可以有效阻止二价铜在氢气氛围下被完全还原成单质铜. 对于该体系中的ML加氢, 亚铜有着比单质铜更佳的催化性能.
循环实验表明, (3/2)CuO -CaCO 至少可以连续稳定使用8次, 其催化活性没有明显损失. 此外, 在纤维素醇解产物中存在腐
x
x
3
3
殖质的情况下, (3/2)CuO
-CaCO
催化剂仍能够有效催化纤维素醇解得到的ML加氢制备GVL. 因此可以利用这个高效廉价
的催化剂开发一种便捷的一锅两步法从木质纤维素生物质制备GVL, 即将酸催化的纤维素醇解、甲醇重整、ML在甲醇溶
剂中加氢三者整合起来.
关键词: γ-戊内酯; 乙酰丙酸甲酯; 加氢; 甲醇重整; 纤维素甲醇解
收稿日期: 2018-10-25. 接受日期: 2018-11-26. 出版日期: 2019-02-05.
*
通讯联系人. 电话/传真: (0592)5952786; 电子信箱: x.tang@xmu.edu.cn
#
通讯联系人. 电话/传真: (0592)5952786; 电子信箱: lulin@xmu.edu.cn
基金来源: 国家自然科学基金 (21676223, 21706223, 21776234, 21606188); 厦门大学校长基金 (20720180084); 福建省自然科学
基金 (2018J01017); 福建省高校青年自然基金重点项目 (JZ160398); 厦门大学能源学院能源发展基金 (2017NYFZ02).
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).