Selective conversion of furfural to cyclopentanone or cyclopentanol using different preparation methods of Cu-Co catalysts

Article abstract of DOI:10.1039/c4gc01601g

Cu-Co catalysts, prepared by a co-precipitation method (CP) and an oxalate sol-gel method (OG), can selectively convert furfural (FFA) to cyclopentanone (CPO) or cyclopentanol (CPL), respectively. The conversion of FFA to CPO or CPL by Cu-Co catalysts were studied in aqueous solutions. We found that the product distribution was influenced by the catalyst support, Cu loading, calcination temperature, hydrogen pressure, the number of times the catalyst was reused and the preparation method of the catalyst. The surface morphology, surface area and composition of the catalysts were studied by XRD, XPS, BET, ICP-AES and TEM characterization. We found that there was a strong interaction between Cu and Co. Cu⁰, Cu₂O and Co⁰ were the main active catalyst phases on the surfaces of the catalysts, but the amounts were different in the different catalysts. Cu⁰, Co⁰ and Cu₂O were the active hydrogenation species, and Cu₂O also played the role of an electrophile or Lewis acid to polarize the CO bond via lone pair electrons on the oxygen atom. According to XRD and XPS, the main phases on the surface of the CP catalysts were Cu⁰ and Cu₂O. The hydrogenation activity of the CP catalyst was relatively weak and the main product was CPO. In contrast, the hydrogenation activity of the OG catalyst was high and the main product was the fully hydrogenated product CPL due to the main active phases of Co⁰ and Cu₂O on the surface of the OG catalyst. At lower hydrogen pressure (2 MPa) and lower Cu loadings (2% for OG, 5% for CP), we obtained the highest yield of 67% CPO and 68% CPL, respectively. This journal is

Full text of DOI:10.1039/c4gc01601g

View Article Online
View Journal
Green
Chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: X. Li, J. Deng, T.
Pan, C. Yu, H. Xu and Y. Fu, Green Chem., 2014, DOI: 10.1039/C4GC01601G.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
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.
www.rsc.org/greenchem

Page 1 of 9
Green Chemistry
Dynamic Article Links ►
Green Chemistry
View Article Online
DOI: 10.1039/C4GC01601G
Cite this: DOI: 10.1039/c0xx00000x
www.rsc.org/greenchem
PAPER
Selective conversion of furfural to cyclopentanone and cyclopentanol by
different preparation methods of Cu-Co catalysts†
a, b
a
a
a
a, b
a
Xing-Long Li, Jin Deng, Tao Pan, Chu-Guo Yu, Hua-Jian Xu* and Yao Fu*
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
CuꢀCo catalysts, prepared by coꢀprecipitation method (CP) and oxalate solꢀgel method (OG), can
selectively convert furfural (FFA) to cyclopentanone (CPO) and cyclopentanol (CPL), respectively. The
conversion of FFA to CPO and CPL by CuꢀCo catalysts was studied in aqueous solution. We found that
product distribution was influenced by different catalyst supports, Cu loadings, calcination temperature,
reused times, hydrogen pressure and the preparation methods of catalyst. The surface morphology,
surface area and composition of catalysts were studied by XRD, XPS, BET and ICPꢀAES and TEM
0
0
characterization. We found that there was a strong interaction between Cu and Co. Cu , Cu O and Co
2
were the main active catalyst phases on the surface of catalysts, but the content of them were different in
0
0
different catalysts. Cu , Co , Cu O were active hydrogenation ingredients, Cu O also played an
2
2
electrophile or Lewis acid sites to polarize CꢀO bond via lone pair electrons on oxygen. According to
0
XRD and XPS, the main phases on the surface of CP catalysts were Cu and Cu O. The hydrogenation
2
activity of CP catalysts was relatively weak and the main product was CPO. In contrast, the
hydrogenation activity of OG catalysts was high. And the main product was full hydrogenation product
0
CPL due to the main active phases Co and Cu O on the surface of OG catalysts. At lower hydrogen
2
pressure (2 MPa) and lower Cu loadings (2% for OG, 5% for CP), we obtained the highest yield of 67%
CPO and 68% CPL, respectively.
example, CPO and CPL have been used to prepare Jasmine
family fragrances and drug materials. In addition, CPO has been
widely used as solvent in the electronics industry because of its
good solubility of various resins. Cyclopentyl methyl ether and
cyclopentyl ethyl ether, which have characteristics of high
hydrophobicity, low latent heat of solvent evaporation, difficultly
forming peroxides, easily drying, etc., have been used as solvents
for Grignard reactions, coupling reactions and other important
1
. Introduction
Efficient utilization of renewable biomass resources becomes
more and more attractive with the evergrowing consumption of
the nonꢀrecoverable fossil fuels. Biomass as unique renewable
resources could be converted to conventional liquids, solids,
1
gases, fuels and other chemicals. The industry applications of
biomass are based on improving the competitiveness for biomass
resources, developing preparation methods for inexpensive
platform molecules and efficiently transferring platform molecule
7
chemical reactions. The demand of CPO and CPL are million
tons per year. Therefore, it will be highly valuable if CPO and
8
CPL can be efficiently prepared from biomassꢀbased FFA.
2
to fuels and chemicals.
Furfural (FFA), an important platform molecule, can be
3
obtained from hemicellulose in lignocellulosic biomass, and
4
further transformed into a series of liquid fuels, fuel additives
and other chemicals, like furfuryl alcohol (FOL), tetrahydroꢀ
5
furfuryl alcohol (THFOL), 2ꢀmethyl tetrahydrofuran (MTHF),
2
6
ꢀmethyl furan (MF), isoprene, pentanediol and levulinic acid,
etc. Currently, FFA is mainly used for the production of furfuryl
alcohol, however it is limited to develop other downriver
industrial products. Thus, further researchs to expand the
utilization of FFA are not only fundamentally important, but also
practically necessary.
Cyclopentanone (CPO) and cyclopentanol (CPL), as fine
chemical raw materials, have been wildly used as solvents and
starting materials for synhtesis of useful products (Scheme 1). For
Hronec et al. reported 81.32% total yield of CPO and CPL by
Green Chem., 2014, [vol], 00–00 | 1
This journal is © The Royal Society of Chemistry 2014

Green Chemistry
Page 2 of 9
View Article Online
DOI: 10.1039/C4GC01601G
9
using 5% Pt/C catalyst at 433 K and 8 MPa H pressure. Later,
hydroxide and 6.34 g sodium carbonate was slowly added into
200 mL aqueous solution containing 3.02 g nitrate copper and
11.6 g nitrate cobalt at room temperature until the pH of solution
was about 10~11. The catalysts were filtered after stirring at 353
K for 12 h. Then the precursors were washed with water until pH
= 7 and dried at 383 K overnight. The precursors were calcined at
2
Hronec et al. indicated that the key intermediate was 3ꢀhydroxyꢀ
ꢀcyclopentenone. In 2013, Hronec et al. reported that the main
reaction product was CPO, instead of the more stable CPL, due to
oligomers on the surface of catalyst at 448 K and 8 MPa H2.
Additionally, Xu et al. obtained 62% yield of CPO by using
NiCuꢀ50/SBAꢀ15 catalyst at 433 K and 4 MPa H . Differently,
1
0
4
11
o
773 K under air and the heating rate was 2 C/min. The oxides
2
the identified three key intermediates were furfuryl alcohol (FOL),
were reduced at 473 K for 3 h and the gas composition was H2:
N (10:90), 100 mL/min. The similar method for preparing 5%
2
12
4
ꢀhydroxyꢀ2ꢀcyclopenꢀtenone and 2ꢀcyclopentenone (2ꢀCPEO).
Nijhuis et al. obtained 16% CPO and 11% CPL by using
Pd/Co O , 20% Ni/Co O , 5% Pd/MnOx, 30% Cu/ZrO and other
3
4
3
4
2
Amberlystꢀ15 and Ru/C catalysts catalyzed dehydration of xylose
CuꢀCoꢀCP catalysts with different Cu loadings and calcination
temperature.
1
3
and hydrogenation of FFA in biphasic system. Then Hronec et
+
al. considered that there are two parallel reactions, including H
30% CuꢀCoꢀOGꢀ500 catalyst was prepared by solꢀgel method.
5.4 g cobalt nitrate, 2.4 g copper nitrate, 100 mL ethanol were
added into 500 mL beaker. Then 100 mL ethanol dissolving 4.3 g
oxalic acid was added under rapid stirring. The reaction liquid
was placed overnight after stirring for 4 h at room temperature.
The precipitates were filtered, washed with ethanol several times
and dried at 383 K overnight. The precursors were calcined at 773
ions catalysis generated by decomposition of water and the metal
1
4
catalysis in rearrangement reaction. Xiao et al. reported 93.4%
yield of CPL by (Cu+Mg)/Al catalyst at 4 MPa H for 10 h, but
2
15
the catalyst is severe deactivation after reused two times. Then
Xiao et al. used 30 wt.% Ni/CNTs for the conversion of FFA to
1
6
CPL.
Ohyama et al. reported the conversion of 5ꢀ
o
hydroxymethyl furfural to a cyclopentanone derivative by ring
K under air and the heating rate was 2 C/min. The oxides were
1
7
rearrangement over supported Au nanoparticles. Recently, the
rearrangement of FFA to CPO and CPL still have many problems,
like the expensive supported metals, the higher reaction hydrogen
pressure, the longer reaction time and the lower catalyst reused
times. Cu catalysts were favorable for selective hydrogenation of
FFA to furfuryl alcohol due to their strong polarization of C=O
bond and the exclusion of furan ring. It was known that furfuryl
alcohol was a key intermediate in rearrangement reaction and its
yield directly affected the yield of final products. Co catalysts had
a strong capability of hydrogenation and good closing ring ability
reduced at 473 K for 3 h and the gas composition was H : N
2
2
(10:90), 100 mL/min. The similar method for preparing 30%
Cu/ZrO and other CuꢀCoꢀOG catalysts with different Cu loadings
2
and calcination temperature.
Cu/HZSMꢀ5 was prepared by impregnation method. 3.8 g
copper nitrate was dissolved into 5 mL water. Then 9 g HZSMꢀ5
(Si/Al = 50) were added in batches under stirring. The precursors
were calcined at 823 K for 6 h after dried for 8 h. The oxides were
reduced at 553 K for 4 h and the gas composition was H : N
2
2
(10:90), 100 mL/min.
1
8
in the synthesis of five membered ring. It was more attractive
for inexpensive CuꢀCo catalysts than other supported noble
metals.
2
.3 Catalyst characterization
Catalysts were characterized by Xꢀray diffraction (XRD), Xꢀray
photoelectron spectroscopy (XPS), BarrettꢀEmmetꢀTaller (BET)
transmission electron spectroscopy (TEM) and inductively
coupled plasma atomic emission spectroscopy (ICPꢀAES).
Herein, we prepared a series of CuꢀCo catalysts by different
methods and found that CPO and CPL could be obtained
selectively over CP catalysts and OG catalysts, respectively. We
have studied the effects of different catalyst supports, Cu loadings,
calcination temperature, reused times, hydrogen pressure and
preparation methods of catalysts in rearrangement reaction. The
surface morphology, surface area and composition of catalysts
were studied by XRD, XPS, BET and ICPꢀAES and TEM
characterization.
2
.4 Typical experiment and product analysis
Studies on rearrangement reaction were performed in a 25 mL
autoclave (Hastelloy, Parr Instrument). In a typical experiment, 2
mmol of furfural, 50 mg of catalyst and 10 mL of H O were
2
added into autoclave. Then the autoclave was sealed, purged with
H four times, and then pressurized with H to a required pressure.
2
2
2
. Experimental
The autoclave was heated to a required temperature and reacted
for a required time (Fig. S6). After reaction, the reactor was
cooled and the solution was transferred with 20 mL ethanol. Then
a certain amount of N,Nꢀdimethylformamide (DMF) was added
as an internal standard substance. The samples were analyzed by
GC (Shimadzu GCꢀ2ꢀ14C, FID) with a DMꢀWAX column (30 m
2
.1 Materials and reagents
Cu (NO ) ꢁ3H O (AR, >99%), Co (NO ) ꢁ6H O (AR, >99%),
3
2
2
3 2
2
NaOH (AR, >96%), Na CO (AR, >99.8%), anhydrous ethanol
2
3
(
AR, >99.7%), FFA (AR, >99%)，furfuryl alcohol (CP, >98.5%),
tetrahydrofurfuryl alcohol (CP, >98%), N,Nꢀdimethylformamide
AR, >94%), CPL (CP, >97%), CPO (CP, >97%) were purchased
×
0.32 mm × 0.25 µm) and GCꢀMS (Thermal Trace GC Ultra
with a Polaris Q ion trap mass spectrometer equipped with a TRꢀ
MS capillary column). The conversion of FFA and the yield of
(
from Sinopharm group CO.LTD. 2ꢀcyclopentenone (2ꢀCPEO)
was purchased from J&K Chemicals. Pure water was purchased
from Wahaha, Hangzhou. FFA was used without further
purification.
5
products were calculated by following formula:
2
.2 Catalyst preparation
2
0% CuꢀCoꢀCPꢀ500 catalyst was prepared by coꢀprecipitation
method. 200 mL aqueous solution containing 4.78 g sodium
2
| Journal Name, [year], [vol], 00–00
This journal is © The Royal Society of Chemistry [year]

Page 3 of 9
Green Chemistry
View Article Online
DOI: 10.1039/C4GC01601G
3. Results and discussion
Table 1 Product distribution for hydrogenation rearrangement of FFA with various catalysts
Yield/%
Entry
Cat.
CꢀFFA/%
MTHF
THFOL
FOL
2ꢀCPEO
CPO
0
CPL
3
CPO+CPL
1
2
3
4
5
6
7
8
5% Pd/Co
3
O
4
100
100
100
86
1
0
0
0
0
0
0
0
82
7
0
1
0
1
0
0
0
0
0
0
3
20% Ni/Co
3
O
4
24
0
29
14
1
53
14
10
65
50
68
53
5% Pd/MnOx
Cu/HZSMꢀ5
81
0
0
14
0
9
30% Cu/ZrO
2
100
100
100
100
0
25
24
10
46
40
26
58
7
a
30% Cu/ZrO
30% Cu/Co
20% Cu/Co
2
0
0
a
3
O
4
0
0
3
O
4
0
0
2 2
(Reaction conditions: 2 mmol FFA, 0.1 g catalyst, 10 mL H O, 6 h, 423 K, 4 MPa H , mole yield. [a]. catalysts were prepared by solꢀgel method.)
We firstly studied the effects of different metal centers and
supports on the conversion of FFA to CPO and CPL. The main
products of THFOL, FOL, 2ꢀCPEO, CPO and CPL were
determined and presented in Table 1. The conversion of FFA was
almost 100% for all samples except for Entry 4 (86%). This may
be due to oligomers, formed by oligomerization of furfuryl
alcohol under acidic conditions (HZSMꢀ5), on the surface of
1
1,19
catalysts reduced the activity of catalysts.
The results slowed
down the conversion rate of FFA and lowered the total yield of
CPO and CPL. The main product was THFOL over supported Pd
catalysts (Entry 1 and Entry 3). It was attributed to the high
hydrogenation activity of Pd metal. Because the exclusion of
furan ring and the easier hydrogenation of aldehyde C=O bond to
alcohol, the total yield of CPO and CPL were higher by using
20
supported Cu catalysts (Entry 5ꢀ8) than other samples.
Improving the selectivity of FOL was helpful to improve the
yield of final products. The selectivity of products was not high
over Cu/ZrO catalysts (Entry 5 and Entry 6). CPO and CPL can
2
be obtained selectively over CuꢀCo catalysts prepared by coꢀ
precipitation method and solꢀgel method, respectively. The
monometallic Cu or Co as catalyst for the hydrogenation
conversion of FFA were also proceeded (Table S2). The results
showed that the yield and selectivity of products were less
satisfaction by using single metal as catalyst than that of CuꢀCo
catalysts. This indicated that the strong interaction between Cu
and Co was the cause of high selectivity.
Fig. 1 Effect of reaction temperature (a. 5% CuꢀCoꢀOGꢀ500 catalyst; b.
We investigated the influence of experimental conditions on
product distribution over different CuꢀCo catalysts.
5
2
% CuꢀCoꢀCPꢀ500 catalyst) on product distribution. Reaction conditions:
mmol FFA, 50 mg catalyst, 10 mL H O, 2 MPa H , 1 h, mole yield.
2
2
3
.1 Effect of reaction temperature
catalyst reduced the hydrogenation activity of catalyst may bring
11
about this result. The yield of CPL increased and then reduced
when the temperature increased from 433 K to 453 K. Continuing
to increase the temperature from 453 K to 473 K, The yield of
CPL reduced and then increased. The reasons subject to further
research.
The effect of reaction temperature on product distribution for the
hydrogenation rearrangement of FFA over 5% CuꢀCoꢀOGꢀ500
catalyst was determined and presented in Fig. 1(a). Under
reaction conditions, the conversion of FFA for all samples was
greater than 98%. The major products were FOL, CPO, CPL and
THFOL. The highest 64% CPL was obtained while only 3% CPO
Compared to Fig. 1(a), Fig. 1(b) was the effect of temperature
on product distribution by using 5% CuꢀCoꢀCPꢀ500 catalyst. FFA
converted almost completely at all temperatures. The main
products were FOL and CPO at lower temperature and the yield
of CPO was only 40%. About 26% FOL were detected at 413K.
was observed at 443 K, 1 h, 2 MPa H . Total yield of CPO and
2
CPL persisted to increase along with the increased temperature,
+
especially from 413 K to 433 K. The reason may be due to the H
ions which were promoted by high temperature and produced
+
+
This suggested that H ions, prepared by dissociation of water,
from water dissociation. H ions played a key role in protonation
2
1
9
were too weak to protonate FOL at lower temperature. The
highest yield of CPO (67%) was achieved at 443 K. The yield of
CPO decreased followed with increasing temperature from 443 K
of FOL and this was a key step in rearrangement of FFA. We
found that the yield of CPO was increased again when the
temperature over 443 K. Oligomers attached on the surface of
This journal is © The Royal Society of Chemistry [year]
Journal Name, [year], [vol], 00–00 | 3

Green Chemistry
Page 4 of 9
View Article Online
DOI: 10.1039/C4GC01601G
to 473 K. The formation of oligomers may be the main reason for
the yield of CPO increased primarily and decreased afterwards.
than 97% under all pressures except for 0.1 MPa. The highest
yield of CPL was 64% at 2 MPa H2.
11,
The corresponding BET results of the two catalysts were showed
in Table S4 and Fig S5.
Fig. 2(b) was the product distribution by using 5% CuꢀCoꢀ
CPꢀ500 catalyst. The main products were CPO, FOL and 2ꢀ
CPEO at 1 MPa H . The highest yield of CPO ( 67%) occurred in
2
3
.2 Effect of hydrogen pressure
2
MPa H . Then the yield was decrease. For all hydrogen
2
The product distribution by using 5% CuꢀCoꢀOGꢀ500 catalyst
was determined and presented in Fig. 2(a). The conversion of
FFA was low (only 33%) and the main product was FOL at
pressures, FFA converted completely except for 1 MPa H . It also
2
illustrated that hydrogen pressure had a certain promoting effect
on the reaction rate. Comparing the product distribution by using
the two catalysts at same conditions, we found that catalyst
activity of 5% CuꢀCoꢀOGꢀ500 catalyst was higher than that of
5% CuꢀCoꢀCPꢀ500 catalyst, especially for the hydrogenation step.
In order to study the structure of the prepared catalysts and the
correlation with their catalytic properties, we conducted Xꢀray
diffraction analysis. Fig. 3 showed the XRD patterns of the
prepared two kinds of catalysts. In 5% CuꢀCoꢀOGꢀ500 catalyst,
atmospheric pressure of hydrogen (0.1 MPa H ). A mixture of
2
CPO and CPL were obtained at 1 MPa H . Further increasing
2
pressure, the yield of CPL increased firstly and then decreased.
This was considered that the intermediates and products further
hydrogenated into other products at higher hydrogen pressure.
This speculation could be partly proved through the increased
yield of THFOL. Incidentally, the conversion of FFA was more
0
the distinct diffraction peaks of Co appeared due to the
23, 24
interaction between Cu and Co (Fig. 3b).
The existence of
excessive hydrogenation product THFOL and the decreased yield
of CPL along with increasing hydrogen pressure were derived
0
from the higher hydrogenation activity of Co and the interaction
25
0
between Cu and Co. Cu and Cu O were the obvious phases in
2
XRD of 5% CuꢀCoꢀCPꢀ500 catalyst (Fig. 3a). Cu O had a strong
2
polarization for C=O and the relative lack of hydrogenation
26ꢀ28
ability.
The total yield of CPO and CPL changed little while
the yield of CPL increased. So we could suggest that the yield of
CPL was improved by further hydrogenation of CPO and the side
reactions occurred rarely. The results for hydrogenation reaction
of CPO can also support this speculation (Table S1). The
complete conversion of CPO but the yield of CPL was only 88%
under 5% CuꢀCoꢀOGꢀ500 catalyst indicated that there were about
1
0% byproducts. The total yield of CPO and CPL was 99% by
using 5% CuꢀCoꢀCPꢀ500 catalyst for hydrogenation of CPO. The
results showed that excessive hydrogenation products and side
reactions did not existence. It also explained the different
hydrogenation ability between the two catalysts.
3
.3 Effect of Cu loadings
The product distribution by using CuꢀCoꢀOGꢀ300 catalyst with
different Cu loadings were determined and presented in Fig. 4(a).
As we could see from the chart, the conversion of FFA was very
low (20%) and only a small amounts of CPO and CPL were
obtained when the Cu loading was 1%. Weaker interaction
between Cu and Co made the reduction of Co oxides too little to
produce more products at 1% Cu loading. As the Cu loading
increased to 2%, the yield of CPL increased to 68% and the
Fig. 2 Effect of hydrogen pressure (a. 5% CuꢀCoꢀOGꢀ500 catalyst, b. 5%
CuꢀCoꢀCPꢀ500 catalyst) on product distribution. Reaction conditions: 2
mmol FFA, 50 mg catalyst, 10 mL H O, 443 K, 1h, mole yield.
2
Fig. 3 XRD. (a). 5% CuꢀCoꢀCPꢀ500; (b). 5% CuꢀCoꢀOGꢀ500.
| Journal Name, [year], [vol], 00–00
4
This journal is © The Royal Society of Chemistry [year]

Page 5 of 9
Green Chemistry
View Article Online
DOI: 10.1039/C4GC01601G
Fig. 6 The XRD diffraction peaks for 5% CuꢀCoꢀOG catalysts
under different calcination temperature
Fig. 4 Effect of Cu loadings (a. CuꢀCoꢀOGꢀ300 catalyst, b. CuꢀCoꢀCPꢀ
6
5
00 catalyst) on product distribution. Reaction conditions: 2 mmol FFA,
0 mg catalyst, 10 mL H O, 443 K, 1h, 2 MPa H , mole yield.
2
2
significantly, but the selectivity of products was poor. This may
suggest that the proportion of active phases was changed along
with the increased Cu loadings.
3
.4 Effect of calcination temperature
Fig. 5(a) was the result of product distribution by using 5% Cuꢀ
CoꢀOG catalysts with different calcination temperature. Results
showed that catalysts had high activity below 873 K. The highest
yield of CPL (64%) was obtained at 773 K. With increasing the
temperature from 973 K to 1073 K, the conversion of FFA
decreased significantly and the main products were FOL, 2ꢀ
CPEO and CPO. Almost none of fully hydrogenated product
CPL was obtained indicated serious deactivation of catalysts. Fig.
6
showed the XRD diffraction peaks for 5% CuꢀCoꢀOG catalysts
under different calcination temperature. The distinct diffraction
0
peaks of Co and Cu O appeared led to the high catalytic activity
2
24, 30
and high product yield below 873 K.
Increasing the
calcination temperature to 973 K and 1073 K, the diffraction
0
peaks of Co and Cu O decreased dramatically and the distinct
2
phases on XRD became (Cu0.3Co0.7) Co O spinel (JCPDS: 25ꢀ
2
4
Fig. 5 Effect of calcination temperature (a. 5% CuꢀCoꢀOG catalyst; b. 5%
CuꢀCoꢀCP catalyst) on product distribution. Reaction conditions: 2 mmol
FFA, 50 mg catalyst, 10 mLH O, 443 K, 1 h, 2 MPa H , mole yield.
2 2
highest yield of CPL was obtained. FFA were converted
completely over 2% Cu loadings. Further increasing the Cu
loading over 5%, the interaction between Cu and Co enhanced
2
3
and the selectivity of products reduced. To further increase the
Cu loading, the selectivity of product reduced obviously due to
the reunion of active metals and the possible formation of solid
2
9
solution between Cu and Co. The TEM microphotographs for
% CuꢀCoꢀOGꢀ500 and 10% CuꢀCoꢀOGꢀ400 were showed in Fig.
S1(a, b).
Similar to Fig. 4(a) at 1% Cu loading, the conversion of FFA
was too low (15%) and the products were FOL and 2ꢀCPEO by
5
1
9
using CP catalyst (Fig. 4b). The highest yield of CPO was
obtained at 5% Cu loading with complete conversion of FFA.
Increasing Cu loading to 20%, the total yield of CPO and CPL
was increased and the proportion of CPL was increased
This journal is © The Royal Society of Chemistry [year]
Journal Name, [year], [vol], 00–00 | 5

Green Chemistry
Page 6 of 9
View Article Online
DOI: 10.1039/C4GC01601G
ICPꢀAES, the metal content of Co and Cu in fresh catalyst were
4.75%, 7.19%, respectively. After reused five times, the metal
8
content of Co and Cu were 84.07%, 6.92%, respectively. The
results indicated that Cu and Co were part of loss after reuse. The
results led to the gradually weakened hydrogenation ability of
catalysts and the gradually increased yield of CPO.
Fig. 8(b) was the reuse of 5% CuꢀCoꢀCPꢀ500 catalyst. The
yield of CPO changed little even after reused five times. FFA
converted completely every time.
So here we identified that the selectivity and yield of CPO
and CPL were almost no changed after reused five times over the
two different preparation methods of catalysts, respectively.
Fig.7 XPS spectra for 5% CuꢀCoꢀOG catalysts under different calcination
temperature. (a): Cu2 p3/2; (b): Cu LMM; (c): Co2 p.
0
270). The large particles of spinel were showed in TEM (Fig.
S1c). Due to the strong interaction of atoms, spinel was difficult
31
to be restored.
The corresponding analysis of Cu2 p3/2, Cu
LMM and Co2 p spectra were showed in Fig. 7. In the Cu2 p3/2
spectra (Fig. 7a), the distinct peaks with electron binding energy
+
0 26
among 932 eV to 933.4 eV were belonged to Cu and Cu .
+
0
Because of the contiguous binding energy of Cu and Cu , the Cu
LMM spectra were required. The distinct peaks with electron
binding energy of 918.3 eV and 914.2 eV were observed and can
+
0
be respectively attributed to Cu and Cu in Cu LMM spectra
2
6, 32
below 873 K (Fig. 7b).
Shen et al. have reported that when
copper is highly dispersed and in intimated contact with the
supports, Cu Auger parameters may deviate significantly from
3
2
the corresponding bulk values. This was consistent with our
observation. Increasing the calcination temperature to 973 K and
2
+
1
073 K, only the distinct peak at 917.6 eV ascribed to Cu can
32
be observed. The change of Cu species has played a certain
influence on the activity of catalysts and the yield of products.
Co2 p spectra showed the changes of the Co species (Fig 7c).
The existent peak of Co (778.8 eV) disappeared when the
calcination temperature was above 873 K. Common
disappearance of Cu and Co eventually led to the collapse of
the catalyst activity and the product yield.
2
9, 32
0
+
0
The product distribution of 5% CuꢀCoꢀCP catalysts with
different calcination temperature were determined and presented
in Fig. 5(b). CPO was obtained selectively while the calcination
temperature increased from 673 K to 873 K and the yields were
Fig. 8 Effect of reuse times (a. 5% CuꢀCoꢀOGꢀ500 catalyst; b. 5% CuꢀCoꢀ
CPꢀ500 catalyst) on product distribution. Reaction conditions: 2 mmol FFA,
50 mg catalyst, 10 mL H O, 443 K, 1 h, 2 MPa H , mole yield.
2
2
6
5%, 67% and 57%, respectively. FFA converted completely
over these catalysts. When the calcination temperature was 973 K,
the conversion of FFA decreased to about 80%, the yield of CPO
dropped to only 26%, and 11% FOL and 18% 2ꢀCPEO were
obtained. The composition of products was similar to that of OG
catalysts at this temperature. Further increasing the calcination
temperature to 1073 K, the conversion of FFA declined sharply
to only about 17% and the products were observed only 8% FOL
and 1% CPO. The formed spinel and the disappeared activity
phases were contributed to the reduced product yield.
3
.5 Reusability of catalyst
The result of reusing 5% CuꢀCoꢀOGꢀ500 catalyst was
determined and presented in Fig. 8(a). The yield of CPL changed
little and the conversion of FFA was complete even after reusing
five times. The yield of CPO was increased continuously, but the
total yield of CPO and CPL was essentially unchanged. The
deposition carbon on the surface of catalyst, the enrichment of
oligomers and the loss of metal may be the main reasons to
reduce the hydrogenation activity of catalysts. Detected by the
6
| Journal Name, [year], [vol], 00–00
This journal is © The Royal Society of Chemistry [year]

Page 7 of 9
Green Chemistry
View Article Online
DOI: 10.1039/C4GC01601G
3
.6 Probable reaction pathway
temperature, reused times, hydrogen pressure and the preparation
methods of catalysts. There was obvious interaction between Cu
The probable reaction pathway for the conversion of FFA to CPO
and CPL over CuꢀCo catalysts was shown in Scheme 2. Several
main compounds of 2ꢀCPEO, FOL, CPO, CPL and THFOL were
detected through the optimization of reaction conditions (Fig. 2b).
We proposed a possible reaction pathway with the analysis of
and Co according to the characterization. The major active phases
0
were Cu O and Co in OG catalysts while the major active phases
2
0
were Cu and Cu O in CP catalysts. The different interaction and
2
the different content of phases in catalysts caused the different
selectivity of final products.
9
, 12, 22
products and characterization.
First was the hydrogenation
of FFA to FOL in aqueous solution. We found that the Cu
loadings and hydrogen pressure affected the conversion of FFA.
Acknowledgements
1
3
Further reactions of FOL were competitive.
One was the
catalysis reaction by H ions . This reaction obtained 4ꢀhydroxyꢀ
ꢀcyclopentenone (4ꢀHOꢀ2ꢀCPEO) which was another key
This work was supported by the 973 Program (2012CB215305,
2013CB228103), NSFC (21402181, 21472033, 21325208,
21272050, 21172209), CAS (KJCX2ꢀEWꢀJ02), FRFCU
(WK2060190025, WK2060190033), CPSF(2014M561835) and
NCETꢀ11ꢀ0627.
+
2
1
0
intermediate for the rearrangement of FFA. Other reactions
were the excessive hydrogenation of FOL to THFOL and the
oligomeric reactions under acidic conditions obtained oligomers.
The carbonꢀloss mainly came from the hardly detected oligomers
and this was attributed to the inherent properties of FFA and FOL.
The oligomers formed inevitably by the resinification of FFA and
Notes and references
a
Collaborative Innovation Center of Chemistry for Energy Materials,
Anhui Province Key Laboratory of Biomass Clean Energy, Department of
Chemistry, University of Science and Technology of China, Hefei 230026,
China. Fax: (+86) -551-63606689;
9
, 10, 12
reaction intermediates in highꢀtemperature water.
balance was lower at high hydrogen pressure and Cu loadings
Fig. 2 and Fig. 4). The high hydrogen pressure may promote the
The Cꢀ
(
E-mail: fuyao@ustc.edu.cn
b
School of Medical Engineering, and Key Laboratory of Advanced
oligomerization of FFA. The increased Cu loadings led to an
increased metal sites, the unexpected side reactions occurred and
several hardly detected byproducts were obtained. The yield of 4ꢀ
HOꢀ2ꢀCPEO directly influenced the yield of final products. Then
the dehydration of 4ꢀHOꢀ2ꢀCPEO to 2ꢀCPEO occurred followed
by the hydrogenation of 2ꢀCPEO to CPO in the presence of
catalyst. Production of CPL was depended on the hydrogenation
activity of catalysts. We suggested that the selectivity of final
products were caused by the different hydrogenation activity of
CPO over different catalysts. Therefore, 5% CuꢀCoꢀOGꢀ500
catalyst and 5% CuꢀCoꢀCPꢀ500 catalyst were used for the
hydrogenation of CPO to verify this speculation (Table S1).
Under the experimental conditions, CPO converted almost
completely and gave about 88% CPL over 5% CuꢀCoꢀOGꢀ500
catalyst while there was still 61% yield of unreacted CPO over
Functional Materials and Devices, Hefei University of Technology, Hefei
2
30009, China. Fax: (+86) -551-62904405 ;
E-mail: hjxu@hfut.edu.cn
† Electronic Supplementary Information (ESI) available. See DOI:
1
0.1039/b000000x/
1
.
(a) J. N. Chheda, G. W. Huber and J. A. Dumesic, Angew. Chem. Int.
Ed., 2007, 46, 7164ꢀ7183; (b) A. Corma, O. de la Torre, M. Renz
and N. Villandier, Angew. Chem. Int. Ed., 2011, 50, 2375ꢀ2378; (c)
M. Stöcker, Angew. Chem. Int. Ed., 2008, 47, 9200ꢀ9211; (d) J. C.
SerranoꢀRuiz, R. M. West and J. A. Dumesic, Annu. Rev. Chem.
Biomol., 2010, 1, 79ꢀ100; (e) L. Deng, Y. Zhao, J. Li, Y. Fu, B. Liao
and Q. X. Guo, ChemSusChem, 2010, 3, 1172ꢀ1175; (f) H. Olcay, A.
V. Subrahmanyam, R. Xing, J. Lajoie, J. A. Dumesic and G. W.
Huber, Energ Environ Sci, 2013, 6, 205ꢀ216.
2. S. Dutta, RSC. Adv., 2012, 2, 12575ꢀ12593.
3. J. P. Lange, E. van der Heide, J. van Buijtenen and R. Price,
ChemSusChem, 2012, 5, 150ꢀ166.
5
% CuꢀCoꢀCPꢀ500 catalyst. This indicated that the hydrogenaꢀ
4
.
(a) N. Li, G. A. Tompsett and G. W. Huber, ChemSusChem, 2010, 3,
154ꢀ1157; (b) W. J. Xu, Q. N. Xia, Y. Zhang, Y. Guo, Y. Q. Wang
tion activity of 5% CuꢀCoꢀOGꢀ500 catalyst was higher than that
of 5% CuꢀCoꢀCPꢀ500 catalyst. The different active phases on the
surface of the two catalysts also showed in XRD (Fig. 3). We
found that the major phases on the surface of 5% CuꢀCoꢀOGꢀ500
1
and G. Z. Lu, ChemSusChem, 2011, 4, 1758ꢀ1761; (c) Y. B. Huang,
Z. Yang, J. J. Dai, Q. X. Guo and Y. Fu, RSC. Adv., 2012, 2, 11211ꢀ
11214.
0
0
5. K. Yan, J. Y. Liao, X. Wu and X. M. Xie, RSC. Adv., 2013, 3, 3853ꢀ
catalyst were Cu O and Co . Co had higher hydrogenation
2
25
0
3856.
activity. But the main phases were Cu and Cu O on the surface
of 5% CuꢀCoꢀCPꢀ500 catalyst. The hydrogenation activity of Cu
2
6
.
Y. RomanꢀLeshkov, C. J. Barrett, Z. Y. Liu and J. A. Dumesic,
0
Nature, 2007, 447, 982ꢀ985.
and Cu O were relatively weaker than that of 5% CuꢀCoꢀOGꢀ500
7. K. Watanabe, Molecules, 2013, 18, 3183ꢀ3194.
2
8
.
M. Hronec, K. Fulajtárova, T. Liptaj, M. Štolcová, N. Prónayová
and T. Soták, Biomass Bioenergy, 2014, 63, 291ꢀ299.
catalyst. Therefore, the major product was not the fully
hydrogenated product CPL but CPO over CP catalysts under
reaction conditions. The different interaction and the different
content of phases in catalysts caused the different selectivity of
final products. Further studies on the detailed mechanism were
necessary.
9
1
.
M. Hronec and K. Fulajtárova, Catal. Commun., 2012, 24, 100ꢀ104.
0. M. Hronec, K. Fulajtárova and T. Liptaj, Appl Catal., A, 2012, 437-
38, 104ꢀ111.
11. M. Hronec, K. Fulajtárova and M. Mičušik, Appl Catal., A, 2013,
68, 426ꢀ431.
4
4
1
1
1
2. Y. L. Yang, Z. T. Du, Y. Z. Huang, F. Lu, F. Wang, J. Gao and J. Xu,
Green Chem., 2013, 15, 1932ꢀ1940.
3. V. V. Ordomsky, J. C. Schouten, J. van der Schaaf and T. A. Nijhuis,
Appl Catal., A, 2013, 451, 6ꢀ13.
4. Conclusions
In summary, we can selective conversion of FFA to CPO and
CPL by CuꢀCo catalysts which were prepared by coꢀprecipitation
method and solꢀgel method, respectively. The product distribution
was influenced by catalyst supports, Cu loadings, calcination
4. M. Hronec, K. Fulajtárova and T. Soták, Appl. Catal., B, 2014, 154ꢀ
1
55, 294ꢀ300.
15. M. Hronec, K. Fulajtárova and T. Soták, J. Ind. Eng. Chem., 2014,
0, 650ꢀ655.
2
This journal is © The Royal Society of Chemistry [year]
Journal Name, [year], [vol], 00–00 | 7

Green Chemistry
Page 8 of 9
View Article Online
DOI: 10.1039/C4GC01601G
1
1
1
1
6. M. H. Zhou, Z. Zeng, H. Y. Zhu, G. M. Xiao and R. Xiao, J. Energy.
Chem., 2014, 23, 91ꢀ96.
7. J. Ohyama, R. Kanao, A. Esaki and A. Satsuma, Chem. Commun.,
2
014, 50, 5633ꢀ5636.
8. M. Zhou, H. Y. Zhu, L. Niu, G. M. Xiao and R. Xiao, Catal. Lett.,
013, 144, 235ꢀ241.
9. M. Choura, N. M. Belgacem and A. Gandini, Macromolecules, 1996,
9, 3839ꢀ3850.
2
2
2
2
0. S. Sitthisa and D. E. Resasco, Catalysis Lett., 2011, 141, 784ꢀ791.
1. A. V. Bandura and S. N. Lvov, J. Phys. Chem. Ref. Data., 2006, 35,
1
5ꢀ30.
2. Y. Nakagawa, M. Tamura and K. Tomishige, ACS Catal., 2013, 3,
655ꢀ2668.
3. G. Fierro, M. L. Jacono, M. Inversi, R. Dragone and P. Porta, Top.
Catal., 2000, 10, 39ꢀ48.
4. J. Y. Kim, J. A. Rodriguez, J. C. Hanson, A. I. Frenkel and P. L. Lee,
J. Am. Chem. Soc., 2003, 125, 10684ꢀ10692.
5. H. C. Zhou, J. L. Song, H. L. Fan, B. B. Zhang, Y. Y. Yang, J. Y.
Hu, Q. G. Zhu and B. X. Han, Green Chem., 2014, 16, 3870ꢀ3875.
6. L. F. Chen, P. J. Guo, M. H. Qiao, S. R. Yan, H. X. Li, W. Shen, H.
L. Xu and K. N. Fan, J. Catal., 2008, 257, 172ꢀ180.
2
2
2
2
2
2
2
2
7. M. Bartók, Á. Molnár, S. Patai (Ed.), 1997, chap. 16.
8. A. lan Chambers, S. D. Jackson, D. Stirling and G. Webb, J. Catal.,
1
997, 166, 301ꢀ314.
9. Y. Yamada, K. Yano, Q. Xu and S. Fukuzumi, J. Phys. Chem. C.,
010, 114, 16456ꢀ16462.
2
2
3
3
0. S. C. Petitto and M. A. Langell, Surf. Sci., 2005, 599, 27ꢀ40.
1. P. Stefanov, I. Avramova, D. Stoichev, N. Radic, B. Grbic and T.
Marinova, Appl. Surf. Sci., 2005, 245, 65ꢀ72.
3
2. X. L. Tang, B. C. Zhang, Y. Li, Y. D. Xu, Q. Xin, W. J. Shen, Appl
Catal., A, 2005, 288, 116–125.
8
| Journal Name, [year], [vol], 00–00
This journal is © The Royal Society of Chemistry [year]

Page 9 of 9
Green Chemistry
View Article Online
DOI: 10.1039/C4GC01601G
Different Cu-Co catalysts have been developed for the hydrogenation-rearrangement of furfural to cyclopentanone
or cyclopentanol.