Catalytic conversion of glucose and cellobiose to ethylene glycol over Ni-WO3/SBA-15 catalysts

Article abstract of DOI:10.1039/c5ra15400f

Hydrogenolysis of glucose and cellobiose, used as the model feedstocks, over Ni-WO₃/SBA-15 catalysts has been investigated to probe the influencing factors for the conversion of cellulose to ethylene glycol (EG). The conversion of glucose and cellobiose to EG showed different dependencies on reaction temperature; a lower reaction temperature was needed for the former. Additionally, the surface atomic ratio of W to Ni on the Ni-WO₃/SBA-15 catalysts was the key factor for the product distribution. Both glucose and cellobiose had their own optimum W-Ni ratio for the production of EG, and the ratio of W to Ni for glucose was slightly lower than that of cellobiose. On the other hand, the Ni-WO₃/SBA-15 catalysts were thoroughly characterized by N₂ adsorption-desorption, X-ray diffraction (XRD), hydrogen-temperature programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The results indicated that the reducibility of Ni-WO₃/SBA-15 catalysts with high Ni loading was more similar to that of pure NiO. More importantly, the change of surface atomic content of Ni and W of Ni-WO₃ catalysts with various Ni loadings resulted from the surface W species of the catalysts being gradually covered by Ni species with the increase of Ni loading.

Full text of DOI:10.1039/c5ra15400f

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Catalytic conversion of glucose and cellobiose to
ethylene glycol over Ni–WO3/SBA-15 catalysts†
Cite this: RSC Adv., 2015, 5, 90904
a
Yueling Cao,ab Junwei Wang, Maoqing Kanga and Yulei Zhua
*
Hydrogenolysis of glucose and cellobiose, used as the model feedstocks, over Ni–WO3/SBA-15 catalysts
has been investigated to probe the influencing factors for the conversion of cellulose to ethylene glycol
(EG). The conversion of glucose and cellobiose to EG showed different dependencies on reaction
temperature; a lower reaction temperature was needed for the former. Additionally, the surface atomic
ratio of W to Ni on the Ni–WO3/SBA-15 catalysts was the key factor for the product distribution. Both
glucose and cellobiose had their own optimum W–Ni ratio for the production of EG, and the ratio of W
to Ni for glucose was slightly lower than that of cellobiose. On the other hand, the Ni–WO3/SBA-15
catalysts were thoroughly characterized by N2 adsorption–desorption, X-ray diffraction (XRD), hydrogen-
temperature programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS) and transmission
electron microscopy (TEM). The results indicated that the reducibility of Ni–WO3/SBA-15 catalysts with
high Ni loading was more similar to that of pure NiO. More importantly, the change of surface atomic
content of Ni and W of Ni–WO3 catalysts with various Ni loadings resulted from the surface W species of
the catalysts being gradually covered by Ni species with the increase of Ni loading.
Received 2nd August 2015
Accepted 19th October 2015
DOI: 10.1039/c5ra15400f
www.rsc.org/advances
the ratio of W to Ru or Ni is proved to be crucial for obtaining
high yield of EG.15,17,20 More importantly, it is believed that the
1. Introduction
homogeneous HxWO3 instead of heterogeneous tungsten
species or the partly reduced WO3 is the real active species to
promote the selective cleavage of C–C bond of cellulose to form
glycolaldehyde.17,19
Utilization of lignocelluloses, the most abundant non-edible
biomass in nature, as a renewable hydrocarbon source will
gain importance in the industrial production of liquid fuels and
chemical substances for sustainability.1,2 So far, there have been
many studies on the conversion of lignocellulosic materials into
glucose, polyol, 5-HMF, organic acids, and gaseous hydrocar-
bons using various processes.3–12 Among the various chemical
transformation processes of cellulose, the one-pot catalytic
transformation of cellulose to ethylene glycol (EG) has attracted
considerable attention because EG is widely used in the
synthesis of resins, automobile antifreeze, cosmetics, etc.5,13
Since the rst report by Ji et al., on cellulose conversion to
EG, much progress has been devoted to in designing effective
catalysts and revealing the reaction mechanism.5,14–22 The
process of one-pot conversion of cellulose to EG involves three
consecutive reactions: (1) hydrolysis of cellulose to celloo-
ligsaccharides and glucose; (2) retro-aldol condensation of
these sugar intermediates to glycolaldehyde; and (3) hydroge-
nation of glycolaldehyde to EG. Additionally, the retro-aldol
condensation and hydrogenation reaction are catalyzed by
tungstic compounds and metal Ni or Ru, respectively.21,22 Thus,
The production of EG from glucose or cellobiose mainly
involves the retro-aldol condensation of glucose or cellobiose to
glycolaldehyde and the hydrogenation of glycolaldehyde to EG.
Meanwhile, some other reactions, such as hydrogenation of
glucose to sorbitol, and isomerization of glucose to mannose
and fructose followed by subsequent hydrogenation to
mannitol and sorbitol, as illustrated in Scheme 1, can also
proceed and will compete with the reaction of retro-aldol
condensation. Thus, the main impediment to the selective
production of EG from cellulose is that how to match the
hydrogenation rate and the formation rate of glycolaldehyde.
When the hydrogenation rate is lower than the formation rate of
glycolaldehyde, it will lead to merely a small portion of glyco-
laldehyde hydrogenated to EG. However, when the hydrogena-
tion rate is higher than the formation rate of glycolaldehyde, it
will lead to more portion of glucose hydrogenated to sorbitol
before it occurring retro-aldol condensation to form
glycolaldehyde.
However, despite these advances, there are still a lot of
problems needed to be resolved. For example, it is interesting to
know whether high EG yield can be obtained under mild reac-
tion conditions. Whether the same ratio of W to Ru or Ni is
suitable for conversion of other substrates, such as cellobiose
aInstitute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, PR China.
E-mail: wangjw@sxicc.ac.cn; Fax: +86 351 4069680; Tel: +86 351 4069680
bUniversity of Chinese Academy of Sciences, Beijing 100049, PR China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c5ra15400f
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Scheme 1 The reaction path of conversion cellobiose and glucose to ethylene glycol and the main competitive reactions.
and glucose, to EG? Whether the mass transfer effect has an grade), tungstophosphoric acid hydrate [H3O40PW12$xH2O]
inuence on the yield of EG because of many reaction systems (Sinopharm Chemical Reagent Co. Ltd., analytic grade), nickel
adopting the Ru or Ni catalyst combined with one kind of nitrate hexahydrate [Ni(NO3)2$6H2O] (Sinopharm Chemical
tungstic species.
Reagent Co. Ltd., analytic grade), and SBA-15 zeolite (Shanghai
In our previous work, Ni–WO3/SBA-15 catalysts showed high Novel Chemical Technology Co., Ltd.). All chemicals were used
activity and selectivity for the one-pot conversion of cellulose to without further purication.
EG.17 However, the reaction path and mechanism of conversion
of cellulose to EG over Ni–WO3/SBA-15 catalysts were unclear.
On the other hand, glucose is the basic unit of cellulose and it is
formed as an intermediate in cellulose conversion to EG, while
cellobiose is the smallest molecule possessing a b-1,4-glycosidic
bond. More importantly, hydrolysis, C–C bond cleavage, and
hydrogenation, all the reactions that occur on cellulose
conversion, are present on cellobiose conversion. Therefore, the
2.2 Preparation of catalysts
All Ni–WO3/SBA-15 catalysts were prepared by a conventional
impregnation method as described previously.17 Typically, the
support, SBA-15, was impregnated with an aqueous solution
containing tungstophosphoric acid hydrate [H3O40PW12$xH2O]
and nickel nitrate hexahydrate [Ni(NO3)2$6H2O]. The impreg-
nation volume of metal solution was calculated using the
comparison of glucose and cellobiose conversion will provide
measured incipient wetness of the support. The impregnated
valuable mechanistic information for the cellulose conversion
catalysts were dried at 100 ꢀC for 12 h and then calcined at 500
to EG. In this work the conversion of glucose and cellobiose over
ꢀC for 3 h. Before the reaction, all of the catalysts were reduced
in a pure hydrogen ow at 500 ꢀC for 1 h. The catalysts are
labeled as x% Ni/support, y% WO3/support or x% Ni–y% WO3/
support, in which x and y stand for the nominal weight loading
Ni–WO3/SBA-15 catalysts has been systematically studied. High
EG yieꢀld could be obtained under lower reaction temperatures
(<200 C), and the reaction temperature needed for glucose is
lower than that of cellobiose. The products distribution was
mainly dependent on the W–Ni ratio of the Ni–WO3/SBA-15
of metal Ni and WO3, respectively.
catalysts. Compared with cellobiose, a slight lower W–Ni ratio
2.3 Catalytic reaction
for glucose conversion is required to obtain higher EG yield.
More importantly, the results from catalyst characterization
indicated that the change of W–Ni ratio with Ni loading mainly
resulted from that the surface atom content of Ni increased with
Ni loading while that of W deceased due to the increasingly Ni
gradually covered the active W species.
The catalytic conversion of glucose or cellobiose was performed
in a stainless-steel autoclave typically at 6 MPa H2 (measured at
room temperature). For each reaction, glucose or cellobiose
(0.5 g), catalyst (0.125 g), and water (40 g) were put in a 100 mL
autoclave, which was then purged with hydrogen three times
before the reactor was sealed and pressurized with hydrogen
(6 MPa). The reaction mixture was heated to a designated
temperature with a strong stirring. The zero reaction time was
regarded as the time when the temperature reached the set
2. Experimental
2.1 Materials
Glucose (Tianjin Dongliqu Tianda Chemical Reagent Factory, temperature. Aer the reaction, the autoclave was cooled to
analytic grade), cellobiose (Aladdin Chemistry Co. Ltd, analytic room temperature with water bath, and the solid residues were
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ltered from the liquid products. The quantication of products
was made by an internal standard method.
Compounds with low boiling points, including EG, 1,2-
propylene glycol (1,2-PG) and glycerol, were analyzed by a Shi-
madzu GC-2014 [CBP20 (polar) column (25 ꢁ 0.22 mm and 0.25
mmlm thickness), ameionizationdetector(FID)]. Thesamples
were injected (split ratio: 50) into a CBP20 (polar) column of 25 m
ꢁ 0.22 mm and 0.25 mm lm thickness. The temperature
program was as follows: holding at 75 ꢀC for 5.0 min, then
increasing from 75 ꢀC to 240 ꢀC at a rate of 30 ꢀC minꢂ1, nally
holding at 240 ꢀC for 20 min. Injector and detector temperatures
were setas 250 ꢀC and 280 ꢀC, respectively. Compoundswithhigh
boiling points, such as glucose, cellobiose, sorbitol and
mannitol, were analyzed by an HPLC system [Ca-NP capillary
chromatography column, evaporated light scattering detector,
water mobile phase, ow rate ¼ 0.6 mL minꢂ1, injection volume
¼ 5.0 mL, Tcolumn ¼ 80 ꢀC, Tdetector ¼ 70 ꢀC].
Fig. 1 N2 adsorption–desorption isotherms: (a) 3% Ni–15% WO3/SBA-
15, (b) 5% Ni–15% WO3/SBA-15, (c) 10% Ni–15% WO3/SBA-15, (d) 15%
Ni–15% WO3/SBA-15.
2.4 Characterization
SBA-15 and similar to a Type-IV isotherm according to the
IUPAC classication, with a H1 hysteresis loop.23,24 The shape of
the isotherm of pure SBA-15 was preserved even for the catalyst
with the highest nickel content, which means that, aer the
impregnation and subsequent calcinations of nickel and tung-
sten precursors, the mesoporous nature of the solid was
maintained. It should be noted that the nitrogen adsorption
isotherms of the Ni–WO3/SBA-15 catalysts showed a gradual
decrease in pore volume and the hysteresis loop became a little
broader in the desorption branch with the increase of Ni
loading, respectively. These results could be conrmed by
physicochemical characterization of Ni–WO3/SBA-15 catalysts
as shown in Table 1. The evaluation of the textural properties of
calcined samples from nitrogen adsorption–desorption
isotherms at ꢂ196 ꢀC revealed that the BET surface area
decreased progressively with the loading of nickel, with
a drastic reduction for the material with the higher Ni content
(Table 1). As shown in Table 1, the BET surface area of 10% Ni–
15% WO3/SBA-15 and 15% Ni–15% WO3/SBA-15 samples were
301.0 and 279.2 m2 gꢂ1, respectively, which is much less than
that of 3% Ni–15% WO3/SBA-15 sample (351.5 m2 gꢂ1). On the
other hand, the pore volume of Ni–WO3/SBA-15 catalysts
decreased with the Ni loading and the reduction became more
signicant with higher loading, which is similar with the trend
of the BET surface. Additionally, the average pore diameters of
all samples barely changed in comparison with the mesoporous
silica, used as support, thus pointing to the presence of nickel
The N2 adsorption–desorption isotherms of calcined catalysts
were measured at liquid nitrogen temperature (77 K) using
a Micromeritics Tristar II (3020). Before the meaꢂsu2rements,
ꢀ
samples were evacuated overnight at 200 C and 10 Pa. Pore
size distributions were calculated by analyzing the adsorption
branch of the N2 sorption isotherm using the Barrett–Joyner–
Halenda method.
Powder X-ray diffraction (XRD) patterns were obtained by
using a Germany Bruker D8 Advance X-ray diffractometer
equipped with a graphite monochromator, operating at 40 kV
and 40 mA and employing nickel-ltered Cu-Ka radiation (l ¼
˚
1.5418 A).
TPR experiments were carried out in a ChemBet 3000 equip-
ped with a thermal conductivity detector (TCD). For these
measurements, 100mgofsamplewitha size intherange of60–80
mesh was placed in a quartz reactor and heated at 450 ꢀC under
aN2 owof30mLminꢂ1, andheldatthistemperaturefor1h.The
reactor was then cooled down to 45 ꢀC and the sample exposed to
a steam of 30 mL minꢂ1 of 10% H2/N2. Subsequently, the sample
was heated up to 700 ꢀC at a heating rate of 10 ꢀC minꢂ1
.
X-ray photoelectron spectroscopy (XPS) studies were per-
formed with an AXIS ULTRA DLD spectrometer equipped with
a hemispherical electron analyzer and an Al Ka (1486.6 eV) X-ray
source. Charge referencing was done against adventitious
carbon (C 1s at 284.6 eV). The pressure in the analysis chamber
was kept lower than 10ꢂ6 Pa.
Transmission electron microscopy (TEM) experiments were
carried out in a JEOL JEM-2100F microscope equipped with an
energy dispersive X-ray spectrometer (EDX) operated at 200 kV.
The samples were dispersed in ethanol and then placed on
a carbon grid before TEM examinations.
Table
catalysts
1 Physicochemical characterization of Ni–WO3/SBA-15
Catalysts
SBET (m2 gꢂ1
)
Vp (cm3 gꢂ1
)
Dpore (nm)
3. Results and discussion
3.1 Characterization of Ni–WO3/SBA-15 catalysts
3% Ni–15% WO3/SBA-15
5% Ni–15% WO3/SBA-15
10% Ni–15% WO3/SBA-15 301.0
15% Ni–15% WO3/SBA-15 279.2
351.5
346.8
0.698
0.680
0.605
0.542
7.9
7.8
8.0
7.8
N2 adsorption–desorption isotherms for SBA-15 supported Ni–
WO3 catalysts are presented in Fig. 1. All of them were typical for
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Fig. 2 Pore size distributions of the 3% Ni–15% WO3/SBA-15 (a), 5%
Ni–15% WO3/SBA-15 (b), 10% Ni–15% WO3/SBA-15 (c) and 15% Ni–
15% WO3/SBA-15 (d).
oxide and tungsten oxide particles blocking partially the
entrance to the mesoporous framework (Fig. 2).
The low-angle powder XRD patterns of the Ni–WO3/SBA-15
catalysts exhibited a well-resolved diffraction peak, which can
be indexed in a hexagonal unit cell as corresponding to the (100)
reection of the SBA-15 silica, conrming that the mesoporous
structure was preserved aer nickel and tungsten incorpora-
tion.23 However, the presence of nickel and tungsten on the
support gave rise to a decrease in the intensity of this low angle
peak, which can be explained by the presence of gradual dete-
rioration of the structure with the increase of nickel loading
during the calcination procedure. Thus, it could be concluded
that the hexagonal arrangement of the SBA-15 frameworks was
retained aer incorporation of the nickel oxide and tungsten
oxide, as could be seen from N2 adsorption–desorption
isotherms and TEM images presented as above and below,
respectively.
Fig. 3 Low-angle (A) and wide-angle (B) XRD patterns of the 3% Ni–
15% WO3/SBA-15 (a), 5% Ni–15% WO3/SBA-15 (b), 10% Ni–15% WO3/
SBA-15 (c) and 15% Ni–15% WO3/SBA-15 (d).
Typical XRD patterns in the wide-angle region for the
samples were shown in Fig. 3B. As shown in Fig. 3B, the char-
acteristic diffraction lines of NiO were clearly visible at 2q (o) ¼
37.2, 43.3 62.9, 75.4 and 79.4 (JCPDS 47-1049), excepting for the
catalyst with the smallest amount of Ni (3% Ni–15% WO3/SBA-
15), and their intensities, as expected, increased with the Ni
loading. It should be noted that the characteristic peaks of WO3
was not observed regardless of the Ni loading, which indicating
that the tungsten oxide were well dispersed in all samples. In
addition, these results implied that the nickel oxide was easier
to aggregate than the tungsten oxide.
It is well known that reducibility of the nickel species
depends on the preparation method, the nature of the support
and precursor, as well as the experimental conditions used for
the reduction step. Fig. 4 shows the TPR proles of the calcined
Ni–WO3/SBA-15 catalysts. All samples exhibited only a broad
peak, which is due to the co-reduction of NiO and WO3 was
happened during H2 temperature-programmed reduction
procedure as our previous report.17 It is interesting to note that
the initial reduction temperature of samples decreased with Ni
loading, from 350 to 300 ꢀC. According our previous report, the
Fig. 4 H2-TPR patterns of the 3% Ni–15% WO3/SBA-15 (a), 5% Ni–15%
WO3/SBA-15 (b), 10% Ni–15% WO3/SBA-15 (c) and 15% Ni–15% WO3/
SBA-15 (d).
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Table 2 XPS data of Ni–WO3/SBA-15 catalysts
Binding energy (eV)
Ni 2p3/2 W 4f5/2
Surface atomic content (at%)
Surface atomic
ratio of W/Ni
Catalysts
Ni
W
O
Si
3% Ni–15% WO3/SBA-15
5% Ni–15% WO3/SBA-15
10% Ni–15% WO3/SBA-15
15% Ni–15% WO3/SBA-15
855.8
855.8
855.7
855.6
35.4
35.6
35.8
35.8
0.266
0.488
0.718
1.101
0.246
0.242
0.192
0.179
73.052
77.220
75.301
74.320
26.436
22.050
27.789
24.400
0.925
0.496
0.267
0.162
shi to higher temperature resulted from the presence of
a strong electronic interaction between NiO and WO3 for the Ni–
WO3/SBA-15 catalysts.17 More importantly, the initial reduction
temperature of 15% Ni–15% WO3/SBA-15 sample was same with
that of Ni/SBA-15 sample based on our previous result.17 Thus, it
could be concluded that the intensity of interaction between
NiO and WO3 gradually decreased with Ni loading. This might
be explained by following reason that the particle size of NiO
increased with the Ni loading as shown in XRD results, which
making the reduction of NiO was more similar with pure NiO
and less proportion of NiO had interaction with WO3.
Catalysts have been characterized by X-ray photoelectron
spectroscopy to obtain more information about the Ni and W
oxidation state and the chemical composition of the catalyst
surface. The binding energy values of Ni 2p and W 4f along with
the relative surface atomic content and the W/Ni atomic ratios
of Ni–WO3/SBA-15 catalysts are presented in Table 2. The bands
at 855.6–855.8 eV and at 35.4–35.8 eV are assigned to Ni2+ and
W6+ species, respectively.25,26 As the Ni loading increased, the
binding energy of Ni 2p negatively shied, which is are in line
with H2-TPR results presented above that the NiO became easier
to be reduce with Ni loading. By contrast, the binding energy of
W 4f showed the opposite trend, shiing to higher binding
energy with the increase of Ni loading, which might result from
the interaction between Ni and W decreased with Ni loading as
mentioned above. More importantly, as shown in Fig. 5, the Ni
2p signal intensity increased with Ni loading while the W 4f
signal intensity exhibited the opposite trend, suggesting that
the surface atomic content of Ni and W presented various
change trends.
Concerning the surface atom content of the Ni–WO3/SBA-15
catalysts, as expected, the surface atom content of Ni increased
with Ni loading, from 0.266 to 1.101%, which is due to more
nickel atoms disperse on the surface of SBA-15. In contrast, the
surface atom content of W showed the opposite trend,
decreasing with the increase of Ni loading (from 0.246 to
0.179%), although the WO3 loading was xed. This might be
due to the following reasons. On the one hand, the dispersion of
WO3 decreased with the decrease of surface area of the catalysts
as mentioned above. More importantly, the surface active sites
of WO3 were increasingly covered with the surface NiO due to
the increase of Ni loading. Concerning the surface W–Ni atomic
ratios, their values decreased from 0.925 to 0.162, as expected,
with the nickel loading. It should be note that the surface W–Ni
atomic ratios of Ni–WO3 catalysts were a main reason for the
product distribution of glucose or cellobiose conversion, which
Fig. 5 X-ray photoelectron spectra in the Ni 2p and W 4f regions for
the Ni–WO3/SBA-15 catalysts with different Ni loading: (a) 3% Ni–15%
WO3/SBA-15, (b) 5% Ni–15% WO3/SBA-15, (c) 10% Ni–15% WO3/SBA-
15, (d) 15% Ni–15% WO3/SBA-15.
would be presented as below. The low Ni loading means the
high W–Ni ratio, which is favorable to form the EG. In contrast,
the high Ni loading means the low W–Ni ratio, thus the sorbitol
would be the main product if glucose or cellobiose conversion
was conducted over the Ni–WO3 catalysts with high Ni loading.
The maintenance of ordered hexagonal arrangement of the
SBA-15 frameworks upon nickel and tungsten introduction is
further supported by TEM images. As shown in Fig. 6A and C,
the Ni–WO3/SBA-15 samples with different Ni loading showed
well-ordered hexagonal arrays of mesopores (1D channels) and
unambiguously conrmed that the hexagonal pore structure of
the SBA-15 was robust enough to survive the nickel and
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Fig. 6 Representative TEM micrographs of 3% Ni–15% WO3/SBA-15 (A and B) and 15% Ni–15% WO3/SAB-15 catalysts (C and D).
tungsten incorporation process. On the other hand, it could be opposite change trends. As mentioned above, the surface ratio
seen from Fig. 6 that the particle sizes of NiO signicantly of W to Ni was a crucial factor for the products distribution.
increased with Ni loading, while that of WO3 only slightly Thus, the diagram of the inuence of surface composition of
increased. These results were in line with XRD results that the Ni–WO3/SBA-15 catalysts with various Ni loading on the prod-
signal intensity of NiO signicantly increased with Ni loading, ucts distribution of glucose and cellobiose conversion was
but the characteristic peaks corresponding to WO3 were not presented in Fig. 7.
observed regardless of Ni loading. More importantly, as shown
in Fig. 6B and D, many WO3 cluster were exposed on the surface
of Ni–WO3/SBA-15 catalysts when the Ni loading was low (3%).
However, part of WO3 clusters on the catalysts surface was
covered by NiO clusters when the Ni loading increased to 15%.
These results TEM corroborated the results obtained by XPS
analysis that the surface composition of Ni and W exhibited
3.2 Effect of reaction temperature on glucose and cellobiose
conversion
As shown in Scheme 1, the hydrogenation of glucose or cello-
biose to form sorbitol and mannitol is competing with their
degradation to form glycolaldehyde, which further forms EG via
catalytic hydrogenation. According to previous report, the
reaction selectivity signicantly depends on temperatures due
to there is a big discrepancy in the activation energies (Ea)
between the C–C bond cleavage of glucose (141.3 kJ molꢂ1) and
the hydrogenation of glucose (49.6 kJ molꢂ1).21 Therefore, we
rst conducted reactions at temperatures from 120 ꢀC to 190 ꢀC
with 3% Ni–15% WO3/SBA-15 catalyst.
Tables 3 and 4 illustrates the products distribution from
glucose and cellobiose, respectively, at six different tempera-
tures. At a relatively low temperature (120 ꢀC), the cellobiose
conversion was only 5.7% while the glucose conversion reached
11.9%, indicating cellobiose had the lower reactivity than that
of glucose due to it only possess half of hemiacetal group. It
should be noted that trace EG was detected for both glucose and
cellobiose conversion, indicating that retro-aldol condensation
could occur at this low temperature but at a very low rate. When
the reaction of glucose conducted at higher temperatures, both
glucose conversion and EG yield increased. The EG yield
reached a maximum (32.3%) at 175 ꢀC, and then decreased with
increasing reaction temperature. This is due to that both the
retro-aldol condensation rate and hydrogenation rate of
Fig. 7 The influence of surface composition of Ni–WO3/SBA-15
catalysts with various Ni loading on the products distribution.
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Table 3 Effect of reaction temperature on glucose conversiona
Yield (%)
EG
Reaction temperature (ꢀC)
Reaction time (min)
Conversion (%)
1,2-PG
Glycerol
120
130
145
160
175
190
180
180
180
120
80
11.9
20.8
70.4
96.6
100
Trace
3.4
18.4
25.5
32.3
26.3
Trace
Trace
0.3
0.7
2.1
0.6
1.3
2.5
3.2
3.6
2.2
30
100
1.6
a
Reaction conditions: glucose 0.5 g, water 40 g, 3% Ni–15% WO3/SBA-15 0.125 g, H2 pressure 6 MPa. EG: ethylene glycol, 1,2-PG: 1,2-propylene
glycol.
Table 4 Effect of reaction temperature cellobiose conversiona
Yield (%)
EG
Reaction temperature (ꢀC)
Reaction time (min)
Conversion (%)
1,2-PG
Glycerol
120
130
145
160
175
190
180
180
180
120
80
5.7
Trace
Trace
4.5
25.5
37.3
42.4
No
No
No
Trace
1.1
No
0.7
0.9
1.7
2.4
2.3
16.0
46.3
83.6
100
100
30
1.1
a
Reaction conditions: cellobiose 0.5 g, water 40 g, 3% Ni–15% WO3/SBA-15 0.125 g, H2 pressure 6 MPa. EG: ethylene glycol, 1,2-PG: 1,2-propylene
glycol.
glycolaldehyde increased with reaction temperature, but the
former was far higher than later, leading to part of glyco-
laldehyde formed from retro-aldol condensation of glucose
occurred side reactions. On the other hand, although cellobiose
showed the same trend of its conversion and EG yield, the
reaction temperature (190 ꢀC) for obtaining the maximum yield
of EG (42.4%) was higher than that of glucose, which resulting
from the low reactivity of cellobiose as mentioned above. On the
other hand, it should be noted that only trace amount of hex-
itols was obtained from all range of reaction temperatures
which is different with previous report, but high EG yield was
obtained at high reaction temperatures.20 This is due to that the
hydrogenation ability of 3% Ni–15% WO3/SBA-15 catalyst was
always insufficient to hydrogenate glucose, but enough to
hydrogenate glycolaldehyde because of the activation energy of
glycolaldehyde hydrogenation is lower than that of glucose
hydrogenation. Zhang et al., reported that the apparent activa-
tion energy are 49.6 and 42.6 kJ molꢂ1 for glucose and glyco-
laldehyde hydrogenation over Ru/C catalysts, respectively.21
Comparing the EG yields in the glucose and cellobiose
reactions at the same conditions (Fig. 8), it can be found that
the former is much faster than the latter in the lower reaction
temperatures, suggesting that the retro-aldol condensation of
glucose might be much easier than that of cellobiose. However,
with the increase of reaction temperature, the EG yield from
Fig. 8 Ethylene glycol yields as a function of reaction temperature for
glucose and cellobiose.
reaction temperature is more favorable for the retro-aldol
condensation of cellobiose in comparison with that of glucose.
3.3 Effect of W–Ni active sites ratio
cellobiose conversion surpassed that from glucose. This is due As our previous report that 3% Ni–15% WO3/SAB-15 catalyst
to that the slow retro-aldol condensation of cellobiose is better possesses the optimum ratio of W to Ni, but this ratio may be
matched with the subsequent hydrogenation of glycolaldehyde not suitable for glucose and cellobiose conversion because the
as previous report.22 Thus, it can be concluded that a higher different reactivity between cellulose and these two model
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Table 5 Effect of W–Ni active sites ratio on glucose conversiona
Yield (%)
EG
Catalyst
Conversion (%)
1,2-PG
Glycerol
Sorbitol
Mannitol
3% Ni–15% WO3/SBA-15
5% Ni–15% WO3/SBA-15
10% Ni–15% WO3/SBA-15
15% Ni–15% WO3/SBA-15
100
100
100
100
32.3
41.5
29.8
13.5
2.1
3.6
2.4
0.8
3.6
4.1
2.9
2.0
Trace
4.1
36.5
59.7
No
Trace
7.5
13.1
a
Reaction conditions: glucose 0.5 g, water 40 g, catalyst 0.125 g, 175 ꢀC, 80 min, H2 pressure 6 MPa. EG: ethylene glycol, 1,2-PG: 1,2-propylene glycol.
Table 6 Effect of W–Ni active sites ratio on cellobiose conversiona
Yield (%)
Catalyst
Conversion (%)
EG
1,2-PG
Glycerol
Sorbitol
Mannitol
3% Ni–15% WO3/SBA-15
5% Ni–15% WO3/SBA-15
10% Ni–15% WO3/SBA-15
15% Ni–15% WO3/SBA-15
100
100
100
100
42.4
42.9
40.5
16.3
1.1
1.8
3.4
0.8
2.3
2.8
2.8
2.0
Trace
4.8
18.5
61.5
No
Trace
2.0
9.1
a
Reaction conditions: cellobiose 0.5 g, water 40 g, catalyst 0.125 g, 190 ꢀC, 30 min, H2 pressure 6 MPa. EG: ethylene glycol, 1,2-PG: 1,2-propylene
glycol.
compounds.17 On the other hand, according to literature, the signicantly prevailed over the C–C bond cleavage reaction,
ratio of W to Ru or Ni active sites proves to be a crucial factor for leading to the major production of sorbitol and minor
the products distribution.15,20 Thus, to explore the best ratio of production of EG.
W to Ni for glucose and cellobiose, the inuence of the W–Ni
ratio on the EG yield was investigated by changing the Ni
loading of Ni–WO3/SBA-15 catalysts with the WO3 amount xed.
4. Conclusion
As shown in Table 5, the EG yield showed a volcano-shaped
curve with the increase of Ni loading. When the Ni loading was
low, it was insufficient for the catalytic hydrogenation, leading
to merely part of reactive intermediates hydrogenated to EG.
A series of SBA-15 silica supported Ni–WO3 catalysts with
different Ni loading were prepared for the selective hydro-
genolysis of glucose and cellobiose to EG in aqueous solution.
Compared with glucose and cellobiose conversion over 3% Ni–
However, when the Ni loading is too high, the EG yield
15% WO3/SBA-15 catalysts, higher reaction temperature for
decreased but the sorbitol yield increased signicantly. On the
cellobiose conversion than that of glucose was needed to obtain
one hand, this is due to that the hydrogenation rate of glucose
the maximum EG yield due to the lower retro-aldol condensa-
increased with the increasing of Ni loading. On the other hand,
tion rate of cellobiose compared with that of glucose. The W–Ni
the Ni covered part active sites of tungsten oxide species,
ratio was a key factor for the products distribution of glucose
leading to the hydrogenation rate of glucose surpassed the
and cellobiose conversion. More specially, when the Ni–WO3/
SBA-15 catalyst with lower Ni loading was used, the retro-aldol
condensation of glucose or cellobiose to glycolaldehyde and
its subsequent hydrogenation would be the main reaction path.
However, the direct hydrogenation of glucose or cellobiose
would prevail if the catalyst with lower W–Ni ratio was used.
Compared with glucose conversion, the lower ratio of W to Ni is
reaction rate of C–C cleavage of glucose. These results are
consistent with XPS results that the surface atom content of Ni
and W exhibited opposite change trend. To be specic, the
relative surface atom content of Ni increased with Ni loading,
but that of W decreased with Ni loading due to the part of W was
gradually covered by Ni.
Table 6 presents the cellobiose conversion with various
more favorable for the conversion of cellobiose to EG. The
ratios of W to Ni. A little unlike the glucose conversion, the EG
systematic catalyst characterization indicated that the surface
yield almost remained unchanged at rst with the increase of Ni
atomic ratio of W to Ni of the Ni–15% WO3 catalysts decreased
loading. This might be due to that compared with glucose
with the increase of Ni loading. There are two reasons for this.
conversion, although the higher ratio of W to Ni of Ni–WO3/
First, nickel and tungsten oxides became less dispersed with the
SBA-15 catalyst has the relatively low hydrogenation rate of
increasing in Ni loading due to the decrease of the BET surface
glycolaldehyde, it is better matched with the slow retro-aldol
of the catalysts. More importantly, the surface active sites of
condensation of cellobiose as mentioned above. When the Ni
tungstic species were gradually covered by the gradually
loading was up to 15%, the direct hydrogenation of cellobiose
increased nickel oxides.
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12 P. Sirous Rezaei, H. Shafaghat and W. M. A. W. Daud, RSC
Adv., 2015, 5, 65408–65414.
Acknowledgements
13 H. R. Yue, Y. J. Zhao, X. B. Ma and J. L. Gong, Chem. Soc. Rev.,
2012, 41, 4218–4244.
14 Y. Zhang, A. Wang and T. Zhang, Chem. Commun., 2010, 46,
862–864.
This work was nancially supported by a grant from the Major
State Basic Research Development Program of China (973
Program) (No. 2012CB215305).
15 M.-Y. Zheng, A.-Q. Wang, N. Ji, J.-F. Pang, X.-D. Wang and
T. Zhang, ChemSusChem, 2010, 3, 63–66.
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90912 | RSC Adv., 2015, 5, 90904–90912
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