Production of ethylene glycol from direct catalytic conversion of cellulose over a binary catalyst of metal-loaded modified SBA-15 and phosphotungstic acid

Article abstract of DOI:10.1039/c8ra03806f

This study presents the utilization of a binary catalyst composed of metal-loaded modified SBA-15 (M/SBA-15) and phosphotungstic acid (H₃PW₁₂O₄₀) for ethylene glycol (EG) production from direct catalytic conversion of cell

Full text of DOI:10.1039/c8ra03806f

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Production of ethylene glycol from direct catalytic
conversion of cellulose over a binary catalyst of
metal-loaded modified SBA-15 and
Cite this: RSC Adv., 2018, 8, 24857
phosphotungstic acid
a
a
Shitao Yu,a Xincheng Cao,
Shiwei Liu, Lu Lia and Qiong Wuab
*
This study presents the utilization of a binary catalyst composed of metal-loaded modified SBA-15 (M/SBA-15)
and phosphotungstic acid (H3PW12O40) for ethylene glycol (EG) production from direct catalytic conversion of
cellulose. M/SBA-15 (M ¼ Ru, Au, Pd, Pt, Rh and Ni) catalysts were prepared using the impregnation method
and characterized by means of XRD, N2 physisorption, TEM and H2-temperature-programmed reduction (H2-
TPR) techniques. Their catalytic performance was then studied in detail on the basis of cellulose conversion
and the selectivity of polyols and EG. The results showed that the mesoporous structure of the SBA-15
sample was well maintained after the metal-loaded modification, and almost all of the selected catalysts gave
about 100% conversion of cellulose. However, the selectivity for EG was greatly different. Among the various
binary catalysts, the combination of Rh/SBA-15 and H3PW12O40 gave the best selectivity to EG (55.5%),
whereas the worst selectivity of EG (11%) was obtained over the Au/SBA-15 and H3PW12O40 system under
identical conditions. In addition to phosphotungstic acid, other W compounds were also studied in
combination with the Ru/SBA-15 catalyst. The results showed that the EG selectivity depended on the W
compounds as follows: H4SiW12O40 < H2WO4 < H3PW12O40. Therefore, the binary catalyst of Rh/SBA-15 and
H3PW12O40 showed the greatest potential for EG production from direct catalytic conversion of cellulose.
Received 3rd May 2018
Accepted 27th June 2018
DOI: 10.1039/c8ra03806f
rsc.li/rsc-advances
reaction of cellulose by an acid catalyst to form glucose and the
hydrogenation of the glucose over the metal catalysts to generate
the polyols.7 Amongst the polyol products, EG has a large market
1. Introduction
The excessive consumption of fossil fuel and the ever-increasing
emissions associated with their consumption have spurred
a great deal of research for alternative energy sources.1 Biomass
as a clean and renewable carbon source on earth has received
increasing attention.2 With regards to the utilization of
biomass, the conversion of cellulose holds great potential due
to its nonedible nature and huge availability.3 Nevertheless,
cellulose, as a biopolymer bonded by b-1,4-glucosidic bonds,
contains abundant hydrogen bonds; hence, it is difficult to
convert it by solvents or catalysts under mild conditions.4
Therefore, the robust structure of cellulose remains a great
concern for its efficient transformation under mild conditions.
In order to achieve high energy efficiency and atom economy
in the conversion of cellulose, different primary routes have been
explored.5–8 One of the most promising routes is direct catalytic
conversion of cellulose to polyols, for which the polyol products
can be directly used as chemicals or precursors to produce
renewable chemicals.9 This process couples the C–C breaking
and is widely used in the pharmaceutical, cosmetic, food, dye,
plastic and automobile industries; thus, it is considered to be
a high-value market product.10 Currently, the manufacture of EG
is mainly dependent on petroleum resources using the method of
oxidation, followed by hydration of ethylene.11 Therefore,
obtaining EG from the direct transformation of cellulose is very
signicant because of its possible environment benets and the
current concern over the depletion of fossil fuel sources. For this
catalytic approach, catalyst plays an important role in the selec-
tivity of a specic polyol product. For example, using Ru/AC as
the catalyst (AC ¼ activated carbon), Liu et al. obtained ꢀ40%
yield of hexitols.12 Zhang et al. obtained EG yield of up to ꢀ54%
using H2WO4 in combination with 1.2% Ru/AC catalyst.13
It is well known that the dispersion and accessibility of
active sites have a signicant impact on the activity and
selectivity of the catalyst. To develop efficient catalysts,
extensive studies have been conducted by using different
technologies. For example, Zhang et al. used the traditional
active carbon (AC) as support for dispersing Ni particles to
improve the activity of the catalyst in the catalytic conversion
of cellulose to EG.14 Although the AC had large surface area,
the active sites exhibited low dispersion and poor accessibility
aCollege of Chemical Engineering, Qingdao University of Science and Technology,
Qingdao 266042, China. E-mail: liushiweiqust@126.com; Fax: +86 532 84022719;
Tel: +86 532 84022719
bDepartment of Chemical
& Biomolecular Engineering, University of Tennessee
Knoxville, 419 Dougherty Engineering Bldg., Knoxville, Tennessee 37996, USA
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due to the microporous structure of AC. Additionally, the
microporous carbon used as support may have a negative
effect on the overall catalytic performance due to its steric
hindrance and diffusion limitations. For this reason, meso-
porous carbon (CMK-3) with WCx active sites was synthesized
to catalyze cellulose.15 The WCx/CMK-3 catalyst exhibited
better catalytic performance than the WCx/AC catalyst due to
its good accessibility and the dispersion of the active sites.
However, the rigorous synthesis conditions and difficulty in
replication greatly limited its application. In 2010, Zheng et al.
developed a series of bimetallic catalysts for the conversion of
cellulose, including Ru–W, Ni–W, Ir–W and Pt–W supported
on different carriers. It was found that the maximum yield of
EG (75.4%) was obtained over the Ni–W/SBA-15 catalyst.16 In
this context, the mesoporous material SBA-15 can be used as
the catalyst for catalytic cracking of cellulose due to its ordered
hexagonal mesostructure and large pore size, which can
facilitate the conversion of bulky molecules.17 However, the
pure silica SBA-15 material had almost no catalytic activity
because of the absence of active sites.18 Therefore, the catalyst
must be further modied and improved to solve this problem.
Among all the modication methods, the impregnation
method has remarkable advantages such as simple prepara-
tion and easier industrial application.19 Up to now, metals,
including Ni,20 La,21 Al,22 Ca23 and Mg,24 modied with SBA-15
have shown good catalytic performance in the catalytic
cracking of vegetable oils. It is worth mentioning that these
catalysts were all prepared using the impregnation method.
Nevertheless, there are few reports related to obtaining the
desired products from catalytic conversion of cellulose over
these catalysts.
2.2 Preparation and characterization of catalysts
SBA-15 was synthesized by the hydrothermal method according
to the literature.25 The molar composition of the mixture was
1TEOS : 0.02P123 : 6HCl : 192H2O.
Ru/SBA-15 catalyst was prepared by the wet impregnation
method. First, 1.0 g SBA-15 powder was immersed into 20 mL
RhCl3$3H2O solution (10 wt%) under stirring at 80 ꢁC. Aer
ꢁ
ꢁ
evaporation at 80 C, the sample was dried at 100 C for 12 h
and then calcined at 550 ꢁC for 6 h in air. The solid obtained was
reduced with H2 (20 cm3 minꢂ1) at 550 C for 2 h at a heating
ꢁ
rate of 2 ꢁC minꢂ1, giving the Ru-SBA-15 catalyst. Other catalysts
such as Ni (Pt, Pd, Au, Rh)/SBA-15 were also prepared using the
same method.
XRD patterns were recorded on a XB-3A instrument oper-
ating at 40 kV and 100 mA with Cu Ka radiation (l ¼ 0.15418
nm) in the 2q range from 0.5ꢁ to 10ꢁ. The experiment conditions
were as follows: a step width of 0.01ꢁ and scan speed of
2ꢁ minꢂ1. The BET specic surface area and pore size distri-
bution of the catalysts were measured from N2 adsorption/
desorption isotherms at ꢂ77 K using a Micromeritics ASAP
2000 system. TEM images were recorded to observe the
dispersion degree of the metal phase. Transmission electron
microscopy (TEM) was conducted on a JEOS-2020 F electron
microscope operating at an accelerating voltage of 200 kV. The
metal contents of the as-synthesized catalyst were measured by
inductively coupled plasma-atomic emission spectrometry
(ICP-AES) technique on
a
Varian VISTA-PRO AX
spectrophotometer.
H2-temperature-programmed reduction (H2-TPR) was per-
formed in a xed reactor. Prior to the TPR, 100 mg samples were
purged in Ar at 100 ꢁC for 1 h. Subsequently, theꢁsamples were
In this study, we evaluated the catalytic performances of
various binary catalysts of M/SBA-15 (M ¼ Ru, Au, Pd, Pt, Rh
and Ni) mesoporous materials and different W compounds
and chose the best binary catalyst to produce EG from the
catalytic conversion of cellulose. To the best of our knowledge,
there is no clear picture of the comparative performance of
these catalysts. Therefore, it is expected that the results will
ꢁ
heated in a ow of pure H2 from 100 C to 800 C at a rate of
10 ꢁC minꢂ1 and were analyzed by a Hiden QIC-20 mass
spectrometer.
2.3 Catalytic cracking cellulose
provide the vital guidance for the rational selection of highly The catalytic conversion of cellulose was carried out in
ꢁ
active binary catalysts for the catalytic conversion of cellulose a Teon-lined stainless autoclave (100 mL) at 245 C for 4 h
to EG.
under 5.0 MPa hydrogen pressure. Typically, the reaction
mixture was composed of cellulose (W1), binary catalyst (0.1 g
M/SBA-15 and 0.02 g W compounds) and 25 mL of H2O, which
were successively placed in the autoclave. Then, the reactor
was purged with nitrogen at about 0.2 MPa to completely
remove the air. The reactor was heated by external electrical
2. Experimental
2.1 Materials
Microcrystalline cellulose (MCC, average molecular weight: 90 000) resistance at a heating rate of 15 ꢁC minꢂ1 and its temperature
was purchased from Sigma-Aldrich and used without further was measured using a calibrated thermocouple. Aer the
purication. Other materials, namely, tungstic acid (H2WO4), reaction, the cellulose (W2) remaining in the reactor was
phosphotungstic acid hydrate (H3O40PW12$xH2O), tungstosilicic collected by centrifugation and used to calculate the cellulose
acid hydrate (H4[Si(W3O10)4]$xH2O), ruthenium chloride trihydrate conversion. The compositions of liquid-phase products were
(RuCl3$3H2O), rhodium chloride trihydrate (RhCl3$3H2O), chlor- analyzed by HPLC equipped with RID (Refractive Index
oplatinic acid hexahydrate (H2PtCl6$6H2O), nickel chloride hexa- Detector). The separation was realized on a column of Bio-Rad
hydrate (NiCl2$6H2O), palladium chloride (PdCl2), chloroauric acid HPX-87X column (8 ꢃ 300 mm) with 0.05 M H2SO4 aqueous
tetrahydrate (HAuCl4$4H2O), triblock copolymer-P123 (EO20PO70- solution as mobile phase, and each product (Wi) was quanti-
EO20), and tetraethyl orthosilicate (TEOS), were all purchased from ed using the external standard method. The conversion
Aldrich and used aer drying without any further treatment.
(wt%) of cellulose and selectivity of the desired product (wt%)
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were calculated as follows:
sample. This may be due to the accumulation of metal species
on the surface of the mesoporous material or deep into the
channel interior, thus hindering the interior channel of the
mesoporous material SBA-15 and resulting in smaller pore
volume. Moreover, the metal species loaded on SBA-15 will
partially block most of the micropores in the M/SBA-15 samples,
thereby increasing the average pore size. All these results indi-
cated that the metal phases were dispersed on the surface of the
SBA-15 support. According to Table 1, the specic surface areas
and total pore volumes of the Pd (Ni, Pt)/SBA-15 samples were
relatively low compared to those of the other samples, which
may be due to the accumulation of excess metal species on the
surface of the SBA-15 support.
W1 ꢂ W2
Conversionð%Þ ¼
Selectivityð%Þ ¼
ꢃ 100%
W1
Wi
ꢃ 100%
W1 ꢂ W2
3. Results and discussion
3.1 Catalyst characterization
The particle size distributions of the metal phase on the
surface of the SBA-15 support were determined by TEM images.
As shown in Fig. 3, the average particle size of different catalyst
was different. The average particle sizes of Rh and Ru on the
SBA-15 support were 5.78 nm and 4.25 nm, respectively (Fig. 3(c
and d)). However, the average particle sizes of Ni/SBA-15 and Pd/
SBA-15 were larger than 20 nm (Fig. 3(e and f)), which may be
due to the aggregation of metal species on the surface of SBA-
15.27 These results showed that the metal particles Au, Ru and
Rh have good dispersibility on the SBA-15 support, which is
consistent with the structural parameters of the different
samples obtained from the N2 adsorption–desorption
experiment.
Fig. 4 displays the H2-TPR proles of the SBA-15 and the M/
SBA-15 samples. As can be seen from Fig. 4, different M/SBA-15
catalysts showed the hydrogen desorption peaks at different
temperatures. This indicates that the metal species were
successfully loaded on the SBA-15 sample and had catalytic
hydrogenation capability. It is worth noting that the Ni (Pd)/
SBA-15 samples showed higher hydrogen desorption peaks
compared to those observed for the other catalysts, which may
be due to the accumulation of excess Ni and Pd metal species on
the surface of the SBA-15 support, which can be conrmed by
the TEM images.
The XRD patterns of the pure silica SBA-15 and M/SBA-15
samples are shown in Fig. 1. Three characteristic reection
peaks of the SBA-15 are present at 2q of 0.9ꢁ, 1.6ꢁ and 1.8ꢁ,
which were indexed as (100), (110) and (200) diffraction peaks,
respectively. The XRD proles matched well with the
hexagonally-structured SBA-15 sample reported by Zhao et al.25
Almost all of the patterns of the M/SBA-15 samples showed the
three peaks with high intensity, indicating that the hexagonal
mesostructure of the SBA-15 was well maintained even aer the
metal species were introduced.
Fig. 2 displays the N2 adsorption–desorption and corre-
sponding pore size distribution isotherms of the SBA-15 and M/
SBA-15 samples. It can be seen from Fig. 2(a) that all of the
samples exhibit type IV isotherms with an H1 type hysteresis
loop, which is a characteristic of mesoporous materials.26 This
indicates that the pure silica SBA-15 and all M/SBA-15 samples
had an ordered mesostructure. The textural parameters of
different samples are summarized in Table 1. It was found that
the SBA-15 material had high specic surface area (580 m2 gꢂ1),
but the surface areas of the M/SBA-15 samples were reduced
within the range of 394–482 m2 gꢂ1. Moreover, the M/SBA-15
samples exhibited smaller total pore volume and larger
average pore size compared to those of the pure silica SBA-15
3.2 Catalytic performance of the M-SBA-15 and H3PW12O40
binary system
The catalytic performances of the various binary catalysts
composed of M/SBA-15 and H3PW12O40 (TPA) were investigated
in the catalytic conversion of cellulose. Table 2 shows the
distribution of the main products, namely, ethylene glycol (EG),
sorbitol (SO), mannitol (MA), 1,2-propylene glycol (PG), and
glycerol (GY), obtained using different tested binary catalysts.
As can be seen from Table 2, cellulose was almost totally con-
verted even in the absence of M/SBA-15 catalysts (Entry 1),
indicating that TPA plays a key role in the cracking cellulose
reaction.
The EG selectivity signicantly improved when the M/SBA-15
catalysts were introduced (Entries 3–8). According to the liter-
ature,27 metal catalyst as a hydrogenation active centre has
a synergistic effect with the W compound, that is, the cellulose
is hydrolyzed by W compound, followed by the metal-catalyzed
hydrogenation of the formed intermediate products to obtain
Fig. 1 XRD patterns of the SBA-15 and M/SBA-15 samples.
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Fig. 2 (a) N2 adsorption–desorption isotherms and (b) BJH pore size distribution of SBA-15 and M/SBA-15 samples.
Table 1 Textural properties of SBA-15 and M/SBA-15 samples
SBETa (m2 gꢂ1
)
Dporesizeb (nm)
Vtotal (cm3 gꢂ1
)
Vmicrod (cm3 gꢂ1
)
Vmesoe (cm3 gꢂ1
)
Metal contentf (wt%)
c
Entry
Catalyst
1
2
3
4
5
6
7
SBA-15
580
422
409
482
436
398
394
7.25
7.32
7.30
7.36
7.33
7.26
7.32
1.15
0.94
0.89
0.97
0.98
0.88
0.9
0.01
0.01
0.02
0.02
0.01
0.01
0.02
1.14
0.93
0.87
0.95
0.97
0.87
0.88
—
Au/SBA-15
Pt/SBA-15
Rh/SBA-15
Ru/SBA-15
Ni/SBA-15
Pd/SBA-15
9.3
9.5
9.8
9.5
9.8
9.7
a
From N2 absorption measurement (BET method). b Average pore diameter calculated by BJH methods. c Total pore volumes were obtained at P/P0
¼ 0.99. d Micropore volume was calculated using the t-plot method. e Mesopore volume calculated as VMeso ¼ VTotal ꢂ VMicro
measured from ICP-AES measurements.
.
Metal content was
f
the EG product. Scheme 1 depicts the possible reaction routes to glucose, (R2) retro-aldol condensation of glucose to form
involved in cellulose conversion to polyols. The main reaction glycolaldehyde (GA), and (R3) the hydrogenation of GA to form
route for the EG formation involves (R1) hydrolysis of cellulose EG.28 Such a reaction route indicates the importance of the
Fig. 3 TEM images of M/SBA-15 (scale bar, 100 nm): (a) Au/SBA-15; (b) Pt/SBA-15; (c) Rh/SBA-15; (d) Ru/SBA-15; (e) Ni/SBA-15; (f) Pd/SBA-15.
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catalyst of Ru/SBA-15 and TPA was used (Entry 5), whereas the
worst selectivity to EG (11%) was observed when using Au/SBA-
15 and TPA as the binary catalyst (Entry 8). Our results indicate
that the binary catalyst of Ru/SBA-15 and TPA achieve higher EG
selectivity than that obtained in a previous report. Ribeiro et al.
reported that the EG yield reached the 34.8% using Ru–W/CNT
as the catalyst.29 Moreover, the selectivity to EG for the catalysts
such as Pd, Ni and Pt modied-SBA-15 were 31.8%, 29.2% and
24.4% (Entries 3–4 and 7), respectively, which is lower than that
obtained for the other metal phase modied-SBA-15 catalysts
such as Ru and Rh modied-SBA-15. Based on the above N2
adsorption–desorption analysis results, Ru (Rh)-SBA-15 catalyst
has larger BET surface area and pore volume than the other
metal phase modied-SBA-15, indicating that the hydrogenated
molecules can more easily contact with hydrogenation active
sites in the Ru (Rh)-SBA-15 catalyst. Moreover, the TEM images
could provide additional clues for the EG selectivity from the
dispersion of metal phase on the SBA-15 support. Ru and Rh
metal particles were well dispersed on the surface of the SBA-15,
but Ni, Pd and Pt-modied catalysts showed distinct dark zones
on the TEM images due to the metal particles aggregation. As
shown in Table 2, it was found that the order of EG selectivity
for M/SBA-15 metal element catalyst was Ru > Rh > Ni > Pd > Ni >
Pt > Au.
Fig. 4 H2-TPR profiles of the SBA-15 and M/SBA-15 samples.
Table
2 The selectivity of the main polyols from the cellulose
conversion over the different binary catalystsa
Selectivity/%
Conversion/% EG SO MA PG
Entry Catalyst/g
GY
1
2
3
4
5
6
7
8
TPA
Ru/SBA-15
100
98
0
0
0
0
0
1.4
0
1.4
13.0 1.0
31.8
29.2
55.5 9.9 2.1 2.6
35.5 3.8 6.8 6.2
24.4 1.2 0.4 10.3 1.5
11.0 0.5 12.6
Pd/SBA-15 + TPA 100
Ni/SBA-15 + TPA 100
Ru/SBA-15 + TPA 100
Rh/SBA-15 + TPA 100
Pt/SBA-15 + TPA 100
Au/SBA-15 + TPA 100
0
0
2.2 11.3 2.0
0.3 10.6 1.9
3.3 Effects of combination of M/SBA-15 with various W
species on the selectivity of polyols and EG product
5.5
2.2
Fig. 5 shows the effect of different binary catalysts on the
selectivity of the polyols, EG and the distribution of the polyol
products. According to Fig. 5(a), it was found that different W
compounds, namely, H2WO4 (TA), H3PW12O40 (TPA) and
H4SiW12O40 (TSA) have an important impact on the selectivity of
polyols. For example, when using TA, TPA and TSA in combi-
nation with Pt/SBA-15 as binary catalysts, the polyols selectivity
were 35.9%, 47.3% and 65.2%, respectively. The results suggest
that W compounds play a key role in the selective formation of
polyols from cellulose. This can be explained by the fact that
the W compounds with acid sites can promote the hydrolysis
0
0
a
Reaction conditions: 0.5 g of cellulose; 0.1 g of catalyst; 0.02 g of
H3PW12O40 (TPA); 25 mL H2O; reaction temperature, 245 ꢁC; reaction
time, 4 h; H2 pressure, 5 MPa.
binary catalyst in the selective formation of EG from cellulose.
From Table 2, it is observed that different combinations of the
binary catalyst have a signicant impact on the selectivity of EG.
The best selectivity to EG (55%) was observed when the binary
Scheme 1 Catalytic conversion for cellulose into polyols.
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that Ru/SBA-15 exhibit excellent catalytic performance in the
selective formation of polyols. This may be due to the fact that
Ru particles are well dispersed on the SBA-15 support to form
more hydrogenation active sites (seeing Fig. 3(d)).
The effect of different binary catalysts on the EG selectivity
was investigated, and the detailed results are shown in Fig. 5(b).
It was found that the binary catalyst of Ru/SBA-15 and TPA gave
the highest EG selectivity (55.5%), whereas the EG selectivity of
46.5% and 24.0% were obtained when the Ru/SBA-15 was
combined with TA and TSA, respectively. This indicates that the
combination of Ru/SBA-15 and TPA show better synergy in the
selective formation of EG from cellulose than other binary
catalysts. In order to further shed light on the potential of the
Ru/SBA-15 catalyst in the catalytic conversion of cellulose, the
effect of binary catalyst of Ru/SBA-15 and different
W
compounds on the distribution of polyol products was investi-
gated. As shown in Fig. 5(c), the addition of W compounds can
effectively improve the polyol products selectivity, particularly
the EG selectivity, which increases from 13.0% to 55.5% aer
the addition of TPA. At the same time, it can be seen that
regardless of which W compound was used in combination with
Ru/SBA-15, EG was always predominant product. These results
indicate that W compounds play an important role in the
selective formation of EG from cellulose. It is worth noting that
the lower EG selectivity (24.0%) and higher SO selectivity
(19.6%) were observed when using TSA and Ru/SBA-15 as the
binary catalyst. The reason for higher SO selectivity and lower
EG selectivity can be explained as follows: TSA catalyze the
cleavage of C–C bonds of cellulose by retro-aldol reaction, but it
is less active to C–C breaking reaction of cellulose so that it
results in lower EG selectivity.13 Based on the above analysis, we
can conclude that the EG selectivity depended on the W
compounds in the presence of the Ru/SBA-15 in the following
order: TSA < TA < TPA. These results show the potential of the
binary catalyst of Ru/SBA-15 and TPA in the selective formation
of EG from cellulose. As Ru/SBA-15 and TPA system has good
selectivity to EG, the binary catalyst was chosen for the further
study.
3.4 The effect of reaction conditions on the distribution of
main products
In order to improve the EG selectivity, the reaction conditions
for the catalytic conversion of cellulose using the binary catalyst
of Ru/SBA-15 and TPA as catalyst were investigated. Fig. 6 shows
the effect of catalyst dosage on the distribution of polyol prod-
ucts. Fig. 6(a) displays the effect of the Ru/SBA-15 dosage on the
distribution of polyol products. As shown in Fig. 6(a), the
selectivity of EG increased with the increase in the Ru/SBA-15
dosage from 0.0 g to 0.1 g. When the catalyst Ru/SBA-15
dosage was 0.1 g, EG selectivity reached the maximum of
55.5%. However, when the Ru/SBA-15 dosage was 0.14 g, the
selectivity of EG decreased to 49.3%. This can be explained by
the fact that the more the amount of Ru/SBA-15, the faster
would be the reaction for EG hydrogenolysis.11 Therefore, the
optimal the amount of Ru/SBA-15 seems to be 0.1 g. Fig. 6(b)
shows the effect of the TPA dosage on the distribution of polyol
Fig. 5 The selectivity of the polyols and EG as well as the main
products for the catalytic conversion cellulose ((a): polyols selectivity;
(b): EG selectivity; (c): product selectivity). Reaction conditions: 0.5 g of
cellulose; 0.1 g of M/SBA-15; 0.02 g of W compound; 25 mL H2O;
reaction temperature, 245 ꢁC; reaction time, 4 h; H2 pressure, 5 MPa.
and C–C breaking reactions of cellulose. Interestingly, regard-
less of the type of W compounds used, the polyols selectivity is
always high in the presence of Ru/SBA-15 catalyst, indicating
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Fig. 6 The effect of catalyst dosage on the selectivity of the main products (a) 0.5 g of cellulose; 0.02 g of TPA; 25 mL H2O; reaction temperature,
245 ꢁC; reaction time, 4 h; H2 pressure, 5 MPa. (b) 0.1 g of Ru/SBA-15 and the other reaction conditions were the same as (a) above mentioned.
Fig. 7 The effect of reaction temperature and time on the selectivity of the main products (a) 0.5 g of cellulose; 0.1 g of Ru/SBA-15; 0.02 g of
TPA; 25 mL H2O; reaction temperature, 245 ꢁC; H2 pressure, 5 MPa. (b) Reaction time, 4 h, and the other reaction conditions were the same as (a).
products. According to Fig. 6(b), when only Ru/SBA-15 was used, provide more energy for the cleavage of C–C bond of sugar
the polyol products such as EG, SO and MA were produced from intermediates.30 When the temperature was increased to 255 ꢁC,
the C–C breaking reaction of cellulose. This indicates that Ru- the selectivity for EG decreased to 47.3%. This may be due to the
SBA-15 not only possesses hydrogenation properties, but also deactivation of active sites or the degradation of EG product at
has hydrogenolysis ability. Compared with no TPA, the addition higher temperature. Therefore, the optimum operating
ꢁ
of TPA can greatly improve the EG selectivity. For example, temperature was set as 245 C. Fig. 7(b) displays the effect of
when the amount of TPA was 0.02 g and on xing the amount of reaction time on the distribution of polyol products. When the
Ru/SBA-15 at 0.1 g, EG selectivity was enhanced from 13.0% to reaction time was increased from 2.0 h to 4.0 h, the EG selec-
55.5%. Nevertheless, when the TPA dosage was 0.03 g, the EG tivity increased from 48.2% to 55.5%, respectively. With pro-
selectivity decreased to 51.2%. Similar to the inuence of the longed reaction time, the selectivity to EG decreased from
Ru/SBA-15 content, the selectivity for EG also showed a volcano 55.5% to 52.1%. This is ascribed to the long reaction time
curve with the change in the amount of TPA, signifying that favoring side reactions such as hydrogenolysis of EG.11 There-
a good balance between Ru/SBA-15 and TPA is required. Based fore, the optimum reaction conditions for EG selectivity were as
ꢁ
on the above results, the binary catalyst combination of 0.1 g follows: Ru/SBA-15: 0.1 g; TPA: 0.02 g; 245 C, 4 h. Under the
Ru/SBA-15 and 0.02 g TPA shows the best catalytic performance abovementioned conditions, the EG selectivity reached nearly
for EG selectivity from catalytic conversion cellulose.
55.5%.
The plot showing the effect of reaction temperature on the
distribution of polyol products is displayed in Fig. 7(a). As the
ꢁ
ꢁ
4. Conclusion
reaction temperature increased from 225 C to 245 C, the EG
selectivity increased from 50.4% to 55.5%, respectively. This
might be due to the fact that more H+ was produced from hot
compressed water at higher temperature to promote the
conversion of cellulose, and/or the higher temperature might
The direct catalytic conversion of cellulose into EG was inves-
tigated over the various binary catalysts composed of M/SBA-15
and W compounds. A remarkable advantage of these binary
catalysts was that it not only led to a nearly 100% conversion of
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cellulose, but also gave the higher selectivity for EG. Among the
binary catalysts, Ru/SBA-15 and TPA system showed the excel-
lent performance for EG selectivity (about 55.5%). More
importantly, compared with single catalyst, the use of the binary
9 J. N. Chheda, G. W. Huber and J. A. Dumesic, Liquid-Phase
catalytic processing of biomass-derived oxygenated
hydrocarbons to fuels and chemicals, Angew. Chem., Int.
Ed., 2007, 46, 7164–7183.
catalyst can signicantly improve the EG selectivity due to the 10 H. Yue, Y. Zhao, X. Ma and J. Gong, Ethylene Glycol:
synergistic effect between M/SBA-15 and W compounds. More-
over, the SBA-15 mesoporous material, which has a large surface
Properties, Synthesis, and Applications, Chem. Soc. Rev.,
2012, 41, 4218–4424.
area and ordered hexagonal mesopore, facilitates not only the 11 Z. Tai, J. Zhang, A. Wang, J. Pang, M. Zheng and T. Zhang,
high dispersion of metal element but also the transport of
reactant and product molecules. Taking into account that the
raw material used is cellulose and the importance of EG in the
Catalytic conversion of cellulose to ethylene glycol over
a low-cost binary catalyst of Raney Ni and tungstic acid,
Chemsuschem, 2013, 6, 652–658.
petrochemical industry, the new binary catalyst of Ru/SBA-15 12 C. Luo, S. Wang and H. Liu, Cellulose conversion into
and TPA is a promising candidate for the production of EG
from cellulose in the future.
polyols catalyzed by reversibly formed acids and supported
ruthenium clusters in hot water, Angew. Chem., 2007, 119,
7780–7783.
13 Z. Tai, J. Zhang, A. Wang, M. Zheng and T. Zhang,
Conflicts of interest
Temperature-controlled
phase-transfer
catalysis
for
There are no conicts to declare.
ethylene glycol production from cellulose, Chem. Commun.,
2012, 48, 7052–7054.
14 N. Ji, T. Zhang, M. Zheng, A. Wang, H. Wang, X. Wang and
J. G. Chen, Direct Catalytic conversion of cellulose into
ethylene glycol using nickel-promoted tungsten carbide
catalysts, Angew. Chem., Int. Ed., 2008, 47, 8510–8513.
Acknowledgements
This study was nancially supported by the Natural Science
Foundation of China (31370570 and 31100430), the Taishan
Scholars Projects of Shandong (ts201511033), the Key R&D 15 Y. Zhang, A. Wang and T. Zhang, A new 3D mesoporous
Project of Shandong (2017GGX40106), and the People's Liveli-
hood Science and Technology Project of Qingdao (173383NSH).
The authors are also grateful for the experimental conditions
carbon replicated from commercial silica as a catalyst
support for direct conversion of cellulose into ethylene
glycol, Chem. Commun., 2010, 46, 862–864.
which the Polyphase Fluid Reaction and Separation Engi- 16 M. Y. Zheng, A. Q. Wang, N. F. Pang, X. D. Wang and
neering Key Laboratory of the Shandong give.
T. Zhang, Transition metal-tungsten bimetallic catalysts
for the conversion of cellulose into ethylene glycol,
ChemSusChem, 2010, 3, 63–66.
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