Mesoporous H-ZSM-5 as an efficient catalyst for conversions of cellulose and cellobiose into methyl glucosides in methanol

Article abstract of DOI:10.1016/j.cattod.2016.01.055

The alcoholysis of cellobiose, which is a dimer of glucose and a model molecule of cellulose, has been studied in methanol medium in the presence of various solid acids. Zeolite H-ZSM-5 was found to be highly efficient for the conversion of cellobiose into methyl glucosides (including methyl-α-glucoside and methyl-β-glucoside) in methanol. The Br?nsted acidity plays a key role in the catalytic alcoholysis of cellobiose. H-ZSM-5 with a lower Si/Al ratio (20) possessed higher density of acidic sites afforded a higher methyl glucoside yield (53%) for the conversion of cellobiose at 423 K. The introduction of mesoporosity into the zeolite significantly enhanced its catalytic performance. Methyl glucosides with a yield of 73% were achieved from cellobiose over a mesoporous H-ZSM-5 (H-meso-ZSM-5-0.5 M) sample with an average mesopore size of 6.1 nm. The mesoporous ZSM-5 could also catalyze the direct transformation of cellulose in methanol, providing methyl glucosides with yields of 51% at 463 K. Our comparative studies revealed that the alcoholysis of cellulose in methanol proceeded more efficiently than the hydrolysis of cellulose in water under similar reaction conditions.

Full text of DOI:10.1016/j.cattod.2016.01.055

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Mesoporous H-ZSM-5 as an efficient catalyst for conversions of
cellulose and cellobiose into methyl glucosides in methanol
Laiqi Xue , Kang Cheng , Hongxi Zhang , Weiping Denga,∗, Qinghong Zhanga,
Ye Wang
a
a,b
a
b
a,∗
State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, National Engineering
Laboratory for Green Chemical Productions of Alcohols, Ethers and Esters, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen
3
61005, Fujian, China
b
Department of Chemistry and Applied Chemistry, Changji University, Changji 831100, Xinjiang, China
a r t i c l e i n f o
a b s t r a c t
Article history:
The alcoholysis of cellobiose, which is a dimer of glucose and a model molecule of cellulose, has been
studied in methanol medium in the presence of various solid acids. Zeolite H-ZSM-5 was found to be
highly efficient for the conversion of cellobiose into methyl glucosides (including methyl-␣-glucoside
and methyl-␤-glucoside) in methanol. The Brønsted acidity plays a key role in the catalytic alcoholysis of
cellobiose. H-ZSM-5 with a lower Si/Al ratio (20) possessed higher density of acidic sites afforded a higher
methyl glucoside yield (53%) for the conversion of cellobiose at 423 K. The introduction of mesoporos-
ity into the zeolite significantly enhanced its catalytic performance. Methyl glucosides with a yield of
Received 30 October 2015
Received in revised form 15 January 2016
Accepted 19 January 2016
Available online xxx
Keywords:
Mesoporous zeolite
Solid acid catalyst
Cellulose
Cellobiose
Alcoholysis
7
3% were achieved from cellobiose over a mesoporous H-ZSM-5 (H-meso-ZSM-5-0.5 M) sample with an
average mesopore size of 6.1 nm. The mesoporous ZSM-5 could also catalyze the direct transformation of
cellulose in methanol, providing methyl glucosides with yields of 51% at 463 K. Our comparative studies
revealed that the alcoholysis of cellulose in methanol proceeded more efficiently than the hydrolysis of
cellulose in water under similar reaction conditions.
Methyl glucosides
©
2016 Elsevier B.V. All rights reserved.
1
. Introduction
Cellulase enzymes are known to catalyze the hydrolysis of cel-
lulose with high efficiency under mild conditions [13]. However,
this enzymatic process is limited by the high cost of enzyme, low
productivity, and complex handling procedure. Thus, many studies
have been devoted to the development of chemocatalytic processes
Catalytic transformation of renewable and inedible lignocellu-
losic biomass into chemicals and fuels represents a promising route
for establishing the sustainable chemistry society [1–8]. Cellulose
is the most abundant component in the lignocellulosic biomass.
The efficient conversion of cellulose into chemicals is of essential
importance for the utilization of lignocellulosic biomass and has
attracted much attention in recent years [3,5,6,8–12]. Cellulose is a
crystalline polymer of d-glucose linked by ␤-1,4-glycosidic bonds.
Because of such linkage and the presence of numerous hydroxyl
groups, there exist extensive hydrogen-bonding networks in cel-
lulose, making the crystalline structure of cellulose robust [8].
Therefore, the selective transformation of cellulose into target
products under mild conditions is highly challenging.
for the hydrolysis of cellulose. Although mineral acids (e.g., H SO4
2
and HCl) showed high performances for the hydrolysis of cellulose,
these homogeneous systems still suffer from problems of the prod-
uct/catalyst separation, reactor corrosion, catalyst recycling, and
treatment of waste effluents. Solid acid catalysts such as carbon
materials bearing SO H groups [14–17], sulfonated resins or metal
3
oxides [18–20], layered metal oxides [21], phosphates [22], and
modified graphene oxides [23] have been reported for the hydroly-
sis of cellulose. High yields of glucose could be attained by using
solid materials bearing SO H groups with strong acidity. How-
3
ever, severe leaching of the SO H groups occurred in most cases
3
under hydrothermal conditions. Moreover, because of the presence
of highly reactive groups (i.e., aldehyde and hydroxyls), glucose
is unstable in hot water. Many side reactions, including isomer-
ization, dehydration, rehydration, retro-aldol, and polymerization,
may take place, thereby significantly decreasing the selectivity
∗ Corresponding authors. Fax: +86 592 2183047.
E-mail addresses: dengwp@xmu.edu.cn (W. Deng), wangye@xmu.edu.cn
Y. Wang).
(
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920-5861/© 2016 Elsevier B.V. All rights reserved.
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Please cite this article in press as: L. Xue, et al., Mesoporous H-ZSM-5 as an efficient catalyst for conversions of cellulose and cellobiose
into methyl glucosides in methanol, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.01.055

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Scheme 1. Conversions of cellulose and cellobiose into methyl glucosides in methanol.
of glucose. In this context, one promising strategy is to develop
bi- or multifunctional catalysts for the transformation of cellulose
into more stable and valuable chemicals such as polyols [24–30],
gluconic acid [31,32], and hydroxymethylfurfural (HMF) [33,34]
through glucose intermediate. For instance, noble metals (e.g., Pt
and Ru) in combination with solid materials containing acidic sites
attracted much attention for the conversion of larger molecules
in recent years [40,41]. We synthesized mesoporous ZSM-5 and
mesoporous Y zeolites, and demonstrated that these mesoporous
zeolites were promising for Fischer–Tropsch synthesis [42–44].
Since cellobiose and cellulose are relatively large molecules, we
expect that the hierarchical zeolites would be suitable for the con-
versions of these molecules. In the present work, we will investigate
the effect of mesoporosity as well as acidity of ZSM-5-based cata-
lysts on their catalytic behaviors for the conversions of cellobiose
and cellulose.
(
e.g., ␥-Al O , carbon nanotubes, and polyoxometalates) were used
2 3
as bifunctional catalysts to catalyze the hydrolysis-hydrogenation
of cellulose to sorbitol and mannitol [24–26]. The reversibly gener-
+
ated H O in hot water combined with Ru/AC (AC: activated carbon)
3
could also convert cellulose into sorbitol [27]. The tungsten-based
catalysts with C C bond cleavage function were used to catalyze
the conversion of cellulose into ethylene or propylene glycols
2. Experimental
[
28–30].
In our previous work, we proposed a strategy to increase the
2.1. Catalyst preparation
selectivity of monosaccharides by using alcohol medium instead
of water medium. We demonstrated that cellulose could be con-
verted efficiently to methyl or ethyl glucosides (including ␣- and
Cellobiose and cellulose were obtained from J&K Chemicals.
SiO , Al O , and H PW12O40 were purchased from Alfa Aesar.
2
2
3
3
Zeolites including H-ZSM-5, H-MOR, H-MCM-22, and H-Y were
purchased from Nankai University Catalyst Co. Mesoporous ZSM-
5 samples were prepared by treating the parent Na-ZSM-5 with
aqueous solutions of NaOH with different concentrations [43].
The desilication occurred and the samples with different mean
sizes of mesopores could be obtained [43]. The Na-form meso-
porous zeolites were then exchanged to their H-forms by a typical
␤
- isomers) in methanol or ethanol in the presence of Keggin-
type heteropolyacids (i.e., H PW12O40 and H SiW12O40) [35,36].
3
4
Besides methanol and ethanol, long chain alcohols were also
employed for the alcoholysis of cellulose. For example, by using
ionic liquids (ILs) as solvents, Corma and co-workers succeeded in
the transformation of cellulose into butyl-, hexyl-, octyl-, decyl-,
and dodecyl-glycosides in the presence of an acidic resin cata-
lyst (i.e., Amberlyst-15) [37,38]. The highest octyl-glycoside yield
could reach 82% after a reaction at 363 K for 1.5 h [37]. A catalyst
combining an IL with polyoxometalates, i.e., polyvinylpyrrolidone-
stabilized heteropolyacid (PVP–HPA), was demonstrated to be
efficient for the alcoholysis of cellulose in butanol [39]. This com-
bined catalytic system provided >87% conversion of cellulose and
ion-exchange method with an aqueous solution of NH NO3 (con-
4
centration, 1.0 M), followed by drying and calcination in air at 823 K.
The obtained samples were subsequently subjected to acid treat-
ment in an aqueous solution of HNO3 (concentration, 0.1 M) at
3
38 K for 6 h to remove the non-framework aluminium species pos-
sibly formed during the desilication process. The finally obtained
samples were denoted as H-meso-ZSM-5-xM, where x was the
concentration of NaOH aqueous solution.
∼90% selectivity of butyl glucosides at 428 K. However, the gradual
leaching of acid sites occurred during the reaction. ILs are effec-
tive to dissolve cellulose and can enhance the alcoholysis, but they
are still expensive, making their practical application less attrac-
tive. The use of a cheaper alcohol as the reaction medium for the
production of alkyl glucosides is a promising route for the practical
transformation of cellulose. The development of stable and efficient
heterogeneous catalysts for the alcoholysis of cellulose under mild
conditions remains a challenging goal.
The present work contributes to the development of hetero-
geneous catalysts for the efficient alcoholysis of cellulose and
cellobiose to methyl glucosides (including methyl-␣-glucoside
and methyl-␤-glucoside) in methanol under mild conditions
2
.2. Catalyst characterization
X-ray diffraction (XRD) patterns were recorded on a Panalyt-
ical X’pert Pro Super X-ray diffractometer with Cu K␣ radiation
40 kV and 30 mA). Transmission electronic microscopy (TEM) mea-
(
surements were carried out on a JEM-2100 electron microscope
operated at an acceleration voltage of 200 kV. Nitrogen physisorp-
tion at 77 K was performed with a Micromeritics ASAP 2010 M
instrument. The sample was pretreated at 573 K in vacuum for
3
h prior to N2 adsorption. The surface area was calculated using
the Brunauer–Emmett–Teller (BET) method in a pressure range of
P/P = 0.05–0.3. The pore size distribution in the mesoporous region
was determined by the Barrett–Joyner–Halenda (BJH) method
(Scheme 1). We will show that zeolite H-ZSM-5 is an excellent
0
solid acid catalyst for the catalytic conversion of cellobiose. The
effect of acidity on catalytic performances will be investigated by
changing the Si/Al ratio in H-ZSM-5. Moreover, hierarchical zeolites
containing both micropores and mesopores, which combine the
advantages of zeolites (with strong acidity and high stability) and
mesoporous materials (with efficient mass transportation), have
[
45] and that in the microporous region was evaluated by the
Horváth–Kawazoe (HK) method [46]. The microporous volume was
estimated by the t-plot method [47].
The ammonia temperature-programmed desorption (NH -TPD)
3
was performed on a Micromeritics AutoChem 2920 II instrument.
Please cite this article in press as: L. Xue, et al., Mesoporous H-ZSM-5 as an efficient catalyst for conversions of cellulose and cellobiose
into methyl glucosides in methanol, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.01.055

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Table 1
3
Conversion of cellobiose catalyzed by H-ZSM-5 with different Si/Al ratios.
Catalystsa
Density of acid sitesb (mmol g )Conv. (%)Yieldc (%)
−1
TONd
–
3.16.7
2.68.6
2.27.8
M-␤-GM-␣-GML
Blank
–
<5
61
50
43
30
11
0
18
13
10
4.2 11
1.6 3.6
0
35
24
22
0
H-ZSM-5 (20) 0.46
H-ZSM-5 (50) 0.25
H-ZSM-5 (80) 0.24
H-ZSM-5 (120)0.14
H-ZSM-5 (260)0.07
0
0
6.3
4.3
Reaction conditions: W(cellobiose) = 0.20 g, W(catalyst) = 0.10 g, V(CH3OH) = 20 mL,
P(N2) = 3 MPa, T = 423 K, t = 4 h.
a
The number in the parenthesis after H-ZSM-5 denotes the Si/Al ratio.
Evaluated from NH3-TPD results in Fig. 2.
M-␣-G, M-␤-G, and ML denote methyl-␣-glucoside, methyl-␤-glucoside, and
b
c
methyl levulinate, respectively.
d
TON was calculated by the mole of methyl glucosides formed per mole of acid
Fig. 1. Yields of methyl glucosides in the conversion of cellobiose with dif-
ferent catalysts. Reaction conditions: W(cellobiose) = 0.20 g, W(catalyst) = 0.050 g,
V(CH3OH) = 20 mL, P(N2) = 3 MPa, T = 423 K, t = 4 h. The number in the parenthesis
denotes the Si/Al ratio.
sites.
Typically, the sample loaded in a quartz reactor was first pretreated
with He at 623 K for 1 h. After the sample was cooled to 373 K in
He gas flow, NH3 adsorption was performed by switching the He
flow to a NH –He (10 vol% NH ) gas mixture and then keeping
3
3
at 373 K for 1 h. The gas phase or the weakly adsorbed NH3 was
purged by high-purity He at the same temperature. NH -TPD was
3
performed in the He flow by raising the temperature to 973 K at a
−1
rate of 10 K min , and the desorbed NH molecules were detected
3
by ThermoStar GSD 301 T2 mass spectrometer with the signal of
m/e = 16.
2.3. Catalytic reaction
The conversions of cellulose and cellobiose were performed in
3
a Teflon-lined stainless-steel autoclave with a volume of 75 cm .
After the catalyst (typically 0.050 g) and cellobiose (typically 0.20 g,
equivalent to 1.2 mmol C H O5 unit) were added into the auto-
clave pre-charged with methanol (typically 20 cm ), N2 with a
pressure of 3.0 MPa was introduced. The reaction was started by
heating the mixture to a reaction temperature. After a certain time
Fig. 2. NH3-TPD profiles of H-ZSM-5 samples with different Si/Al ratios. (a) H-ZSM-
5
(20), (b) H-ZSM-5 (50), (c) H-ZSM-5 (80), (d) H-ZSM-5 (200), (e) H-ZSM-5 (260).
6
10
The number in the parenthesis denotes the Si/Al ratio.
3
displayed in Fig. 1 except for SiO , which does not possess acidity,
2
(
4 h), the reaction was stopped by cooled water, and the products
can also catalyze the conversion of cellobiose into methyl gluco-
sides. H-form zeolites including H-ZSM-5, H-Y, H-MCM-22, and
H-MOR with Brønsted acidity were more efficient for the formation
of methyl glucosides from cellobiose than Al O , which possessed
were analyzed by HPLC (Shimazu LC-20A) equipped with a RI detec-
TM
tor and a Shodex
SH1011 column (10 ␮m, 6.5 × 300 mm). The
conversion of cellulose was calculated by the change of the weight
of cellulose after the reaction. The yield of a product was defined
as the percentage of the molar amount of the target product in the
2
3
mainly Lewis acidity. Among all the solid acid catalysts investi-
gated, H-ZSM-5 afforded the highest yield to methyl glucosides
(53%). H-Y, H-MCM-22, and H-MOR produced methyl glucosides
with yields of 10–30% under the same reaction conditions.
To gain insights into the role of acidity, we investigated the
catalytic performances of H-ZSM-5 samples with different Si/Al
ratios for the transformation of cellobiose in methanol. As shown
in Table 1, the decrease in Si/Al ratio increased the conversion of
cellobiose and the yields of both methyl ␣- and ␤-glucosides. A
higher yield of methyl glucosides was attained over H-ZSM-5 with a
lower Si/Al ratio. Over the H-ZSM-5 with a lower Si/Al ratio (20–80),
methyl levulinate was also formed as a by-product. This suggests
the occurrence of the consecutive degradation of methyl glucosides
(Scheme 1).
total molar amount of C H10O5 unit in cellulose or cellobiose.
6
3
. Results and discussion
3.1. Catalytic behaviors of H-ZSM-5 for the conversion of
cellobiose in methanol
We investigated the catalytic performances of metal oxides
(
i.e., SiO , Al O ), zeolites (H-ZSM-5, H-MOR, MCM-22, H-Y), and
2 2 3
a heteropolyacid (H PW12O40) for the conversion of cellobiose
3
in methanol at 423 K. No products were observed in absence
of a catalyst. Among the catalysts investigated, the Keggin-type
H PW12O40, a strong Brønsted acid, showed the highest yield of
3
We characterized the acidity of H-ZSM-5 samples with differ-
methyl glucosides (82%, including ␣ and ␤ isomers) from cel-
lobiose (Fig. 1). High activities of heteropolyacid in the conversions
of cellobiose and cellulose were already reported in our previous
ent Si/Al ratios by NH -TPD. Fig. 2 displays that all the H-ZSM-5
3
samples exhibit two NH3 desorption peaks at around 500 K and
750 K. The lower and higher temperature desorption peaks could
be assigned to hydrogen-bonded NH3 molecules and the NH3
molecules chemisorbed on Brønsted acid sites, respectively [48].
The intensities of both peaks decreased markedly with increasing
papers [35,36]. Although promising, H PW12O40 is highly soluble
3
in methanol, and this makes its recovery and isolation from the
reaction solution not easy. It is of interest that the solid catalysts
Please cite this article in press as: L. Xue, et al., Mesoporous H-ZSM-5 as an efficient catalyst for conversions of cellulose and cellobiose
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Fig. 3. TEM images. (a) H-ZSM-5, (b) H-meso-ZSM-5-0.3 M, (c) H-meso-ZSM-5-0.5 M, (d) H-meso-ZSM-5-1.0 M.
the Si/Al ratio, indicating a decrease in the density of acid sites.
Table 1 shows that the TON was in a range of 6.3–8.6 except for the
sample with a Si/Al ratio of 260.
Since the Brønsted acid sites would play key roles in the conver-
sion of cellobiose or cellulose, we have estimated the density of
Brønsted acid sites on the H-ZSM-5 sample from the high tempera-
3.2. Synthesis and characterizations of mesoporous H-ZSM-5
ture peak in NH -TPD profiles. As displayed in Table 1, the density of
3
−
1
Brønsted acid sites decreased gradually from 0.46 to 0.07 mmol g
It is known that the Brønsted acid sites are predominantly
located inside the micropores of zeolites. The micropore size of
with an increase in the Si/Al ratio from 20 to 260. The correlation
of this trend with that for the catalytic performance (Table 1) sug-
gests that the Brønsted acid site is responsible for the conversion of
cellobiose. Based on the density of the Brønsted acid site, we have
further calculated the turnover number (TON) for the formation of
methyl glucosides, i.e., the moles of methyl glucosides formed per
mole of acidic sites, for each H-ZSM-5 catalyst. The result listed in
H-ZSM-5 (∼0.55 nm) is close to the diameter of a glucose unit
(
∼0.58 nm). The diffusion of cellobiose, which is a dimer of glucose,
into the micropores of H-ZSM-5 may be limited. This may limit the
increase in the yield of methyl glucosides over the H-ZSM-5 with
a higher density of Brønsted acid sites. Actually, the TON for the
H-ZSM-5 with a Si/Al ratio of 20 became lower than that for the
Table 2
Textural properties of mesoporous H-ZSM-5.
SBETa (m g
2
−1
)
Smicrob (m g
2
−1
)
Sexterc (m g
2
−1
)
Smesod (m g
2
−1
)
Vtotale (cm g
3
−1
)
Vmicrof (cm g
3
−1
)
Vmesog (cm g
3
−1
)
Dmesoh (nm)
Sample
H-ZSM-5
354
373
416
395
304
241
241
210
50
132
175
186
29
116
164
196
0.18
0.23
0.33
0.49
0.13
0.11
0.11
0.10
0.04
0.13
0.25
0.46
–
H-meso-ZSM-5-0.3M
H-meso-ZSM-5-0.5M
H-meso-ZSM-5-1.0M
4.2
6.1
13
a
BET surface area.
b
Microporous surface area evaluated by the t-plot method.
External surface area evaluated by the t-plot method.
Mesoporous surface area valuated by the BJH method.
Total pore volume evaluated by the single-point desorption at P/P0 = 0.975.
Microporous volume evaluated by the t-plot method.
c
d
e
f
g
h
Mesoporous volume evaluated by the BJH method.
Mean pore diameter for mesopores evaluated by the BJH method.
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Fig. 5. XRD patterns. (a) H-ZSM-5, (b) H-meso-ZSM-5-0.3 M, (c) H-meso-ZSM-5-
.5 M, (d) H-meso-ZSM-5-1.0 M.
Fig. 4. N2 adsorption-desorption isotherms and pore size distributions (inset) for
the H-ZSM-5 and mesoporous H-meso-ZSM-5 (20)-xM samples.
0
sample with a Si/Al ratio of 50. Thus, the introduction of meso-
porosity would be helpful in enhancing the catalytic performance
by accelerating the diffusions of reactants and products.
of NaOH aqueous solution led to a decrease in the microporous vol-
ume and microporous surface area, which were estimated by the
t-plot method [47]. Meanwhile, the mesoporous surface area and
mesoporous volume, calculated by the BJH method, increased sig-
nificantly (Table 2). These results further confirmed the generation
of mesopores during the desilication by NaOH aqueous solutions.
It should be mentioned that the mesoporous surface area was very
similar to the external surface area evaluated by the t-plot method
We synthesized mesoporous ZSM-5 samples with different
mesopore sizes by post-treating crystalline Na-ZSM-5 with a Si/Al
ratio of 20 in NaOH aqueous solutions with different concentra-
tions at 343 K, followed by ion exchange to transform the Na-form
samples into H-form samples. The H-form mesoporous samples
were denoted as H-meso-ZSM-5-xM, where x was the concen-
tration of aqueous NaOH solution used for post-treatment. Fig. 3
shows typical TEM micrographs for H-ZSM-5 and H-meso-ZSM-
(Table 2), suggesting that the generation of mesopores mainly con-
tributed to the increase in the external surface area.
5
samples. H-ZSM-5 crystals possess plate-like morphology. The
We also investigated the change of crystalline structure of ZSM-
post-treatment with aqueous NaOH solutions resulted in the gen-
eration of mesopores in ZSM-5 crystals. The sizes of mesopores
increased with an increase in the NaOH concentration.
5
after post-treatment by XRD (Fig. 5). All the diffraction peaks
belonging to crystalline ZSM-5 could be observed for H-meso-ZSM-
-xM samples, but the intensities of the diffraction peaks decreased
5
To gain more information about the porous property of the
mesoporous ZSM-5, we performed N2 physisorption measure-
ments. Fig. 4 displays the N2 adsorption/desorption isotherms of
mesoporous H-ZSM-5 samples together with H-ZSM-5. H-ZSM-5
exhibits the type I isotherm, which is typical of a microporous
zeolite. After treating ZSM-5 with aqueous NaOH solutions, the
isotherms of samples gradually changed from the type I to the
type IV, and hysteresis loops were observed. This clearly suggests
the generation of mesopores. By using the BJH method, we evalu-
ated the pore-diameter distribution in mesoporous region for the
H-meso-ZSM-5-xM samples. Relatively narrow pore-diameter dis-
tributions were observed for the samples with x = 0.3 and 0.5 (inset
figure in Fig. 4). The average size of mesopores depended on the
concentration of NaOH used for post-treatment. A higher concen-
tration of NaOH resulted in a larger average size of mesopores. With
an increase in x value from 0.3 to 1.0, the average size of mesopores
increased from 4.2 to 13 nm (Table 2). The pore volumes and surface
areas of the H-meso-ZSM-5-xM samples were also evaluated from
to some extent when the NaOH aqueous solution with a concentra-
tion of 1.0 M was used for the post-treatment (Fig. 5d). Therefore,
the crystalline structure of ZSM-5 was maintained for the H-meso-
ZSM-5-xM samples, although the regularity of the long-range order
decreased for the sample treated by 1.0 M NaOH.
Our NH -TPD measurements for the H-meso-ZSM-5-xM sam-
3
ples revealed that, similar to H-ZSM-5, these samples also exhibited
two NH3 desorption peaks at around 500 K and 750 K (Fig. 6). The
increase in the concentration of NaOH used for post-treatment
slightly decreased the intensity of the peak at 750 K, which could be
ascribed to the desorption of NH chemisorbed on the Brønsted acid
3
sites. Using NH -TPD results, we estimated the density of Brønsted
3
acid sites. The result showed that the density of Brønsted acid sites
−
1
was in a range of 0.41–0.49 mmol g for the H-meso-ZSM-5-xM
samples (Table 3), which was comparable to that for H-ZSM-5.
Thus, the Brønsted acidity of the H-meso-ZSM-5-xM samples was
almost sustained after the introduction of mesopores though the
post-treatment with NaOH aqueous solutions.
N physisorption measurements. The increase in the concentration
2
Table 3
Catalytic performances of mesoporous H-ZSM-5 with different mesopore sizes for the conversion of cellobiose.
Catalysts
Mesopore (nm)
Density of acid sitesa (mmol g−1
)
Conv. (%)
Yieldb (%)
TONc
M-␤-G
M-␣-G
ML
H-ZSM-5
–
0.46
0.49
0.44
0.41
61
70
83
90
18
20
27
25
35
38
46
49
3.1
2.4
3.2
2.2
6.7
6.9
9.7
10
H-meso-ZSM-5-0.3M
H-meso-ZSM-5-0.5M
H-meso-ZSM-5-1.0M
4.2
6.1
13
Reaction conditions: W(cellobiose) = 0.20 g, W(catalyst) = 0.10 g, V(CH3OH) = 20 mL, P(N2) = 3 MPa, T = 423 K, t = 4 h.
a
Estimated from NH3-TPD results in Fig. 6.
M-␣-G, M-␤-G, and ML denote methyl-␣-glucoside, methyl-␤-glucoside, and methyl levulinate, respectively.
TON was calculated by the mole of methyl glucosides formed per mole of acid sites.
b
c
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Fig. 7. Catalytic performances of H-meso-ZSM-5-0.5 M for the conversion of
cellobiose at different temperatures. Reaction conditions: W(cellobiose) = 0.20 g,
W(catalyst) = 0.050 g, V(CH3OH) = 20 mL, P(N2) = 3 MPa, t = 4 h.
Fig. 6. NH3-TPD profiles. (a) H-ZSM-5, (b) H-meso-ZSM-5-0.3 M, (c) H-meso-ZSM-
5
-0.5 M, (d) H-meso-ZSM-5-1.0 M.
3.3. Catalytic behaviors of mesoporous H-ZSM-5 for the
conversion of cellobiose in methanol
Table 3 displays the catalytic performances of the H-meso-ZSM-
5
-xM series of samples as well as H-ZSM-5 (Si/Al = 20) for the
conversion of cellobiose in methanol at 423 K. As compared to the
parent H-ZSM-5, the H-meso-ZSM-5-xM catalysts exhibited better
activities and higher yields of methyl glucosides. With increasing
the concentration of NaOH used for post-treatment, the yield of
methyl glucosides increased significantly. Over the H-meso-ZSM-
5
-0.5 M and H-meso-ZSM-5-1.0 M catalysts, the yields of methyl
glucosides reached 73% and 74%, respectively. We also calculated
the TON for the formation of methyl glucosides based on the den-
Fig. 8. Recycling uses of the H-meso-ZSM-5-0.5 M catalyst for the conver-
sion of cellobiose. Reaction conditions: W(cellobiose) = 0.20 g, W(catalyst) = 0.10 g,
V(CH3OH) = 20 mL, P(N2) = 3 MPa, T = 423 K, t = 4 h.
sity of Brønsted acid sites obtained from NH -TPD measurements.
3
As listed in Table 3, the catalyst treated with a higher concentration
of aqueous NaOH solution afforded a higher TON. This suggests that
the acid sites in mesoporous H-ZSM-5 work more efficiently for the
transformation of cellobiose to methyl glucosides. The combination
of the catalytic performances of these catalysts with their textural
properties in Table 2 allows us to conclude that the catalyst with
larger mesopores is beneficial to the transformation of cellobiose.
The generation of mesopores, in particular the mesopores with
larger average sizes (6.1 and 13 nm), may create larger amounts
of acid sites located inside the mesopores but outside the microp-
ores. These acid sites can be accessed by cellobiose molecules more
facilely. The diffusion limitation can also be improved in the pres-
ence of larger mesopores. Thus, the formation of methyl glucosides
can be enhanced owing to the generation of mesopores.
To gain further insights into the transformation of cellobiose
in methanol over the H-meso-ZSM-5-0.5 M, we have investigated
the effect of reaction temperature on catalytic performances. Fig. 7
shows that the conversion of cellobiose is only ∼30% at a relatively
low temperature (403 K) in methanol. The conversion increased
significantly with temperature. The yield of methyl glucosides
also increased with temperature and reached up to 94% at 433 K.
A further increase in temperature to 453 K rather decreased the
yield of methyl glucosides but increased that of methyl levulinate,
indicating the transformation of methyl glucosides to methyl lev-
ulinate at higher temperatures. The yield of methyl levulinate
reached 10% in the conversion of cellobiose in methanol at 453 K.
The catalyst stability is another crucial factor for solid acid
catalysts. We have examined the recycling uses of the H-meso-
ZSM-5-0.5 M catalyst for the conversion of cellobiose in methanol.
After each run, the catalyst was recovered by filtration, wash-
ing and drying, and then was re-used in the next run. Fig. 8
shows that the conversion of cellobiose and the yield of methyl
Table 4
Catalytic performances of H-ZSM-5 and H-meso-ZSM-5-0.5 M for the conversion of
cellulose.
Time (h) Conv. (%) Yielda (%)
M-␤-G M-␣-G ML
TONb
Catalyst
H-ZSM-5
H-ZSM-5
H-meso-ZSM-5-0.5M
H-meso-ZSM-5-0.5M 12
H-meso-ZSM-5-0.5M 18
4
12
6
<5
21
40
64
73
0.3
5.0
10
21
11
0.9
8.3
16
30
21
0
0.2
1
3.3
8.3
0.15
1.7
3.6
7.2
4.5
Reaction conditions: W(ball-milled cellulose) = 0.10 g, W(catalyst) = 0.10 g,
V(CH3OH) = 20 mL, P(N2) = 3 MPa, T = 463 K.
a
M-␣-G, M-␤-G, and ML denote methyl-␣-glucoside, methyl-␤-glucoside, and
methyl levulinate, respectively.
b
TON was calculated by the mole of methyl glucosides formed per mole of acid
sites.
glucosides decrease slightly after repeated uses for five runs. The
yield of methyl glucosides could be maintained at ∼60%.
3.4. Mesoporous H-ZSM-5 for the conversion of cellulose in
methanol
We have further investigated the catalytic performance of the
H-meso-ZSM-5-0.5 M as well as H-ZSM-5 for the conversion of ball-
milled cellulose in methanol at 467 K. H-ZSM-5 exhibited a low
activity at a short reaction time (4 h) (Table 4). With prolonging
reaction time to 12 h, 21% of cellulose was converted, yielding ∼13%
Please cite this article in press as: L. Xue, et al., Mesoporous H-ZSM-5 as an efficient catalyst for conversions of cellulose and cellobiose
into methyl glucosides in methanol, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.01.055

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promising catalytic system for the direct transformation of cellu-
lose under mild conditions.
Acknowledgements
This work was supported by the National Natural Science Foun-
dation of China (91545203 and 21473141), the Research Fund for
the Doctorial Program of Higher Education (20130121130001), and
the Program for Innovative Research Team in Chinese Universities
(IRT 14R31).
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Fig. 9. Comparison of the conversion of cellulose in methanol with that in
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T = 463 K, t = 12 h. MG denotes the sum of methyl-␣-glucoside and methyl-␤-
glucoside. Glu. denotes glucose.
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Please cite this article in press as: L. Xue, et al., Mesoporous H-ZSM-5 as an efficient catalyst for conversions of cellulose and cellobiose
into methyl glucosides in methanol, Catal. Today (2016), http://dx.doi.org/10.1016/j.cattod.2016.01.055