Ru/P-containing porous biochar-efficiently catalyzed cascade conversion of cellulose to sorbitol in water under medium-pressure H2 atmosphere

Article abstract of DOI:10.1246/bcsj.20200095

This paper discloses a simple and productive strategy for the preparation of biochar-based bifunctional catalysts. In this strategy, very cheap bamboo powder is thermally carbonized to yield P-containing porous biochars (PBCs) by the activation of concentrated phosphoric acid (H₃PO₄), and the latter can be transformed into the target catalysts via loading Ru nanometer particles (NPs) on them (marked as Ru/PBCs). A series of characterizations and measurements support that PBCs have stable and rich micro-meso pores and small strong acidic protons (0.100.28 mmol￠g¹¹) attributable to the grafted and/or skeleton phosphorus groups, as well as a strong affinity to β-1,4-glycosidic bonds, thus exhibiting a good acid catalytic activity for the hydrolysis of cellulose to glucose. More importantly, they are excellent acidic supports for the loading of Ru NPs owing to high BET surface area, which can give the loaded Ru NPs uniform and narrow distribution (16 nm). The resulting bifunctional Ru/PBCs catalysts possess excellent hydrolytic hydrogenating activity for the one-pot cascade conversion of cellulose and the optimized conditions can achieve ca. 89% hexitol yield with 98% sorbitol selectivity under relatively mild conditions. This work provides a good example for the preparation of biomass-derived bifunctional catalysts and their applications in biorefinery.

Full text of DOI:10.1246/bcsj.20200095

Document type: Article
Ru/P-Containing Porous Biochar-Efficiently Catalyzed Cascade
Conversion of Cellulose to Sorbitol in Water under
Medium-Pressure H2 Atmosphere
Feng Mao, Shuainan Chen, Qiao Zhang, Long Yang, Feifei Wan, Dabo Jiang,
Manman Xiong, Chao Zhang, Yachun Liu, and Zaihui Fu*
National & Local Joint Engineering Laboratory for New Petro-chemical Materials and Fine Utilization of Resources,
College of Chemistry and Chemical Engineering, Hunan Normal University, Changsha 410081, P. R. China
E-mail: fzhhnnu@126.com
Received: April 3, 2020; Accepted: April 27, 2020; Web Released: August 8, 2020
Zai hui Fu
Zai hui Fu, is a professor at the Institute of Fine Catalytic Synthesis, Hunan Normal University. His research
interests involve molecular design of new catalytic materials, green catalytic oxidation and enzyme-like
catalytic conversion. Related research achievements are published in many domestic and foreign academic
journals.
1. Introduction
Abstract
This paper discloses a simple and productive strategy for
Biomass has drawn a lot of attention as an environmentally
friendly and sustainable resource for the production of fuel and
chemical products. Cellulosic biomass cannot be digested by
humans and is very abundant in nature.1 Therefore, cellulose is
the most promising natural resource for conversion into more
valuable chemicals. Cellulose can be converted into sugar
alcohols, oxygenated bio-oil2 and hydrocarbons by various
chemical transformations. Especially, sorbitol, which is the
hydrogenated form of glucose, is targeted in this work because
it is a good model system to study the hydrolysis and then
hydrogenation of cellulose. Sorbitol has been classified as one
of the twelve most important bio-based platform chemicals as it
can be widely used as a sweetener, a moisture controller in
cosmetics, and in medical applications.3
Conventionally, sorbitol can be obtained by two-step con-
version of cellulose, including its selective hydrolysis to glu-
cose by acid catalysis, and then the hydrogenation of glucose
by metal catalyst. A great deal of effort has been put toward the
hydrolysis of cellulose to glucose with enzymes,4 mineral
acids5 and supercritical water.6 The obtained glucose can then
be efficiently hydrogenated into sorbitol with loaded Ru
nanometer particles (NPs) under relatively mild temperature
(120 °C) and hydrogen atmosphere.3 However, this two-step
conversion pathway suffers from several problems such as
complex operating procedures and high operating costs, rela-
tively low conversion efficiency, as well as difficult to separate
products and enzymes or mineral acids. To date, therefore, a
series of investigations have been reported to direct converting
the preparation of biochar-based bifunctional catalysts. In this
strategy, very cheap bamboo powder is thermally carbonized to
yield P-containing porous biochars (PBCs) by the activation of
concentrated phosphoric acid (H3PO4), and the latter can be
transformed into the target catalysts via loading Ru nanometer
particles (NPs) on them (marked as Ru/PBCs). A series of
characterizations and measurements support that PBCs have
stable and rich micro-meso pores and small strong acidic
protons (0.10-0.28 mmol¢g¹1) attributable to the grafted and/
or skeleton phosphorus groups, as well as a strong affinity to β-
1,4-glycosidic bonds, thus exhibiting a good acid catalytic
activity for the hydrolysis of cellulose to glucose. More impor-
tantly, they are excellent acidic supports for the loading of Ru
NPs owing to high BET surface area, which can give the loaded
Ru NPs uniform and narrow distribution (1-6 nm). The result-
ing bifunctional Ru/PBCs catalysts possess excellent hydro-
lytic hydrogenating activity for the one-pot cascade conversion
of cellulose and the optimized conditions can achieve ca. 89%
hexitol yield with 98% sorbitol selectivity under relatively mild
conditions. This work provides a good example for the pre-
paration of biomass-derived bifunctional catalysts and their
applications in biorefinery.
Keywords: Biochars
j
Bifunctional catalyst
j
Cellulose conversion
1026 | Bull. Chem. Soc. Jpn. 2020, 93, 1026–1035 | doi:10.1246/bcsj.20200095
© 2020 The Chemical Society of Japan

Table 1. One-pot hydrolytic hydrogenation of cellulose using various catalysts
Catalyst
Substrate
Reaction conditions
Target product yield/%
Ref.
Ru NPs and liquid acid
Ru/C
cellobiose
cellulose
120 °C, 12 h, 4 MPa H2
245 °C, 0.5 h, 6 MPa H2
160 °C, 5 h, 5 MPa H2
190 °C, 24 h, 5 MPa H2
230 °C, 6 h, 4 MPa H2
225 °C, 1.5 h, 6 MPa H2
225 °C, 24 h, 6 MPa H2
180 °C, 24 h, 5 MPa H2
170 °C, 24 h, 4 MPa H2
205 °C, 3 h, 5 MPa H2
190 °C, 2.5 h, 6 MPa H2
205 °C, 1 h, 5 MPa H2
150 °C, 10 h, 4 MPa H2
180 °C, 10 h, 4 MPa H2
165 °C, 36 h, 5 MPa H2
150 °C, 8 h, 5 MPa H2
Sorbitol (100)
Hexitol (39.3)
Hexitol (60.5)
Hexitol (31.0)
Hexitol (58.2)
Sorbitol (48.4)
Sorbitol (44.8)
Sorbitol (69.0)
Sorbitol (59.6)
Sorbitol (64.1)
Hexitol (85.5)
Sorbitol (74.0 or 71.0)
Sorbitol (61.2)
Sorbitol (63.8)
Sorbitol (71.1)
Sorbitol (87.1)
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
H2SO4 and Ru/C
Pt/Al2O3
microcrystalline cellulose
microcrystalline cellulose
microcrystalline cellulose
microcrystalline cellulose
microcrystalline cellulose
H3PO4 pre-treated cellulose
ball-milled cellulose
ball-milled cellulose
ball-milled cellulose
ball-milled cellulose
ball-milled cellulose
ball-milled cellulose
ball-milled cellulose
H3PO4 pre-treated cellulose
Ni/ZSM-5
Ni2P/AC(1:2)
Ru/[Bmim]3PW12O40
Ru/CNT
Ru/NbOPO4-pH2
Ru/AG-CNT1200
ZPA and Ru/C
Ru-Ni/AC or Ru-Ni/CNT
Ru/SiO2-SO3H
Ru/CCD-SO3H
Ru/AC-SO3H
Ru/PBC
This Work
cellulose into sorbitol in a one-pot reaction by green and effi-
cient ways in comparison to the above two-step conversion
systems, which are summarized in Table 1. Kou et al.7 and Liu
et al,8 successively reported two pioneering studies for this
one-pot conversion reaction, the former used the PVP-
stabilized Ru NP together with liquid acid as an excellent com-
bination catalyst that could achieve the quantitative conversion
of cellobiose to sorbitol, and the latter employed Ru/C and H+
generated in situ in hot water at 245 °C to efficiently catalyze
the one-pot conversion of cellulose to hexitol (39.3% yield).
Subsequently, Palkovits et al.9 reported that mineral acids
together with supported metal catalysts could efficiently
catalyze the one-pot conversion of cellulose to sugar alcohol,
giving a 72% cellulose conversion and 84% sugar alcohol
selectivity at relatively low reaction temperature and short
reaction time. The extensive use of mineral acids, however, can
result in difficulty in the separation of products and corro-
sion. Various metal NPs-loaded acidic supports, as bifunctional
solid catalysts, have been developed to realize a green one-
pot process to convert cellulose to sorbitol,10-21 among them,
Pt/Al2O3,10 Ni/ZSM-5,11 Ni2P/AC(1:2)12 and Ru/[Bmim]3-
loading of Ru (10 wt%), long reaction time or unsatisfied
sorbitol yield.
Recently, porous carbon materials have been investigated as
potential environment-friendly adsorption materials22 and sold
acid catalysts.23-25 Among them, the porous biochars prepared
from the chemical activation of lignocellulosic materials with
H3PO4 under moderate temperature (300-400 °C) have a stable
and rich porosity as well as a small amount of strongly acidic
sites through the formation of oxygen-phosphorus surface
groups,26-30 which have been successfully used to catalyze the
dehydration of alcohol and conversion of starch-rich food
waste into glucose and 5-HMF.31,32 But in most instances their
widespread use as robust solid acid catalysts still requires the
grafting of strongly acidic sulfonic acid groups by further
sulfonation with concentrated sulfuric acid.33 Due to the above
porosity and acidity, we speculate that the H3PO4-activated
biochars (PBCs), as excellent acidic supports, may be directly
used to construct robust bifunctional catalysts via loading
metals, thereby effectively achieving the cascade conversion of
cellulose to sorbitol under H2 atmosphere in one pot. Here, we
report a simple and productive strategy for the preparation of
Ru-loaded PBC bifunctional catalyst. In this strategy, the P-
containing porous bamboo carbon (PBC) supports can be con-
veniently prepared by one-step thermal carbonization of a
forestry processing waste bamboo powder at moderate temper-
ature under the activation of concentrated H3PO4. They can
then be transformed into the desired catalysts via loading Ru
nanometer particles (NPs) on them (marked as Ru/PBCs, see
Scheme 1). A series of characterizations indicated that PBC
materials have stable and rich micro-meso pores and a small
amount of P-containing strong acidic groups, which are much
superior to the extensively reported sulfonated biomass carbon
materials obtained by two step preparation, especially in carbon
skeleton stability and porosity. Moreover, PBC materials have
a much stronger affinity to β-1,4-glycosidic bonds than the non-
phosphate-mediated biomass carbon material, thus exhibiting a
high acid catalytic activity for the hydrolysis of cellulose to
glucose in water. More importantly, they, owing to high BET
surface area, can bestow the loaded Ru NPs with uniform and
13
PW12O40 can catalyze the one-pot conversion of micro-
crystalline cellulose in water under H2 atmosphere, but provide
low sorbitol or hexitol yield (22-58%) even using high temper-
ature (190-230 °C) owing to the poor acidity of their supports.
Ball-milled or phosphoric acid (H3PO4) pre-treated cellulose
exhibits a high reactivity owing to the destruction of its super
strong hydrogen bonding network,14,15 and its cascade con-
version catalyzed by the weak acidic bifunctional catalysts14-18
can more efficiently proceed at relatively low temperature
(170-205 °C) compared to untreated microcrystalline cellulose,
affording a relatively high sorbitol or hexitol yield (64-85%).
Notably, three strong acidic catalysts Ru/SiO2-SO3H,19 Ru/
CCD-SO3H20 and especially Ru/AC-SO3H21 exhibited a high
catalysis efficiency for this one-pot cascade reaction under
relatively low temperature (150-180 °C), affording 61, 64 and
71% sorbitol yields, respectively. However, these three cata-
lysts still have some defects, including the complex or lowly
efficient grafting of sulfonic groups on the supports, the high
Bull. Chem. Soc. Jpn. 2020, 93, 1026–1035 | doi:10.1246/bcsj.20200095
© 2020 The Chemical Society of Japan | 1027

OH
OH
OH
O
OH
O
O
O
HO
HO
HO
HO
O
OH
O
O
HO
OH
OH
OH
OH
n
Cellulose
H3PO4 impregnation
carbonization
Ru
RuCl3
H2O, 150oC
5MPaH2
CH2OH
H
CH2OH
Reduction
8h
HO
HO
H
H
HO
H
OH
H
H
Bamboo powder
Forestry processing waste
Pore
OH
PBC
Ru/PBC
OH
OH
+
H
OH
H
CH2OH
CH2OH
Mannitol, 1.6%
Sorbitol,87%
Scheme 1. Synthetic routes of Ru/PBC catalyst and its catalytic one-pot conversion of cellulose to sorbitol.
narrow distribution on them, and the resulting bifunctional Ru/
PBC catalysts possess excellent hydrolytic hydrogenating activ-
ity for the one-pot cascade conversion of cellulose to sorbitol
in water under medium-pressure H2 atmosphere, which are of
comprehensive advantages in catalyst availability, reaction con-
ditions, catalysis efficiency and sorbitol yield compared to the
reported hydrolytic hydrogenating catalysis systems at present.
electron microscopy (TEM) images of the samples were ob-
tained from a JEOL JEM-2100 transmission electron micro-
scope at an accelerating voltage of 200 kV. Transmission FT-IR
spectra of the samples were recorded from 400 to 4000 cm¹1 on
a Nicolet Nexus 510P FT-IR spectroscopy using a KBr disk.
Powder X-ray diffraction (XRD) analyses of the samples were
conducted on a Rigaku 2550 X-ray diffractometer using Cu Kα
radiation (λ = 0.15406 nm) and a graphite monochromator,
operated at a voltage of 40 kV, a current of 250 mA and a slit
width of 0.15 mm. XRD patterns were collected in the angular
range of 10-80° with a scanning rate 2°/min. The measure-
ment of acid density of samples by chemical titration34-36 was
performed as follows: The P-derived strong acid density was
determined by ultrasonic exchange with saturated sodium chlo-
2. Experimental Section
2.1 Reagents and Materials. Materials and reagents used
in this study were forestry processing waste bamboo powder,
concentrated phosphoric acid (H3PO4), ethylene glycol, ruthe-
nium (III) chloride, microcrystalline cellulose (99%), cello-
biose, glucose, and sorbitol, all of which were of analytical
grade. Water used in the laboratory was prepared with a
Millipore Milli-Q ultrapure water-purification system.
2.2 Preparation of PBC Catalyst. 10 g bamboo pow-
der was impregnated with 85wt% H3PO4 (its mass ratio (X)
to bamboo powder was 1, 1.5 or 2) at room temperature for
12 h, then, the impregnated samples were heated at a rate of
10 °C min¹1 and carbonized at different temperatures (Y = 300,
350, and 400 °C) for 5 h under N2 atmosphere, Finally, the
carbonized samples were repeatedly washed with plenty of hot
water and dried at 100 °C to obtain the P-containing biochars
(marked as PBC-X-Y). For comparison, a direct carbonization
material (marked as BC-300) of bamboo powder was also
prepared at 300 °C in the absence of 85 wt% H3PO4.
2.3 Preparation of Ru/PBC-X-Y Catalysts. PBC-X-Y
(1 g) and an appropriate amount (depending on Ru loading
amount) of RuCl3 aqueous solution (0.07 M) were added into
a flask and stirred at room temperature for 12 h. The above
mixture was evaporated at 80 °C and dried at 60 °C in a vacuum
drying oven overnight. Afterwards, the dried solid was treated
with 20 mL ethylene glycol at 90 °C for 8 h under magnetic
stirring. Finally, the treated solid was washed repeatedly with
ethyl alcohol and dried at 100 °C to obtain the desired catalysts
(denoted as Z%Ru/PBC-X-Y, here, Z% indicates the theoret-
ical loading of Ru, which was 1, 1.25, 2.5 and 5 wt%, respec-
tively). The actual Ru loading amount of a typical sample
5%Ru/PBC-1.5-300 measured by ICP method was ca. 4 wt%.
2.4 Characterization of Catalysts. Nitrogen adsorption-
desorption isotherms were measured at liquid nitrogen temper-
ature using a Tristar 3000 fully automatic surface area and pore
analyzer. X-ray photoelectron spectroscopy (XPS) of the sam-
ples was measured on a VG Multi Lab 2000 system with a
monochromatic Mg-Kα source operated at 20 kV. Transmission
¹1
ride solution followed by titration with 0.01 mol¢L NaOH
aqueous solution. The density of strong acid plus COOH and
the total acid density including OH were determined by ultra-
sonic exchange using NaHCO3 and NaOH solutions, respec-
¹1
tively, followed by titration with 0.01 mol¢L HCl solution.
2.5 Adsorption of Cellobiose. The adsorption capacity of
PBC materials on the β-1,4-glycosidic bonds was examined
using cellobiose as a mimetic compound and the specific
operation process of cellobiose adsorption could be found in
our previous publications.37 The obtained adsorption data indi-
cated that PBC materials have a far stronger affinity to β-1,4-
glycosidic bonds compared to BC-300 (See Supporting
Information (SI), Table S1), and this unique property of PBC
materials facilitates the hydrolysis of cellulose as the rate-
determining step in the cascade conversion of cellulose to
sorbitol.
2.6 Pre-treatment of Cellulose. Microcrystalline cellulose
(15 g) was poured into 85% H3PO4 (150 mL) and stirred in a
water bath at room temperature for 3 h and further stirred for 4 h
at 50 °C. After adding a suitable amount of distilled water and
stirring vigorously for 3 h, the treated solid was washed with
distilled water under ultrasonic conditions until the washing
water was neutral. The washed cellulose was ultrasonicated for
1 h in absolute ethanol, filtered and dried at 60 °C for 24 h to
obtain the pretreated cellulose. The X-ray diffraction (XRD)
pattern of microcrystalline cellulose shown in Figure S1 clearly
indicated that a partial destruction of the crystal structure of
cellulose occurred after treatment with 85%H3PO4. in agree-
ment with previously reported results.14
2.7 Conversion of Cellulose to Sorbitol. 0.3 g H3PO4-
treated cellulose, 0.1 g catalyst, and 25 mL deionized water
were introduced into a 100 mL high pressure reactor, and the
1028 | Bull. Chem. Soc. Jpn. 2020, 93, 1026–1035 | doi:10.1246/bcsj.20200095
© 2020 The Chemical Society of Japan

reactor was purged with 5 MPa of hydrogen gas. Then, the
reaction was carried out at 150 °C with a stirring rate of 500
rpm for 8 h. After reaction, the cooled reaction samples were
separated to remove the solid (a mixture of catalyst and resid-
ual cellulose) by centrifugation. After weighing the estimat-
ed residual cellulose, the recovered solid was repeatedly
washed with hot water and dried at 60 °C overnight for next
use as a catalyst. The obtained filtrate was analyzed with an
Alltech1500 HPLC equipped with a BP-100 H+ carbohydrate
column. The eluent was diluted with H2SO4 solution (0.005 M)
with a flow rate of 0.6 mL/min. The column and detector
temperatures were 45 °C. The quantification of products was
performed using an external standard method. Cellulose con-
version and sorbitol yield were calculated by the following
equations.
been incorporated into the skeleton of PBC-X-Y materials or
grafted to their surfaces in some forms, thus leading to an in-
crease in carbonized yield and an introduction of P-containing
strong acid protons.38 Entries 3-6 further shows that enhancing
the impregnated ratio of H3PO4 and elevating the carbonized
temperature are beneficial to slightly increase the carbonization
yield and the introduction of strong and weak acid groups, but
the impregnated ratio shows no obvious regularity in adjusting
the strong acidity. Among the prepared PBC-X-Y materials,
PBC-1.5-400 has the highest strong acid content of 0.28
mmol¢g¹1, PBC-1.5-300 has the highest total acid content of
¹1
1.48 mmol¢g and the second highest strong acid content of
¹1
0.17 mmol¢g
.
Porosity: Porosity of some typical materials PBC-1.5-300
and PBC-1.5-400 as well as 5%Ru/PBC-1.5-300 and its recov-
ered sample was measured using a low temperature nitrogen
adsorption apparatus and the determined specific surface areas
(SBET), total pore volumes (Vp) and average porous sizes (D)
are summarized in Table 3. As compared to the nonporosity of
BC-300,39 Figure 1a displays that according to the IUPAC
classification, the isotherms of all the materials are of mixed
type. At very low relative pressures they belong to type I with a
fast-increase of N2 uptake, which corresponds to a microporous
structure.40 At moderate and relatively high pressures, their
isotherms are type IV with type H4 of broad and inconspic-
uous hysteresis, which can be an indicative characteristic of
slit-shaped mesopores.41 The slop of the isotherms remarkably
increases with the increase of carbonization temperature, corre-
sponding to the significant increase in SBET and Vp values in
Table 3. Figure 1b shows that the BJH pore distribution curves
of these three materials are very narrow and similar to each
other, which consist almost entirely of pores smaller than 3 nm.
The porous parameters listed in Table 3 further reveal that
the specific surface areas of all the materials are composed of
the external (St-plot) and internal (Smicro) surface areas with
different ratios and the external surface area is dominant at
high carbonization temperature. Their average pore sizes are
between 2.24 and 2.35 nm, and have no significant difference
Cellulose conversion ð%Þ
¼ ½ðadded cellulose ꢀ residual celluloseÞ=added celluloseꢁ
ꢂ 100%
Sorbitol yield ð%Þ
¼ ðmoles of sorbitol=moles of glucose unit in
added celluloseÞ
ꢂ 100%
3. Results and Discussion
3.1 Characterization of Catalysts.
Surface Acidity:
Table 2 lists the data for the yield and surface acid density of
PBC-X-Y prepared by bamboo powder carbonization with
different amount of H3PO4 at different temperatures. Entry 1
shows that the yield of BC-300 obtained by a direct carbon-
ization of bamboo powder at 300 °C only has 34.0 wt% and its
surface acidity originates from weakly acidic carboxyl (COOH,
0.21 mmol¢g¹1) and hydroxyl (OH, 0.51 mmol¢g¹1) groups.
The use of H3PO4 as an activator can increase the yield of PBC-
¹1
X-Y materials by 8-12 wt% and introduce 0.1-0.28 mmol¢g
strong acid protons but slightly enhances the above weakly
acidic groups (Entries 2-6), supporting that H3PO4, as sup-
ported by the P contents (0.4-4.3 wt%) measured with ICP, has
Table 2. Yield of bamboo powder carbonization with H3PO4 under different conditions and surface acid groups of PBCs
¹1
P contenta
(wt %)
Density of acidic groups (mmol¢g
)
Carbon yield
/wt%
Total acidity
Entry
Sample
¹1
(mmol¢g
)
Strong acid
-COOH
-OH
1
2
3
4
5
6
BC-300
34.0
42.4
45.2
43.8
45.1
45.8
0
0.21
0.31
0.59
0.46
0.60
0.57
0.51
0.54
0.72
0.69
0.69
0.59
0.72
0.95
1.48
1.27
1.45
1.44
0
PBC-1-300
PBC-1.5-300
PBC-2-300
PBC-1.5-350
PBC-1.5-400
0.10
0.17
0.12
0.16
0.28
0.4
1.6
0.8
1.5
4.3
aMeasured by ICP.
Table 3. Porous parameters of PBC-1.5-300, PBC-1.5-400 and 5% Ru/PBC-1.5-300.
SBET
St-plot
Smicro
Pore Volume Vp
Pore Size D
Sample
¹1
¹1
¹1
¹1
(m2¢g
)
(m2¢g
)
(m2¢g
)
(cm3¢g
)
(nm)
PBC-1.5-300
PBC-1.5-400
Fresh 5%Ru/PBC-1.5-300
Recovered 5%Ru/PBC-1.5-300
896
1379
744
419
1046
355
477
233
389
257
0.502
0.811
0.424
0.258
2.24
2.35
2.28
2.32
446
189
Bull. Chem. Soc. Jpn. 2020, 93, 1026–1035 | doi:10.1246/bcsj.20200095
© 2020 The Chemical Society of Japan | 1029

550
500
450
400
350
300
250
200
150
100
1708
1610
1186
1082
3425
PBC-1.5-400
PBC-1.5-350
(a)
PBC-1.5-300
BC-300
PBC-1.5-300
Ru/PBC-1.5-300
PBC-1.5-400
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber/cm-1
0.0
0.2
0.4
0.6
P/P0
0.8
1.0
Relative Pressure
(
)
Figure 2. FTIR spectra of BC-300 and PBC-1.5-Y samples
obtained using 1.5 H3PO4 impregnation ratio at different
temperatures.
PBC-1.5-300
Ru/PBC-1.5-300
PBC-1.5-400
2.5
2.0
1.5
1.0
0.5
0.0
(b)
polyphosphate groups in PBC materials, as supported by ICP
results in Table 2. It can be further seen from Figure 2 that as
the carbonization temperature is elevated from 300 to 400 °C,
the intensity of two peaks at 3425 and 1186 cm¹1 gradually de-
creases, along with an increase in the peak intensity at 1080
cm¹1, supporting that at the high carbonization temperature,
PBC material becomes hydrophobic and contains a high per-
centage of polyphosphate species, which the latter likely con-
tributes to improve the incorporation of P-containing species
and its derived strong acidity in PBC material, as supported by
the results of Table 2.
0
50
100
150
200
250
Pore Diameter (nm)
Figure 1. N2 adsorption-desorption isotherms (a) and pore
size distributions (b) for PBC-1.5-300, PBC-1.5-400 and
5%Ru/PBC-1.5-300.
XPS: The chemical states for the surface atoms of PBC-
1.5-300 and Ru/PBC-1.5-300 were investigated by X-ray
photo-electron spectroscopy (XPS) and the high resolution
XPS spectra for the surface P and Ru atoms of Ru/PBC-1.5-
300 are shown in Figure 3. The survey XPS spectra of these
two samples and the composition of the surface elements can
be found in Figure S2 and Table S2, respectively. Figure 3a
shows that a broad P 2p peak with the centered binding energy
of about 133.5 eV is observed in its energy spectrum, which is
indicative of the characteristic of pentavalent tetracoordinated
phosphorus (PO4) as in phosphates and/or polyphosphates.46
Further analysis by Gaussian simulation reveals the P 2p spec-
trum may be deconvoluted into two main characteristic peaks:
One peak at 134.0 eV is assigned to phosphorus groups bound
to carbon through an oxygen atom, such as C-O-PO3H2, (C-
O)2PO2H and (C-O)3PO.29,47,48 Another peak at 133.2 eV is C-
P characteristic bonding as in C-PO3H2 and C2PO2H groups.48
Notably, two peaks in lower binding energy that are attributed
to C3PO (132.0 eV) and C3P (131.0 eV) groups29 are very weak
in the current P 2P spectrum, indicating that these two groups
may be ignored in PBC materials. Figure 3b shows that two
broad peaks for Ru 3p1/2 and Ru 3p3/2 appear centered at 483.7
and 461.4 eV, respectively, corresponding to the metallic
Ru.13,19 By further dividing above peaks gives another two
weak peaks at 487.0 and 463.7 eV, which are assigned to
between each other. Notably, the SBET and Vp values of the
fresh and especially recovered Ru/PBC-1.5-300 are reduced
significantly compared the support PBC-1.5-300 but the D val-
ues are almost unchanged. These findings indicate that H3PO4
is an effective activating agent, can promote the expansion of
the cellulosic structure of biomass, corresponding directly to
the development of porosity. And the porosity of PBC mate-
rials is easily adjusted by varying the carbonization temper-
ature, in consistence with the results previously reported in
the literature.29,32 The significant reduction in the porosity of
5%Ru/PBC-1.5-300 should be attributed to the micropores of
the carrier occupied by the loaded Ru NPs and the further
decrease in porosity after catalysis reaction may originate from
the occupied effect of catalyst’s micropores by the by-produced
polymers in cellulose conversion.42
FT-IR: Figure 2 is the FTIR spectra of BC-300 and PBC-
1.5-Y samples obtained using 1.5 H3PO4 impregnation ratio
at different temperatures. In that, all the carbon materials all
exhibit some characteristic absorption peaks that include
stretching vibrations of OH groups in 3650-3000 cm¹1, COOH
at 1708 cm¹1, Ar-OH at 1610 cm¹1 and polycyclic aromatics in
1400-1600 cm ,
¹1 43 indicating that they consist of aromatic car-
bon sheets with attached hydrophilic COOH and OH. Notably,
two obvious IR peaks at 1200-1000 cm¹1 can be also found in
the FT-IR spectra of the P-containing materials. Among them,
Ru3+ 13
The results support that the Ru species on Ru/PBC-
.
1.5-300 exists mainly in metal form, and a small amount of the
unreduced Ru3+ species is also present on the support.
XRD: As shown in Figure 4, the XRD patterns of PBC-
1.5-300 and Ru/PBC-1.5-300 are very similar to each other
and present two characteristic diffraction peaks at 2θ of 15-50°.
The strong peak at 23.5° is assigned to amorphous carbon com-
¹1
one peak at 1186 cm is assigned to P=O or C-O stretch-
ing vibration in P=OOH or C-O-P groups.44 Another peak at
¹1
1080 cm is attributed to the symmetrical vibration of P-O-P
bond in polyphosphate.45 This indicates the existence of P-
containing carbonaceous species and the incorporation of
1030 | Bull. Chem. Soc. Jpn. 2020, 93, 1026–1035 | doi:10.1246/bcsj.20200095
© 2020 The Chemical Society of Japan

C-PO(OH)
(a)
(b)
2
(a) P2p
C
-PO(OH)
C-O-PO(OH)
2
2
(CO) -PO(OH)
2
(CO) -PO
3
C
PO
3
C
P
3
(c)
(e)
(d)
138
136
134
132
130
Binding Energy (eV)
(b) Ru3p
0
Ru
3+
Ru
(f)
Figure 5. TEM image (a) of PBC-1.5-300, TEM image
(b) and HRTEM image (c) of 5%Ru/PBC-1.5-300 and its
Ru particle size distributions (d), TEM image (f) of Ru/
PBC-1.5-400 and its Ru particle size distributions (e).
500
490
480
470
460
450
Binding Energy (eV)
Figure 3. XPS spectra for (a) P 2p and (b) Ru 3p of 5%
Ru/PBC-1.5-300.
image in Figure 5c. The dispersed Ru NPs are all between 1
and 6 nm and their average size is ca. 3.1 nm (see Figure 5d).
Unexpectedly, the dispersion of Ru NPs on the carrier PBC-
1.5-400 with a higher porosity is not as good as on PBC-1.5-
300 with a lower porosity (Figures 5d vs 5b), and they present
a broader size distrubtion of 1-12 nm, with an average size of
4.6 nm (Figure 5e). This may be because the hydrophilicity of
PBC carrier, as supported by the above FT-IR spectra, becomes
worse with increasing carbonization temperature and thereby
results in a decrease in the impregnation efficiency of hydro-
philic precursor RuCl3 into it.
PBC-1.5-300
Ru/PBC-1.5-300
3.2 Catalytic Performance of Samples for Conversion of
Cellulose in Water. Table 4 lists the data for the conversion
of cellulose catalyzed by various catalysts in water at 150 °C.
Entry 1 shows that under hydrothermal conditions, cellulose is
slightly hydrolyzed to produce a trace amount of cellobiose and
glucose in the absence of catalyst. The non-phosphate activated
BC-300 also exhibits a very poor activity for cellulose hydrol-
ysis (Entry 2), which should be due to lack of strong acidity
and a poor affinity to β-1,4-glycosidic bonds of cellulose, as
supported by Table 2 and Table S1. In sharp contrast, all the
phosphate-activated PBC-X-Y materials, due to the strong
acidity and affinity to β-1,4-glycosidic bonds of cellulose, are
very active for cellulose hydrolysis and can achieve 29.0-
56.7% glucose and 2.1-5.5% cellobiose yields under hydro-
thermal conditions, along with the formation of a small amount
of 5-HMF (1.2-2.7% yield, Entries 3-7). According to the
difference between the above target products (32.8-62.0%) and
cellulose conversion (47.7-85.3%), it is estimated that about
15-23% cellulose in this hydrolysis is converted into other by-
products that may consist of soluble polymers and insoluble
humins.52 The hydrolysis activity of PBC materials increases
first and then decreases with increasing the impregnation mass
ratio of H3PO4 to bamboo powder from 1 to 2 (Entries 3-5),
10
20
30
40
50
60
70
80
2θ (degree)
Figure 4. XRD patterns of the PBC-1.5-300 and 5%Ru/
PBC-1.5-300 catalysts.
posed of aromatic carbon sheets oriented in a random fashion,15
another weak broad peak at 35-50° is attributable to a axis of
graphite structure.49,50 Notably, a characteristic diffraction peak
for meal Ru is not found in the XRD pattern of Ru/PBC-1.5-
300, likely implying that the loaded Ru NPs are small size and
dispersed uniformly on the support PBC-1.5-300,15,51 as sup-
ported by the following TEM images.
TEM: Morphologies of PBC-1.5-300, 5%Ru/PBC-1.5-300
and 5%Ru/PBC-1.5-400 were observed by TEM and the
obtained images are shown in Figure 5. Figure 5a shows that
the dense and irregular aggregation of very small PBC NPs are
clearly observed in the TEM image of PBC-1.5-300, thus ren-
dering this carrier with a layer structure and rich slit micropores
produced by PBC NPs aggregation, as supported by the St-plot
parameters in Table 3. A TEM image of 5%Ru/PBC-1.5-300
in Figure 5b clearly displays many black dots attributable to
metal Ru NPs uniformly dispersed on PBC-1.5-300, which are
attributable to metal Ru NPs, as supported by the HRTEM
Bull. Chem. Soc. Jpn. 2020, 93, 1026–1035 | doi:10.1246/bcsj.20200095
© 2020 The Chemical Society of Japan | 1031

Table 4. Hydrolysis and hydrogenation of cellulose in water over various catalystsa
Yield of products/%
Entry
Catalyst
Conv./%
Cellobiose
Glucose
5-HMF
Sorbitol
Mannitol
1
2
3
4
5
6
7
8c
No catalyst
BC-300
PBC-1-300
PBC-1.5-300
PBC-2-300
PBC-1.5-350
PBC-1.5-400
PBC-1.5-300
Ru/PBC-1.5-300
Ru/PBC-1.5-300
Ru/PBC-1.5-350
Ru/PBC-1.5-400
Ru/PBC-1.5-300
Ru/PBC-1.5-300
Ru/PBC-1.5-300
18.6
23.2
47.7
0.3
0.7
0.5
1.1
29.0
50.1 (54.5)b
0
0.4
1.7
1.3 (0)b
2.7
1.2
1.6
1.7
1.0
0
0
0
0
0
0
0
2.1
84.0 (89.5)b
79.3
4.2 (3.1)b
0 (0)b
0
0 (0)b
0
2.3
5.5
3.7
0
1.8
0
0
0
0
0
43.4
48.4
56.7
84.1
58.6
0
0
0
0
0
83.3
85.3
100
93.7
98.5
96.8
100
100
0
0
0
0
87.1
80.1
74.6
90.7
93.2
9.2
0
0
0
0
1.6
1.7
2.8
1.7
0.8
1.0
9
10b
11b
12b
13b,c
14b,d,e
15b,f
0
0
0
0
100
37.6
0
0
0
aReaction condition: cellulose, 0.3 g; catalyst, 0.1 g; H2O, 25 mL; reaction temperature, 150 °C; reaction time, 8 h;
c
d
e
b5 MPa H2; Using cellobiose as a substrate; Using glucose as a substrate; Reaction temperature, 120 °C; reaction
f
time, 8 h; Using microcrystalline cellulose as a substrate.
while the hydrolysis activity continuously ascends with elevat-
ing carbonization temperature from 300 to 400 °C (Entries 4, 6,
7), which well accords with the strong acidity of PBC materials
in Table 2. The data in parentheses of Entry 4 shows that if
this acid catalysis is performed under 5 Mpa H2 atmosphere,
glucose yield is slightly enhanced by about 4% and no 5-HMF
is detected out, suggesting that under H2 atmosphere, the effi-
ciency of this acid catalysis hydrolysis can be improved
slightly and the dehydration of glucose to 5-HMF may be also
restrained. Entry 8 demonstrates that cellobiose can be com-
pletely converted to yield up to 84.1% glucose under the acid
catalysis of PBC-1.5-300, revealing that it has a far higher
reactivity than insoluble cellulose. Entry 9 shows that 5%Ru/
PBC-1.5-300 can further improve the efficiency of cellulose
hydrolysis under non-hydrogenated conditions and provide
58.6% glucose yield and a small amount of cellobiose and 5-
HMF, which may stem from a contribution of its residual Ru3+
species as a Lewis acid.13 Entry 10 illuminates that 5%Ru/
PBC-1.5-300, as a bifunctional catalyst, can efficiently catalyze
the one-step hydrolytic hydrogenation of cellulose at 150 °C
under 5 Mpa H2 atmosphere, affording up to 87.1% sorbitol
yield and small amount of mannitol (1.6% yield). A compar-
ison of two sets of data in Entries 9 and 10 may clearly find that
the one-step cascade conversion of cellulose to sorbitol has a
huge advantage in reducing by-products (lowering by about
13%) and enhancing the bio-derived target chemicals compared
to its single-hydrolysis to glucose. This may be due to the
following reasons: The loaded Ru NPs enhance the acidity of
PBC carrier via dissociating H2 to generate spillover H spe-
cies,53 including the above residual Ru3+ species. On the other
hand, the Ru NPs have a good hydrogenolytic activity for the
cleavage of β-1,4-glucosidic bonds of cellulose and oligo-
saccharides, especially an excellent activity for glucose hydro-
genation,14 thus significantly accelerating cellulose conversion
into sorbitol and reducing the generation of by-products.
Entries 10-12 showcase that cellulose conversion is hardly
affected by the carbonization temperature of PBC carrier, but
sorbitol yield presents a gradual decrease from 87.1 to 74.6%
with elevating the temperature from 300 to 400 °C. This is
mainly because the size and distribution of the loaded Ru NPs
that are closely relative to hydrogenating activity54 are adjusted
by the carbonization temperature and the small size and uni-
form distribution of Ru NPs on PBC-1.5-300 carrier, as sup-
ported by the above TEM images, possess the highest hydro-
genating activity. Notably, using the same catalytic conditions
as Entry 10, the one-pot hydrolytic hydrogenation of cellobiose
can yield up to 90.7% sorbitol yield (Entry 13), the direct
hydrogenation of glucose also proceeds efficiently even at
120 °C, providing 93.2% sorbitol yield (Entry 14). But recal-
citrant micro crystalline cellulose, owing to the existence of its
super hydrogen bonding network,55 has a much lower reactivity
in one-pot hydrolytic hydrogenation than material treated with
H3PO4, only providing a poor 9.2% sorbitol yield (Entry 15).
In the following experiments, we investigated the effect of
variables on the one-pot hydrolytic hydrogenation of cellu-
lose in water under 5 Mpa H2 and the results are shown in
Figures 6-9. Figure 6 gives the effect of Ru loading amount on
the one-pot reaction. In that, cellulose conversion is affected by
Ru loading and sorbitol yield presents a gradual increase from
76.9 to 87.1% with elevating the Ru loading from 1 to 5wt%,
along with a slight increase in mannitol yield. Figure 7 displays
that cellulose conversion is continuously enhanced to 100%
with increasing the dosage of 5%Ru/PBC-1.5-300 catalyst and
sorbitol yield first ascends and then descends when catalyst
dosage is enhanced from 0.05 to 0.2 g, giving rise to a maxi-
mum of 87.1% at 0.1 g catalyst. Notably, cellobiitol, a hydro-
genated product of cellobiose,53,54 can be detected out at a low
catalyst dosage of 0.05 g, while another hydrogenated product
mannitol produced by fructose hydrogenation or sorbitol
isomerisation15,19 is enhanced when catalyst dosage exceeds
0.1 g. These findings support that the distribution of hydrogen-
ated products is dominated by the strong acid amount of
1032 | Bull. Chem. Soc. Jpn. 2020, 93, 1026–1035 | doi:10.1246/bcsj.20200095
© 2020 The Chemical Society of Japan

100
80
60
40
20
0
100
80
60
40
20
0
Cellulose conversion
Sorbitol yield
Mannitol yield
Cellulose conversion
Sorbitol yield
Mannitol yield
Cellobiitol yield
Cellobiitol yield
4
6
8
10
12
Reaction Time (h)
1
2
3
4
5
Ru loading amount/wt%
Figure 9. Effect of reaction time on the conversion of
cellulose to sorbitol. (cellulose, 0.3 g; catalyst, 0.1 g; H2,
5 MPa; H2O, 25 mL; temperature, 150 °C)
Figure 6. Effect of the Ru loading amount of catalyst on the
conversion of cellulose to sorbitol. (cellulose, 0.3 g; cata-
lyst, 0.1 g; H2, 5 MPa; H2O, 25 mL; reaction temperature,
150 °C; reaction time, 8 h)
5%Ru/PBC-1.5-300. When the reaction temperature is elevat-
ed from 140 to 160 °C, cellulose conversion is progressively
enhanced from 87.1 to 100% and sorbitol yield initially rises
and drops next, providing the highest 87.1% at 150 °C. The
yield of mannitol slightly increases from 1.2 to 3.5% as the
temperature is elevated from 140 to 170 °C. A decrease in
sorbitol yield at 140 °C still originates from the insufficient
hydrolysis of cellulose, which can be confirmed by an obvious
increase of cellobiitol at this temperature. And its decrease at
160-170 °C likely results from higher temperature giving rise
to the conversion of cellulose to undesirable by-products and
fructose hydrogenation or sorbitol isomerisation to mannitol.56
Figure 9 gives the effect of reaction time on this one-pot
conversion. In that, cellulose conversion and sorbitol yield
uninterruptedly rise with prolonging reaction time and respec-
tively give rise to 98.5 and 87.1% at 8 h, along with a decrease
of cellobiitol and an increase of mannitol. After that, the con-
version further increases to 100% at 10 h, while sorbitol yield is
slightly reduced with extending the time to 10 h, which is in
agreement with stated results from the reaction temperature.
Finally, the stability of 5%Ru/PBC-1.5-300 and its carrier
PBC-1.5-300 was checked by performing recycling experi-
ments in catalytic hydrolysis and hydrogenation and the ob-
tained results for the hydrolytic hydrogenation of cellulose in
one-step and the direct hydrogenation of glucose are presented
in Figure 10. As shown in Figure 10a, the hydrolytic hydro-
genation efficiency of 5%Ru/PBC-1.5-300 gradually decreases
with its recycling times, after three successive runs, the conver-
sion of cellulose and the yield of sorbitol are reduced from 98.5
to 77.3% and from 87.1 to 58.8%, respectively. In sharp con-
trast, this catalyst exhibits an excellent reusability for the direct
hydrogenation of glucose under the same reaction conditions
and the hydrolytic hydrogenation efficiency hardly varies after
three successive runs, still providing ca. 90% sorbitol yield
(See Figure 10b). These findings indicate that the deactivation
of catalyst in the hydrolytic hydrogenation of cellulose should
mainly originate from leaching of its strong acid sites, as
supported by the following fact: the strong acid amount of
catalyst is reduced from 0.17 to 0.10 mmol¢g¹1 after three runs,
corresponding to the generation and increase of cellobiitol
(Figure 10a). On the other hand, a deposition of the insoluble
humins formed during reaction on the acidic sites and Ru NPs
of catalyst may partially contribute to catalyst deactivation. A
100
80
60
Cellulose conversion
Sorbitol yield
Mannitol yield
40
20
0
Cellobiitol yield
0.05
0.10
0.15
0.20
Catalyst dosage (g)
Figure 7. Effect of catalyst dosage on the conversion of
cellulose to sorbitol. (cellulose, 0.3 g; H2, 5 MPa; H2O, 25
mL; reaction temperature, 150 °C; reaction time, 8 h.)
100
80
60
Cellulose conversion
Sorbitol yield
Mannitol yield
40
Cellobiitol yield
20
0
140
150
Temperature
160
oC
170
(
)
Figure 8. Effect of reaction temperature on the conversion
of cellulose to sorbitol. (cellulose, 0.3 g; catalyst, 0.1 g; H2,
5 MPa; H2O, 25 mL; reaction time, 8 h)
catalyst determined by its dosage, the insufficient hydrolysis
of cellulose to cellobiose easily occurs at low catalyst dosage,
thus leading to the generation of cellobiitol. The conversion of
sorbitol to mannitol and especially other unknown by-products,
as supported in Table S3, can occur at high catalyst dosage,
thus leading to a decrease in sorbitol. Figure 8 gives the effect
of reaction temperature on the one-pot reaction catalyzed by
Bull. Chem. Soc. Jpn. 2020, 93, 1026–1035 | doi:10.1246/bcsj.20200095
© 2020 The Chemical Society of Japan | 1033

Cellulose conversion
Sorbitol yield
Cellobiitol yield
Mannitol yield
100
80
60
40
20
0
sorbitol from the one-pot cascade conversion of cellobiose and
especially the direct hydrogenation of glucose. With such kind
of robust Ru/PBC catalyst in hand, we are interested in further
improving the acidity and porosity of this catalyst as well as the
loading efficiency of Ru NPs on it, thus significantly enhancing
its hydrolytic hydrogenation performance for highly efficient
synthesis of sorbitol from one-step conversion of cellulose.
(a)
We acknowledge the financial support for this work by the
National Natural Science Fund of China (21676079,
21546010), the Natural Science Fund of Hunan Province
(2018JJ3335, 14JJ2148, 11JJ6008, 10JJ2007), Hunan 2011
Collaborative Innovation Center of Chemical Engineering &
Technology with Environmental Benignity and Effective
Resource Utilization.
1
2
3
Number of operations
Sorbitol yield
Mannitol yield
Glucose conversion
100
80
60
40
20
0
(b)
Supporting Information
Adsorption experiment of cellobiose, XRD patterns of
Microcrystalline cellulose before and after treatment with
H3PO4, survey XPS spectra for the PBC-1.5-300 and 5%Ru/
PBC-1.5-300, further conversion of sorbitol, recyclability of
PBC-1.5-300 catalyst on hydrolysis of cellobiose, recyclability
of 5%Ru/PBC-1.5-300 catalyst on hydrolytic hydrogenation
of cellobiose. This material is available on https://doi.org/
10.1246/bcsj.20200095.
1
2
3
Number of operations
Figure 10. Recyclability of 5%Ru/PBC-1.5-300 catalyst
for hydrolytic hydrogenation of cellulose (a) and direct
hydrogenation of glucose (b). (Reaction condition: sub-
strate, 0.3 g; catalyst, 0.1 g; H2, 5 MPa; H2O, 25 mL; reac-
tion temperature, 150 °C; reaction time, 8 h)
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