Ru Nanoparticles on a Sulfonated Carbon Layer Coated SBA-15 for Catalytic Hydrogenation of Furfural into 1, 4-pentanediol

Article abstract of DOI:10.1007/s10562-020-03520-5

Furfural (FFR) is one of the most important biomass-derived chemicals. Its large-scale availability calls for the exploration of new transformation methods for further valorization. Herein, we demonstrate that Ru nanoparticles (Ru NPs)-supported on a sulfonated carbon layer coated SBA-15 can be employed as an efficient bi-functional catalyst for one step conversion of FFR into 1,4-pentanediol (1,4-PeDO). The optimum bi-functional catalyst can afford the full the conversion of FFR and 86% selectivity to 1,4-PeDO. The catalysts have been characterized thoroughly by using a complementary combination of powder X-ray diffraction, N₂ adsorption–desorption, scanning/transmission electron microscopy, Fourier transform infrared spectroscopy, elemental analysis, and X-ray photoelectron spectroscopy. The characterization revealed that acidic groups (–SO₃H) have been introduced on the surface of the carbon layer coated SBA-15 support after sulfonation with 98% H₂SO₄ and the surface acidity can be tuned facilely by the sulfonating time. Meantime, Ru(0) sites was highly dispersed via an impregnation and sequential reduction and directly adjacent to the surface –SO₃H group. There existed an electronic interaction between Ru(0) sites and sulfonic groups, in which the electronic transfer from sulfonic sites to Ru(0) sites occurred. Br?nsted acid sites (–SO₃H) have a significant influence on the FFR conversion and the selectivity to 1,4-PeDO. The ordered mesoporous structure, the appropriate density of acid sites and the electron-rich Ru(0) sites accounted for the the excellent performance of the catalyst for an efficient production of 1,4-PeDO from FFR. Graphic Abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-020-03520-5

Catalysis Letters
https://doi.org/10.1007/s10562-020-03520-5
Ru Nanoparticles on a Sulfonated Carbon Layer Coated SBA‑15
for Catalytic Hydrogenation of Furfural into 1, 4‑pentanediol
Kai Cui1 · Wei Qian1 · Zhengjiang Shao1 · Xiuge Zhao1 · Honghui Gong1 · Xinjia Wei1 · Jiajia Wang1 · Manyu Chen1 ·
Xiaoming Cao1 · Zhenshan Hou1
Received: 3 September 2020 / Accepted: 24 December 2020
© The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature 2021
Abstract
Furfural (FFR) is one of the most important biomass-derived chemicals. Its large-scale availability calls for the exploration
of new transformation methods for further valorization. Herein, we demonstrate that Ru nanoparticles (Ru NPs)-supported
on a sulfonated carbon layer coated SBA-15 can be employed as an efcient bi-functional catalyst for one step conversion
of FFR into 1,4-pentanediol (1,4-PeDO). The optimum bi-functional catalyst can aford the full the conversion of FFR and
86% selectivity to 1,4-PeDO. The catalysts have been characterized thoroughly by using a complementary combination of
powder X-ray difraction, N2 adsorption–desorption, scanning/transmission electron microscopy, Fourier transform infrared
spectroscopy, elemental analysis, and X-ray photoelectron spectroscopy. The characterization revealed that acidic groups
(–SO3H) have been introduced on the surface of the carbon layer coated SBA-15 support after sulfonation with 98% H2SO4
and the surface acidity can be tuned facilely by the sulfonating time. Meantime, Ru(0) sites was highly dispersed via an
impregnation and sequential reduction and directly adjacent to the surface –SO3H group. There existed an electronic inter-
action between Ru(0) sites and sulfonic groups, in which the electronic transfer from sulfonic sites to Ru(0) sites occurred.
Brönsted acid sites (–SO3H) have a signifcant infuence on the FFR conversion and the selectivity to 1,4-PeDO. The ordered
mesoporous structure, the appropriate density of acid sites and the electron-rich Ru(0) sites accounted for the the excellent
performance of the catalyst for an efcient production of 1,4-PeDO from FFR.
Kai Cui and Wei Qian have contributed equally.
Supplementary Information The online version of this article
(https://doi.org/10.1007/s10562-020-03520-5) contains
supplementary material, which is available to authorized users.
* Xiaoming Cao
xmcao@ecust.edu.cn
* Zhenshan Hou
houzhenshan@ecust.edu.cn
1
Key Laboratory for Advanced Materials, Research Institute
of Industrial Catalysis, School of Chemistry and Molecular
Engineering, East China University of Science
and Technology, Shanghai 200237, China
Vol.:(0123456789)
1 3

K. Cui et al.
Graphic Abstract
Keywords Furfural · Hydrogenation · SBA-15 · Carbon layers · Sulfonation, Ru
as ReOx, MoOx, VOx or WOx)-incorporated Rh and Ir cata-
lysts attracted much attention for the hydrogenolysis of
FFR or derivatives to synthesize 1,2- or 1,5-PeDO with
excellent selectivity [15–19]. Nevertheless, there were a
few reports on a catalytic production of 1,4-PeDO from
hydrogenolysis of FFR. It is worth noting that the pre-
viously reported catalysts for the synthesis of 1,4-PeDO
from FFR or FAL were carried out under harsh reaction
conditions. For example, the direct conversion of FFR
could give 1,2-PeDO (16% yield), 1,5-PeDO and 1,4-
PeDO (6.2% yield) in ethanol over the spinel-type Pt/
CoAl2O4 catalyst at 413 K, 1.0 MPa H2 for 24 h [20]. The
Rh-Ir-ReOx/SiO2 catalyst was also used for the selective
hydrogenation of FFR in water, which produced only 13%
yield of 1,4-PeDO at 393 K, 8.0 MPa H2 for 24 h [11].
Thereafter, the yield of 1,4-PeDO was reported to increase
up to ca. 30% considerably on Pd-Ir-ReOx/SiO2 catalyst
under the similar reaction conditions [21].
1 Introduction
Development of new methodologies for biomass transfor-
mation is gaining extensive attention. As biomass, a via-
ble resource of carbon and extensively available in nature,
has shown its potential for the production of carbon-based
energy sources and several valuable platform chemicals, it
can probably replace or provide an alternative to the cur-
rently used fossil fuel and high value-added fne chemicals
[1–5]. To utilize the biomass efectively, efcient technolo-
gies are needed for the selective tailoring of oxygen content
and functionality of the biomass-derived raw materials. C5
and C6 sugars are the main components of biomass feed-
stock [6]. Furfural (FFR) is already produced on an indus-
trial scale from these sugars via acidic hydrolysis, and the
vast majority of FFR can be converted into furfuryl alcohol
(FAL), tetrahydrofurfuryl alcohol (THFA), and 2-methyl-
furan (2-MeTF), which are used as solvents, plasticisers,
monomers in the production of resins, in the agrochemicals
industry, or as gasoline blends. Notably, FAL and its deriv-
atives can also be transformed into pentanediols (PeDOs)
such as 1, 2-, 1, 4- or 1, 5-pentanediol (PeDO), which can
be employed as a component of disinfectants or microbi-
cides, as an ingredient of various cosmetic products, and as
a monomer of polyesters and polyurethanes [7–10].
Although many reaction routes have been reported to
aford a signifcant yield of 1,4-PeDO, such as hydro-
genation of levulinic acid (LA), γ-valerolactone (GVL)
or ethyl levulinate in the presence of heterogeneous noble
metal-based catalysts, the reaction could normally occur
at > 473 K and 6–15 MPa H2 [22–26]. Hence, the devel-
opment of the heterogeneous catalysts for the efective
synthesis of PeDOs, especially 1,4-PeDO, from C5-furan
compounds under more mild condition is a highly prom-
ising and challenging work. Most recently, Zhang and
co-workers reported the catalytic conversion of FFR to
1,4-PeDO over Ru/CMK-3 catalysts in H2O at 353 K. The
Thus far, the selective hydrogenolysis of FFR or its
derivatives at the C-O bonds in the furan ring to pro-
duce PeDOs mainly focused on using supported catalysts
of group VIII precious metals (Ru, Pt, Rh, and Ir etc.)
[10–14]. In particular, low-valence metallic oxides (such
1 3

Ru Nanoparticles on a Sulfonated Carbon Layer Coated SBA-15 for Catalytic Hydrogenation of…
weak acid sites were provided by the positively charged
Ru species and the water-dissolved pressurized CO2 for
the reaction [13]. Thereafter, they found that in combina-
tion with Amberlyst-15, the Ru-6.3FeOx/AC catalyst could
aford a 1,4-PeDO yield of 86% [27]. Besides, Shimazu’
group has also reported novel Ni–Sn alloy catalysts that
could convert FFR to 1,4-PeDO under the condition of
3.0 MPa, 433 K, in which the efects of the solvent, reac-
tion temperature and H2 pressure on catalytic activity have
been investigated [28]. However, the current catalytic sys-
tems for FFR hydrogenation normally show a weak and
moderate acidity [13], and in some cases either the acidic
medium or other additives are needed during the reac-
tions. It has been reported that Brönsted acid sites could
facilitate the hydrogenation of FFR by the hydrolytic ring-
opening and lactonization reaction [29–31], but the efects
of the density of Brönsted acid sites on the production of
1,4-PeDO from FFR remained to be clarifed.
2 Experimental
2.1 Materials
All chemicals and solvents were commercially avail-
able and used as received without further purifcation.
Ruthenium(III) chloride (RuCl3·nH2O, Ru, 37.01%),
sucrose, NaCl (99%), NaOH (99%) and phenolphthalein
were from Sinopharm Chemical Reagent Co. Ltd. Con-
centrated sulfuric acid (98%), hydrochloric acid (38%)
tetraethyl orthosilicate (TEOS, 98.00%), ethanol (Anhy-
drous 99.99%), pluronic P123 and all the substrates were
purchased from Shanghai Tian Lian Chemical Technol-
ogy Co. Ltd. High purity N2 (99.99%) and H2 (99.99%)
were supplied by Shang Nong Gas Factory. Commercial
Ru/AC (5 wt%) was obtained from Sino-pharm Chemical
Reagent Co. Ltd. Furfural (99%), furfuryl alcohol (99%),
tetrahydrofurfuryl alcohol (98%), 1,4-pentanediol (97%),
5-hydroxy-2-pentanone (95%), diethyl ether and n-butanol
(99%) were obtained from Aladdin. The distilled water
was used in all experiments.
As a cheaper Pt-group metal, ruthenium (Ru) is a highly
competitive alternative as a catalyst component. Notably, Ru-
based catalysts displayed high catalytic efciency for hydro-
genation and also C-O bond cleavage under the aqueous con-
dition [32, 33]. In the previous work, we have found that the
carbon layer coated SBA-15 (C-SBA-15) is hydrothermally
stable in aqueous-hydrogenation and showed a high BET sur-
face area (more than 500 m2·g−1) [34]. Based on our previous
work, we attempted initially to carry out the hydrogenation of
FFR by using Ru/C-SBA-15 as a catalyst, but unfortunately the
product distribution is rather wide and a large amount of the
products (THFA) from furan ring hydrogenation was detected.
This revealed that the acid sites could be crucial for the for-
mation of diols while the Ru/C-SBA-15 catalyst lacked the
acid sites. Herein, in this work we have designed a metal–acid
bi-functional catalyst. For this purpose, the sulfonated carbon
layer coated SBA-15 (SC-SBA-15) was obtained by sulfonat-
ing C-SBA-15 with 98% concentrated sulfuric acid. Sequen-
tially, Ru sites were introduced into the modifed support by
impregnation and reduction to attain the bi-functional cata-
lysts containing both metal sites and acid sites. Notably, the
density of acid sites on the catalysts was highly dependent
on the sulfonating time. The further characterization on the
properties of catalytic active sites has provided a deep insight
into the relationship between the metal–acid sites and catalytic
performance. Additionally, the infuences of reaction param-
eters on the product selectivity along with the reaction kinetics
using MATLAB program were studied. Based on these results
above, reaction pathway has been also elucidated.
2.2 Catalyst Preparation
2.2.1 Preparation of SC‑SBA‑15
SBA-15 was synthesized according to the previous report
(the details for the synthesis of SBA-15 are given in support-
ing information) [35]. The carbon layer coated SBA-15 was
synthesized using the following procedure: 0.5 g sucrose
were dissolved in deionized water and then 1 g SBA-15
was added into the mixture. The resulting aqueous suspen-
sion stirred in an open evaporating dish at 50 °C until the
water evaporated and a white solid was obtained. The white
solid was ground, transferred into a quartz boat, followed
by pyrolyzing in a tube furnace under high purity nitrogen
fow at 550 °C for 4 h with a ramp rate of 2.5 °C·min−1. The
carbon coated SBA-15 was denoted as C-SBA-15. Next, 1 g
C-SBA-15 was added to 15 mL of concentrated sulfuric acid
(H2SO4, 98%) in a 50 mL glass tube, the resulting reaction
mixture was ultra-sonicated for 2 h in ambient conditions,
and then was heated under the protection of nitrogen fow
(10 mL·min−1) at 110 °C for another 3, 6, 9 h with stirring.
The reaction mixture was cooled to ambient temperature
and was then added dropwise to 50 mL ice-cold water in
30 min under mechanical stirring. Finally, the suspension
was centrifuged, the solid product was collected and washed
at least three times with ice water, then dried at 80 °C for
12 h under the vacuum. The sulfonated C-SBA-15 samples
with the diferent sulfonating time were denoted as SC-SBA-
15_3h, SC-SBA-15_6h, and SC-SBA-15_9h, respectively.
1 3

K. Cui et al.
2.2.2 Preparation of the Ru/SC‑SBA‑15 Catalysts
the intersection of the liquid and solid. A water droplet with
a volume of 2 μL was dispensed by a piezo doser onto each
sample disk. A CHNS elemental analyzer (Vario MICRO
cube) was used to perform elemental analysis. The inductively
coupled plasma atomic emission spectroscopy (ICP-AES)
analysis was carried out on a Varian ICP-710ES instrument.
The acidities of the -SO3H group were measured by the ion
exchange method [36]. Briefy, 0.1 g catalyst was mixed with
5 mL of 1 mol·L–1 NaCl solution and stirred at room tempera-
ture for 4 h. The protons of the -SO3H group were selectively
exchanged with Na+ and was then released into the solution.
The suspension was fltered and the concentration of H+ in
fltrate was then measured by titration with 0.01 mol·L–1 of
NaOH solution using phenolphthalein as an indicator. Total
acidity was also measured through a similar process. Specif-
cally, 0.1 g of catalyst was mixed with 5 mL of 0.01 mol·L–1
NaOH solution. After sufcient mixing and fltration, total acid
density was titrated by 0.01 mol·L–1 HCl using phenolphtha-
lein as an indicator.
The supported Ru catalysts were prepared by the conven-
tional incipient wetness impregnation. Typically, 1.0 g SC-
SBA-15-6 h was added to 8.0 mL ethanol with three drops
of hydrochloric acid. And then 4.0 mL ethanol solution of
RuCl3 (7 mg·mL−1) was added the above solution under vig-
orous stirring. After continuous stirring vigorously at 50 °C
about for 12 h, the solvent was removed by evaporation at
80 °C, yielding a solid powder. The as-prepared powder was
transferred into a crucible and then placed into a quartz tube
furnace maintaining 300 °C for 2 h under fowing H2 atmos-
phere with a heating rate of 2.5 °C·min−1 prior to the char-
acterization and reaction. The resulting catalyst was denoted
as Ru/SC-SBA-15_6h. Additionally, Ru/SC-SBA-15_3h and
Ru/SC-SBA-15_9h were synthesized in a similar method.
Ru/C-SBA-15 catalyst (no sulfonation) was also prepared
using C-SBA-15 as a support for the sake of comparison.
To get a deep insight into the role of -SO3H group in the
Ru/SC-SBA-15_6h catalyst, in another control experiment,
the proton of -SO3H group was removed selectively by the
ion exchange with NaCl aqueous solution [36]. Afterwards,
the resulting catalyst (Ru/SC-SBA-15_6h_E) was employed
for FFR hydrogenation.
2.3 Catalytic Reactions
The hydrogenation reaction was performed in batch stainless
steel autoclave with a 20 mL polytetrafuoroethylene liner.
The autoclave was equipped with gas supply system and a
magnetic stirrer. In a typical procedure, a certain amount of
catalyst was dispersed in 5.0 mL water, and then put into a
certain amount of FFR. After purging with hydrogen for three
times. The autoclave was sealed with the required hydrogen
pressure and heated to the specifed temperature in 25 min.
Reaction time started after the set temperature was attained.
After the reaction was fnished, the reactor was quenched in an
ice-water bath to stop the reaction. Straight after, the catalyst
was separated from the solution by fltration. The products in
aqueous phase were extracted by diethyl ether several times
and analyzed by GC and MS on Shimadzu GC-2014 equipped
with an KB-50 MS (30 m long, 0.32 mm i.d., 0.50 μm flm
thickness) and an Agilent 6890/5973 GC–MS system equipped
with a HP-5 MS column (30 m long, 0.25 mm i.d., 0.25 μm
flm thickness) using n-butanol as the internal standard. All the
products were identifed by GC–MS. The quantitative determi-
nation of FFR, FAL, THFA, 1,4-PeDO and 5-hydroxy-2-pen-
tanone (5-HP) was performed with the authentic samples by
GC using individual calibration curve method (Figs. S1–S5)
and thus the correction factors were obtained accordingly. The
conversion of substrates and yield towards products were cal-
culated as follows:
2.2.3 Catalyst Characterization
Powder X-ray diffraction (XRD) analysis of the samples
were collected on a Rigaku D/MAX 2550 VB/PC instrument
equipped with a 9 kW rotating anode Cu source at 45 kV and
100 mA (0–5°, 5–75°, 0.2° s−1). Raman spectroscopy was per-
formed using a Thermo Scientifc DXR Raman microscope
equipped with a 532 nm laser excitation source operated at
25 mW. Quanta chrome NOVA 2200e equipment was used
to perform BET surface area analysis at−196 °C with liquid
nitrogen. Nitrogen physisorption was performed after degas-
sing at 200 °C for 5 h to a vacuum of 10–3 Torr before analysis.
The pore size distribution from the adsorption isotherm was
calculated by the BJH method. Thermo Scientifc ESCALAB
250 was used to perform X-ray photoelectron spectroscopy
(XPS) analysis. Field emission scanning electron microscopy
(FESEM) images were performed on JSM electron micro-
scopes (JEOL JSM-6360LV, Japan). High angle annular
dark feld scanning TEM (HAADF-STEM) was performed
on a Talos F200X G2/Talos F200X G2 transmission electron
microscope operating at 200 kV with a nominal resolution of
0.16 nm. At least 150 Ru particles were counted for particle
size distribution analysis. The samples for HAADF were pre-
pared by dropping the ethanol solutions containing the NPs
onto the holey carbon-coated Cu grids. Water contact angle
(CA) was carried out by the Contact Angle Meter (CA100C,
Innuo Company, Shanghai, China) using the droplet profle as
a method. The CA was determined using a tangent placed at
Amount of substrates converted (mole)
Conversion (% ) =
× 100%
Amount of substrate taken (mole)
(1)
1 3

Ru Nanoparticles on a Sulfonated Carbon Layer Coated SBA-15 for Catalytic Hydrogenation of…
Amount of a product formed (mole)
Yield (% ) =
× 100%
Amount of substrate taken (mole)
Ru/C-SBA-15
(2)
Ru/SC-SBA-15_3h
(100)
The catalytic experiments were repeated three times, and
the standard deviations for the conversion and yield were
within 3%. The recyclability of the Ru/SC-SBA-15_6h
catalyst was evaluated in six consecutive runs at 140 °C and
1.5 MPa. Briefy, the hydrogenation of FFR was operated
in a high-pressure batch autoclave of stainless steel with
a 20 mL polytetrafuoroethylene liner. After reaction, the
catalyst was washed with ethanol and water several times to
remove the products, followed by drying at 80 °C for 10 h.
Then the dried catalyst can be used for the next run.
Ru/SC-SBA-15_6h
Ru/SC-SBA-15_9h
0
10 20 30 40 50 60 70 80
2 Theta(o)
(110)
(200)
Ru/C-SBA-15
Ru/SC-SBA-15_3h
Ru/SC-SBA-15_6h
Ru/SC-SBA-15_9h
In kinetic studies, MATLAB program has been used for
solving the ordinary diferential equations as indicated in the
section of results and discussion, and the kinetic parameters
k1-k8 were determined accordingly. The function of lsqnon-
lin nonlinear ftting in MATLAB was also adopted to mini-
mize the error between experimental and predicated data.
The obtained reaction rate constants were then employed to
evaluate the apparent activation energy (Ea) by plotting lnk
versus 1000/T through Arrhenius equation.
1
2
3
o
4
5
2 Theta( )
Fig. 1 XRD patterns of the diferent Ru-based catalysts
These results indicated that the porous structure of SBA-15
was preserved regardless of carbon doping, sulfonation and
the sequential fabrication of Ru species. However, with the
extension of sulfonation time, the (100), (110) and (200) dif-
fraction peaks of Ru/SC-SBA-15 catalysts shifted to higher
angle. Especially, Ru/SC-SBA-15_9h shifted to a much
larger extent likely due to the formation of more sulfonic
groups by sulfonating and thus the mesoporous structure of
SBA-15 was infuenced to some extent. Next, the wide angle
XRD patterns were also presented in Fig. 1 (insert), it could
be seen that Ru-based catalysts showed a broad difraction
peak at 2θ=23.0° that was assigned to the amorphous silica.
Moreover, with the increase of sulfonating time, there was
no obvious changes among these difraction peaks of the
samples, while the peak at 24° and 43° assigned to carbon
structures were almost indiscernible due to the low content
of carbon materials on the SBA-15 [34]. Particularly, the dif-
fraction peaks from Ru species were almost not observed in
all samples, indicating that Ru species are highly dispersed
on the support surface or beyond the XRD detection limit
[40].
3 Results and Discussion
3.1 Catalyst Characterization
The conversion of FFR to diols involves hydrogenation,
ring-opening and de-oxygenation, in which the acid sites
and metal sites have a signifcant efect on the activity and
selectivity of FFR hydrogenation [13, 27, 37, 38]. However,
the efect of acid density on the selectivity of products has
not been investigated thoroughly in FFR hydrogenation. In
this work, the carbon layer coated on SBA-15 was frstly
sulfonated with concentrated sulfuric acid, and then Ru
species was introduced with low loading (ca. 1 wt%). As
shown in Table S1, the C and H contents of the as-prepared
catalysts have been determined by elemental analysis and
the S, Ru and Si contents by ICP-AES, respectively. This
further confrms that sulfonic acid groups were incorporated
on the catalysts surface after the H2SO4 treatment and the
sulfonating did not exert any impact on a sequential loading
of Ru species.
Raman spectroscopy was very sensitive to subtle struc-
tural variations in carbon materials. Thus Ru/SC-SBA-
15_6h and Ru/C-SBA-15 catalysts were characterized
by Raman spectroscopy. As shown in Fig. S6, it could be
observed clearly that sulfonation has no efect on the struc-
ture of the carbon layer and two strong peaks at 1358 cm−1
and 1598 cm−1 can be assigned to the D and G bands of
the disordered and graphitized carbons, respectively [41,
42]. In addition, the second-order (2D) band was the most
prominent feature in the Raman spectrum of graphene,
and its shapes is sensitive to the number of layers of gra-
phene. From Fig. S6, a very sharp 2D band was observed at
The small-angle and wide-angle XRD patterns (Inset) of
the Ru-based catalysts are shown in Fig. 1. It was observed
that from small-angle XRD patterns, all the samples except
Ru/SC-SBA-15_9h presented an intense (100) refection
and two less intense (110) and (200) refections, appearing
at 2θ=0.5–1.1° and 2θ=1.3–2.1° respectively, which were
characteristic of the hexagonal p6mm symmetry of SBA-
15 [39], while Ru/SC-SBA-15_9h showed only (100) peak.
1 3

K. Cui et al.
approximately 2753 cm−1 for Ru/SC-SBA-15_6h and Ru/C-
SBA-15, and the sharp of 2D band (more specifcally the
absence of a typical graphite shoulder) was characteristic
feature of few-layered graphene [43, 44].
other acidic functional groups besides -SO3H group, includ-
ing carboxylic and hydroxyl groups [36].
The XPS characterizations were employed to investigate
the surface valence state of the catalysts. As shown in Fig. 2,
the high resolution XPS spectra of Ru 3p revealed the sur-
face characteristics of the Ru species, and the spectra were
calibrated using carbon at 284.4 eV. For Ru/C-SBA-15, the
intense doublet peaks of 3p3/2 and 3p1/2 for Ru0 appeared
at 461.8 and 483.8 eV, while the weak 3p3/2 and 3p1/2
peaks appeared at 464.2 and 486.6 eV were attributed to
Run+ [45, 46]. Comparatively, the surface Ru NPs were in
an electron-poor state as compared with the sulfonic group.
If the interaction existed between the sulfonic group and Ru
species, the electron transfer occurred between two species.
Then, the binding energy of the surface ruthenium atoms
would move to a lower value [45]. In fact, as compared with
the Ru 3p3/2 and 3p1/2 binding energy of the Ru/C-SBA-15
(Fig. 2), either Ru0 or Run+, that of Ru/SC-SBA-15_6h (Ru0:
461.1 and 483.3; Run+: 463.8, 486.1 eV) were indeed shifted
Then, the structure of catalysts was further studied by the
nitrogen adsorption–desorption method. Fig. S7 showed the
nitrogen adsorption–desorption isotherms and pore size dis-
tribution of the Ru-based catalysts. As shown from Fig. S7,
all the Ru-based catalysts exhibited IV-type isotherms with
H1 hysteresis loops at the relative pressure between about
0.6 and 0.8 while the support was laced with carbon and sul-
fur, indicating that the mesopores were relatively uniform in
size and with a center of about 7.5 nm (Fig. S7, insert). The
corresponding texture properties (BET surface area, pore
diameter and total pore volume) are also shown in Table 1.
The BJH pore size distribution also showed that the samples
did exhibit the ordered pores. Especially, the Ru/C-SBA-15
showed the highest surface area, total pore volume and pore
size among the Ru-based catalysts. With the increase of the
sulfonation time, the resulting samples aforded obvious
decreases of the surface areas, total pore volume and pore
size because the pores of the catalysts were partly blocked
by the sulfonic groups. For example, the BET surface area,
pore volume and pore diameter of Ru/SC-SBA-15_9h were
decreased considerably, as compared with other Ru catalysts
(Table 1), revealing that the doping of more sulfonic groups
caused a dramatic shrinkage of the mesoporous structure.
Besides, as shown in Table 1, the sole carbonization process
was also accompanied with emerge of oxygen-containing
groups, such as –OH and –COOH, on the C-SBA-15 sample
(total acid 0.24 mmol·g−1). However, after sulfonation, the
amount of sulfonic groups increased considerably on the
basis of ICP-AES or a titration analysis, which aforded a
similar results (Table 1). It should be noting that the present
sulfonation process not only introduced -SO3H groups, but
also led to an increase of total acidity (Table 1), where the
2.5
Ru/SC-SBA-15_6h
Ru 3p
Ru0
0(483.3 eV)
(461.1 eV)
Ru
Run+
2.0
1.5
1.0
0.5
0.0
Run+
(463.8 eV)
(486.1 eV)
(461.7 eV)
(483.8 eV)
(486.6 eV)
Ru/C-SBA-15
(464.2 eV)
450
460
470
480
490
500
B.E.(eV)
Fig. 2 XPS spectra of Ru 3p of Ru/C-SBA-15 and Ru/SC-SBA-15_6h
Table 1 Physical properties of
a
b
Catalysts
SBET
Vtotal
Pore sizec
Total acid
densityd
-SO3H
Acid densityf
diferent Ru catalysts
(m2·g–1) (cm3·g–1) (nm)
Densitye
(mmol·g−1
)
(mmol·g−1
)
(mmol·g−1
)
Ru/C-SBA-15
602
0.91
0.84
0.76
0.70
7.8
7.6
7.3
7.1
0.24
0.49
0.81
1.12
–
0.12
0.29/(0.22)
0.48
–
Ru/SC-SBA-15_3h 526
Ru/SC-SBA-15_6h 453
Ru/SC-SBA-15_9h 368
0.09
0.23
0.39
aSurface area was calculated from the nitrogen adsorption isotherm using the BET method
bTotal pore volume was calculated from nitrogen sorption isotherms at P/P0 =0.99
cPore size was calculated by the BJH method
dTotal acid and
eThe proton acid of the -SO3H group were determined by a titration method, respectively [36]. The values
in the parenthesis referred to the acid amount (mmol·g−1) of the catalyst after recycling for six times
fThe amount of -SO3H groups was calculated on the basis of ICP-AES analysis (Table S1)
1 3

Ru Nanoparticles on a Sulfonated Carbon Layer Coated SBA-15 for Catalytic Hydrogenation of…
toward lower binding energy signifcantly (about 0.5 eV),
implying that the specifc interaction could endow Ru sites
with higher electron density.
Simultaneously, C 1s and Ru 3d of Ru/C-SBA-15 and Ru/
SC-SBA-15_6h were shown in Fig. 3, and the spectra were
calibrated using silicon at 103.4 eV. It could be observed
that C 1s spectra of Ru/C-SBA-15 exhibited three decon-
voluted binding energy peaks: the strong peak at 284.5 eV
was ascribed to the aromatic carbon (sp2 carbon), the peak
at 286.5 eV corresponded to carbonyl (C=O) and the peak
at 288.3 eV was ascribed to carboxylic group (−COOH),
respectively (Fig. 3a) [47, 48]. C 1s of Ru/SC-SBA-15_6h
exhibited no obvious changes, as compared with that of
Ru/C-SBA-15, which confrmed that the oxidation state of
the elements remained unchanged after the H2SO4 treat-
ment. Notably, Ru 3d5/2 peak of Ru/C-SBA-15 appeared at
281.7 eV belonged to Ru0 [49]. The binding energies of Ru
Fig. 4 FESEM images of diferent Ru-based catalysts. a Ru/C-
3d5/2 of Ru/SC-SBA-15_6h was also shifted to lower value
(281.1 eV) due to the introduction of sulfonic groups, which
also suggested that the sulfonic acid on the carbon layer
could coordinate with Ru species and thus might donate
electron density to active Ru sites on the support, in line
with that of the Ru 3p spectra above (Fig. 2).
SBA-15, b Ru/SC-SBA-15_3h, c Ru/SC-SBA-15_6h and d Ru/SC-
SBA-15_9h
time was extended to 9 h (Fig. 4d). Actually, as evidenced
by N2 adsorption–desorption measurement, the Ru/SC-SBA-
15_9h catalyst displayed a partial collapse of pore structure
(Table 1).
Based on the characterizations by elemental analysis,
XRD, Raman and XPS, it indicated that a large amount of
sulfonic groups was generated on the carbon layers and the
dispersed Ru species could be preferentially coordinated
with sulfonic groups. Next, the morphology of carbon coated
on SBA-15 and the sulfonated carbon layers coated SBA-
15 supports needed to be identifed by SEM. As shown in
Fig. 4a, SEM images of Ru/C-SBA-15 displayed a uniformly
fbrous macroscopic structure with relatively uniform size
of 200–400 nm. Comparatively, the sulfonated Ru-based
catalysts showed a slight collapse of mesoporous structure,
as compared with that of Ru/C-SBA-15 although they also
exhibited the similar rope-like units in the 200–500 nm
diameter range (Fig. 4b–d). However, the mesoporous struc-
ture could be damaged more obviously as the sulfonating
Subsequently, the dispersion of Ru particles on a sul-
fonated carbon layer coated SBA-15 was identifed by high-
angle annular dark-feld scanning transmission electron
microscopy (HAADF-STEM) images and provided further
evidence (Fig. 5). Ru particles on a carbon modifed support
(Ru/C-SBA-15) had a slight aggregates and uneven distri-
bution owing to weak interaction between carbon and Ru
species (Fig. 5a), and the mean size of Ru particles was
about 3.2 nm. Nevertheless, once introducing SO3H groups
(Ru/SC-SBA-15_3h), the degree of aggregation with Ru
was greatly mitigated and the size of Ru NPs decreased to
1.8 nm (Fig. 5b). It was surprising to fnd that the aver-
age particle size on Ru/SC-SBA-15_6h catalyst was only
Fig. 3 XPS spectra of a C 1s of
b
a
C1s (284.5)
Ru/C-SBA-15 and b Ru/SC-
Ru/SC-SBA-15-6h
C1s (284.5)
SBA-15_6h
Ru/C-SBA-15
C1s (286.5)
C1s (288.3)
C1s (286.5)
C1s (288.3)
Ru3d5/2(281.7)
Ru0
Ru3d5/2(281.1)
Ru0
295
290
285
280
275
295
290
285
280
275
B.E.(eV)
B.E.(eV)
1 3

K. Cui et al.
Fig. 5 HAADF-STEM images
and the particle size distribu-
tion of a Ru/C-SBA-15, b Ru/
SC-SBA-15_3h, c Ru/SC-SBA-
15_6h and corresponding EDS
elemental mappings of Ru, O,
C, S; d Ru/SC-SBA-15_9h
1.0 nm. Simultaneously, the fne Ru particles were dispersed
uniformly on the surface of the catalyst and had almost no
aggregation even after the reduction process (Fig. 5c), likely
resulting from the synergistic role of -SO3H groups and
mesoporous structure of SBA-15. Besides, the correspond-
ing elemental mapping also confrmed that Ru species were
indeed distributed homogeneously on the sulfonated support
and actually were consistent with that of C and S elements.
Combination of XPS and STEM characterization (Figs. 2
and 5), there was the electronic interaction of the Ru species
with the adjacent -SO3H groups, which could prevent the
nanosized Ru particles from the aggregation in the course
of catalyst preparation. As such, the possible coordination
between Ru centers and the adjacent sulfonic acid groups on
the catalyst surface occurs and has been depicted in Fig. S8.
On the other hand, SC-SBA-15_6h catalyst with the high
BET area would also favor for dispersion of metal species
[34]. Unfortunately, when the sulfonation time exceeded 9 h,
Ru NPs partially aggregated and Ru particles grew to 2.5 nm
(Fig. 5d). This was because an excessive sulfonation will
destroy pores of SBA-15 partially, which caused a loss of
porous structure (Table 1).
the formation of more hydrophilic functional groups (–OH,
–COOH, –SO3H) on the surface of the catalysts in line with
the previous titration analysis.
3.2 Hydrogenation of FFR
3.2.1 The Role of Surface Sulfuric Acid Groups on the Ru
Catalysts
Firstly, the diferent Ru catalysts have been used for the
hydrogenation of FFR under the identical reaction condi-
tions in aqueous phase. As shown in Table 2, Ru/C-SBA-15
catalyst provided a full conversion of FFR, indicating that
the Ru sites on the catalyst were easily accessible to FFR.
However, the FAL and THFA were produced in a large
amount arising from the reduction of aldehyde group and
furan ring of FFR molecules along with the formation of a
wide range of the other products, but 1,4-PeDO was formed
with only 36% yield (Table 2, entry 1). This revealed that
the weak acid sites (–OH or –COOH groups) were insuf-
cient to open the furan ring efciently, and sequentially did
not initiate the production of 5-hydroxy-2-pentanone (5-HP)
and 1,4-PeDO. In addition, a small amount of 2-methylfuran
(2-MeTHF) was detected by GC–MS, likely arising from
hydrodeoxygenation of THFA. These results demonstrated
that although Ru/C-SBA-15 exhibited high hydrogenation
activity by virtue of the mesoporous structure and active Ru
sites, the yield of 1,4-PeDO was rather poor owning to the
absence of appropriate acid sites.
In the next step, the surface hydrophilicity of the difer-
ent Ru-based catalysts were evaluated by using static water
contact angle (WCA). One hand, it can be seen that Ru/C-
SBA-15 catalyst was rather hydrophilic (WCA was only
29°) even without sulfonation due to the presence of surface
polar groups like (–OH, –COOH). On the other hand, as
shown in Fig. S9, WCAs became even smaller as the sul-
fonating time increased. These results clearly demonstrated
that the hydrophilicity of the carbon materials was further
enhanced by treating with concentrated sulfuric acid due to
However, if the sulfonated Ru/SC-SBA-15_6h catalyst
with appropriate sulfonic acid density (0.29 mmol·g−1
,
Table 1) was employed for hydrogenation of FFR.
1 3

Ru Nanoparticles on a Sulfonated Carbon Layer Coated SBA-15 for Catalytic Hydrogenation of…
Table 2 Hydrogenation of furfural over diferent catalysts
Entries
Catalysts
Yield (%)
FAL
THFA
5-HP
1,4-PeDO
Others
1
2
Ru/C-SBA-15
8
–
–
–
–
4
20
–
26
7
18
–
8
11
10
14
–
36
87
63
55
59
51
–
12
6
10
19
15
9
Ru/SC-SBA-15_6h
Ru/C-SBA-15+p-TsOH
Ru/C-SBA-15+H2SO4
Ru/C-SBA-15+CF3SO3H
Ru/SC-SBA-15_6h_E
Ru/SC-SBA-15_6h+NaOH
5%Ru/ACd
3a
4a
5a
6b
7c
8
19
15
16
22
34
67
46
33
–
–
Reaction conditions: 2 mmol furfural, 20.0 mg catalyst, 140 °C, 1.5 MPa H2, 4 h and 4.0 mL H2O. All furfural was consumed nearly completely
in the reactions. The reactions were repeated at least 3 times, and the standard deviation of yields is within 3%
aThe molar amount of liquid acid was equivalent to that of Ru/SC-SBA-15_6h (1.78×10–2 mmol)
bThe proton of the -SO3H group in the catalyst was removed by ion exchange with NaCl
cNaOH was added in the equivalent of acid sites in Ru/SC-SBA-15
dThe commercial 5%Ru/AC catalyst was used 4.0 mg. Others include oligomeric and tar-like products and could not be identifed by GC
Comparatively, Ru/SC-SBA-15_6h aforded much higher
yield of 1,4-PeDO than that of Ru/C-SBA-15 catalyst, indi-
cating the crucial role of the sulfonic acid groups. The yield
of 1,4-PeDO increased up to 87%, and meantime the forma-
tion of by-products was suppressed signifcantly (Table 2,
entry 2). Especially, Ru/SC-SBA-15 still aforded a lower
activity than that of Ru/SC-SBA-15_6h even if the strong
liquid acids were added in the equivalent of acid sites
(Table 2, entries 3–5), which suggested clearly that the
surface sulfuric acid groups on the catalyst would be more
favorable for producing 1,4-PeDO, as compared with that
of the Brönsted acid in the aqueous phase. Notably, when
the proton of –SO3H group in Ru/SC-SBA-15_6h catalyst
were exchanged selectively into Na+ and was then released
into the solution, the resulting Ru/SC-SBA-15_6h_E cata-
lyst only showed a 1,4-PeDO yield of 51% (Table 2, entry
6). It should be noting that Ru/SC-SBA-15_6h_E catalyst
still gave a slight higher yield of 1,4-PeDO than that of
Ru/C-SBA-15, which could be caused by the role of weak
acid sites (-COOH, -OH etc.) in promoting the reaction, as
indicating in the previous report [13, 27]. Moreover, if the
total acid sites were neutralized with the equivalent NaOH,
no 1,4-PeDO was found and only FAL (in 20% yield) and
THFA (in 34% yield) were detected by GC, along with the
unidentifed products likely arisen from the polymerization
of FFR and the other intermediate species (Table 2, entry 7)
[50, 51]. Similarly, the commercial Ru/AC catalyst only gave
THFA without opening ring under the same condition. These
results proved clearly that the strong acid sites (-SO3H) were
crucial for selective hydrogenation of FFR into 1,4-PeDO,
but the role weak acidic sites (-OH and -COOH) cannot be
excluded.
Based on all the results above, it was demonstrated that
that there might be a coordination interaction between sur-
face acidic groups and the adjacent Ru sites, where the elec-
tron transfer from the sulfonic groups to Ru sites occurred,
as evidenced by XPS, STEM image and its elemental map-
pings (Figs. 2, 3 and 5). It should be noting that the elec-
tron-rich Ru sites could facilitate adsorption and homolytic
dissociation of H2 [26]. The adjacent Brönsted acid sites
were responsible for opening the furan ring, and thus the
active hydrogen atoms led to the facile hydrogenation of
the intermediates. Overall, the synergistic efect between a
surface Brönsted acid sites and Ru sites promoted the FFR
hydrogenation and resulted in a high 1,4-PeDO yield.
Next, the efect of surface sulfonic acid group on the FFR
hydrogenation has been investigated. As shown in Fig. 6,
it was worth noting that all Ru-based catalysts can aford
full conversion of FFR under the present condition, and it
was observed that sulfonic acid group on the catalyst had a
great impact on the distribution of products. Ru/C-SBA-15
with the low acid amount gave only around 36% yield to
1,4-PeDO in FFR hydrogenation. As sulfonic acid density
increased to 0.29 mmol·g−1, the yield of 1,4-PeDO achieved
the optimum (87%), and the further increasing sulfonic acid
density to 0.48 mmol·g−1 would result in a sharp decrease
1 3

K. Cui et al.
100
80
60
40
20
0
As such, the present catalyst provided high 1,4-PeDO yield
(87%) and a full conversion of FFR under rather mild condi-
tions, and the catalytic performance was comparable with or
better than that of the previous report [13, 27, 29].
3.2.2 Kinetics and Reaction Pathway
GVL
LA
Others
1,4-PeDO
5-HP
THFA
FAL
To get a deep insight into the reaction pathway observed
with the present Ru catalyst, the efect of the reaction tem-
perature on product distribution has been evaluated thor-
oughly. As depicted in Fig. 7a, FFR was converted com-
pletely at 80 °C within 8 h, but FAL and THFA were formed
as the dominant products, accompanied by a small amount
of 5-HP, 1,4-PeDO and 1,2-PeDO. As reaction time was
prolonged to 10 h, the FAL yield decreased gradually with
a concomitant increase of the THFA (yield up to 32%), and
meantime THFA or a part of FAL could be further con-
verted to 1,2-PeDO and 5-HP. When the reaction was carried
out at 100 °C, the reaction rates increased and the product
yields showed the similar tendency with that of Fig. 7a at the
beginning of 6 h (Fig. 7b). However, the yield of 1,4-PeDO
rose gradually with the consumption of 5-HP. As the reac-
tion continued on, the dominant products was 1,4-PeDO,
accompanied by a trace of 1, 2- PeDO.
0.48
0
0.29
0.12
-SO H(mmol/g)
3
Fig. 6 Efect of the -SO3H densities on product distribution for the
FFR hydrogenation. Conditions: 2.0 mmol furfural, 20.0 mg cata-
lysts, 1.5 MPa H2, 140 °C, 4 h and 4.0 mL H2O. FFR: Furfural; FAL:
furfuryl alcohol; THFA: tetrahydrofurfuryl; 1,4-PeDO: 1,4-pen-
tanediol; 5-HP: 5-hydroxy-2-pentanone; LA: levulinic acid, GVL:
γ-valerolactone
in yield of 1,4-PeDO. This can be explained by following
reasons. Firstly, excessive acid sites would promote more
by-reactions like polymerization, acid hydrolysis, leading to
LA, GVL and other side-products in a considerable amounts,
which decreased the selectivity to 1,4-PeDO signifcantly.
Secondly, the excessive sulfonation would lead to the par-
tial collapse of mesoporous structure of SBA-15 (Fig. 4d),
along with a decrease of BET surface area (Table 1, entry.
4), which might restrict the hydrogenation of the intermedi-
ate products to some degree. Third, the excessive sulfonation
might result in too strong hydrophilicity of catalyst (Fig.
S9d), it might be not favorable due to competitive adsorp-
tion of the substrate and water molecules. Therefore, Ru/SC-
SBA-15_6h with the sulfonic acid density of 0.29 mmol·g−1
gave the optimum result for the selective hydrogenation of
FFR into 1,4-PeDO under the present condition.
As the reaction temperature was further increased to
120 °C (Fig. 7c), FFR was consumed completely within 4 h,
and the main product was 1,4-PeDO. On the other hand, the
product from THFA dehydration, namely 2-MeTHF started
to appear. The by-product 1,2-PeDO is almost undetectable
by GC. Finally, the catalytic performance was examined at
140 °C (Fig. 7d). To our surprise, the conversion of FFR
reached 100% only within 1.5 h, the main products were
1,4-PeDO along with the intermediate FAL and 5-HP. As
the reaction time was prolonged to 4 h, the yield of 1,4-
PeDO reached highest (87%), and a small amount of THFA
and 2-MeTHF were also detected. However, if the reaction
temperature continued to increase to 150 °C, the yield of
1,4-PeDO remained almost unchanged. Meantime, the yield
of THFA decreased slightly, along with forming 2-MeTHF
from the dehydration of THFA (Table S2). Hence, these
kinetic profles clearly revealed that the catalytic process
involves the following sequence (1) the hydrogenation of
FFR to FAL followed by (2) the conversion of FAL to 5-HP
or THFA and then (3) the hydrogenation of 5-HP or THFA
to 1,4-PD.
Figure S10 showed conversion/time profles and yield of
1,4-PeDO/time profles of hydrogenation reactions catalyzed
by the diferent Ru catalysts at 140 °C. It was found that Ru/
SC-SBA-15_6h catalyst indeed aforded the highest FFR
conversion and the yield of 1,4-PeDO among the catalysts
used in this work. This suggested that Ru/SC-SBA-15_6h
catalyst owned the appropriate acid sites and fne-dispersed
metal sites, and a good match between two sites has been
achieved, which were required to promote the formation of
1,4-PeDO. In other words, the ordered mesoporous structure,
and the electronic interaction between the sulfonic groups
and metal Ru species were the decisive factors for the selec-
tive conversion of FFR into 1,4-PeDO in the present system.
Next, Based on the product distribution, a skeleton reaction
network related to FFR conversion over Ru/SC-SBA-15_6h
was constructed (Scheme 1). k1 was the rate constant from
FFR to FAL; k2 was the rate constant from FAL to THFA; k3
was the rate constant from FAL to 1,2-PeDO; k4 was the rate
constant from FAL to 5-HP; k5 was the rate constant from
THFA to 2-MeTHF; k6 was the rate constant from 1,2-PeDO
to 1,4-PeDO; k7 was the rate constant from 5-HP to 1,4-PeDO;
1 3

Ru Nanoparticles on a Sulfonated Carbon Layer Coated SBA-15 for Catalytic Hydrogenation of…
100
80
60
40
20
0
100
80
60
40
20
0
100
80
60
40
20
0
100
Fig. 7 FFR conversion of and
product yield/time profles
of hydrogenation reactions
catalyzed by Ru/SC-SBA-
a
Conversion (%)
2-MeTHF
THFA
b
Conversion (%) 80
2-MeTHF
THFA
FAL
5-HP
1,4-PeDO
1,2-PeDO
FAL
60
40
20
0
15_6h catalyst at diferent
5-HP
1,4-PeDO
1,2-PeDO
temperatures (bars denote stand-
ard deviations). Conditions:
2.0 mmol furfural, 20.0 mg Ru/
SC-SBA-15_6h, 1.5 MPa H2
and 4.0 mL H2O, a 80 °C, b
100 °C, c 120 °C and d 140 °C.
FFR: Furfural; FAL: furfuryl
alcohol; THFA: tetrahydrofurfu-
ryl; 1,4-PeDO: 1,4-pentanediol;
5-HP: 5-hydroxy-2-pentanone;
1,2-PeDO: 1,2-pentanediol;
2-MeTHF: 2-methylfuran
0
2
4
6
8
10
0
2
4
6
8
10
Time (h)
Time (h)
100
80
60
40
20
0
100
80
60
40
20
0
100
80
60
40
20
0
100
80
60
40
20
0
c
d
Conversion (%)
2-MeTHF
THFAL
FAL
5-HP
1,4-PeDO
1,2-PeDO
Conversion (%)
2-MeTHF
THFA
FAL
5-HP
1,4-PeDO
1,2-PeDO
0
2
4
6
8
10
0
1
2
3
4
5
Time (h)
Time (h)
Scheme 1 Reaction pathways
of furfural hydrogenation on the
Ru/SC-SBA-15_6h catalyst
and k8 was the rate constant from THFA to 1,2-PeDO. All
reactions were considered as pseudo-frst order reactions. In
order to obtain the kinetic parameters, we conducted FFR
conversion experiments at diferent reaction temperatures (80,
100, 120, and 140 °C), and recorded the conversion of FFR
and the yield of all intermediates and by-products (Fig. 7) for
the following kinetics studies.
(
)
dCFAL
dt
= k1CFFR − k2 + k3 + k4 CFAL
(4)
dCTHFA
dt
= k2CFAL − (k5 + k8)CTHFA
(5)
(6)
(7)
(8)
dC2 - MeTHF
According to the total reaction path (Scheme 1), the change
of products concentrations as a function of time were pre-
sented by the following diferential equations in the presence
of excess of H2:
= k5CTHFA
dt
dC5 - HP
= k4CFAL − k7C5 - HP
dt
dCFFR
= − k1CFFR
(3)
dt
dC1,2 - PeDO
= k3CFAL + k8CTHFA − k6C1,2 - PeDO
dt
1 3

K. Cui et al.
Table 3 Estimated kinetic
parameters for furfural
conversion
T
Rate constants (×10–3 min−1
)
(oC)
k1
k2
k3
k4
k5
0.07
0.61
2.39
6.63
96.12
k6
k7
k8
80
100
120
140
15.03
20.96
31.03
45.80
21.45
1.07
2.51
4.29
11.30
46.30
0.09
0.80
2.13
5.05
81.33
10.98
19.84
30.22
40.46
26.35
0.02
0.11
1.10
3.81
14.30
22.80
36.80
49.01
25.32
0.19
0.79
2.03
4.92
65.03
Ean (KJ/mol)
109.65
Reaction conditions: 2 mmol furfural, 20.0 mg Ru SC-SBA-15-6 h, 1.5 MPa H2 and 4.0 mL H2O. The
standard deviation is within 3%
4
3
k
1
2
k
3
k
2
k
1
4
k
5
0
k
6
-1
-2
-3
-4
k
7
k
8
2.4
2.5
2.6
2.7
2.8
2.9
1/T *1000 (1/K)
Fig. 9 The recyclability of Ru/SC-SBA-15-6 h for hydrogenation of
furfural to 1,4-PeDO (bars denote standard deviations). Reaction con-
ditions: Substrate/Ru=1000 (molar ratio), 80.0 mg catalysts, 4.0 mL
H2O, 4 h, 1.5 MPa H2, 140 °C
Fig. 8 Arrhenius plots for the hydrogenation reaction of furfural (bars
denote standard deviations). The observed rate constants (k) were
obtained by ftting with MATLAB at diferent temperatures according
to Fig. 7
route was the conversion of FFR to FAL, FAL to 5-HP and
fnally 5-HP to 1,4-PeDO, respectively.
dC1,4 - PeDO
(9)
= k6C1,2 - PeDO + k7C5 - HP
dt
3.2.3 Reusability Test
where the concentrations of FFR, FAL, THFA, 2-MeTHF,
1,2-PeDO, 5-HP and 1,4-PeDO were in mol/L. By solving
these ordinary diferential equations (ODEs) simultaneously
using MATLAB program, the kinetic parameters k1-k8 were
determined, respectively (Table 3). The function of lsqnonlin
nonlinear ftting in MATLAB was also utilized to minimize
the error between experimental and predicated data [52].
Then the obtained reaction rate constants were used to
evaluate the apparent activation energy (Ean) by plotting ln
k versus 1/T through Arrhenius equation (Fig. 8). Table 3
summarized the rate constants and activation energies of
each reaction. We found that all rate constants increased
with temperature increasing. And among all the activation
energies of the reactions, Ea1, Ea4, and Ea7 were relatively
small compared with other activation energies and below
30 kJ/mol, which demonstrated clearly that the preferential
Next, the reusability of the catalyst was determined because
catalyst recyclability exhibited an indispensable part in the
economic evaluation of chemical compound transforma-
tions. Therefore, we conducted a reusability test on the Ru/
SC-SBA-15_6h catalyst, and the result was shown in Fig. 9.
After the reaction, the metal Ru catalyst could be separated
by a simple fltration. The recovered catalyst was dried for
8 h at 80 °C and then used in the next reaction. As shown in
Fig. 9, the catalyst can be reused for at least six consecutive
catalytic recycles. The yield of 1,4-PeDO showed a slight
decrease, but the activity of the catalyst remained almost
unchanged, demonstrating that Ru/SC-SBA-15_6h was
highly stable in the aqueous reaction.
The spent Ru/SC-SBA-15_6h catalyst has been char-
acterized for the possible structural changes. As shown in
1 3

Ru Nanoparticles on a Sulfonated Carbon Layer Coated SBA-15 for Catalytic Hydrogenation of…
Fig. S11, the recycling test could not infuence the ordered
mesoporous structure of the Ru catalyst. Meantime, the
sulfonic acid density of the reused catalyst was determined
quantitatively by the titration method (Table 1), it was found
that even after six catalytic recycles, the sulfonic acidity
of the catalyst showed a negligible loss and remained at
0.22 mmol·g−1. It suggested that a sulfonated carbon layer
coated SBA-15 was highly water-resistant and the dispersed
Ru species was robust for the catalytic hydrogenation likely
via a coordination with a sulfonic groups.
of other biomass molecules, thus opening up a new route
to produce high-value-added chemicals directly from FFR.
Acknowledgements The authors are grateful for support from the
National Natural Science Foundation of China (21773061, 21978095),
the innovation Program of Shanghai Municipal Education Commission
(15ZZ031).
References
Finally, the catalytic performance of the present system
was compared with the other earlier reports for the hydro-
genation of furfural into 1,4-PeDO. As shown in Table S3,
the present bi-functional catalyst can aford the comparable
or higher yield of 1,4-PeDO to that of the reported systems.
Notably, the present catalytic system was able to catalyze
the reaction under milder conditions (short reaction time
and low H2 pressure). Besides, the present catalyst is simple
and can be easily available by a conventional method. Mean-
time, it was highly stable in consecutive catalytic recycles.
Inspired by the above results, the design of more-efcient
bi-functional catalysts for the catalytic direct conversion of
FFR to high-value-added chemicals with high stability is
currently underway in our laboratory.
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In summary, the highly efcient metal–acid bi-functional
catalyst has been prepared by using the carbon layer coated
C/SBA-15 as a catalyst support, which was then sulfonated
with 98% concentrated sulfuric acid, followed by incorpo-
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