Active ruthenium catalysts prepared by Cacumen Platycladi leaf extract for selective hydrogenation of maleic anhydride

Article abstract of DOI:10.1016/j.apcata.2015.02.014

Ruthenium-based catalysts were prepared by a biogenic method via Cacumen Platycladi leaf extract and tested in the liquid phase hydrogenation of maleic anhydride to the corresponding succinic anhydride. The reaction conditions were optimized by varying the Ru loading, reaction temperature, hydrogen pressure, reaction time and organic solvents to achieve the superb catalytic performance. Reusability tests and comparison with commercial catalysts were also studied on the biosynthesized Ru-based catalysts. Furthermore, a variety of characterization techniques, such as TEM, HRTEM, EDS and XPS showed the effectively introduction of ruthenium nanoparticles into the carbon supports. The analyses of FTIR and TG confirmed that the plant extract served as both reducing and protecting agents.

Full text of DOI:10.1016/j.apcata.2015.02.014

Accepted Manuscript
Title: Active ruthenium catalysts prepared by Cacumen
Platycladi leaf extract for selective hydrogenation of maleic
anhydride
Author: Yangqiang Huang Yao Ma Youwei Cheng Lijun
Wang Xi Li.
PII:
S0926-860X(15)00106-4
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.apcata.2015.02.014
APCATA 15251
To appear in:
Applied Catalysis A: General
Received date:
Revised date:
Accepted date:
15-12-2014
4-2-2015
11-2-2015
Please cite this article as: Y. Huang, Y. Ma, Y. Cheng, L. Wang, X. Li.,
Active ruthenium catalysts prepared by Cacumen Platycladi leaf extract for
selective hydrogenation of maleic anhydride, Applied Catalysis A, General (2015),
http://dx.doi.org/10.1016/j.apcata.2015.02.014
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*Graphical Abstract (for review)
Page 1 of 29

*Highlights (for review)
Highlights:
●
●
●
A green process for preparation ruthenium-based catalysts.
Maleic anhydride can be selectively hydrogenated to succinic anhydride.
The biosynthesized Ru-based catalysts showed excellent stability.
1
Page 2 of 29

Active ruthenium catalysts prepared by Cacumen Platycladi
leaf extract for selective hydrogenation of maleic anhydride

Yangqiang Huang, Yao Ma, Youwei Cheng , Lijun Wang and Xi Li.
Department of Chemical and Biological Engineering, Zhejiang University,
Hangzhou 310027, PR China
Abstract:
Ruthenium-based catalysts were prepared by a biogenic method via Cacumen
Platycladi leaf extract and tested in the liquid phase hydrogenation of maleic
anhydride to the corresponding succinic anhydride. The reaction conditions were
optimized by varying the Ru loading, reaction temperature, hydrogen pressure, reaction
time and organic solvents to achieve the superb catalytic performance. Reusability tests
and comparison with commercial catalysts were also studied on the biosynthesized
Ru-based catalysts. Furthermore, a variety of characterization techniques, such as
TEM, HRTEM, EDS and XPS showed the effectively introduction of ruthenium
nanoparticles into the carbon supports. The analyses of FTIR and TG confirmed that
the plant extract served as both reducing and protecting agents.
Keywords:
Maleic anhydride; Selective hydrogenation; Succinic anhydride; Ruthenium
nanoparticles

Corresponding author. E-mail address: ywcheng@zju.edu.cn (Y. Cheng)
1
Page 3 of 29

1
. Introduction
Maleic esters, anhydrides and acids hydrogenation is a widely applied chemical
process as all its products, such as succinic anhydride (SA), γ-butyrolactone (GBL),
,4-butanediol (BDO) and tetrahydrofuran (THF) are important chemicals used as
1
solvents or raw materials to produce polymers like polyurethanes [1-3]. In particular,
SA is required as an intermediate to undergo various reactions in the area of polymers,
agrochemicals, pharmaceuticals, and food industrial [4, 5]. The market potential of
the products based on succinic acid and anhydride is evaluated to be 270 000 tons per
year [6]. These products are synthesized by the following four processes: (I) Reppe
process [7] in which acetylene is reacted with formaldehyde; (II) Acro process [8] in
which propylene oxide is isomerized first to allyl alcohol and then hydroformylation;
(
III) Mitsubishi Kasei process (MKC) [9] in which maleic anhydride is hydrogenated
on Ru complexes; (IV) Davy McKee process [10] which focused on hydrogenation of
dialkyl maleates on Cu-based catalysts or ion-exchange resins. Among them, direct
hydrogenation of maleic anhydride (MA) is reckoned to be the most clean and
economical process to produce SA. MA is a convenient feedstock for its availability
and low price due to the construction of large fluidized-bed plants based on
Alusuisse-Lummus, BP/UCB, and DuPont technologies [1, 11]. The reaction pathway
of MA hydrogenation is illustrated in Fig. 1 [11].
It is reported that the gas-phase hydrogenation of MA is carried out with the
presence of the copper-based catalysts [12-14], while the liquid-phase hydrogenation
of MA is performed mainly on the noble metal catalysts containing Ru, Pd, or Rh
[
15-18]. The drawback of the reported efficient catalysts is the deactivation problem
because of the coke deposition during the hydrogenation process. This clearly
indicates that new catalysts are needed to overcome the problems of complicated
synthesis of catalyst, high consumption of metal, relatively low activity, high reaction
temperature and long reaction time.
Transition metal nanoparticles (NPs) have been widely recognized in catalysis
2
Page 4 of 29

due to their novel chemical and physical properties in recent years [19, 20]. Ascribed
to the quantum size effect and surface effect, metal NPs can exhibit fascinating
activity and selectivity, which radically distinguish themselves from their bulk
counterparts [21]. Ru NPs, among the most efficient and also economical (its price is
one third to fifth of that for Pd) noble metals, are attractive and have been adopted in
many hydrogenation processes, such as hydrogenation of benzene to cyclohexane [22,
2
3], selective hydrogenation of D-glucose [24], xylose [25], and α,β-unsaturated
aldehydes [26]. We have previously investigated the Ru-based catalysts for the
selective hydrogenation of dimethyl terephthalate. In fact, the carbon nanotubes
supported Ru NPs with low loading (0.4 wt%) could exhibit both desirable activity
and stability [27]. Furthermore, some findings have been reported regarding the
hydrogenation of maleic anhydride using Ru complexes [15]. Likewise, a series of
ruthenium-carbon catalysts were synthesized by Hong et al. using a single-step
surfactant-templating method and showed excellent catalytic performance for the
hydrogenation of succinic acid [28]. In summary, the Ru based catalytic system is
believed to be a promising candidate for the hydrogenation of MA.
Generally speaking, solution-based chemical synthetic strategies, which are
effective and powerful ways to nanomaterials, are turned out to be more economical
and simpler compared to that in the solid or gaseous state [20]. Recently, researchers
have made great progress in controllable synthesis of noble NPs. However, these
conventional chemical methods will inevitably encounter the problems of using
various capping agents or auxiliary surfactants; moreover during the synthesis,
numerous conditions and parameters will result in poor reproducibility. Recently, an
effective system for preparation of noble metal NPs, namely the biosynthesis methods
using biological organisms or plants, has attracted intensive research interest. The
biosynthesis methods can be applied to produce stable noble NPs with a narrow size
distribution in a simple way. Zhan et al. provided two novel modes, namely
sol-immobilization (SI) and adsorption-reduction (AR) methods [29]. Their
biosynthesized Au NPs supported on TS-1 showed high activity and efficiency for the
epoxidation of propylene [30]. In a previous study, we examined the possibility of
3
Page 5 of 29

synthesizing Ru NPs by the use of Cacumen Platycladi (CP) leaf extract. The
bioreduction catalysts exhibited excellent catalytic activity compared with the
commercial Ru/C catalysts in the hydrogenation of benzene to cyclohexane [31].
These inspiring results give us more confidence that the eco-friendly bioreduction
approach of synthesizing Ru NPs will provide a new direction in the near future.
The present paper includes the preparation of Ru catalysts by the SI method
through immobilizing the reduced Ru nanoparticles on the supports. Several analysis
techniques, such as low temperature N physisorption, X-ray diffraction (XRD)，
2
transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy
(EDS), X-ray photoelectron spectroscopy (XPS), fourier transform infrared
spectroscopy (FTIR), and thermogravimetric (TG), are adopted to offer insights of the
intrinsic structure-property relationship of the catalysts. The bioreduction catalysts are
probed in the liquid phase hydrogenation of maleic anhydride. Furthermore, in order
to optimize the hydrogenation process, the effect of various preparation and reaction
conditions on the catalytic performance is also studied.
2
. Experimental details
2
.1 Materials
Carbon (Activated charcoal, LOT-242276) was purchased from Sigma-Aldrich,
Cacumen Platycladi (CP) leaf was obtained from Zhejiang university hospital. Maleic
anhydride (AR, >99.0%) was purchased from Aladdin Chemical Co. Ltd. Other
chemical reagents mentioned were all of A.R grade from Sinopharm Chemical
Reagent Co. Ltd. and used without further purification. The deionized water with a
-6
conductance below 10 S/cm was used in all synthesis and washing processes.
2
.2 Catalyst preparation
The bioreduction Ru-based catalysts were prepared through immobilizing the
4
Page 6 of 29

biosynthesized Ru nanoparticles (Ru NPs) onto the carbon supports. In a typical
synthesis procedure, milled powder CP leaf of 1 g dosage was added to 100 mL of
deionized water under stirring for 4 h. The mixture was then filtrated to get filtrate (10
g/L) and used for further preparation of Ru NPs. Then, Ru NPs were biosynthesized
through a simple procedure by reducing the aqueous RuCl (50 mL, 2.2 mM) with the
3
CP extract (30 mL). After 0.5 h, an appropriate amount of dried activated carbon was
added immediately into the solution at the same temperature. After another 5 h, the
solids were collected by filtration and thoroughly washed with deionized water. The
o
resulting solid was dried in a vacuum oven at 60 C for 12 h, and the X wt% Ru/AC
o
catalysts were obtained after calcination at 500 C for 3 h in the atmosphere of
nitrogen (X was the nominal Ru loading).
2
.3 Catalysts characterization
The Micromeritics ASAP 2020 instrument was applied for monitoring the
low-temperature N adsorption-desorption behaviors, and the Barrett-Joyner-Halenda
2
(BJH) method was used to calculate the textural properties including pore size
distribution and total pore volume. XRD patterns were collected on a XRD-6000
X-ray diffractometer (Shimadzu) with Cu Kα radiation (λ = 0.154 nm) at 40 kV and
3
0 mA, in a 2θ angle ranging from 10 to 90 º with a scanning rate of 2 º/min and a
step size of 0.02 º/s. TEM and HRTEM images of samples were taken with a FEI
Tecnai G2 F20 S-TWIN microscope operating at an accelerating voltage of 200kV.
EDS analysis was used to determine the elemental composition of the colloidal
particles. XPS analyses were performed on a VG ESCALAB MARK II equipment
with focused monochromic Mg Kα (BE=1253.6 eV). The binding energy (BE) values
were calculated with respect to C1s peak at 284.6 eV with an uncertainly of ±0.2 eV.
A Nicolet 5700 FTIR infrared spectrometer was used to collect the Fourier transform
infrared (FTIR) spectra. TG profiles were measured with a Pyris 1 TGA
(Perkin-Elmer).
5
Page 7 of 29

2
.4 Catalytic Activity Measurement
All experiments were performed in a 100 mL stainless steel (SS-316) reactor. In
each test, the reactor was charged with 10 mmol of maleic anhydride, 5 mL of
tetrahydrofuran, and 50 mg of catalyst. The reactor was pressurized with nitrogen to
remove air and heated up to the desired temperature. Then, the autoclave was
pressurized with H to the designed pressure. Analysis of liquid reactants was
2
performed by gas chromatograph (Kexiao, GC-1690 with flame ionization detector).
The gas chromatograph was equipped with an OV-1 column and the acetic anhydride
was chosen as the internal standard substance. The conversion rate was defined as the
ratio of consumed maleic anhydride to supplied maleic anhydride. The selectivity was
calculated by dividing moles of a product by total moles of maleic anhydride
consumed. To ensure reproducibility of the results, repeated experiments were carried
out under identical conditions and data were found to be reproducible within ±2 %
variation.
3. Results and discussion
3
.1 Hydrogenation of maleic anhydride to succinic
anhydride.
3
.1.1 Effect of Ru loading.
The effect of various Ru loading (0.25-5.0 wt%) on the hydrogenation of MA
was shown in Fig.2. It could be noticed that Ru loading had a remarkable effect on
MA conversion while the SA selectivity was well preserved in the experiment. The
conversion of MA increased monotonously with the increase of Ru content from 0.25
to 2.0 wt% while the SA selectivity maintained at a relatively high level around
9
9.0 %. The inferior performance with the low Ru loading (0.25 and 0.50 wt%) might
6
Page 8 of 29

be attributed to the insufficient presence of active ruthenium sites, which lowered
down the activity of MA hydrogenation. The conversion of MA reached 99.4 % at a
Ru loading of 2.0 wt%. When we continuously increased the Ru loading to 5.0 wt%,
the catalytic performance was slightly changed; however, we had lower Ru capture
efficiency, which could be inferred from the results of ICP-AAS shown in Table 2. In
addition, the experimental results indicated that incomplete Ru loading would occur in
the case of high Ru loading (≥3.0 wt%). Consequently, the optimum Ru loading was
2
1
.0 wt % since the catalysts showed a higher MA conversion (99.4 %) and had almost
00 % Ru capture efficiency, which was important from an economic point of view
during the process.
3
.1.2 Effect of Reaction Temperature and Hydrogen Pressure.
It is well known that the reaction temperature is vital in obtaining the desired
product [5, 32, 33]. The effect of reaction temperature on MA hydrogenation (Fig. 3)
o
led to almost 100 % MA conversion and more than 99.5 % selectivity of SA at 150 C.
Increasing the reaction temperature, MA conversion increased largely, however, the
selectivity of SA decreased significantly. The conversion of MA increased from 40.3
o
to 99.4 % when the reaction temperature increased from 100 to 150 C. The
unsatisfactory MA conversion rate under low reaction temperature might be caused by
the thermal effect on the kinetics. Nevertheless, further hydrogenation of SA to GBL
along with the hydrogenolysis to propionic acid and n-butanol at higher temperature
would inevitably lead to lower SA selectivity. The selectivity of SA decreased from
o
o
o
9
9.6 % at 150 C to 83.5 % at 200 C. For this reason, 150 C was selected as the
proper reaction temperature for MA hydrogenation to SA.
Fig. 4 illustrated the catalytic performance of liquid phase hydrogenation of MA
at different hydrogen pressures. The influence of the hydrogen pressure on the MA
hydrogenation showed that 99.4 % MA conversion with 99.6 % selectivity of SA
could be obtained at a pressure of 6 MPa. The conversion of MA increased steadily
with the increase of pressure, while the selectivity of SA was almost 100 % under our
7
Page 9 of 29

present experimental conditions. It was seen that MA conversion increased from 55.1
to 99.4 % when the hydrogen pressure was raised from 1 to 6 MPa. Similar results
were reported by other applied metallic nickel catalysts in the MA hydrogenation [34].
The results suggested that under proper reaction conditions, the biosynthesis Ru
catalysts could selectively hydrogenate MA to SA.
3
.1.3 Effect of Reaction Time and Solvent.
Furthermore, in order to get more insights into the turnover frequency values of
the hydrogenation reaction, the catalytic behaviors versus reaction time on the
biosynthesized catalysts were investigated, and relevant results were given in Fig. 5. It
could be noted that the reaction time was critical in obtaining the desired MA
conversion accompanied with moderate TOF values. As seen in Fig. 5, MA
conversion increased from 81.2 to 99.4% with the increase of reaction time from 10 to
3
1
0 min and then stayed at around 100 % as the reaction time increasing from 30 to
20 min. However, the TOF values, defined as molar of MA substrate converted per
molar of Ru loading, decreased monotonously with the reaction time increasing from
0 to 120 min. Moreover, a longer reaction time would lead to the synthesis of
1
overhydrogenation products such as GBL or THF, which would be detrimental to the
SA selectivity. As a consequence, it could be speculated that the reaction at about 30
min was preferable considering the tradeoff between SA yield and TOF values.
Choosing a proper solvent to facilitate the MA hydrogenation process is
o
important because MA is in the solid state at room temperature (mp 52.8 C). Gao et
al. suggested coupling two contradictory hydrogenation and dehydrogenation reaction
processes over a single catalyst. In their reaction system, the ethanol not only served
as a solvent but also acted as a hydrogen feedstock for MA hydrogenation [35]. MA
o
conversion and products selectivity in different employed solvents at 150 C and 6
MPa were listed in Table S1. Solvent effect might play a crucial role in the
hydrogenation of MA. Meanwhile, in choosing the solvent, several points should be
taken into consideration, such as good solubility, easy separability, thermal stability
8
Page 10 of 29

and resistance to reduction. The conclusion drawn from Table S1 showed that the
reaction without solvent was inert to catalytic activity which could be caused by the
difficult interaction between the reactants and the catalysts. After reaction for 30 min,
the conversion of MA for the solvent of acetic anhydride, methylbenzene,
tetrahydrofuran and acetone stood at 91.2 %, 98.5 %, 99.4 % and 99.7 % respectively.
The conversion of MA increased when the polarities of solvent decreased, which was
in contradiction with those reported by Feng et al. [34]. Moreover, the selectivity of
SA was not affected when we used various solvents except for acetic anhydride.
Therefore, a proper solvent should easily dissolve MA, companied with a desired
yield of SA.
3
.1.4 Catalyst reusability and comparison with commercial catalysts.
Since the stability of heterogeneous catalysts was an important parameter, the
catalytic recycling tests were conducted to assess the biosynthesized Ru-based
catalysts. The catalysts were carefully recollected and reused in subsequent cycles as
the same conditions as the fresh catalysts. As shown in Table 1, the MA conversion,
SA selectivity and TOF values showed minor variation during the consecutive five
cycles, suggesting the remarkable stability of the Ru based catalysts. For comparison,
blank experiment was carried out in the identical manner by replacing the Cacumen
Platycladi extract with deionized water. Interestingly, an induction period could be
observed for the ruthenium catalyst in the blank test. In addition, Ru could be detected
by atomic absorption spectroscopy (AAS) analysis in the filtrate obtained from the
reusability experiments. The results indicated that the leaching of Ru nanoparticles
from the catalysts occurred in the blank test and Cacumen Platycladi extract played a
pivotal role in the catalyst preparation.
Furthermore, it is of interest to compare the bioreduction catalysts with the
conventional 5.0 wt% Ru supported on carbon (purchased from Aladdin Industrial
Corporation, China). As shown in Table 1, the conventional 5.0 wt% Ru/C catalysts
had a MA conversion of 94.6 % with a SA selectivity of 99.5 % and a TOF value of
9
Page 11 of 29

-1
1
965.3 h . Evidently, the catalytic performance of the biosynthesized catalysts was
comparable in term of selectivity of SA and superior in term of MA conversion and
TOF value to that of the conventional impregnation catalysts, even with a lower Ru
loading.
3
.2 Catalysts characterization
In order to confirm the existence of Ru nanoparticles and its interaction with the
supports, a variety of methods were adopted to characterize the structure of the
biosynthesized Ru catalysts.
N physisorption was adopted to detect the mesoporous structure of the supports
2
and catalysts. As shown in Table 2, both the SBET and V decreased slightly after
p
introducing Ru nanoparticles, exhibiting the immobilization of the Ru nanoparticles
into the channels of the activated carbon. Nevertheless, no significant changes in the
average pore diameter of the catalysts were observed which might be a result of low
amount of ruthenium. Moreover, when Ru loading was lower than 2 wt%, the
ICP-AAS results indicated that the authentic value in the as-synthesized catalysts was
the same as the nominal metal loading, thus achieving 100 % Ru capture efficiency.
Nevertheless, the catalysts with a relative heavy loading of Ru (for example, 5 wt%)
showed an inferior capture efficiency of around 70 %.
The XRD patterns were recorded for the fresh supports and the bioreduction
Ru-based catalysts (Fig. S1 of Supplementary Information). It could be noticed that
the XRD pattern of 2.0 wt% Ru/AC was similar to that of activated carbon, exhibiting
o
a weak shoulder peak at around 2θ=25 , which was assigned to the diffraction of the
graphite phase (JCPDS File, no.41–1487). Only the intensity of the peaks was
attenuated after introducing Ru nanoparticles into the supports [36]. That diffraction
signals of the Ru nanoparticles could not be observed in Fig. S1 might be due to the
low concentration and small particle size.
TEM and EDS characterization have been introduced to get information on the
morphology of Ru nanoparticles. The images of the bioreduction Ru catalysts clearly
10
Page 12 of 29

showed high and homogeneous dispersion of spherical metal nanoparticles throughout
the surface of activated carbon, giving an average particle size of 2.17 nm (Fig. 6 a-c).
Specifically, the HRTEM image in Fig. 6 (d) showed d-spacing of 2.06 Å and 2.14 Å,
corresponding to (101), and (002) facets of Ru, respectively (JCPDS File, no.
6
5-7645). TEM-EDS further confirmed the presence of ruthenium at different
micrographs spots (Fig. 7; Cu was from the copper grid). The morphological
properties and particle size of the recycling catalysts did not show any obvious change
after being recycled for five times (Fig. S2 of Supplementary Information).
The surface element and electronic state of the 2.0 wt% Ru/AC catalysts were
evaluated by using an XPS apparatus (Fig. S3 of Supplementary Information). The
peaks corresponding to chlorine, carbon, ruthenium, oxygen and chlorine were
distinctly detected (the Cl was from the residue plant biomass). The Ru lines were
3d
deconvoluted to two peaks which was attributed to Ru(0) and Ru(IV), respectively.
The XPS measurements could confirm the presence of Ru metal particles on the
surface of carbon supports.
3
.3 The functionality of Cacumen Platycladi extract.
The conventional chemical methods of synthesizing metal nanoparticles will
inevitably suffer from the problems of using different stabilizer and reducer. However,
these auxiliary materials would be not only energy intensive but also hostile to
environment. Thus, in the bioreduction approach, without adding auxiliary organic
substance, we should further specify the functionalities presented in the residual plant
biomass.
FTIR analyses were used to monitor the chemical structure variation of the
Cacumen Platycladi extract before and after bioreduction. Representative FTIR spectra
of Cacumen Platycladi leaf extract before and after the reaction were presented in Fig.
8
. The spectra of the plant extract before the reaction (curve a) showed a number of
-1
vibration bands at 2921, 1626, 1375, 1256, 1050, and 775 cm . These six notable band
might be assigned to several functional groups, such as C=C–H or –C–OH. The
11
Page 13 of 29

-1
absorbance bands at 2921, 1626 and 1050 cm were weakened after the reaction. The
-1
intensive bands at 2921 and 1626 cm were associated with the stretching vibration of
-1
v(=C–H) and v(–C=C), respectively while the band at 1050 cm may be assigned to the
stretching vibration of v(–C–O) [37]. Therefore, this comparison provided information
that the reductive groups of C=C or–OH in the Cacumen Platycladi extract were
responsible for the chemical transformation of ruthenium ions.
Intensive studies show that the major components of the Cacumen Platycladi
extract are flavonoids, reducing sugars, polysaccharides, and proteins, and other
substances (amino acids or polyphenols) [38, 39]. Among them, flavonoids and
reducing sugars were important reductants responsible for the chemical
transformation of ruthenium ions. Zhan reported the synthesis of gold nanoparticles
with different shapes using Cacumen Platycladi extract [38]. Zhang demonstrated the
green synthesis of Au-Ag alloy nanoparticles using Cacumen Platycladi extract [40].
Chen explored the size controllable synthesis of Ni nanoparticles by the plant-mediated
method using the alfalfa extract [41]. These previous results reached the same
conclusion that the flavonoids and reducing sugars were the main categories of the
ingredients in the plant extract which affected the chemical transformation of the noble
-1
metals. The decrease in intensity at 2921 and 1626 cm , which is ascribed to C=C
or–OH, indicated the component change of flavonoids and reducing sugars [42]. Hence,
these flavonoids and reducing sugars in the extract were responsible for the reduction of
Ru ions.
-1
Moreover, the new band centered at 1740 cm in the Cacumen Platycladi leaf
extract after bioreduction could be contributed by the stretch vibration of the carbonyl
groups [v(–C=O)] [40], which might be the oxidation product of polyols. This freshly
band could play a pivotal role in protecting the Ru nanoparticles. As in the chemical
routes of synthesizing noble nanoparticles, the stabilization of the particles using
stabilizer, such as PVP, was resulted from the adsorption of the PVP –C=O group to
the particles surface [43]. The evolution of the peaks indicated the existence of –C=C
and –C=O group which could act as capping ligands for the nanoparticles. Meanwhile,
XPS spectra of 2.0 wt% Ru/AC (vide supra) indicated the present of large amount of C
12
Page 14 of 29

and O on the surface of Ru nanoparticles. The C and O have a probability of binding to
the Ru nanoparticles via the functional groups. Simultaneously, TG analysis confirmed
the presence of some residual plant biomass around the Ru nanoparticles (Fig. S4 of
Supplementary Information). Thus, it was reasonable to speculate that these plant
biomass were responsible for stabilization of the nanoparticles. On the basis of the
results of the above FTIR and TG techniques, we believed that polyols such as
flavonoids and reducing sugars containing C=C–H and C–O–H functional groups were
responsible for the reduction of Ru precursors while the components containing –C=O
functional groups served as the protecting agents.
4. Conclusions
The ruthenium based catalysts prepared by Cacumen Platycladi leaf extract
could be served as effective catalysts in selective hydrogenation of maleic anhydride.
o
The optimized conditions, Ru loading of 2 wt%, reaction temperature of 150 C,
hydrogen pressure of 6 MPa, and the time length of 30 min with the choice of
tetrahydrofuran as solvent, could lead to succinic anhydride selectivity of 99.6 % with
almost 100% conversion of maleic anhydride. The biosynthesized Ru-based catalysts
could be reused for five cycles and the activity was also comparable to the
commercial Ru/C catalysts, even with a lower Ru loading. Based on the
characterization analyses, the successfully introduction of Ru nanoparticles was
achieved by the means of the bioreduction method, while the main components
containing C=C–H, C–O–H and –C=O in the plant leaf extract served as both reducing
and protecting agents. We believed that this research would open up new
opportunities for the preparation of bioreduction catalysts and their application in MA
hydrogenation.
13
Page 15 of 29

Acknowledgments
We gratefully acknowledge the key program (No. U1361112) of the National
Natural Sciences Foundation of China, and the Fundamental Research Funds for the
Central Universities (2013QNA4035) for the financial support.
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15
Page 17 of 29

Table
Table captions in sequence
Table 1 Catalyst reusability studies during MA hydrogenation and comparison with commercial
catalysts.
Table 2 Textural properties of the supports and synthesized catalysts
1
Page 18 of 29

Table 1
Catalyst reusability studies during MA hydrogenation and comparison with commercial catalysts.
Conversion of MA Selectivity of SA
TOF
Catalyst
Entry
-1
(%)
(%)
99.6
99.5
99.6
99.4
99.5
99.6
99.5
(h )
Fresh
99.4
99.5
99.2
99.1
99.1
98.9
94.6
2084.9
2073.6
2054.8
2049.5
2038.6
2039.3
1965.32
st
1
recycle
nd
2
recycle
recycle
recycle
recycle
a
Ru/AC
rd
3
4
5
th
th
b
Ru/C
Fresh
Reaction conditions: MA concentration 2 mol/L (18 wt%), catalyst 50 mg, reaction temperature 150
o
C, hydrogen pressure 6 MPa.
a
Ruthenium catalysts (2.0 wt%) prepared by Cacumen Platycladi leaf extract.
b
Conventional 5.0 wt% Ru/C catalyst from Aladdin Industrial Corporation, China.
2
Page 19 of 29

Table 2
Textural properties of the supports and synthesized catalysts
Ru loading
S
V
Dp
a
BET
2
p
Sample
b
-1
3
-1 c
d
(wt %)
(m ·g )
995
991
964
959
949
865
862
o
(cm ·g )
1.08
(nm)
actived carbon(AC)
.25 % Ru/AC
-
3.7
4.0
4.1
3.9
4.0
4.0
3.9
0
0.25
0.5
1.0
2.0
2.4
3.6
1.01
0
.5 % Ru/AC
.0 % Ru/AC
.0 % Ru/AC
.0 % Ru/AC
.0 % Ru/AC
0.95
1
0.95
2
3
5
0.94
0.84
0.87
a
o
Preparation conditions: preparation temperature 60 C, calcination temperature 500 C.
b
c
d
Determined by ICP-AAS. Pore volume. Average pore diameter.
3
Page 20 of 29

Figure
Figure captions in sequence
Fig. 1. Reaction pathway of the hydrogenation of maleic anhydride.
Fig. 2. Effect of Ru loading on MA conversion and SA selectivity. Reaction conditions: MA
o
concentration 2 mol/L (18 wt%), catalyst 50 mg, reaction temperature 150 C, hydrogen pressure 6
MPa, reaction time 30 min.
Fig. 3. Catalytic performance of bioreduction catalysts (2.0 wt% Ru/AC) as a function of reaction
temperature. Reaction conditions: MA concentration 2 mol/L (18 wt%), catalyst 50 mg, hydrogen
pressure 6 MPa, reaction time 30 min.
Fig. 4. Catalytic performance of bioreduction catalysts (2.0 wt% Ru/AC) as a function of
hydrogen pressure. Reaction conditions: MA concentration 2 mol/L (18 wt%), catalyst 50 mg,
o
reaction temperature 150 C, reaction time 30 min.
Fig. 5. Catalytic performance of bioreduction catalysts (2.0 wt% Ru/AC) as a function of reaction
time. Reaction conditions: MA concentration 2 mol/L (18 wt%), catalyst 50 mg, reaction
o
temperature 150 C, hydrogen pressure 6 MPa.
Fig. 6. TEM and HRTEM images of 2.0 wt% Ru/AC.
Fig. 7. EDS spectrum and its elemental analysis of 2.0 wt% Ru/AC.
Fig. 8. FTIR spectra of Cacumen Platycladi extract (a) before bioreaction and (b) after
bioreaction.
1
Page 21 of 29

Fig. 1. Reaction pathway of the hydrogenation of maleic anhydride.
2
Page 22 of 29

Conversion of MA
SA
GBL
1
00
100
80
60
40
20
0
8
6
4
2
0
0
0
0
0
0.25
0.50
1.0
2.0
3.0
5.0
Ruthenium loading (wt%)
Fig. 2. Effect of Ru loading on MA conversion and SA selectivity. Reaction conditions: MA
o
concentration 2 mol/L (18 wt%), catalyst 50 mg, reaction temperature 150 C, hydrogen pressure 6
MPa, reaction time 30 min.
3
Page 23 of 29

MA
SA
GBL
PA+n-butanol
TOF
1
00
2000
1500
1000
500
0
8
6
4
2
0
0
0
0
0
100
125
150
175
200
o
Reation temperature ( C)
Fig. 3. Catalytic performance of bioreduction catalysts (2.0 wt% Ru/AC) as a function of reaction
temperature. Reaction conditions: MA concentration 2 mol/L (18 wt%), catalyst 50 mg, hydrogen
pressure 6 MPa, reaction time 30 min.
4
Page 24 of 29

MA
SA
GBL
TOF
1
00
2000
1500
1000
500
0
8
6
4
2
0
0
0
0
0
1
2
3
4
5
6
7
Hydrogen pressure (MPa)
Fig. 4. Catalytic performance of bioreduction catalysts (2.0 wt% Ru/AC) as a function of
hydrogen pressure. Reaction conditions: MA concentration 2 mol/L (18 wt%), catalyst 50 mg,
o
reaction temperature 150 C, reaction time 30 min.
5
Page 25 of 29

MA
SA
GBL
TOF
5
4
3
2
000
000
000
000
1
00
8
6
4
2
0
0
0
0
0
1000
0
10
20
30
60
120
Reaction time (min)
Fig. 5. Catalytic performance of bioreduction catalysts (2.0 wt% Ru/AC) as a function of reaction
time. Reaction conditions: MA concentration 2 mol/L (18 wt%), catalyst 50 mg, reaction
o
temperature 150 C, hydrogen pressure 6 MPa.
6
Page 26 of 29

Fig. 6. TEM and HRTEM images of 2.0 wt% Ru/AC.
7
Page 27 of 29

Fig. 7. EDS spectrum and its elemental analysis of 2.0 wt% Ru/AC.
8
Page 28 of 29

b
a
3000
2500
2000
1500
1000
500
-
1
Wavenumber (cm )
Fig. 8. FTIR spectra of Cacumen Platycladi extract (a) before bioreaction and (b) after
bioreaction.
9
Page 29 of 29