Y. Ma et al. / Catalysis Communications 57 (2014) 40–44
41
treated in water baths and depressurized with a connected pressure
regulator. Liquid samples were centrifuged to separate the catalysts
from the mixture and then analyzed by gas chromatography on a gas
chromatograph (Kexiao, GC-1690). ICP-AAS experiment was intro-
duced to investigate the amount of ruthenium leaching after the reac-
tion. Turnover frequency (TOF) value was calculated as moles of
maleic anhydride transformed per mole of Ru in catalysts per hour.
3. Results and discussion
3.1. Catalysts characterization
An overview of the biosynthesized catalyst samples and their differ-
ent characteristics was given in Table 1. The nitrogen adsorption–
desorption results (Fig. S1 and S2) indicated that the activated carbon
and the carbon nanotubes were distinct from one another in the aver-
age pore size and the surface area. After introducing the ruthenium
particles, the BET surface and the pore volume in the two different sup-
ports decreased, indicating Ru nanoparticles partially occupied the
mesopores of the supports. Analysis of the average pore size indicated
that the Ru nanoparticles played a pivotal role in slightly extension of
the catalyst pores. The diverse textural properties of the supports
might have an influence on the catalytic properties.
Fig. 1. Reaction network of hydrogenation of maleic anhydride.
This could be listed as one of the few successes in applying the
biosynthesized nanoparticles to catalytic system.
Among the different types of supports used in heterogeneous catal-
ysis, carbon materials enjoy a rising popularity due to their unique char-
acteristics. Recently, new carbon form like the carbon nanotubes (CNTs)
has generated an intense effervescence in the scientific community
Fig. 2 showed the TEM and HR-TEM images of the bioreduction cat-
alysts. Well-defined spherical shapes with uniform size of Ru nanopar-
[
21–26]. Hence, the aim of this work is to apply the simple bioreduction
method to synthesizing highly efficient, stable and more economical
carbon-supported Ru-based catalysts, to further boost the hydrogena-
tion of MA to SA. As a preliminary result, these bioreduction catalysts
were proved to be a candidate for the highly selective hydrogenation
of MA to SA.
3
ticles were produced by reducing RuCl with the C. Platycladi (CP) leaf
extract. Strikingly, from the histogram of their size distribution, a slight-
ly smaller Ru size was obtained on the activated carbon compared with
the carbon nanotubes. From the EDX analysis (Fig. 3), the ruthenium
peak clearly confirms the existence of ruthenium in the catalysts. On
the basis of the EDX results, ruthenium nanoparticles have been suc-
cessfully prepared by using CP extract.
2
. Experimental details
The XRD pattern of the two catalysts exhibited the standard peaks of
carbon with the literature data (Fig. 4) [27,28]. No peaks, however, were
detected for Ru species, indicating low percentage of ruthenium or well
dispersion of the Ru nanoparticles on the supports.
2
.1. Catalyst preparation
Ru-based catalysts were prepared by the adsorption–reduction
method using Cacumen Platycladi (CP) leaf extract. An aqueous RuCl
solution (50 mL, 2.2 mM) containing appropriate amount of the as-
received AC or CNTs was treated in a water bath (60 °C) for 1 h, and
3
Thermal analyses of the sample were introduced to ascertain the
content of the residue plant biomass on the bioreduction catalysts
(Fig. 5). The TG and DTG analyses indicated that plant biomass weighted
as 13.5 (26.0) wt.% on uncalcined AC(CNTs) support, against only 6.1
(15.0) wt.% on calcined AC(CNTs) support. An appropriate content of
the residue plant biomass might play an important role in preventing
the sintering of the ruthenium particles [29]. FTIR analysis of the CP ex-
tract before bioreduction and the residue plant biomass showed that the
functional groups of C_C\H or \C\O\H in the plant extract were re-
sponsible for the reduction of Ru(III). Therefore, we speculated that the
polyols, such as reducing sugars and flavonoids, played a role in the
bioreduction [30]. In addition, these functional groups could be
adsorbed on the surface of the Ru nanoparticles to avoid agglomeration
[31]. The analysis of the TG diagram suggested that the two supports
possessed different adsorption properties, which might call for different
calcination treatments in nitrogen.
3
then, 30 mL CP extract was added to reduce RuCl . After another 5 h,
the suspension was filtered, and the residual filter cake was washed
thoroughly with distilled water. All the catalysts were dried overnight
at 100 °C and calcined in nitrogen at 500 °C for 3 h.
2
.2. Catalysts characterization
N
2
adsorption–desorption isotherms were obtained on a
Micromeritics ASAP 2020 instrument at liquid nitrogen temperature
(
−196 °C). Transmission electron microscopy (TEM) was carried out
on a Tecnai G2 F20 S-TWIN (FEI) at an accelerating voltage of 200 kV.
X-ray diffraction (XRD) was performed on a Shimadzu powder X-ray
diffractometer with Cu Kα radiation. Thermogravimetric (TG) analysis
e
was carried out on a METTLER TGA/SDTA 851 thermobalance under
flowing N
.3. Catalyst test
The catalytic performance of the catalyst samples for liquid hydroge-
2
atmosphere.
Table 1
Textural properties of the supports and synthesized catalysts.
2
Sample
Ru
loading
Surface
area
Pore
Average
pore size
(nm)
volume
a
(m2·g−1)
(cm3·g−1)
(wt.%)
nation of MA to SA was carried out in a 100 mL capacity stainless steel
batch reactor. The reactor was filled with the appointed maleic anhy-
dride dissolved in 5 mL tetrahydrofuran (20 wt.%) and the catalyst load-
ing used in the catalytic tests was 0.05 g. The reactor was purged with
nitrogen to remove air. After the autoclave was heated up to the reac-
Activated carbon (AC)
–
907
845
779
221
216
194
0.64
0.61
0.58
1.44
1.05
0.93
3.7
3.8
4.0
15.8
19.2
19.4
1
2
.0% Ru/AC
.0% Ru/AC
1.0
2.0
–
Carbon nanotube (CNT)
1.0% Ru/CNT
1.0
2.0
2.0% Ru/CNT
2
tion temperature of 150 °C, the desired pressure of H was introduced.
a
Upon completion of the reaction, the reactor was rapidly cooled after
Determined by ICP-AAS.