Facile fabrication of composition-tuned Ru-Ni bimetallics in ordered mesoporous carbon for levulinic acid hydrogenation

Article abstract of DOI:10.1021/cs401030u

Bimetallic catalysts are of great importance due to their unique catalytic properties. However, their conventional synthesis requires tedious multistep procedures and prolonged synthetic time, and the resulting bimetallics usually disperse unevenly and show poor stability. It is challenging to develop a facile and step-economic synthetic methodology for highly efficient bimetallic catalysts. In this study, we report an elegant metal complex-involved multicomponent assembly route to highly efficient Ru-Ni bimetallics in ordered mesoporous carbons (OMC). The fabrication of composition-tuned Ru-Ni bimetallics in OMC (Ru_xNi_1-x-OMC, x = 0.5-0.9) was facilely realized via in situ construction of CTAB-directed cubic Ia3d chitosan-ruthenium-nickel- silica mesophase before pyrolysis and silica removal. The resulting Ru _xNi_1-x-OMC materials are in-depth characterized with X-ray diffraction, N₂ adsorption-desorption, transmission electron microscopy, infrared spectrum, and X-ray absorption fine structure. This facile fabrication method renders homogeneously dispersed Ru-Ni bimetallics embedded in the mesoporous carbonaceous framework and creates a highly active and stable Ru_0.9Ni_0.1-OMC catalyst for the hydrogenation of levulinic acid (LA) to prepare γ-valerolactone (GVL), a biomass-derived platform molecule with wide application in the preparation of renewable chemicals and liquid transportation fuels. A high TOF (>2000 h^-1) was obtained, and the Ru_0.9Ni_0.1-OMC catalyst could be used at least 15 times without obvious loss of its catalytic performance.

Full text of DOI:10.1021/cs401030u

Research Article
pubs.acs.org/acscatalysis
Facile Fabrication of Composition-Tuned Ru−Ni Bimetallics in
Ordered Mesoporous Carbon for Levulinic Acid Hydrogenation
†
,‡
†
‡
,†
Ying Yang, Guang Gao, Xin Zhang, and Fuwei Li*
†State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of
Sciences, Lanzhou, Gansu 730000, P. R. China
‡
State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Changping, Beijing 102249, China
*
S Supporting Information
ABSTRACT: Bimetallic catalysts are of great importance due to their unique
catalytic properties. However, their conventional synthesis requires tedious
multistep procedures and prolonged synthetic time, and the resulting bimetallics
usually disperse unevenly and show poor stability. It is challenging to develop a
facile and step-economic synthetic methodology for highly efficient bimetallic
catalysts. In this study, we report an elegant metal complex-involved multi-
component assembly route to highly efficient Ru−Ni bimetallics in ordered
mesoporous carbons (OMC). The fabrication of composition-tuned Ru−Ni
bimetallics in OMC (Ru Ni −OMC, x = 0.5−0.9) was facilely realized via in situ
x
1−x
construction of CTAB-directed cubic Ia3d chitosan-ruthenium−nickel−silica
mesophase before pyrolysis and silica removal. The resulting Ru Ni −OMC
x
1−x
materials are in-depth characterized with X-ray diffraction, N2 adsorption−
desorption, transmission electron microscopy, infrared spectrum, and X-ray
absorption fine structure. This facile fabrication method renders homogeneously
dispersed Ru−Ni bimetallics embedded in the mesoporous carbonaceous framework and creates a highly active and stable
Ru Ni −OMC catalyst for the hydrogenation of levulinic acid (LA) to prepare γ-valerolactone (GVL), a biomass-derived
0.9 0.1
platform molecule with wide application in the preparation of renewable chemicals and liquid transportation fuels. A high TOF
−
1
(
>2000 h ) was obtained, and the Ru Ni −OMC catalyst could be used at least 15 times without obvious loss of its catalytic
0
.9 0.1
performance.
KEYWORDS: embedded bimetallics, ordered mesoporous carbon, pyrolysis, self-assembly, levulinic acid hydrogenation, high stability
1
. INTRODUCTION
as well as its affinity to the mesoporous supports, which
depends greatly on the synthetic methodology. Despite
continuous efforts, the facile fabrication of homogeneously
dispersed bimetallics firmly embedded in ordered mesoporous
carbons via a step-economic route still remains a challenge.
Catalytic conversion of levulinic acid (LA) to γ-valerolactone
Bimetallics are of great importance owing to their tunable
composition, size, and electronic properties linked to various
applications including magnetism, electronics, photonics, and
especially catalysis. To construct durable bimetallic catalysts,
two metals are commonly dispersed onto porous carbons to
prepare heterogeneous bimetallic catalysts, benefiting from the
wide adaptability of chemically inert and (hydro)thermally
1
−4
(
GVL) plays a key role in low-carbon and sustainable biomass
conversion; GVL can be widely used as a fuel additive, food
11,12
5
ingredient, and intermediate for fine chemical production.
stable carbons in various harsh conditions. Mesoporous
For this process, studies have shown that traditional Ru/C is
one of the most active heterogeneous catalysts; however, its
easy aggregation and leaching leading to low stability is still a
carbons are much favored since they offer great advantages
over conventional activated carbons (AC) owing to their well-
controlled mesopore structures which are favorable to trans-
1
3,14
6
concern.
Ruthenium with oxophilic metal twining hydro-
portation of the substrate and product. Recent advances in the
genation catalysts, such as composition-tuned Ru Re /C and
3
4
fabrication of bimetallic mesoporous carbons focus on
preconstruction of mesoporous carbon by a hard-templating
approach before metal impregnation and reduction, or
preformation of bimetallics stabilized by protecting agents
before anchorage.
usually created weakly attached bimetallics that were unevenly
distributed on the hydrophobic carbons, leading to easy particle
aggregation and catalyst leaching. It is known that the
catalytic performance of supported bimetallics is highly
sensitive to the nanoparticle (NP) dispersion and composition,
Ru Sn /C, displayed improved stability in the presence of
3
.6
1
15,16
sulfuric acid and alkylphenol solvent.
However, both
ruthenium-containing bimetallic carbons also face the dilemma
of tedious multistep synthesis and the corresponding limited
performance owing to the unevenly dispersed NPs and their
7
−9
However, such postsynthetic methods
10
Received: November 6, 2013
Revised: March 24, 2014
Published: March 25, 2014
©
2014 American Chemical Society
1419
dx.doi.org/10.1021/cs401030u | ACS Catal. 2014, 4, 1419−1425

ACS Catalysis
Research Article
weak affinity with AC. Evidently, such a dilemma could be
overcome by renovating the ruthenium-containing bimetallic
mesoporous carbon design.
Scheme 1. Synthesis of Ru Ni1−x−OMC Catalysts
x
From the latest research on the carbon supported metal
catalysts, we know that direct pyrolysis of metal coordination
polymers or metal organic frameworks under an inert
atmosphere can afford homogeneously dispersed metal NPs
1
7,18
firmly embedded in a carbonaceous matrix.
However,
owing to the uncontrollable transformation of flexible precursor
compounds during pyrolysis, the resulting carbonaceous
frameworks are always disordered and microporous. Con-
struction of ordered mesoporous carbons has been well
demonstrated by the pyrolysis of self-assembled block
copolymer templates and polymerizable precursors re-
1
9−22
cently.
Inspired by the advantages of the both method-
ologies and as our continuing interest in the development of
1
7,23
nanoparticle catalysts supported on the functional carbons,
we hypothesize that pyrolysis of surfactant-templated metal
coordination polymers may in situ fabricate homogeneously
dispersed metal NPs firmly embedded in ordered mesoporous
carbons. A polymerizable precursor possessing excellent
chelation with metals is the key to realizing this design, since
present polymerizable precursors, like phenolic resin and its
room temperature for 2 h, the resulting gel was transferred to a
polyethylene container and heated at 100 °C for 1 day. The as-
made product was washed, dried, and pyrolyzed in a tubular
furnace under a N atmosphere. The heating rate was 2 °C/min
2
below 350 and 5 °C/min above 350 °C, and pyrolysis was
carried out at 750 °C for 2 h. The resulting solid with different
compositions was denoted as Ru Ni −OMSC and subjected
2
4
derivatives, are hard to chelate metal ions to form metal
coordination polymers due to the absence of chelating sites. It
is known that chitosan is a very abundant biodegradeble and
biocompatible polysaccharide obtained by the alkaline
x
1−x
to alkaline etching with 3.0 M NaOH solution to remove silica
layers, affording Ru Ni −OMC.
x
1−x
2
.2. Material Characterization. Powder X-ray diffraction
25
deacetylation of chitin and possesses rich hydroxyl and
(
XRD) was collected with a Bruker D8 Advance X-ray
26
amine moieties with strong affinity for metal ions. Therefore,
it is speculated that chitosan may be a suitable chelating agent
for constructing metal coordination polymers.
diffractometer with nickel filtered Cu Kα radiation (λ =
1
.5406 Å). The samples were scanned in the range 2θ = 1.2−
0.0° and in steps of 2°/min. Morphology and microstructure
1
We herein report in situ fabrication of composition-tuned
Ru−Ni bimetallic mesoporous carbons by constructing cubic
Ia3d chitosan−ruthenium−nickel−silica mesophase via CTAB-
directed self-assembly of different proportions of ruthenium
chloride and nickel acetate with 8-quinolinol modified chitosan
of Ru Ni −OMC series were analyzed using a FEI Tecnai G2
x
1−x
F20 transmission electron microscope (TEM) equipped with
an energy dispersive X-ray spectroscopic analyzer operated at a
voltage of 200 kV. Samples were sonicated for 5 min in EtOH;
one drop of the suspended sample was dripped in a holely
carbon film supported on a 300 mesh copper grid. N2
adsorption/desorption isotherms were recorded at 77 K with
a Micromeritics Tristar II 3020. Before measurements, the
samples were outgassed at 300 °C for 3 h. The specific surface
area was calculated by using the Brunauer−Emmett−Teller
(BET) method, and the pore size distributions were measured
by using Barrett−Joyner−Halenda (BJH) analysis from the
desorption branch of the isotherms. Synchrontron X-ray
diffraction measurements were performed at the 11-ID-C
beamline of the Advanced Photon Source (APS) at Argonne
National Laboratory. High-energy X-rays of 115 keV energy
and 0.6 mm × 0.6 mm beam size were used to obtain two-
dimensional (2D) diffraction patterns in the transmission
geometry using a Perkin-Elmer large area detector placed at 1.6
m from the sample. X-ray absorption fine structure (XAFS) was
carried out on a beamline at the 20-ID and 20-BM at APS at
Argonne National Laboratory. The XAFS data were obtained in
the transmission mode at the Ni K-edge (8333.0 eV) and Ru K-
edge (22117.0 eV). Other relative information and character-
ization techniques can be found in the Supporting Information
in detail.
(
CTS-HQ) before pyrolysis and silica removal. This facile route
renders homogeneously dispersed Ru−Ni bimetallic NPs inside
the ordered mesoporous carbons without using any stabilizer
and additional reductant and was confirmed by various
characterization techniques. For catalytic hydrogenation of
levulinic acid, composition tunable Ru Ni −OMC exhibits
0
.9 0.1
−1
the highest TOF value (2191 h ) and stability (15 times
recyclability) of the reported bimetallic catalysts.
2
. EXPERIMENTAL SECTION
.1. Sample Preparation. The synthetic procedures for
Ru−Ni bimetallic mesoporous carbons are depicted in Scheme
. Because chitosan only dissolves in acidic solvents such as
2
1
HCl aqueous solution or acetic acid, to enhance its solubility
under the hydrothermal synthesis conditions and coordination
ability with the meal precursors, the chitosan was first modified
by reaction with 5-chloromethyl-8-quinolinol to afford 8-
quinolinol modified chitosan, CTS-HQ, involving a two-step
chemical transformation from 8-quinolinol (see Supporting
Information and Figures S1−S5). Then, the precursor
composite, Ru Ni −C SC, was prepared by CTAB-directed
x
1−x
16
self-assembly of different proportions of RuCl ·nH O and
Metal content was estimated by inductively coupled plasma
atomic emission spectroscopy (ICP-AES) analysis conducted
on a Perkin-Elmer emission spectrometer. Each 10 mg sample
of vacuum-dried material was placed in a PTFE lined digester
and dissolved in 5 mL of boiling aqua fortis solution.
Microwave digestion was carried out for 10 min to completely
3
2
Ni(CH COO) ·4H O with CTS-HQ under a basic medium.
3
2
2
The molar ratio of the precursor gels used in the preferred
preparation is 0.12 CTAB/8.0 NH (25 wt %)/114 H O/10
3
2
EtOH/1 TEOS/0.5 CTS-HQ/0.625 M (M = Ru Ni1−x), where
x
x was set as 0.5, 0.7, and 0.9. After the mixture was stirred at
1
420
dx.doi.org/10.1021/cs401030u | ACS Catal. 2014, 4, 1419−1425

ACS Catalysis
Research Article
dissolve the metal species. After cooling, each solution was
filtered through a 0.45 μm polyethersulfone filter and then
submitted for metal analysis.
2.3. Catalytic Test. The LA hydrogenation reactions were
carried out in a 100 mL magnetically stirred Parr 4560
autoclave equipped with a P.I.D. controller 4843. In a typical
procedure, 15 mg of catalyst and 5.0 g of LA were introduced
into the autoclave. The sealed autoclave was charged and
deflated with N three times before it was pressurized with H2
2
to 4.5 MPa at room temperature and heated at 150 °C for a
certain reaction duration. Then, the reactor was cooled with
cold water, the reaction mixture was centrifugated, and the solid
catalyst was washed and could be directly used for the next
cycle. The separated liquid reaction solution was quantitatively
analyzed with Agilent 6820 gas chromatography using toluene
as an internal standard.
3. RESULTS AND DISCUSSION
In this study, chitosan was first modified by 5-chloromethyl-8-
quinolinol to enhance its chelation with metal ions and
interaction with surfactant CTAB via electronic attraction in
the aqueous phase, facilitating the formation of a CTAB-
directed cubic Ia3d chitosan−ruthenium−nickel−silica meso-
phase. During the self-assembly process, CTS-HQ not only
binds and disperses metals well in sol−gel process but also
interacts with positive CTA+ to enlarge the surfactant
hydrophobic volume, rendering a decrease in micelle curvature
to form cubic a Ia3d mesophase along with silica (Figure
Figure 1. (A) Small angle X-ray diffraction with TEM (inset) and (B)
high-energy X-ray diffraction patterns of (a) Ru Ni −C SC, (b)
0
.9 0.1
16
Ru Ni −OMSC, (c) Ru Ni −OMC, (d) Ru Ni −OMC, and
0.9 0.1
0.9 0.1
0.7 0.3
(e) Ru Ni −OMC.
0.5 0.5
2
7−29
S6).
Owing to the difference in chemical and thermal
stability between chitosan and surfactant CTAB, as well as the
reducibility of carbons, the following pyrolysis is a unique “one
stone, three birds” strategy to remove CTAB, carbonize CTS-
HQ, and reduce metal ions in a single step. During pyrolysis,
silica framework acts as a hard template to consolidate the cubic
Ia3d structure, and its removal affords replicated intercrossed
carbonaceous mesopores with large surface areas and pore
volumes.
Ru Ni −containing samples are chosen as representatives
0.9 0.1
for structural, spectroscopic, and textual property studies, since
the same transformation occurs over different Ru Ni −C SC
x
1−x
16
samples. Small angle X-ray diffraction patterns clearly reveal the
cubic Ia3d featured (211), (220), (321), (400), and (420)
3
0,31
diffractions in the 2θ range from 2 to 5°,
except for shift
toward higher 2θ values that occurred after pyrolysis, linking to
lattice contraction (Figure 1A). However, only one broad
diffraction peak remains upon silica removal, suggesting that
the long-range ordered mesostructure suffers from a little
shrinkage. The TEM image with its FFT pattern provides a
direct visualization of well-ordered arrays of mesoporous
channels for Ru Ni −OMC (Figure 1A, inset). The high-
Figure 2. (A) The HAADF-STEM image for Ru Ni −OMC. (B)
0
.9 0.1
The corresponding carbon, nickel, and ruthenium elemental maps
using EDX for large and small particles as marked in HAADF-STEM.
(C) The electron microdiffraction pattern for single large particle in A.
0
.9 0.1
energy X-ray diffraction pattern of Ru Ni −OMC provides
0
.9 0.1
broad but clear (101), (102), and (110) diffractions (Figure
B), ascribed to the formation of finely hcp structured Ru−Ni
(D) The selected area electron diffraction (SAED) pattern for
2
Ru Ni −OMC.
0.9 0.1
3
2
bimetallic NPs. Interestingly, Ru Ni −OMC exhibits
characteristic (111), (200), (220), (311), and (222)
0
.7
0.3
The embedded Ru−Ni bimetallic NPs can be directly
discerned in the atomic resolution high-angle annular dark-field
(HAADF) images. For Ru Ni −OMC, Figure 2A clearly
diffractions, indicating the formation of fcc bimetallic nano-
3
3−35
crystallites,
and these diffraction peaks shift to higher
0.9 0.1
angles as the atomic percentage of Ru decreased for Ru Ni −
shows homogeneously distributed bright spots, corresponding
to highly dispersed large (5.2 ± 0.4 nm) and smaller (1.8 ± 0.2
nm) particles (Figure S7). The composition of both large and
smaller particles was demonstrated by investigating carbon,
nickel, and ruthenium elemental maps using EDX (Figure 2B).
0.5 0.5
OMC, demonstrating a lattice contraction originating from the
substitution of the smaller Ni atoms in place of the larger Ru
atoms. Correspondingly, the lattice constants based on (220)
diffractions also decrease (Table S1).
1
421
dx.doi.org/10.1021/cs401030u | ACS Catal. 2014, 4, 1419−1425

ACS Catalysis
Research Article
It reveals that the large particle proves to be Ni-aggregated
nanocrystallite with sporadic Ru inserted and around it,
providing an fm3m symmetry confirmed by electron micro-
diffraction (Figure 2C), while the smaller one is Ru-rich NP,
suggesting the formation of composition-tuned Ru−Ni
bimetallic NPs. The selected area electron diffraction (SAED)
pattern of Ru Ni −OMC mainly displays hcp features
one prominent peak at ∼2.1 Å from either the Ni−Ru or Ni−
Ni contributions, different from ∼1.6 Å from the Ni−O pairs
from Ru Ni −C16SC (Figure 3B), confirming the formation
0
.5 0.5
42
of alloyed Ru−Ni NPs. As for Ru K-edge analysis, Ru Ni −
0
.5 0.5
OMC is more similar to Ru Ni −C SC in the XANES
0.5 0.5
16
2
(Figure 3C), k -weighted EXAFS (Figure S10), and Fourier
transformed EXAFS (r space, Figure 3D) features, rather than
Ru foil. It can be ascribed to the dominance of low Z
backscatters around Ru atoms, which would be O in our
0
.9 0.1
36
(
Figure 2D). Similar to immiscible bimetals Au−Pt and
37
Ag−Rh in bulk form alloyed on the nanoscale, trapping Ni
43
and Ru into an alloyed particle is not easy, due to the large
system, revealing that the formed Ru(0) species were partially
38
standard reduction-potential difference; fortunately, it is
facilely realized in our experiment through a fast in situ
reduction process. Figure S7 shows the TEM images and the
corresponding particle size distributions for Ru Ni −OMC
oxidized upon hot alkaline treatment. As for Ru Ni −OMC
x
1−x
series, exploration of the short-ranged structure from 1 to 3 Å is
meaningful, since the local information may closely correlate
with catalytic properties. As illustrated in Figure 3B,c−e,
Ru Ni −OMC series show the declined peak intensity
x
1−x
series. It is clear that all Ru Ni −OMC samples exhibit both
x
1−x
x
1−x
small and large NPs with a bimodal size distribution, bearing
decreased average diameter for both large and small NPs as the
atomic percentage of Ru increases. Correspondingly, high
resolution TEM images exhibit an increased lattice separation
as for the fringes in the (111) direction (Figure S8), confirming
XRD findings.
around 2.1 Å as the molar percentage of Ru increases, ascribed
to less Ru or Ni coordinated with central Ni atoms, also verified
by Figure S11. On the contrary, there is an increased Ni−C
contribution centered at 1.5 Å, suggesting the stronger metal−
support interaction for composition-tuned Ru Ni −OMC.
0
.9 0.1
On the other hand, Ni content plays an insignificant role on the
local structure of Ru (Figure S12). It is clear that Ru Ni
To further verify the formation of alloyed Ru−Ni NPs in
ordered mesoporpus carbons, metal-specific XAFS was
measured via separated Ru and Ni K-edge scans. Herein,
Ru Ni -containing samples are more representative owing to
−
1−x
x
OMC series exhibit identical Ru−O and Ru−Ru/Ni con-
44
tributions at 1.5 and 2.3 Å, respectively. These results indicate
that Ru NPs prefer homogeneous nucleation to form small Ru-
rich bimetallics with strong interaction with support, while Ni
NPs prefer heterogeneous nucleation to form large Ni-rich
NPs.
0.5 0.5
the similar content for bimetals. As illustrated in Figure 3A,
FT-IR spectra are also sensitive to the change that occurred
during the synthetic process. Ru Ni −C SC shows the
0.9 0.1
16
characteristic C−H stretching from the CTA+ fragment at 2927
−1
and 2855 cm , pyridyl and aromatic ring vibrations between
−
1
1
600 and 1300 cm , as well as silica framework vibration mode
−
1
at 1085 and 465 cm (Figure S13), confirming that CTS-HQ
and silica have been incorporated into the CTAB-directed
45−47
Ru Ni −C SC mesophase.
However, only character-
0
.9 0.1
16
istic silica peaks remain upon pyrolysis, suggesting that
surfactant removal and CTS-HQ carbonization occurred.
Further silica removal is supported by the disappearance of
silica peaks after alkaline etching. We conducted elemental
analysis (C, H, and N) of Ru Ni −OMC, Ru Ni −OMC,
0.9 0.1
0.7 0.3
and Ru Ni −OMC; their N content ranged from 1.6 to 1.9
0.5 0.5
wt %, and no obvious difference was observed.
Simultaneously, pyrolysis followed by silica removal creates
mesoporous structures. N2 adsorption reveals a IV type
isotherm with a distinct H1 type hysteresis loop for
Figure 3. X-ray absorption near edge structure (XANES) of the Ni−K
edge (A) and Ru−K edge (C), and the magnitude of the Fourier
Ru Ni −OMSC and Ru Ni −OMC (Figure 4A), confirm-
0.9 0.1
0.9 0.1
4
8,49
2
transforms (not corrected for phase shifts) of the k weighted Ni−K
ing mesoporous materials with slit pores.
Upon silica
edge (B) and Ru−K edge (D) EXAFS of (a) Ru Ni −C SC, (b)
removal, the pore size slightly increases by 2.1%, while the
specific surface area and pore volume increase dramatically,
nearly double those of Ru Ni −OMSC (Table S2). The
0.5 0.5
16
Ru Ni −OMSC, (c) Ru Ni −OMC, (d) Ru Ni −OMC, (e)
0.5 0.5
0.5 0.5
0.7 0.3
Ru Ni −OMC, (f) Ni foil, and (g) Ru foil.
0.9 0.1
0.9 0.1
S
/S
ratio and V /V
ratio decrease from 0.79 to
meso micro
meso
micro
different from Ru Ni −C SC, Ru Ni −OMSC and
0.56 and from 2.35 to 1.89, suggesting more microstructures
0
.5
0.5
16
0.5
0.5
Ru Ni −OMC exhibit a newly present pre-edge peak and
were formed upon silica removal. As for Ru Ni −OMC
0.5 0.5
x
1−x
negative shift in the adsorption edge position, suggesting that
series, it is observed that the surface area and pore volume
enhance with the increase of ruthenium content, probably
because of more small Ru-rich bimetallic NP formation.
3
9,40
the Ni(+2) species are mostly reduced,
though they carry
some positive charges because of a slightly positive shifted edge
4
1
position as compared to the Ni reference.
In the
Notably, all Ru Ni1−x−OMC samples show narrow pore size
x
corresponding k space, Ru Ni −OMSC and Ru Ni −
distribution (Figure 4B) centered at ca. 4.30 nm.
0
.5 0.5
0.5 0.5
−
1
OMC show clear oscillations at a higher k region of k > 8 Å as
compared to Ru Ni −C SC (Figure S9), indicating the
The hydrogenation of LA to GVL was chosen as a probe
reaction to investigate the catalytic performances of Ru Ni −
0
.5 0.5
16
x
1−x
dominance of high Z backscatters, which would be Ni or Ru.
OMC series, since GVL has been identified as a platform
Consistently, Ru Ni −OMSC and Ru Ni −OMC exhibit
molecule from renewable biomass with wide application in
0
.5 0.5
0.5 0.5
1
422
dx.doi.org/10.1021/cs401030u | ACS Catal. 2014, 4, 1419−1425

ACS Catalysis
Research Article
blank OMC support exhibits insignificant LA conversion owing
to the absence of active sites (entry 1). All Ru Ni −OMC
x
1−x
samples (0.3 wt %) were active toward the catalytic
hydrogenation of 5.0 g of LA under 4.5 MPa of H at 150
2
°
C for 2 h, affording high selectivity to GVL without any
solvent. It is interesting that the LA conversion and GVL yield
are improved with the increase in Ru composition (entries 2−
4
), while the Ni/C with 3.3 wt % Ni loading only provided 3%
yield of GVL under the same reaction conditions, suggesting
that the Ru species is the main active component. Ru Ni −
0
.7 0.3
OMC afforded a 94% yield of GVL with a TOF value as high as
1
2
936 h− (entry 3); Ru Ni −OMC and Ru−OMC all gave
0.9 0.1
near quantitative LA conversions with the TOF value attaining
1
−1
2
501 h− and 2288 h (entries 4 and 5), respectively. These
three catalysts are much more active than that of Ru Ni −
0
.5 0.5
OMC and commercial Ru/C (entry 8). Considering that LA
aqueous solutions could be directly obtained from the acid-
catalyzed conversion of biomass, water was then explored as a
potential solvent using Ru Ni −OMC as the representative
0.9 0.1
catalyst, and a similar LA conversion (97%) but lower GVL
yield (84%) were obtained under the same catalyst loading with
that over Ru Ni −OMC, suggesting such Ru Ni −OMC
0.9 0.1
x
1−x
could also work smoothly for the aqueous LA solution (entry
9).
Figure 4. (A) N adsorption/desorption isotherms and (B) pore size
2
distribution profiles of (a) Ru Ni −C, (b) Ru Ni −OMSC, (c)
0.9 0.1
0.9 0.1
It is known that the textural properties of the catalyst also
affect its catalytic performances significantly. Ru Ni −C,
Ru Ni −OMC, (d) Ru Ni −OMC, and (e) Ru Ni −OMC.
0.9 0.1
0.7 0.3
0.5 0.5
0
.9 0.1
prepared as a comparison via directpyrolysis of a chitosan−
ruthenium−nickel coordination polymer (see Supporting
Information), lacks a uniform mesopore distribution (Figure
4a) and exhibits a much lower LA conversion of 34% with a
trace GVL yield (entry 7), suggesting that the mesoporous
arrays also play an important role in achieving high catalytic
activity and selectivity. Mesoporous Ru0.9Ni0.1−OMSC showed
moderate GVL yield (entry 6), and then its yield could be
readily improved to 97% over Ru0.9Ni0.1−OMC; this obvious
activity difference indicates that the larger surface areas and
pore volumes are essential to enhancing the catalytic efficiency
as well. It is concluded that Ru Ni −OMC showed the best
chemical synthesis and liquid transportation fuels. It has been
proved that the introduction of a heterometal species into Ru/
1
5,16
C could enhance its catalytic performance,
since the
formation of bimetallic NPs is beneficial to the homogeneous
dispersion of smaller Ru NPs and enhances their interaction
with the carbonaceous support, which was also herein detected
by the in-depth characterization of the present Ru Ni −OMC
x
1−x
catalysts. The selected results on Ru Ni −OMC catalyzed LA
x
1−x
hydrogenation are summarized in Table 1; as expected, the
Table 1. Catalytic Hydrogenation of LA with Different
0.9 0.1
a
Catalysts
catalytic performances of any catalysts in this study, which
highly depended on the homogeneously dispersed small Ru-
rich NPs and the ordered mesoporous arrays with large surface
area and pore volumes; all of these physicochemical properties
may facilitate the LA adsorption and GVL diffusion well.
Besides the efficient catalytic activity, stable recyclability is
also crucial for an outstanding heterogeneous catalyst from the
viewpoint of both academic research and industrial applications.
As for LA hydrogenation, traditional Ru/C has been proved to
be one of the most active catalysts so far. However, Liu et al.
found that the initial 99% conversion of LA catalyzed
metal loading
mmol g−
1
(
)
LA
conversion
(%)
GVL
yield
(%)
b
TOF
−
1
entry
catalyst
OMC
Ni
Ru
(h )
1
2
6
Ru0.5Ni0.5
−
−
−
0.4363
0.2683
0.0817
0.3424
0.4589
0.5557
45
41
94
97
1716
2936
2501
OMC
3
4
Ru0.7Ni0.3
OMC
96
99
Ru0.9Ni0.1
OMC
13
commercial Ru/C dropped to 42% in the fourth reuse. As
illustrated in Figure 5, Ru Ni −OMC lost 13% of GVL yield
0.7 0.3
5
6
Ru−OMC
0.6076
0.4302
99
39
97
36
2288
1199
after six cycles, while Ru Ni −OMC was quite stable and
0.9 0.1
Ru0.9Ni0.1
−
0.0532
0.0717
OMSC
could be used at least 15 times without a significant loss of
activity. To further verify its stability, the Ru concentration in
the reaction solution was checked by ICP-AES to be negligible
leaching of Ru species into the liquid phase. The HAADF
STEM image of the spent Ru Ni −OMC (Figure S14)
7
8
Ru0.9Ni0.1−C
commercial
Ru/C
0.5045
0.4940
34
48
15
30
426
870
c
9
Ru0.9Ni0.1
OMC
−
0.0817
0.5557
97
84
2167
0.9 0.1
shows less agglomeration after 15 times usage as compared with
a
that of Ru Ni −OMC after being recycled six times;
0
.7 0.3
Reaction conditions: LA, 5.0 g (43 mmol); catalyst, 0.3 wt % (15
b
−1
therefore it still exhibits 90% of GVL yield. As far as we
mg); H , 4.5 MPa; 2 h; and 423 K. TOF, h (turnover frequency):
moles of GVL produced per Ru mole metal ion per hour. LA, 2.0 g
2
c
know, as the prepared Ru Ni −OMC catalyst is the most
0.9 0.1
(
17.2 mmol); catalyst, 0.3 wt % (6 mg); H O, 3.0 g; H , 4.5 MPa; 2 h;
stable Ru-based heterogeneous catalyst reported in the LA
hydrogenation, and its robust nature can be ascribed to the
2
2
and 423 K.
1
423
dx.doi.org/10.1021/cs401030u | ACS Catal. 2014, 4, 1419−1425

ACS Catalysis
Research Article
ACKNOWLEDGMENTS
■
Financial support from the Chinese Academy of Sciences, the
National Natural Science Foundation of China (21373246,
2
1303229, and 21173269), and the Science Foundation of
China University of Petroleum, Beijing (2462013YJRC018) is
greatly appreciated. The proposals (GUP28010 and
GUP31195) given by Advanced Photon Source of the Office
of Science, U.S. Department of Energy under Contract DE-
AC02-06CH11357 are acknowledged. We also thank Prof.
Haichao Liu and Dr. Junfang Nie for their help in the ICP-AES
analysis.
REFERENCES
■
Figure 5. Recyclability test for Ru0.9Ni0.1−OMC (blue) and
Ru Ni −OMC (gray). Reaction conditions: LA (5.0 g), catalyst
(
(
1) Wei, Z. H. Chem. Soc. Rev. 2012, 41, 7994−8008.
2) Yu, W.; Porosoff, M. D.; Chen, J. G. G. Chem. Rev. 2012, 112,
780−5817.
3) Kellya, T. G.; Chen, J. G. G. Chem. Soc. Rev. 2012, 41, 8021−
034.
(4) Guczi, L. Catal. Today 2005, 101, 53−64.
(5) Lee, J.; Kim, J.; Hyeon, T. Adv. Mater. 2006, 18, 2073−2094.
(6) Pang, J. F.; Wang, A. Q.; Zheng, M. Y.; Zhang, Y. H.; Huang, Y.
0
.7 0.3
(
15 mg), H (4.5 MPa), 423 K, and 2 h.
2
5
(
8
enhanced interaction of embedded small Ru−Ni bimetallic NPs
with the carbonaceous support, as revealed by advanced
50
electron microscopy. This strong metal support interaction
Q.; Chen, X. W.; Zhang, T. Green Chem. 2012, 14, 614−617.
7) Liu, X. Y.; Wang, A. Q.; Wang, X. D.; Mou, C-.Y.; Zhang, T.
Chem. Commun. 2008, 3187−3189.
8) Witham, C. A.; Huang, W.; Tsung, C. K.; Kuhn, J. N.; Somorjai,
G. A.; Toste, F. D. Nat. Chem. 2010, 2, 36−41.
9) Fulvio, P. F.; Liang, C. D.; Dai, S.; Jaroniec, M. Eur. J. Inorg.
can also be demonstrated by the presence of Ni−C pairs (ca.
(
1.5 Å) in Ru Ni −OMC (Figure 3B,e). To make the
0.9 0.1
hydrogenation of LA yield of GVL commercially competitive,
the development of a highly acitive and stable catalyst that is
(
5
0,51
also the main limitation of the reported examples
is among
(
the biggest challenges. Herein, the elaborately composition-
Chem. 2009, 605−612.
tuned Ru Ni −OMC catalyst provided an alternative.
0.9 0.1
(10) Li, X. Y.; Wang, X.; Song, S. Y.; Liu, D. P.; Zhang, H. J. Chem.
Eur. J. 2012, 18, 7601−7607.
4. CONCLUSION
(
11) Wright, W. R. H.; Palkovits, R. ChemSusChem 2012, 5, 1657−
In summary, facile fabrication of composition-tuned Ru−Ni
bimetallics homogeneously dispersed in ordered mesoporous
carbons has been successfully achieved by constructing a
CTAB-directed chitosan−ruthenium−nickel−silica mesophase
before pyrolysis and silica removal. Deep investigation reveals
that the catalytic performance highly depends on both Ru−Ni
bimetallics and carbonaceous supports, as well as their
ensemble effect, verified by various characterization techniques
and a comparative catalytic test. The elaborately tuned
1667.
(12) Li, W.; Xie, J.-H.; Lin, H.; Zhou, Q.-L. Green Chem. 2012, 14,
2
(
(
388−2390.
13) Yan, Z.-P.; Lin, L.; Liu, S. J. Energy Fuels 2009, 23, 3853−3858.
14) Galletti, A. M. R.; Antonetti, C.; Luise, V. D.; Martinelli, M. A.
Green Chem. 2012, 14, 688−694.
15) Braden, D. J.; Henao, C. A.; Heltzel, J.; Maravelias, C. C.;
Dumesic, J. A. Green Chem. 2011, 13, 1755−1765.
16) Alonso, D. M.; Wettstein, S. G.; Bond, J. Q.; Root, T. W.;
(
(
Dumesic, J. A. ChemSusChem 2011, 4, 1078−1081.
(17) Li, Z. L.; Liu, J. H.; Huang, Z. W.; Yang, Y.; Xia, C. G.; Li, F. W.
ACS Catal. 2013, 3, 839−845.
Ru Ni −OMC catalysts demonstrated unprecedented cata-
0.9 0.1
lytic activity and stability for the catalytic hydrogenation of LA
to GVL, ascribing to the homogeneous embedding of Ru−Ni
bimetallics in a mesoporous carbonaceous matrix with a strong
metal−support interaction. The development of such efficient
Ru−Ni bimetallic mesoporous carbons successfully proves the
concept of composition-tuned multicomponent assembly and
also gives a strong indication of its generality in the facile
fabrication of a variety of heterogeneous bi- and/or trimetallic
OMCs through this step-economic multicomponent assembly
procedure.
(18) Ma, S. Q.; Goenaga, G. A.; Call, A. V.; Liu, D.-J. Chem.Eur. J.
2011, 17, 2063−2067.
(19) Ma, T.-Y.; Liu, L.; Yuan, Z.-Y. Chem. Soc. Rev. 2013, 42, 3977−
4
(
9
(
003.
20) Wan, Y.; Shi, Y. F.; Zhao, D. Y. Chem. Mater. 2008, 20, 932−
45.
21) Deng, Y. H.; Yu, T.; Wan, Y.; Shi, Y. F.; Meng, Y.; Gu, D.;
Zhang, L. J.; Huang, Y.; Liu, C.; Wu, X. J.; Zhao, D. Y. J. Am. Chem.
Soc. 2007, 129, 1690−1697.
(22) Liu, R. L.; Shi, Y. F.; Meng, Y.; Zhang, F. Q.; Gu, D.; Chen, Z.
X.; Tu, B.; Zhao, D. Y. J. Am. Chem. Soc. 2006, 128, 11652−11662.
(23) Li, Z. L.; Liu, J. H.; Xia, C. G.; Li, F. W. ACS Catal. 2013, 3,
2440−2448.
ASSOCIATED CONTENT
Supporting Information
The details of the preparation of materials and their
characterization. This information is available free of charge
via the Internet at http://pubs.acs.org/.
■
*
S
(24) Ryoo, R.; Joo, S. H.; Kruk, M.; Jaroniec, M. Adv. Mater. 2001,
13, 677−681.
(25) Liu, F. Y.; Carlos, L. D.; Ferreira, R. A. S.; Rocha, J.; Ferro, M.
C.; Tourrette, A.; Quignard, F.; Robitzer, M. J. Phys. Chem. B 2010,
1
(
(
14, 77−83.
AUTHOR INFORMATION
Corresponding Author
E-mail: fuweili@licp.cas.cn.
Notes
■
*
26) Guibal, E. Prog. Polym. Sci. 2005, 30, 71−109.
27) Huang, J. H.; Tian, G.; Wang, H. S.; Xu, L.; Kan, Q. B. J. Mol.
Catal. A: Chem. 2007, 271, 200−208.
(28) Kleitz, F.; Choi, S. H.; Ryoo, R. Chem. Commun. 2003, 2136−
The authors declare no competing financial interest.
2137.
1
424
dx.doi.org/10.1021/cs401030u | ACS Catal. 2014, 4, 1419−1425

ACS Catalysis
Research Article
(
29) Liu, X. Y.; Tian, B. Z.; Yu, C. Z.; Gao, F.; Xie, S. H.; Tu, B.; Che,
R. C.; Peng, L.-M.; Zhao, D. Y. Angew. Chem., Int. Ed. 2002, 41, 3876−
878.
30) Liang, C. D.; Li, Z. J.; Dai, S. Angew. Chem, Int. Ed. 2008, 47,
3
(
3
(
(
696−3717.
31) Wan, Y.; Zhao, D. Y. Chem. Rev. 2007, 107, 2821−2860.
32) Viau, G.; Brayner, R.; Poul, L.; Chakroune, N.; Lacaze, E.;
Fiev
33) Chen, G. Z.; Desinan, S.; Nechache, R.; Rosei, R.; Rosei, F.; Ma,
D. L. Chem. Commun. 2011, 47, 6308−6310.
34) Chen, G. Z.; Desinan, S.; Rosei, R.; Rosei, F.; Ma, D. L. Chem.
Eur. J. 2012, 18, 7925−7930.
35) Chen, L.; Chen, J. M.; Zhou, H. D.; Zhang, D. J.; Wan, H. Q.
Mater. Sci. Eng., A 2007, 452−453, 262−266.
36) Zhou, S. H.; Jackson, G. S.; Eichhorn, B. Adv. Funct. Mater.
007, 17, 3099−3104.
37) Kim, J.; Lee, Y. M.; Sun, S. H. J. Am. Chem. Soc. 2010, 132,
996−4997.
38) Braos-García, P.; García-Sancho, C.; Infantes-Molina, A.;
Rodríguez-Castellon, E.; Jimenez-Lopez, A. Appl. Catal. A: Gen.
010, 381, 132−144.
39) Sarma, L. S.; Chen, C.-H.; Kumar, S. M. S.; Wang, G.-R.; Yen,
́ ́
et-Vincent, F.; Fievet, F. Chem. Mater. 2003, 15, 486−494.
(
(
(
(
2
(
4
(
́
́
́
2
(
S.-C.; Liu, D.-G.; Sheu, H.-S.; Yu, K.-L.; Tang, M.-T.; Lee, J.-F.; Bock,
C.; Chen, K.-H.; Hwang, B.-J. Langmuir 2007, 23, 5802−5809.
(
40) Daniel, O. M.; DeLaRiva, A.; Kunkes, E. L.; Datye, A. K.;
Dumesic, J. A.; Davis, R. J. ChemCatChem 2010, 2, 1107−1114.
(
41) Sun, S. H.; Zhang, G. X.; Gauquelin, N.; Chen, N.; Zhou, J. G.;
Yang, S. L.; Chen, W. F.; Meng, X. B.; Geng, D. S.; Banis, M. N.; Li, R.
Y.; Ye, S. Y.; Knights, S.; Botton, G. A.; Sham, T.-K.; Sun, X. L. Sci.
Rep. 2013, 3, 1−9.
(
42) Li, D. L.; Atake, I.; Shishido, T.; Oumi, Y.; Sano, T.; Takehira,
K. J. Catal. 2007, 250, 299−312.
43) Qiao, B. T.; Wang, A. Q.; Yang, X. F.; Allard, L. F.; Jiang, Z.;
Cui, Y. T.; Liu, J. Y.; Li, J.; Zhang, T. Nat. Chem. 2011, 3, 634−641.
44) Zaikovskii, V. I.; Nagabhushana, K. S.; Kriventsov, V. V.;
(
(
Loponov, K. N.; Cherepanova, S. V.; Kvon, R. I.; Bo1nnemann, H.;
Kochubey, D. I.; Savinova, E. R. J. Phys. Chem. B 2006, 110, 6881−
6890.
(
2
(
1
45) Gallo, J. M. R.; Pastore, H. O.; Schuchardt, U. J. Catal. 2006,
43, 57−63.
46) Maurya, M. R.; Sikarwar, S. J. Mol. Catal. A: Chem. 2007, 263,
75−185.
47) Maurya, M. R.; Chandrakar, A. K.; Chand, S. J. Mol. Catal. A:
(
Chem. 2007, 270, 225−235.
(48) Corma, A. Chem. Rev. 1997, 97, 2373−2419.
(49) Robles-Dutenhefner, P. A.; Rocha, K. A. D.; Sousa, E. M. B.;
Gusevskaya, E. V. J. Catal. 2009, 265, 72−79.
50) Zhou, W. P.; Lewera, A.; Larsen, R.; Masel, R. I.; Bagus, P. S.;
Wieckowski, A. J. Phys. Chem. B 2006, 110, 13393−13398.
51) Yu, X.; Pickup, P. G. J. Power Sources 2008, 182, 124−132.
(
(
1
425
dx.doi.org/10.1021/cs401030u | ACS Catal. 2014, 4, 1419−1425