Versatile dual hydrogenation-oxidation nanocatalysts for the aqueous transformation of biomass-derived platform molecules

Article abstract of DOI:10.1039/c2gc35176e

Carbon-supported Pd nanoparticles have been proved to be efficient dual hydrogenation-oxidation nanocatalysts in both the selective aqueous oxidation of benzyl alcohol and the hydrogenation of furfural in water under microwave irradiation. Nanocatalysts b

Full text of DOI:10.1039/c2gc35176e

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PAPER
Versatile dual hydrogenation–oxidation nanocatalysts for the aqueous
transformation of biomass-derived platform molecules†
a,b,c
d
b,c
a
Eduardo J. García-Suárez,*
Alina Mariana Balu, Mar Tristany, Ana Beatriz García,
b,c
d
Karine Philippot* and Rafael Luque*
Received 6th February 2012, Accepted 29th February 2012
DOI: 10.1039/c2gc35176e
Carbon-supported Pd nanoparticles have been proved to be efficient dual hydrogenation–oxidation
nanocatalysts in both the selective aqueous oxidation of benzyl alcohol and the hydrogenation of furfural
in water under microwave irradiation. Nanocatalysts based on trioctylphosphine and triphenylphosphine-
stabilized-Pd NPs on oxidized carbon support were found to be the most active. The presence of oxygen
groups on the surface of the carbon support, particularly those of acidic character, improve the Pd NPs
immobilization as well as the water affinity, and consequently the catalytic performances of the system.
In terms of catalytic applications, supported metal nanoparti-
cles ranging from noble (Pt, Pd, Au) to transition metals (Cu,
Ni) have been widely employed in redox catalysed reactions
Introduction
Supported metal nanoparticles (SMNPs) have focused many
research endeavours from the scientific community due to thei1r
inherent advantages compared to non supported nanoparticles.
The stabilisation and control (in terms of nanoparticle size and
distribution), recoverability and robustness as well as preventing
agglomeration of the particles that can be achieved via depo-
sition in a porous framework predates all alternative method-
ologies reported to date (e.g. capping agents such as surfactants
or ligands, ionic liquids, etc.). The decoration of supports with
metal nanoparticles (MNPs) has been achieved by a number of
different methodologies (e.g. (photo)chemical, (sono)electroche-
mical, mechanochemical deposition, etc.) over various solid
15
16
including selective oxidation of alcohols,
alkenes
and
17
18
alkynes as well as in hydrogenation of alkenes–alkynes and
19
carbonyl compounds. However, few reports to date deal with
catalysts able to perform either oxidation or hydrogenation reac-
2
0
tions depending on the selected reaction conditions. Sup-
ported-Pd nanoparticles are one example of such catalytic
systems that can in principle be designed to display the dual
redox activity due to excellent hydrogenation (under reducing
atmosphere) and oxidation properties (both under air and oxi-
dants including hydrogen peroxide).
2
1
Following our recent results in the development of environ-
mentally sound methodologies for the design of catalytic (nano)
materials for the synthesis of fine chemicals and biofuels via low
3
4
supports including mesoporous silica, inorganic oxides, mol-
5
6
7
8
ecular sieves, polymers, capsules, apatites or activated
9
21
carbons. The use of mesoporous carbon materials as supports to
impact chemical transformations, herein we report the dual use
of Pd NPs supported on a variety of mesoporous carbon
materials as both oxidation and hydrogenation catalysts. This
work was encouraged by the preliminary activity observed for
some of the described systems in the aerobic oxidation of benzyl
stabilise MNPs is known as leading to highly dispersed and
active materials (particularly for catalytic applications) due to
their excellent mechanical properties as well as optimum pore
size distributions, high stability and surface chemistry which can
1
0
22
lead to functionalised materials. MNPs supported on carbon
materials have been applied in different areas including medi-
alcohol in water. The selected chemical transformations, as
proof of concept for catalytic activity, include the microwave-
assisted selective oxidation of benzyl alcohol to benzaldehyde
under mild conditions and the hydrogenation of a range of plat-
form molecules such as furfural and organic acids (e.g. itaconic,
pyruvic, levulinic acids) both under conventional heating and
microwave irradiation. These biomass-derived compounds have
attracted a great deal of interest due to their versatility and wide
11
12
13
cine, sensors and optics, environmental remediation and
14
catalysis.
a
Instituto Nacional del Carbón (CSIC), Francisco Pintado Fe 26, 33011
Oviedo, Spain. E-mail: eduardo@incar.csic.es
b
CNRS, LCC (Laboratoire de Chimie de Coordination), 205, Route de
23,24
range of valuable derivative products they can lead.
Narbonne, F-31077 Toulouse, France. E-mail: karine.philippot@
lcc-toulouse.fr
c
Université de Toulouse, UPS, INPT, LCC, F-317077 Toulouse, France
Departamento de Química Orgánica, Universidad de Córdoba,
d
Experimental
Campus de Excelencia Agroalimentario CeiA3, Edificicio Marie Curie
Chemical reagents and solvents
(C-3), Ctra Nnal IV-A, Km 396, E14014 Cordoba, Spain. E-mail:
q62alsor@uco.es
Tris(dibenzylideneacetone)dipalladium (0) complex [Pd (dba) ]
(from Strem Chemicals), triphenylphosphine (TPP) and
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c2gc35176e
2
3
1
1434 | Green Chem., 2012, 14, 1434–1439
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trioctylphosphine (TOP) (both from Sigma-Aldrich) were used
of ([Pd (dba) ]) was dissolved in 12 mL of distilled and
2
3
without any further purification. THF and pentane solvents
degassed THF in a Fisher–Porter reactor. 200 mg of the carbon
(
from SDS) were distilled over sodium-benzophenone or P O5
support (MB-H O or MB-1500) were subsequently added to
2
2 2
respectively or dried in a purification column, respectively.
Reagents and solvents were degassed before use by means of
three freeze–pump–thaw cycles.
the solution and the mixture was stirred for 3 h. The solvent was
then evaporated and the impregnated carbon material dried under
vacuum for 1 h. The Fisher–Porter reactor was afterwards press-
urized up to 3 bar with H and the solid stirred overnight. After
2
pressure releasing, the resulting catalysts were stored in a glove-
box prior to their characterisation and use. The catalysts were
Carbon supports
denoted as Pd/MB-H O and Pd/MB-1500.
2 2
Mesoporous carbon beads (MB) of particle size in the range
0
.5–1.0 mm with spherical shape were used as the starting
support. They are commercially available phenolic resin-based
Characterisation techniques
2
5
activated carbon with a bi-modal pore texture. MB carbon
material was heated at 1500 °C for 1 h in a graphite electrical
The surface area and pore size distribution of the carbon supports
were derived from the N adsorption–desorption isotherms per-
2
formed at −196 °C in a Micromeritics ASAP 2420 volumetric
adsorption system. Prior to measurement, samples were degassed
overnight by heating at 250 °C under vacuum. Specific surface
areas (SBET) were calculated using the Brunauer–Emmett–Tellet
−1
furnace, at a heating rate of 10 °C min in Ar flow. The new
material prepared was denoted MB-1500. Oxidation of MB was
carried out by treatment with hydrogen peroxide (30 wt% in
water) at 50 °C for 16 h followed by washing with distilled
water, thus obtaining a carbon material support denoted as
MB-H O .
2
(BET) method, taking 16.2 nm for the cross-sectional area of
2
2
the nitrogen-adsorbed molecule. Total pore volumes (V ) were
t
o
determined by the amount of N adsorbed at p/p = 0.99. Pore
size distributions were obtained by applying the DFT (density
2
Synthesis of isolated Pd NPs
2
6
functional theory) method to the N adsorption isotherms and
they are given as ESI (ESI S1†).
HRTEM images of the MNPs/carbon material catalysts were
obtained at the Service de Microscopie Electronique de l’Univer-
sité Paul Sabatier Toulouse (TEMSCAN) with a JEOL JEM
2
Pd nanoparticles were prepared by the organometallic approach
using either triphenylphosphine (TPP) or trioctylphosphine
TOP) as stabilizing ligands. Typically, 0.084 mmol of Pd pre-
cursor [Pd (dba) ] were dissolved in 40 mL of THF in a Fisher–
Porter reactor. Then, the corresponding ligand (TPP or TOP dis-
solved in 10 mL of THF) was added to the metal precursor sol-
ution in a ligand–metal molar ratio of 0.5 at −30 °C to avoid the
formation of the molecular complex. The reaction mixture was
(
2
3
2
0
010 microscope working at 200 kV with a resolution point of
.235 nm. The samples were prepared using ultramicrotomy
technique. Thin slices were obtained by cutting down the middle
of catalyst carbon spheres. They were deposited on carbon
copper grids for the analysis. Statistical size distributions and
mean diameter sizes of Pd NPs supported on the carbon
materials were carried out manually by measuring ca. 300 par-
ticles when possible on enlarged TEM micrographs.
pressurized up to 3 bar with H and stirred overnight at room
2
temperature. The Fisher–Porter reactor was then depressurized
and the solvent evaporated to a volume of ca. 2 mL. Pd NPs
were afterwards precipitated and washed with pentane and dried
under vacuum overnight to obtain a black powder which was
kept in a glove-box (Ar, H O < 1 ppm; O < 0.1 ppm) until use.
Pd contents of the MNPs/carbon material catalysts were deter-
mined by Atomic Absorption Spectroscopy (AAS) in an
AA-6300 Shimadzu spectrophotometer. All samples were treated
with H O , HNO and HCl before analyses.
2
2
2
MNPs/Carbon material catalyst preparation
2
2
3
The carbon supported catalysts were prepared in two different
ways.
Catalytic experiments
1
.
Impregnation of the carbon supports with a colloidal sus-
Microwave-assisted oxidation of benzyl alcohol. In a typical
reaction, a mixture containing 2 mmol of benzyl alcohol, 0.4 mL
of H O (50 wt%), 2 mL of water and 0.05 g of catalyst was
microwaved in a CEM-DISCOVER reactor for 3 min at
maximum power output (300 W), reaching a maximum tempera-
ture between 100–110 °C (average temperature 90 °C). The
microwave method was power-controlled and reactions were
carried out in closed vessel mode (pressure 120–200 psi devel-
oped in the system).
pension of purified Pd NPs. Previously isolated Pd NPs were
dispersed in distilled THF (12 mL). The colloidal suspension
was divided in two equal portions and each of them was added
to a Schlenk flask containing 200 mg of MB-H O or MB-1500
as carbon supports. The reaction mixtures were stirred for 3 h at
room temperature followed by a careful evaporation of the
solvent. Pd NPs/carbon materials catalysts were then dried under
vacuum overnight. The catalysts were denoted as Pd(TPP)/
MB-1500 and Pd(TPP)/MB-H O or Pd(TOP)/MB-1500 and
2
2
2
2
2
2
Microwave-assisted hydrogenation of furfural. In a typical
reaction, a mixture containing 2 mmol of furfural, 1.5 mL of
formic acid, 1.5 mL of water and 0.1 g of catalyst was micro-
waved in a CEM-DISCOVER reactor for 30–45 min at 100 °C
(power output 100–150 W). In this case, the microwave method
was temperature-controlled (which was measured by a fiber optic
Pd(TOP)/MB-H O . These names stand for the metal (Pd), the
2
2
ligand (TPP or TOP) and the carbon support (MB-1500 or
MB-H O ) used.
2
2
2
. Impregnation of the carbon supports with a solution of the
palladium zero precursor followed by hydrogenation. 0.2 mmol
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Table 1 Textural properties of the carbon material supports and
catalysts, Pd contents and Pd NPs mean size in the catalysts
a
b
c
S
(
BET
V
t
Pd
Pd NPs mean
d
m g−1)
2
(cm g−1) (wt%) size (nm)
3
MB
MB-H
MB-1500
Pd(TOP)/MB-H
Pd(TOP)/MB-1500
Pd(TPP)/MB-H
Pd(TPP)/MB-1500
Pd/MB-H
1294
1211
909
1020
798
995
815
1.14
2
O
2
1.10
0.99
1.01
0.86
0.93
0.90
0.99
0.87
—
—
—
—
2
O
2
2.58
2.01
1.34
1.38
2.21
1.68
1.9 ± 0.3
1.9 ± 0.3
2.2 ± 0.5
1.8 ± 0.3
1.8 ± 0.4
2.8 ± 0.5
2
O
2
2
O
2
1055
755
Pd/MB-1500
a
b
c
BET surface area. Total pore volume. Determined by Atomic
d
Absorption Spectroscopy. Measured by HRTEM.
probe) and reactions were carried out in closed vessel mode
(
pressure 150–250 psi developed in the system) as formic acid
efficiently decomposes under the investigated microwave
irradiation conditions into CO and H and leads to over-pressure
2
2
Fig. 1 HRTEM images of Pd/MB-H O (a) and Pd/MB-1500 (c) cata-
2
2
in the systems under power-controlled conditions.
lysts, and their corresponding size histograms (b) and (d).
Upon reaction completion (in both cases), samples were col-
lected, extracted with an organic solvent (typically toluene) and
subsequently analysed by GC and GC/MS in an Agilent 6890N
fitted with an HP-5 capillary column (30 m × 0.32 mm ×
0
.25 μm) and a flame ionization detector (FID).
Results and discussion
The textural properties of the starting MB, oxidized MB-H O2
2
and high temperature treated MB-1500 carbon materials investi-
gated in this work are summarised in Table 1. The chemical oxi-
dation with H O of MB does not affect significantly the textural
2
2
Fig. 2 High magnification HRTEM micrographs of (a) Pd/MB-H O2
and (b) a Pd nanoparticle on MB-1500.
2
2
−1
parameters. BET surface areas of 1294 and 1211 m g were
calculated for MB and MB-H O , respectively. However, the
2
2
heat treatment of MB causes a significant decrease of the surface
area as expected. DFT calculations on the nitrogen adsorption
isotherms showed bi-modal pore size distributions for the carbon
supports, with a mesopore distribution centred at approx 34 nm
dispersed Pd NPs without aggregation were obtained on both
carbon materials. Larger nanoparticles with a mean diameter of
2.8 nm were measured in Pd/MB-1500 against a value of 1.8 nm
(
ESI S1†).
in Pd/MB-H
explained on the basis of the higher amount of oxygen groups,
particularly those of acidic character, on the surface of MB-H O
2 2
carbon support which can act as NPs stabilizers, thus limiting
their growth.
2 2
O (Table 1). This difference in size can be
The support surface oxygen functional groups available to
interact with MNPs was reported to increase as follows
MB-1500 < MB < MB-H O . It was thus expected that the
hydrophilicity of the supports rises in a parallel. This trend was
22
2
2
confirmed by the oxygen distribution in the different functional
groups as calculated from XPS data (ESI S2 and S3†).
Pd NPs stabilized with TPP and TOP were described in a
recent report. Spherical Pd NPs with a mean size of 2.2 nm
2
2
22
The Pd content in the MNPs/carbon materials catalysts is
reported in Table 1. Higher Pd loadings were obtained with the
showing aggregation in some areas were observed by HRTEM
for Pd(TPP)/MB-H O catalyst (ESI S4†). Since this tendency
2 2
MB-H O2 carbon support. Considering the above mentioned
to agglomerate was not observed at all for Pd(TPP)/MB-1500
2
surface properties of the carbon supports, this difference can be
attributed to the higher surface area (an increase of the support
surface area is expected to improve MNPs immobilization) and/
or the higher amount of surface oxygen (MNPs are expected to
interact with the surface oxygen groups which could also
improve their immobilization) of MB-H O carbon material
sample (ESI S5†), it was related to the presence of a higher
amount of oxygen groups, on the surface of MB-H O . Homo-
2 2
geneous in shape and well-dispersed supported Pd NPs with a
mean diameter of 1.9 nm were in contrast observed when TOP
was used as stabilizer ligand (ESI S4 and S5†). In this case, the
steric hindrance due to the long aliphatic chains of TOP limits
the approach and therefore the interaction between the Pd NPs
and the carbon support surface oxygen groups, thus preventing
2
2
22
(Table 1).
HRTEM images of Pd/MB-H O and Pd/MB-1500 catalysts
2
2
22
are presented in Fig. 1 and 2. Spherical and homogeneously
their agglomeration.
1436 | Green Chem., 2012, 14, 1434–1439
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The catalytic activity of the different carbon-supported Pd
nanoparticles was investigated in a series of chemical transform-
ations including oxidation and hydrogenation reactions. From
previous work, the hydrophilicity of the carbon support was
known to significantly influence the activity of these catalysts in
correlates well with the stronger water affinity of MB-H O2
2
support (due to its higher oxygen content), being in good agree-
22
ment with previous results. In any case, the best results were
achieved with Pd(TOP)/MB-H O2 catalyst with larger Pd
2
content (2.58 wt%) as well as smaller Pd NPs size (1.9 nm).
Therefore, both Pd NPs amount and size appear to be key-
factors for the optimum performance of this catalyst. Interest-
ingly, blank runs performed without catalyst in similar reaction
conditions led to low conversion of benzyl alcohol to benz-
aldehyde (10–30%) (similar to those obtained with the non-
impregnated carbon supports, blank experiments, Table 2) after
longer times of reaction. This indicates that the oxidation of
benzyl alcohol proceeds under microwave irradiation even
without any added catalyst. Longer reaction times (≥5 min) led
to increasing quantities of benzoic acid upon over-oxidation of
benzaldehyde. Other catalysts including Pd/MB-H O and Pd/
2
2
the aerobic oxidation of benzyl alcohol in water. Quantitative
conversion to benzaldehyde was obtained after 3.5 h reaction at
8
0 °C with all of the carbon-supported Pd NPs catalysts.
The catalytic activity of the carbon-supported Pd NPs was first
evaluated in the microwave-assisted selective oxidation of
benzyl alcohol to benzaldehyde using aqueous hydrogen per-
oxide as oxidant (Table 2 and Fig. 3). The catalysts showed
good to excellent activities, with almost complete selectivity
(
90–95%) to benzaldehyde in all cases. The most remarkable
feature is the high activities achieved after short reaction times
typically 3–5 min) under comparable conditions (90 °C, water).
(
2
2
Particularly, excellent results were obtained with Pd(TPP)/
MB-H O2 and Pd(TOP)/MB-H O after 3 min reaction. This
MB-1500 provided significantly lower yields of products, prob-
ably due to the additional stability and activity given by the com-
2
2 2
22
bination of ligand-NPs and oxidised support, as well as to the
lower Pd content observed for these catalytic systems (Table 1,
last two entries).
Table 2 Microwave-assisted selective aqueous oxidation of benzyl
a
alcohol catalyzed by carbon-supported Pd NPs
Due to the interesting Pd redox properties, the aforementioned
Pd catalytic systems were also applied in hydrogenation pro-
cesses. Hydrogenation of biomass-derived platform molecules
including C4 organic acids with Ru and Pd nanoparticles sup-
ported on carbonaceous materials as catalysts was recently
reported in the literature. For that purpose, the redox bifunc-
tional activity of the carbon-supported Pd catalysts was tested in
the microwave-assisted transfer hydrogenation of furfural
Reaction Conversion Selectivity to
27
Catalyst
time (min) (mol%)
benzaldehyde (mol%)
Blank (no catalyst)
MB-H O
2 2
MB-1500
2 2
Pd(TOP)/MB-H O
Pd(TOP)/MB-1500
Pd(TPP)/MB-H
Pd(TPP)/MB-1500
Pd/MB-H
30
30
30
3
<20
<30
<20
>95
70
>99
>99
>99
90
(Scheme 1).
Hydrogenation is generally the most common route to
upgrade furfural, from which the high yield preparation of
numerous high added value chemicals can be attained, depend-
ing on the extension of the reduction step. Furfuryl alcohol can
be generally obtained under mild reduction conditions using Cu-
3
92
2
O
2
3
3
90
60
95
87
2
O
2
5
5
60
50
>95
>95
Pd/MB-1500
28
based catalysts. The use of noble metal supported catalysts
e.g. Pt, Ir NPs on different supports) combined with more
a
2 2 2
Reaction conditions: 2 mmol benzyl alcohol, 2 mL H O, 0.3 mL H O
50% v/v), 0.05 g catalyst, microwaves, 300 W, 90 °C (100–110 °C
maximum temperature reached), 100–200 psi (pressure developed in the
(
(
severe hydrogenation conditions including higher temperatures
systems).
Fig. 3 Selectivity switch to benzoic acid (over-oxidation) for Pd(TOP)/
MB-H
benzyl alcohol, 2 mL H
2
O
2
at different reaction times. Reaction conditions: 0.2 mL
O, 0.3 mL H (50% v/v), 0.1 g catalyst,
2
2 2
O
microwaves, 300 W, 90 °C (100–110 °C maximum temperature
reached), 150–200 psi (pressure developed in the systems).
Scheme 1 Products distribution in the hydrogenation of furfural.
Green Chem., 2012, 14, 1434–1439 | 1437
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Table 3 Microwave-assisted hydrogenation of furfural catalyzed by
carbon-supported Pd NPs
Besides the strong water affinity of the MB-H O support (due
2
2
a
to its high oxygen content), this catalyst has also the largest Pd
content (2.58 wt%) and the smallest Pd NPs mean size (1.9 nm)
which, as mentioned above, are most likely to be important par-
ameters for the optimum performance of Pd(TOP)/MB-H O in
2
2
both selected redox reactions.
The extension of the hydrogenation in the microwave assisted
reaction (and thus the selectivity to products) seems to be
strongly influenced by two main parameters: temperature and
reaction time. The power of microwave irradiation and the quan-
tity of catalyst did not seem to have a major effect in a selectivity
switch from THF to furan, although both improved the conver-
sion in the systems at shorter times of microwave irradiation.
However, a major selectivity to either furan or THF could be
achieved playing with temperatures and reaction time. In this
context, additional hydrogenation reactions were carried out
Reaction
time
(min)
Selectivity Selectivity
Conversion to furan
to THF
(mol%)
Catalyst
(mol%)
(mol%)
Blank (no catalyst)
MB-H O
2 2
MB-1500
2 2
Pd(TOP)/MB-H O
60
60
60
30
—
—
—
>90
75
69
65
70
45
—
—
—
15
20
10
<10
30
35
—
—
—
80
72
85
80
70
65
Pd(TOP)/MB-1500 30
Pd(TPP)/MB-H
Pd(TPP)/MB-1500
Pd/MB-H
2
O
2
30
30
45
45
2 2
O
Pd/MB-1500
using Pd(TOP)/MB-H O2 as catalyst (Fig. 4 and 5). Higher
2
a
Reaction conditions: 2 mmol furfural, 1.5 mL formic acid, 1.5 mL
water, 0.1 g catalyst, microwaves, 100 °C, 100–150 W (average power),
50–200 psi (pressure developed in the systems).
temperatures (≥120 °C) or longer reaction times generally
improved selectivities to THF. At high temperatures, formic acid
decomposition into CO2 + H2 takes place to a larger extent
1
(which was clearly noticed by a significant pressure increase, see
and pressures can lead to complete hydrogenation of the furanic
ring, yielding 2-methyltetrahydrofuran (MTHF), which has been
24
recently highlighted as an interesting fuel blender compound
as well as a green solvent with improved extraction character-
istics for polar compounds and a relatively high boiling point
29
(
80 °C). Last, but not less importantly, decarbonylation of the
aldehyde moiety of furfural, followed by ring hydrogenation
3
0
leads to furan and further to tetrahydrofuran. Furan derivatives
find interesting applications as fuel blenders while THF is a well
known and widely utilised organic solvent and polymer precur-
sor, with an annual production in excess of 0.2 million tonnes
24
per year.
The transfer hydrogenation reaction was carried out under
microwave irradiation using a formic acid–water 1 : 1 mixture
both as solvent and hydrogen donor. Optimised results in
Table 3 show that THF is efficiently produced from furfural in
high selectivities (>90%) after short reaction times, typically
Fig. 4 Influence of the temperature on the selective hydrogenation of
furfural to THF catalysed by Pd(TOP)/MB-H . Inset corresponds to
the temperature (red line) and pressure (blue line) profiles of one typical
2 2
O
experiment. Reaction conditions: 2 mmol furfural, 1.5 mL formic acid,
1
1
.5 mL water, 0.1 g catalyst, microwaves, 120–150 W (average power),
50–200 psi (pressure developed in the systems), 30 min reaction.
3
0–45 min. The other major product obtained is furan
(Scheme 1) while only traces of tetrahydrofurfuryl alcohol are
observed. Furfuryl alcohol, 2-MTHF and related compounds
were not found under the reaction conditions used. These results
are in good agreement with previous work reporting the ability
of Pd-based catalysts in promoting decarbonylation over hydro-
3
0,31
genation in the first step.
readily hydrogenated to THF at relatively high hydrogen pressure
pressure in the microwave vessel was in all cases above
Upon decarbonylation, furan is
(
2
00 psi).
A full account on the various mechanisms of decarbonylation
and ring hydrogenation in the formation of such compounds has
been elegantly described in a recent report by Sitthisa and
30
Resasco. Decarbonylation seems to be related to the favourable
formation of acyl surface species on Pd catalysts as compared to
other metals (e.g. Ni, Cu) while ring hydrogenation occurs in
Pd-based systems through a strong interaction of the furan ring
Fig. 5 Influence of the time of microwave irradiation on the selective
hydrogenation of furfural to THF catalysed by Pd(TOP)/MB-H
Reaction conditions: 2 mmol furfural, 1.5 mL formic acid, 1.5 mL water,
microwaves, 120–150 W (average power), 150–200 psi (pressure devel-
oped in the systems), 100 °C.
2 2
O .
3
0
with Pd (as opposed to Cu or Ni). In the oxidation of benzyl
alcohol (Table 2), the Pd(TOP)/MB-H O system was found to
2
2
be the most effective catalyst for the hydrogenation to THF.
1438 | Green Chem., 2012, 14, 1434–1439
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Fig. 4 inset) and thus the more hydrogen produced drives the
reaction towards the two step decarbonylation and subsequent
hydrogenation to THF. Longer times of irradiation obviously
favoured the second hydrogenation step also leading to high
selectivities to THF (Fig. 5).
13 B. Sunkara, J. Zhan, K. Jingjing, W. Igor, H. Yingqing, H. Jibao,
E. Jennifer, G. L. McPherson and T. V. John, Langmuir, 2011, 27, 7854–
7859.
1
4 (a) B. Wu, Y. Kuang, X. Zhang and J. Chen, Nano Today, 2011, 6, 75–
90; (b) L. F. Mabena, S. Sinha Ray, S. D. Mhlanga and N. J. Coville,
Appl. Nanosci., 2011, 1, 67–77.
15 (a) T. Matsumoto, M. Ueno, N. Wang and S. Kobayashi, Chem.–Asian J.,
Thus, this approach offers a simple and straightforward
pathway to THF from furfural in comparison with other reported
alternatives from related biomass-derived platform molecules
2
2
008, 3, 196–214; (b) J. Han, Y. Liu and R. Guo, Adv. Funct. Mater.,
009, 19, 1112–1117; (c) A. Villa, D. Wang, N. Dimitratos, D. Su,
V. Trevisan and L. Prati, Catal. Today, 2010, 150, 8–15; (d) B. Feng,
Z. Hou, H. Yang, X. Wang, Y. Hu, H. Li, Y. Qiao, X. Zhao and
Q. Huang, Langmuir, 2010, 26, 2505–2513; (e) A. M. Balu, A. Pineda,
K. Yoshida, J. M. Campelo, P. L. Gai, R. Luque and A. A. Romero,
Chem. Commun., 2010, 46, 7825–7827; (f) M. Tristany, K. Philippot,
Y. Guari, V. Collière, P. Lecante and B. Chaudret, J. Mater. Chem., 2010,
32
(
e.g. succinic acid), featuring the in situ generation of hydro-
gen in the systems by using a renewable-derived solvent together
with mild reaction conditions and short reaction times.
Finally, our protocol may also pave the way for the utilisation
of designer redox-bifunctional nanoparticle catalytic systems for
oxidation and hydrogenation of related platform molecules (e.g.
γ-valerolactone). Further investigations in our group are ongoing
to translate the optimised batch microwave chemistry into more
scalable continuous flow processes by mimicking the moderate
to high temperatures and pressures achieved in a sealed micro-
20, 9523–9530; (g) A. Chen, Z. M. Cui, F. Niu, L. Jiang and W.
G. Dong, Chem. Commun., 2010, 46, 6524–6526; (h) C. Hao and
X. Zhao, Adv. Mater. Res., 2010, 113–114; (i) J. Okal, M. Zawadzki and
W. Tylus, Appl. Catal., B, 2011, 101, 548–557; ( j) V. B. Komvakis,
M. Marti, A. Delimitis, I. A. Vasalos and K. S. Triantafyllidis, Appl.
Catal., B, 2011, 103, 62–71; (k) C. M. Cirtiu, A. F. Dunlop-Brière and
A. Moores, Green Chem., 2011, 13, 288–291.
16 (a) G. G. Wildgoose, C. E. Banks and R. G. Compton, Small, 2006, 2,
182–193; (b) B. Li, P. He, G. Yi, H. Lin and Y. Yuan, Catal. Lett., 2009,
TM
33
wave vessel using the X-Cube flow reactor.
133, 33–40; (c) N. Dimitratos, J. A. Lopez-Sanchez and G. J. Hutchings,
Chem. Sci., 2012, 3, 20–44; (d) J. M. Campelo, T. D. Conesa, M.
J. Gracia, M. J. Jurado, R. Luque, J. M. Marinas and A. A. Romero,
Green Chem., 2008, 10, 853–858.
Acknowledgements
R.L. gratefully acknowledges support from the Spanish MICINN
via the concession of a RyC contract (ref. RYC-2009-04199)
and funding under projects P10-FQM-6711 (Consejeria de
Ciencia e Innovacion, Junta de Andalucia) and CTQ2011
17 M. Yu, Y. Wang, W. Sun and X. Yao, Adv. Synth. Catal., 2012, 354, 71–76.
1
8 (a) D. Astruc, F. Lu and J. R. Aranzaes, Angew. Chem., Int. Ed., 2005,
4, 7852–7872; (b) M. Haruta, Chem. Rec., 2003, 3, 75–87;
c) M. Jahjah, Y. Kihn, E. Teuma and M. Gomez, J. Mol. Catal. A:
4
(
Chem., 2010, 332, 106–112; (d) E. V. Starodubtseva, M. G. Vinogradov,
O. V. Turova, N. A. Bumagin, E. G. Rakov and V. I. Sokolov, Catal.
Commun., 2009, 10, 1441–1442.
2
8954-C02-02 (MICINN). E.J. García-Suárez thanks MCIIN,
CSIC and FYCIT for José Castillejo, JAE DOC and Clarin post-
doctoral grants, respectively. CNRS is also acknowledged for
financial support.
19 (a) Z. Yang, S. Guo, X. Pan, J. Wang and X. Bao, Energy Environ. Sci.,
2011, 4, 4500; (b) N. Neelakandeswari, G. Sangami, P. Emayavaramban,
S. Ganesh Babu, R. Karvembu and N. Dharmaraj, J. Mol. Catal. A:
Chem., 2012, in press.
20 M. S. Kwon, N. Kim, C. M. Park, J. S. Lee, K. Y. Kang and J. Park, Org.
Lett., 2005, 7, 1077–1079.
References
21 (a) H. Liu, Y. Li, R. Luque and H. Jiang, Adv. Synth. Catal., 2011, 353,
3
107–3113; (b) R. A. Arancon, H. R. Barros, A. M. Balu, C. Vargas and
1
(a) R. J. White, R. Luque, V. L. Budarin, J. H. Clark and D.
J. Macquarrie, Chem. Soc. Rev., 2009, 38, 481–494; (b) J. M. Campelo,
D. Luna, R. Luque, J. M. Marinas and A. A. Romero, ChemSusChem,
R. Luque, Green Chem., 2011, 13, 3162–3167; (c) A. M. Balu,
B. Baruwati, E. Serrano, J. Cot, J. Garcia–Martinez, R. S. Varma and
R. Luque, Green Chem., 2011, 13, 2750–2758.
2 E. J. Garcia-Suarez, M. Tristany, A. B. Garcia, V. Collière and
K. Philippot, Microporous Mesoporous Mater., 2012, 153, 155–162.
3 M. J. Climent, A. Corma and S. Iborra, Chem. Rev., 2011, 111, 1072–
2
009, 2, 18–45.
2
2
2
2
2
2
2
(a) G. Salas, C. C. Santini, K. Philippot, V. Collière, B. Chaudret,
B. Fenet and P. F. Fazzini, Dalton Trans., 2011, 40, 4660–4668;
(b) G. Salas, A. Podgorsek, P. S. Campbell, C. C. Santini,
1
133.
4 J. C. Serrano, R. Luque and A. Sepulveda-Escribano, Chem. Soc. Rev.,
011, 40, 5266–5281.
A. A. H. Padua, M. F. Costa Gomes, K. Philippot, B. Chaudret and
M. Turmine, Phys. Chem. Chem. Phys., 2011, 13, 13527–13536; (c) J.
L. Pellegatta, C. Blandy, V. Collière, R. Choukroun, B. Chaudret,
P. Cheng and K. Philippot, J. Mol. Catal. A: Chem., 2002, 178, 55–61;
2
5 S. R. Tennison, O. P. Kozynchenko, V. V. Strelko and A. J. Blackburn,
Porous carbons, US pat., 0032092, 2008.
(
d) C. Pan, K. Pelzer, K. Philippot, B. Chaudret, F. Dassenoy, P. Lecante
and M. J. Casanove, J. Am. Chem. Soc., 2001, 123, 7584–7593;
e) J. Dupont and J. D. Scholten, Chem. Soc. Rev., 2010, 39, 1780–1804.
6 E. Ramirez, S. Jansat, K. Philippot, P. Lecante, M. Gómez, A. Masdeu
and B. Chaudret, J. Organomet. Chem., 2004, 689, 4601–4610.
7 (a) C. S. K. Lin, R. Luque, J. H. Clark and C. Du, Biofuels, Bioprod.
Biorefin., 2012, 6, 88–104; (b) R. Luque, J. H. Clark, K. Yoshida and P.
L. Gai, Chem. Commun., 2009, 5305–5307; (c) D. Pham Minh,
M. Besson, C. Pinel, P. Fuertes and C. Petitjean, Top. Catal., 2010, 53,
(
3
4
V. Polshettiwar and A. Molnar, Tetrahedron, 2007, 63, 6949.
S. S. Próckl, W. Kleist, M. A. Gruber and K. Köhler, Angew. Chem., Int.
Ed., 2004, 43, 1881.
5
C. P. Mehnert, D. W. Weaver and J. Y. Ying, J. Am. Chem. Soc., 1998,
1270–1273; (d) C. Delhomme, D. Weuster-Botz and F. E. Kuehn, Green
1
20, 12289–12296.
Chem., 2009, 11, 13–26; (e) J. C. Serrano-Ruiz and J. A. Dumesic, Green
Chem., 2009, 11, 1101–1104; (f) D. M. Alonso, J. Q. Bond, J.
C. Serrano-Ruiz and J. A. Dumesic, Green Chem., 2010, 12, 992–999.
8 K. J. Zeitsch, The Chemistry and Technology of Furfural and its Many
By-Products, Elsevier, Amsterdam, 1st edn, 2000, Sugar Series, vol. 13,
pp. 150–155.
6
7
Z. K. Esumi, R. Isono and T. Yoshimura, Langmuir, 2004, 20, 237–242.
S. V. Ley, C. Ramarao, R. S. Gordon, A. B. Holmes, A. J. Morrison, I.
F. McConvey, I. M. Shirley and S. C. Smith, Chem. Commun., 2002,
2
2
1134–1136.
8
9
E. Roduner, Nanoscopic Materials. Size-Dependent Phenomena, Royal
Society of Chemistry, Cambridge, 2006, pp. 239–262.
M. Lakshmi Kantam, K. B. S. Kumar, P. Srinivas and B. Sreedhar, Adv.
Synth. Catal., 2007, 349, 1141–1149.
9 V. Pace, P. Hoyos, M. Fernandez, J. V. Sinisterra and A. Alcantara, Green
Chem., 2010, 12, 1380–1382.
3
3
3
0 S. Sitthisa and D. E. Resasco, Catal. Lett., 2011, 141, 784–791.
1 R. D. Srivastava and A. K. Guha, J. Catal., 1985, 91, 254–262.
2 (a) R. Luque and J. H. Clark, Catal. Commun., 2010, 11, 928–931; (b) R.
M. Deshpande, V. V. Buwa, C. V. Rode, R. V. Chaudhari and P. L. Mills,
Catal. Commun., 2002, 3, 269–274.
1
0 P. Serp and J. L. Figueiredo, Carbon Materials for Catalysis, Wiley-
VCH, Weinheim, Germany, 2009.
11 K. C. Hwang, J. Phys. D: Appl. Phys., 2010, 43, 1–13.
1
2 (a) R. Singh, T. Premkumar, S. Thathan, G. Ji-Young and E. Kurt,
Chem.–Eur. J., 2010, 16, 1728–1743; (b) R. Baron, G. G. Wildgoose and
R. G. Compton, J. Nanosci. Nanotechnol., 2009, 9, 2274–2282.
3
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