Efficient hydrogenation of carbonyl compounds using low-loaded supported copper nanoparticles under microwave irradiation

Article abstract of DOI:10.1016/j.apcata.2010.02.028

Highly active and dispersed copper (Cu) nanoparticles on mesoporous silicas have been prepared via microwave irradiation of a solution of copper precursors with a previously synthesized mesoporous hexagonal silica (HMS) support. The protocol allowed differently low-loaded (typically 0.5 wt%) Cu materials containing Cu metal and small quantities of metal oxides. Materials were then tested as catalysts in the hydrogenation of carbonyl compounds under microwave irradiation. Cu materials were found to be highly active, selective and reusable in the reduction of substituted aromatic ketones and aldehydes, providing quantitative conversion of starting material within 5-10 min reaction at mild reaction conditions with complete selectivity to the alcohols.

Full text of DOI:10.1016/j.apcata.2010.02.028

Applied Catalysis A: General 379 (2010) 38–44
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Efficient hydrogenation of carbonyl compounds using low-loaded supported
copper nanoparticles under microwave irradiation
Kenta Yoshida , Camino Gonzalez-Arellano , Rafael Luque , Pratibha L. Gaia,d
a
b
c,∗
a
Nanocentre, Department of Chemistry, The University of York, Heslington, YO10 5DD, York, UK
Green Chemistry Centre of Excellence, The University of York, Heslington, YO10 5DD, York, UK
Departamento de Química Orgánica, Campus de Rabanales, Edificio Marie Curie, Ctra Nnal IV, Km 396, Universidad de Córdoba, E-14014, Córdoba, Spain
Department of Physics, The University of York, Heslington, YO10 5BR, York, UK
b
c
d
a r t i c l e i n f o
a b s t r a c t
Article history:
Highly active and dispersed copper (Cu) nanoparticles on mesoporous silicas have been prepared via
microwave irradiation of a solution of copper precursors with a previously synthesized mesoporous
hexagonal silica (HMS) support. The protocol allowed differently low-loaded (typically 0.5 wt%) Cu mate-
rials containing Cu metal and small quantities of metal oxides. Materials were then tested as catalysts in
the hydrogenation of carbonyl compounds under microwave irradiation. Cu materials were found to be
highly active, selective and reusable in the reduction of substituted aromatic ketones and aldehydes, pro-
viding quantitative conversion of starting material within 5–10 min reaction at mild reaction conditions
with complete selectivity to the alcohols.
Received 10 December 2009
Received in revised form 11 February 2010
Accepted 22 February 2010
Available online 1 March 2010
Keywords:
Metal nanoparticles
Microwave irradiation
Cu
©
2010 Elsevier B.V. All rights reserved.
Transfer hydrogenation
1
. Introduction
interior pore structure. It also has the added advantage of inhibit-
ing particle growth to a particular size regime as well as reducing
particle aggregation and controlling size and even shape of the
supported nanoparticles, critical for certain applications.
Supported metal nanoparticles (SMNPs) on porous materi-
als offer added advantages of high activities, selectivities and
reusability of the materials in a range of applications where the
use of homogeneous nanoparticle systems of challenging separa-
tion/isolation is not the most adequate (e.g. medicinal applications)
[6].
We have recently reported an easy and efficient route to the
preparation of a wide range of SMNPs including Au, Ag, Pd and more
recently Fe and Cu on a variety of porous materials for different
catalytic applications such as the oxidation of alcohols and alkenes
[7,8], S-arylation of thiols [9], C–C coupling reactions [10–12] and
hydroisomerisation of n-alkanes [13].
Cu and Fe are particularly interesting metals as they are eco-
nomical, widely available and environmentally friendly compared
to noble and heavy metals for many applications. Many recent
reports can be found on Fe supported metal oxide nanoparticles
on different supports for catalytic applications [14–16]. Neverthe-
less, compared to Fe, Cu SMNPs have received less attention despite
its promising redox properties and applications in related catalytic
processes, mostly related to oxidations and oxidative protocols
Nanoscale materials including nanoscale forms of carbon (i.e.
fullerenes and nanotubes), inorganic materials and nanoparticles
have recently attracted a great deal of attention [1]. In particular,
metal nanoparticles (MNPs) are beginning to receive more inter-
est, compared to their nano organic cousins, due to their relatively
higher chemical activity and specificity of interaction [1,2]. MNPs
have significantly different properties compared to their bulk coun-
terparts. They provide highly active and specific active centres for
a wide range of applications including medicine, catalysis, sensors
and so on, but typically they are very small and thermodynami-
cally unstable due to their high surface energies. Structures at the
nanoscale regime are very unstable and tend to aggregate quickly
to stabilise. In order to produce stable particles, it is necessary to
terminate the particle growth reaction, and there are a number
of methods by which this has been achieved including the use of
organic ligands [3], inorganic capping materials [3,4] colloids and
soluble polymers and solid porous supports [2–5].
Among them, the use of solid porous supports with defined pore
sizes and characteristics is one of the most useful methodologies to
stabilise and support MNPs as it allows the generation of specific
adsorption sites, creating a partition between the exterior and the
[
9,17,18]. Mitsudome et al. have reported hidrotalcite-supported
Cu nanoparticles (4.6 wt% Cu, 7.5 nm mean nanoparticle diameter)
as efficient catalysts in the liquid phase oxidant-free dehydro-
genation of alcohols [19]. Tu et al. have similarly prepared Cu
∗ Corresponding author. Tel.: +34 057212065; fax: +34 957212066.
E-mail addresses: ky512@york.ac.uk (K. Yoshida), q62alsor@uco.es (R. Luque),
pgb500@york.ac.uk (P.L. Gai).
0
926-860X/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2010.02.028

K. Yoshida et al. / Applied Catalysis A: General 379 (2010) 38–44
39
nanoparticles supported on SBA-15 for the oxidation of CO and
demonstrated metallic copper species (generated after calcination
and reduction of the materials at high temperatures) were highly
active in the process [20]. Evangelisti et al. prepared supported Cu
nanoparticles on different supports (e.g. Al O , Fe O , TiO ) via
ysed by GC/GC-MS using an Agilent 6890N GC model equipped,
with a 7683B series autosampler, fitted with a DB-5 capillary
column and an FID detector. Experiments were conducted on a
closed vessel (pressure controlled) under continuous stirring. The
microwave method was generally power-controlled where the
samples were irradiated with different power outputs (e.g. settings
at maximum power).
2
3
2
3
2
metal vapor synthesis (MVS) that were also employed in the oxi-
dation of a range of organic compounds with molecular oxygen
[
21]. Other reports include the preparation of silica-supported Cu
Response factors of the reaction products were determined
with respect to the original ketones from GC analysis using known
compounds in calibration mixtures of specified compositions. Iso-
lated yields were obtained from final reaction mixtures as follows:
the resulting mixture upon reaction completion was diluted with
diethylether, filtered through Celite and the filtrate was dried over
nanoparticles for glycerol hydrogenolysis [22], CO and NO oxida-
tion [23], the oxidative coupling of 2,6-dimethylphenol [24] and
the water–gas shift reaction [25].
However, despite the use of such SMNPs in various oxidation
processes, only few reports can be found on the use of Cu SMNPs
in hydrogenations [26–28]. In this regard, transfer hydrogenation
processes with stable hydrogen donors are highly advantageous
methodologies in organic synthesis for the hydrogenation of a
range of compounds including carbonyl compounds and related
substrates [29]. Compared to traditional hydrogenations, these pro-
tocols are generally simpler and environmentally friendly as they
avoid the use of molecular hydrogen (thus minimising risks of
explosions, leaks and related hazards), high-pressurised devices
and favour mild reaction conditions that normally lead to improved
selectivities [30]. Among these milder reaction conditions, these
processes have been recently reported to be amenable to the use
of microwave-assisted protocols that provide efficient hydrogen
transfer systems in very short times of reaction [31]. Most reported
optimised systems for this reaction comprise of noble metal homo-
geneous complexes (e.g. Ru, Rh, Ir, Pd) whose mechanisms have
also been thoroughly investigated [32,33]. Heterogeneously catal-
ysed processes have recently been brought to many scientists as
comparatively more efficient methodologies that benefit from a
facile recovery and reuse of the catalyst, improved catalysts sta-
bilities (and even activities sometimes) in terms of leaching and
degradation. To the best of our knowledge, this is the first report
of a microwave-assisted hydrogenation protocol using low-loaded
supported Cu nanoparticles.
MgSO . The solvent was then evaporated and the final residue
4
obtained subsequently purified by column chromatography (silica
gel, hexane/EtOAc) to give the different pure alcohols.
2.2. Materials characterisation
Nitrogen physisorption was measured with a Micromeritics
◦
instrument model ASAP 2000 at −196 C. The samples were
◦
−2
outgassed for 2 h at 100 C under vacuum (p < 10 Pa) and sub-
sequently analysed. The linear part of the BET equation (relative
pressure between 0.05 and 0.22) was used for the determination of
the specific surface area. The pore size distribution was calculated
from the adsorption branch of the N2 physisorption isotherms and
the Barret–Joyner–Halenda (BJH) formula. The cumulative meso-
pore volume VBJH was obtained from the PSD curve.
Scanning electron micrographs (SEM) and elemental composi-
tion of the calcined samples were recorded using a JEOL JSM-6300
Scanning Microscope with energy-dispersive X-ray analysis (EDX)
at 20 kV. Samples were coated with Au/Pd on a high-resolution
sputtering SC7640 instrument at a sputtering rate of 1.5 kV/min,
up to 7 nm thickness.
The materials nanostructures were imaged in an advanced JEOL
2200FS double aberration corrected transmission electron micro-
scope/scanning transmission electron microscope (AC-TEM/STEM),
operating at 200 kV [35]. Both TEM and high angle annular dark
field (HAADF) STEM (HAADF-STEM) [36] were carried out in the
AC-TEM/STEM. With the dual aberration correctors in AC-TEM
and AC-HAADF-STEM, imaging from the same regions of the sup-
ported nanocatalyst sample provide insights into the atomic level
structure. Low electron dose imaging was used throughout. With
aberration correction, a continuous range of interpretable spatial
frequencies can be transferred by the electron optics without the
contrast inversions and therefore data are much more directly
interpretable. More directly interpretable (sub) Angstrom level
imaging, complemented by compositional data, uniquely provides
new direct insights into the structure of nanoparticles, critical
to understanding the nanostructures and reactivity properties of
nanocatalysts. In high angle annular dark field STEM (HAADF-
STEM) imaging we exploit the fact that electrons scattered at high
angles (>30 mrad) obey Rutherford scattering law, with the scatter-
ing cross section proportional to Z2 where Z is the atomic number.
Imaging of the electrons scattered at high angles using HAADF-
STEM detector allows the detection of catalyst nanoparticles with
higher Z, on lighter supports such as silicas or carbons.
We report here the facile, swift and environmentally friendly
microwave-assisted hydrogenation of carbonyl compounds using
novel microwave-mediated supported Cu nanoparticles on pre-
synthesized mesoporous silicas.
2
. Experimental
2
.1. Materials syntheses
The synthesis of the parent hexagonal mesoporous silica (HMS)
support was performed following a previously reported procedure
34]. A typical procedure for the straightforward preparation of the
[
mesoporous supported metal nanoparticles was as follows: 0.4 g
HMS and 2.0 mL of a solution of copper nitrate (50 mg, Aldrich,
9
for 2–5 min at 300 W (maximum power output, 60–100 C temper-
ature reached). The mixture was filtered off and the recovered solid
(
9.9%) in ethanol were microwaved on a CEM-DISCOVER reactor
◦
Cu/HMS-1) was thoroughly washed with ethanol and acetone and
◦
oven-dried overnight at 100 C prior to its utilisation in the trans-
fer hydrogenation reaction. Alternatively, the material Cu/HMS-2
was prepared following an identical protocol using CuCl ·xH O as
XPS measurements were performed in a ultra high vacuum
2
2
TM
metal precursor. The obtained materials were highly reproducible
from batch to batch. For comparative purposes, a similar material to
Cu/HMS-1, denoted as Cu/HMS-3, was synthesized following a pre-
viously reported modified impregnation/reduction methodology
(UHV) multipurpose surface analysis system (Specs model, Ger-
−
10
many) operating at pressures <10
mbar using a conventional
X-ray source (XR-50, Specs, Mg-K␣, 1253.6 eV) in a “stop-and-
go” mode to reduce potential damage due to sample irradiation.
The survey and detailed Cu high-resolution spectra (pass energy
25 and 10 eV, step size 1 and 0.1 eV, respectively) were recorded
at room temperature with a Phoibos 150-MCD energy analyser.
Powdered samples were deposited on a sample holder using
[
11] using CuNO ·xH O as metal precursor.
3
2
Microwave reaction experiments were also carried out in the
CEM-DISCOVER reactor model with PC control and monitored by
sampling aliquots of reaction mixture that were subsequently anal-

4
0
K. Yoshida et al. / Applied Catalysis A: General 379 (2010) 38–44
Table 1
Textural properties and metal loadings (determined by elemental analysis) of various copper nanoparticle supported mesoporous silica materials.
SBET (m2
g
−1
)
Pore size (nm)
Pore volume (mL g
−1
)
Metal loading (%)
Material
HMS
721
586
692
625
2.3
2.0
<2.0
<2.0
0.57
0.36
0.41
0.39
–
Cu/HMS-1
Cu/HMS-2
Cu/HMS-3
0.51
0.47
0.59
double-sided adhesive tape and subsequently evacuated under
3. Results and discussion
−6
vacuum (<10 Torr) overnight. Eventually, the sample holder
containing the degassed sample was transferred to the analysis
chamber for XPS studies. Binding energies were referenced to the
C1s line at 284.6 eV from adventitious carbon. The curve deconvo-
lution of the obtained XPS spectra was obtained using the Casa XPS
program.
The metal content in the materials was determined using
Inductively Coupled Plasma (ICP) in a Philips PU 70000 sequen-
tial spectrometer equipped with an Echelle monochromator
N physisorption experiments showed the type IV isotherm pro-
2
file, typical of mesoporous materials (Fig. 1) for the supported Cu
on hexagonal mesoporous silicas (HMS). Samples were denoted as
Cu/HMS-1 to 3 depending on the methodology employed for their
preparation and/or their Cu precursors (see Section 2). Data regard-
ing the pore size distribution, surface area and pore volume have
been included in Table 1. Textural properties of the materials after
supporting the nanoparticles were not significantly affected by the
incorporation of copper, regardless of the Cu precursor utilised, due
to the low Cu loadings in the materials (Fig. 1 and Table 1). Pore size
around 2–2.5 nm and was found to decrease with an increase of
the metal loading, rendering porous materials at the mesoporosity
edge (pore diameters <2.0 nm, Table 1).
(
0.0075 nm resolution). Samples were digested in HNO3 and sub-
sequently analysed by ICP at the University of Newcastle.
2.3. Catalytic experiments
SEM micrographs of the Cu supported silica materials (Fig. 2)
showed the mesoporous materials were composed of aggregates
with spheroidal particle morphologies in spike-like aggregates,
with typical aggregate sizes of ca. 1–5 ␮m. The particle morphol-
ogy did not significantly change with the Cu incorporation (Fig. 2,
bottom).
In a typical experiment, 1 mmol acetophenone (0.12 mL), 2.0 mL
-propanol with NaOH (0.1 mol L ) and 0.005 g catalyst were
microwaved for 5 min at 300 W. Response factors of the reac-
tion products were determined with respect to the corresponding
starting material from GC analysis using known compounds in cal-
ibration mixtures of specified compositions.
−1
2
The reusability of the catalysts upon reaction completion was
also investigated. In a typical recycling experiment, the quantities
of substrate and catalyst had to be increased 10 times in a sin-
gle experiment to facilitate the catalyst recovery. Thus, 10 mmol
−
1
acetophenone (1.2 mL), 3.0 mL 2-propanol with NaOH (0.1 mol L
)
and 0.05 g catalyst were microwaved for 5–10 min at 300 W. After
achieving complete selectivity to the alcohol and a conversion over
9
0%, the catalyst was filtered off, washed with ethanol and acetone
◦
and oven-dried overnight at 120 C prior to its use in another run.
Fig. 1. N2-adsorption/desorption profiles and pore size distributions (inset) of (a)
Fig. 2. SEM micrographs of mesoporous silica (top) and CuNO3-silica materials (bot-
HMS and (b) Cu/HMS-1.
tom).

K. Yoshida et al. / Applied Catalysis A: General 379 (2010) 38–44
41
Fig. 3. AC-HAADFS-STEM and AC-TEM micrographs oftheCu/HMS-1 materialusingCuNO3 as precursor. (a) and(b) AC-HAADF-STEMimages. Bluearrowsindicate the presence
of subnanometer clusters; (c) and (d) AC-TEM images. (b), (c) and (d) correspond to the areas (i), (ii) and (iii) indicated by squares in the low-magnification image (a).
TEM micrographs of Cu/HMS-1 and Cu/HMS-3 are shown in
Figs. 3 and 5, respectively. In Fig. 3b and d, metallic copper nanopar-
ticles of average 3–5 nm in diameter were observed as well as a
number of sub nanometer clusters (Fig. 3b, ∼0.5 nm in size, indi-
cated by blue arrows).
Fig. 3c shows single crystalline copper oxide nanoparticles (size
over 10 nm) separating out at surface of the Cu/HMS-1 material. In
any case, the quantity of such copper oxide particles was small.
Fig. 4 depicts the crystal size distribution of the copper/copper
oxide nanoparticles obtained for the Cu/HMS-1 by HRTEM. Aver-
age crystal size was 3.79 nm. On the particular copper dispersed
in (in)organic materials, few nanoparticle sizes of less than 5 nm
are reported [20–22,37,38]. A similar nanoparticle size distribu-
tion was found for materials Cu/HMS–2 (not shown) and Cu/HMS-3
(Fig. 5) for which a majority of Cu metallic nanoparticles with sizes
between 3–6 nm were observed. It is worth pointing out at this
stage that the metal precursor did not seem to affect the properties
of the Cu/HMS materials in terms of nanoparticle size distribution
and/or textural properties.
In any case, all hexagonal mesoporous silica particles main-
tained their spherical shape and nanoporous structure. Average
particle size was ca. 360 nm. Interestingly, an almost negligible con-
tribution of sub nanometer Cu clusters was found for Cu/HMS-3
prepared using an alternative impregnation/reduction methodol-
ogy [11] as compared to Cu/HMS-1 and 2 (Fig. 5). This clearly
demonstrates that the methodology to prepare the supported
nanoparticles significantly influences the sintering of small parti-
cles and consequently nanoparticle size distribution in the SMNPs,
as we have previously observed [7,11]. The effect of microwave irra-
diation is clear. Rapid heating of reaction mixtures, specially those
containing polar solvents (e.g. ethanol, water), leads to a rapid and
almost simultaneous precipitation of the metal solution of the pre-
cursor which in turn renders materials with small particle sizes and
narrow size distributions at very short reaction times (less than
3
min). In addition to that, the solvent (EtOH) facilitates the reduc-
tion of the metal in solution to elemental metal, offering a better
control of particle size and morphology [39].
The obtained results demonstrated that the porous silica sup-
port effectively prevented the coalescence of such copper/copper
oxide nanocrystals thus maintaining narrow nanoparticle sizes
(
<5 nm).
The nature of copper species was subsequently investigated by
XPS. Results are summarised in Fig. 6. The XPS peak centred at about
50 eV corresponds to Cu2p1/2, while the peak at 933 eV with a
shoulder at ca. 935.5 eV corresponds to Cu2p3/2 [40,41]. The pres-
9
Fig. 4. Nanoparticle size distributions of the copper/copper oxide nanocrystals in
Cu/HMS-1.

4
2
K. Yoshida et al. / Applied Catalysis A: General 379 (2010) 38–44
Fig. 5. AC-TEM and AC-HAADF-STEM images of Cu/HMS-3 material. (a) low-magnification AC-TEM image; (b)–(d) are AC-HAADF-STEM images. (c) and (d) correspond to
the (i) and (ii) areas, respectively, indicated in the squares in (b). Scale markers in (a) and (b) 500 nm; (c) 50 nm.
ence of the shake-up peak (about 940–945 eV) is characteristic of
Results obtained for Cu/HMS materials in the microwave-
assisted hydrogenation of acetophenone under optimised condi-
tions are summarized in Table 2. Blank runs (no catalyst as well
as HMS as catalyst) gave virtually no conversion in the systems,
implying the transfer hydrogenation activity can be fully ascribed
to copper present in the materials (Table 2, entries 1 and 2). The
catalytic activity of the materials was highly reproducible with Cu
nanoparticles obtained in four different batches exhibiting very
similar activities and selectivities under identical reaction condi-
tions.
2+
2+
Cu species, particularly of CuO (in the absence of Cu species, no
shake-up peaks will be present [42]). The presence of lower Cu2p3/2
binding energy peaks (932.8 eV) indicates the existence of reduced
+
0
copper species [40]. However, the distinction between Cu and Cu
species (that appear at very similar binding energies) is only feasi-
ble through examination of the Auger spectra [22]. In any case, we
0
believe the peak at 932.8 eV might be related to Cu species, in a
similar way to the metal reduced nanoparticles found for several
materials previously reported by our group and others that were
reduced from metal cations in ethanol under microwave irradiation
and even at room temperature [7,10,11,39].
Results demonstrated the outstanding activities of the Cu/HMS
materials in the hydrogenation reaction. The activities in the mate-
Fig. 6. Cu2p XPS spectra of Cu-HMS-1 (left) and Cu-HMS-3 (right) exhibit significant differences in the content of Cu reduced species.

K. Yoshida et al. / Applied Catalysis A: General 379 (2010) 38–44
43
Table 2
conversion obtained after 24 h reaction using conventional heat-
ing (reflux conditions, 85 C). Such activity values obtained with
Catalytic activity of Cu supported silica materials in the transfer hydrogenation of
acetophenone under microwave irradiation
◦
a
novel, environmentally friendly and cheap supported Cu nanopar-
ticles are remarkably superior to any previously reported results on
transfer hydrogenations [31,43–45] and are so far the first report
of cheap supported transition metal catalysts in the hydrogenation
of ketones under microwave irradiation.
.
Interestingly, the employed catalytic quantities of Cu/HMS in
the reaction seemed to provide an optimum performance in the
hydrogenation of acetophenone, with reduced activities below and
above 0.005 g catalyst. Experiments run in the absence of NaOH
gave virtually no activity in hydrogenation, demonstrating the need
for a base in the hydrogenation protocol.
Entry
Catalyst
Conversion (mol%)
Salcohol (mol%)
1
2
3
4
5
blank
HMS
Cu/HMS-1
Cu/HMS-2
Cu/HMS-3
–
–
–
>99
>99
>99
<5
>99
90
83
a
After optimisation of the reaction conditions for acetophenone,
the scope of the methodology was subsequently extended to a
wide variety of aromatic ketones and aldehydes for the particular
case of the most active Cu/HMS-1 catalyst (Table 3). The protocol
was found to be amenable to a wide range of substrates and sub-
stituents within the aromatic ring, providing in general excellent
conversions and selectivities to the corresponding alcohols in very
short times of reaction (typically 5–15 min). Most importantly the
supported Cu nanoparticles were highly stable and reusable under
the investigated conditions, preserving almost entirely its initial
catalytic activity after 5 cycles.
Reaction conditions: 1 mmol acetophenone, 2 mL 2-propanol with NaOH
−
1
◦
(
0.1 mol L ), 0.005 g catalyst, 300 W, 120–130 C, 5 min reaction.
rials seem to correlate well with the Cu nanoparticle size and with
the presence of reduced Cu species, thus being Cu/HMS-1 the most
active material in the hydrogenation reaction (smaller Cu parti-
cles + higher contribution of sub nanometer Cu particles as well
as a superior contribution of Cu ) compared to Cu/HMS-2 and 3
0
0
(
Table 2, entries 1 vs 2 and 3).
Almost quantitative conversion to 1-phenyl ethanol was
achieved in 5 min under microwave irradiation compared to a <60%
Table 3
a
Catalytic activity of Cu/HMS-1 in the microwave-assisted hydrogenation of aromatic carbonyl compounds .
Entry
1
Substrate
Time (min)
Conversion (mol%)b
>99 (92)
Salcohol (mol%)
10
>99
2
3
4
5
6
7
10
10
15
15
15
15
95 (89)
92 (90)
96 (88)
>99 (93)
>99 (93)
90(84)
>99
>99
>99
>99
>99
>99
8
15
20
15
94 (89)
>99 (96)
88 (80)
>99
>99
9c
1
0c
>99
>99
Reusedd
10
92
a
−1
◦
Reaction conditions: 1 mmol substrate, 2 mL 2-propanol with NaOH (0.1 mol L ), 0.005 g catalyst, 300 W, 120–130 C.
Isolated yields are given in brackets.
b
c
K2CO3 was used as base replacing NaOH due to low selectivity to the target product found in the reactions employing NaOH.
Reused recovered catalyst after 5 uses.
d

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4
K. Yoshida et al. / Applied Catalysis A: General 379 (2010) 38–44
The structure of the mesoporous material was almost pre-
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2
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[
[
[
A simple base switch in the reaction (K CO was used instead of
2
3
NaOH) afforded the target product in high yields (Table 3, entries 9
and 10). ICP analysis of the reaction filtrate (upon reuse as well as
half-way through the reaction) showed no Cu leached in solution or
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