A.M. Raspolli Galletti et al. / Applied Catalysis A: General 468 (2013) 95–101
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The content of Pd was determined by inductively coupled
plasma-optical emission spectrometers (ICP-OES) with a Spectro-
Genesis instrument equipped with a software Smart Analyzer
Vision. For ICP-OES, the sample was heated over a heating plate
in a porcelain crucible in the presence of aqua regia (2 ml) for four
times, dissolving the solid residue in 0.5 M aqueous HCl. The limit
of detection (lod) calculated for Pd was 2 ppb.
X-ray diffraction (XRD) patterns were measured with a Thermo
ARL X’TRA powder diffractometer, operating in the Bragg-Brentano
geometry and equipped with a Cu-anode X-ray source (K␣,
ꢀ = 0.15418 nm), using a Peltier Si(Li) cooled solid state detector.
FT-IR spectra were recorded with Jasco FT/IR-6200 spectrometer
from KBr pellets or film casted from water solutions onto a BaF2
window.
Thermogravimetric analyses were performed with a SII Nano-
Technology EXTAR TG/DTA7220 thermal analyzer at 10 ◦C/min in
nitrogen atmosphere (200 ml/min). 5 mg of each sample in an alu-
mina pan was analyzed in the 40–900 ◦C temperature range. The
intrinsic viscosity of chitosan was measured with an Ubbelohde
viscometer in 0.2 M CH3COOH/0.1 M CH3COONa aqueous solutions
at 30 ◦C. The obtained data were used for the determination of the
chitosan molecular weight by using the Mark–Houwinkparameters
reported by Wang [42].
pressurized with hydrogen to 1 MPa and heated up to the desired
temperature, maintaining a stirring speed of 500 rpm, a value which
was ascertained to assure the absence of mass transfer limitations.
The absence of mass transfer limitation at stirring speed of 500 rpm
was investigated by performance of hydrogenation tests with vari-
ous stirring speed. The pressure value was manually held constant
at 1 MPa by repeated hydrogen feeds. The course of the reaction
was monitored by periodically sampling the liquid through a valve
and analyzing it by gas-chromatography. GC analyses were per-
formed with a HP 5890 gas-chromatograph equipped with a HP
3396 integrator, a flame ionization detector and a PONA capillary
column (50 m × 0.2 mm × 0.5 m) with a stationary phase 100%
dimetylpolysiloxane (carrier gas nitrogen, flow 1 ml/min). Activity
data were expressed as converted moles of EC (g Pd h)−1 measured
after 1 min of reaction and at 100 mol% EC conversion. The repro-
ducibility of repeated catalytic runs was within 5%. The recyclability
of the catalyst was verified employing the used catalyst in a suc-
cessive catalytic cycle, once recovered by centrifugation, washing
with 20 ml of EtOH and drying.
2.6. Hydrogenation reactions of ethyl cinnamate to ethyl
hydrocinnamate employing MW irradiation
Hydrogenation reactions were carried out in the 80 ml glass
reactor. In each run, 18.3 mg of 3.50 wt% Pd/chitosan catalyst was
suspended in EtOH/H2O 25/0.0375, ml/ml in the reactor, then it
was closed, evacuated up to 1 kPa and subsequently the vessel was
pressurized to 1 MPa of hydrogen and the reaction was performed
at 50 ◦C, sampling the mixture after 1, 3, 5 and 10 min and analyzing
the samples by gas-chromatography as previously described.
The BET surface area was determined by nitrogen adsorption,
using a single point ThermoQuest Surface Area Analizer Qsurf S1.
Before the measurement, the catalyst was treated at 100 ◦C as
degassing temperature for 5 h under a nitrogen flow of 35 ml/min.
1H NMR analysis of chitosan was performed on a Varian NMR
spectrometer operating at 300 MHz. The sample was solubilized in
D2O/CD3COOD and the spectrum was acquired at 60 ◦C.
The X-ray photoelectron spectroscopy analysis of the catalyst
was performed with a VG Microtech ESCA 3000 Multilab spectrom-
eter, using the unmonochromatised Al K␣ source (1486.6 eV) run
at 14 kV and 15 mA. Survey spectra were collected at constant pass
energy of 50 eV. Individual peak energy regions were collected at
constant pass energy of 20 eV. The sample was mounted on a stub
holder using double-sided adhesive tape. In order to avoid the con-
tact with air, the sample mounting was performed inside a glove
bag filled with N2 and then the holder was loaded inside the XPS
machine under a N2 atmosphere. The C 1s peak, set at 285.1 eV,
arising from carbon, was used as reference for the binding energy
values. Differential surface charging was ruled out by checking
ent X-ray exposures. Analysis of the peaks was performed with the
software provided by VG, based on non-linear least-square fitting
routine using a weighted sum of Lorentzian and Gaussian compo-
nent curves after background subtraction according to Sherwood
[43]. Atomic concentrations were calculated from peak intensity
with the standard set of VG Escalab sensitivity factors. The binding
energy values are quoted with a precision of 0.15 eV.
2.7. One pot preparation of Pd/chitosan catalyst and its direct use
in the hydrogenation of ethyl cinnamate under MW irradiation
In the 80 ml glass reactor 1.4 mg of Pd(OAc)2 with 18.6 mg of
chitosan were suspended in EtOH/H2O 25/0.0375, ml/ml and the
mixture was MW-irradiated in nitrogen atmosphere at 100 ◦C for
5 min. When the reaction was complete, the reactor was rapidly
cooled to room temperature and the nitrogen discharged. Immedi-
ately after, 1.25 ml of EC and 1 MPa of hydrogen were introduced
and the hydrogenation reaction was carried out at 50 ◦C under
MW-irradiation, sampling the mixture after 1, 3, 5 and 10 min
and analyzing the samples by gas-chromatography as previously
described.
3. Results and discussion
3.1. Synthesis and characterization of 3.5 wt% Pd/chitosan
catalyst
both as solvent and reducing agent. The procedure was adapted
from our previously reported method regarding the preparation of
palladium nanoparticles supported on polymeric supports, such as
polyketone [4] or inorganic ones (␥-Al2O3) [27]. In this research
as support was chosen high molecular weight chitosan, character-
ized by Mv of 1.05 × 106 Da and a deacetylation degree of 0.73, in
order to limit possible leakage due to dissolution or degradation.
Chitosan flakes in 37–74 m size range were selected (by 400 mesh
sieve in an ASTM C136 – 06 sieve column) whose surface area was
1.8 m2 g−1 from BET analysis. This is a very small value if compared
with the more traditional inorganic supports, such as active car-
bon or alumina [26] and it is surely a crucial point to be considered
when chitosan is employed as support for the synthesis of metal
systems for catalytic applications. However, in the case of organic
2.5. Hydrogenation reactions of ethyl cinnamate to ethyl
hydrocinnamate in the autoclave
Hydrogenation reactions were carried out in a stainless steel
300 ml mechanically stirred Parr 4560 autoclave equipped with a
P.I.D. controller 4843. In each run, 74.3 mg of 3.50 wt% Pd/chitosan
catalyst was introduced in the autoclave, then it was closed, evac-
uated up to 65 Pa and a solution of 5.0 ml of ethyl cinnamate in
100/0.15, ml/ml of EtOH/H2O was introduced by suction. These con-
ditions were chosen because in the “one pot” method the amount
of water amount present in the catalytic synthesis remains in the
catalytic test also. Being conscious of the possible effect of the
water amount on the catalytic tests, we decided to keep constant
the water (ml)/chitosan (g) ratio (exactly equal to 2) both in the
“one pot” synthesis and in the catalytic runs. The reactor was then