“Save money” during hydrogenation reactions by exploiting the superior performance of Pd-NPs deposited on carbon black by magnetron sputtering

Article abstract of DOI:10.1016/j.tet.2016.11.043

The magnetron-sputtering approach was used for the deposition of small (ca. 3.7 nm) and uniformly distributed Pd(0)-fcc nanoparticles (Pd-NPs) with partially oxidised surfaces on commercially available carbon black. The pores of the support were uniformly filled by Pd-NPs, and the surface area was drastically reduced by blockage of the pores. The metal concentration increases with the augmentation of the sputtering time without changing the metal NP size. These Pd-nanocatalysts are high efficient for the hydrogenation of nitrobenzene to aniline (TOF up to 141.7 min^?1), 1,3-cyclohexadiene to cyclohexene (TOF up to 24.0 s^?1), and cyclohexene to cyclohexane (TOF up to 35.1 s^?1) under 4 bar of dihydrogen (H₂) at mild temperatures (75–90 °C). The magnetron sputtering is one of the simplest, reliable, fast, clean and cheap methods for the preparation of Pd/C catalysts.

Full text of DOI:10.1016/j.tet.2016.11.043

Accepted Manuscript
“Save money” during hydrogenation reactions by exploiting the superior performance
of Pd-NPs deposited on carbon black by magnetron sputtering
Meher Ali, Gabriel Abarca, Dario Eberhardt, Aitor Gual, Fabiano Bernardi, Sergio R.
Teixeira, Jairton Dupont
PII:
S0040-4020(16)31198-X
10.1016/j.tet.2016.11.043
TET 28257
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 6 August 2016
Revised Date: 8 November 2016
Accepted Date: 15 November 2016
Please cite this article as: Ali M, Abarca G, Eberhardt D, Gual A, Bernardi F, Teixeira SR, Dupont
J, “Save money” during hydrogenation reactions by exploiting the superior performance of Pd-NPs
deposited on carbon black by magnetron sputtering, Tetrahedron (2016), doi: 10.1016/j.tet.2016.11.043.
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Meher Ali, Gabriel Abarca, Dario Eberhardt, Aitor Gual, Fabiano Bernardi, Sergio R. Teixeira, and Jairton
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Tetrahedron
journal homepage: www.elsevier.com
“Save Money” During Hydrogenation Reactions by Exploiting the Superior
Performance of Pd-NPs Deposited on Carbon Black by Magnetron Sputtering
Meher Ali,a Gabriel Abarca,a Dario Eberhardt,b Aitor Gual,c Fabiano Bernardi,b Sergio R. Teixeira,b and
Jairton Duponta,c
a Institute of Chemistry, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves, 9500, Porto Alegre, 91501-970 RS, Brazil
b Institute of Physics, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves, 9500, Porto Alegre, 91501-970 RS, Brazil
c School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD, United Kingdom
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
The magnetron-sputtering approach was used for the deposition of small (ca. 3.7 nm) and
uniformly distributed Pd(0)-fcc nanoparticles (Pd-NPs) with partially oxidised surfaces on
commercially available carbon black. The pores of the support were uniformly filled by
Pd-NPs, and the surface area was drastically reduced by blockage of the pores. The metal
concentration increases with the augmentation of the sputtering time without changing the
metal NP size. These Pd-nanocatalysts are high efficient for the hydrogenation of
nitrobenzene to aniline (TOF up to 141.7 min–1), 1,3-cyclohexadiene to cyclohexene (TOF
up to 24.0 s–1), and cyclohexene to cyclohexane (TOF up to 35.1 s–1) under 4 bar of
dihydrogen (H2) at mild temperatures (75-90 ºC). The magnetron sputtering is one of the
simplest, reliable, fast, clean and cheap methods for the preparation of Pd/C catalysts.
Available online
Keywords:
Sputtering
Palladium
Nanoparticles
Hydrogenation
Disproportion
2016 Elsevier Ltd. All rights reserved
.
Among the advantages of this technique, the most important are
the atomic efficiency of the process and the faster generation-
isolation of small and well-dispersed nanostructures of high purity,
and then, precious metal (money) is saved.27-32 Recently, our group
has developed a new sputtering chamber, which allows the constant
mixing of the solid support, and thus, the distribution of the metallic
nanoparticles in all spatial planes of the support (Figure 1).33 Pd-
and Ru-NPs generated by magnetron-sputtering are small and
uniformly distributed.33-36 Furthermore, access of the reagents to the
surface metal-active sites during use of the catalytic materials is
facilitated as the M-NPs are deposited on the most external layers of
the support. This effect is of crucial importance for catalysts based
on highly porous supports (i.e., SiO2 and Al2O3), and is probably due
to hindered diffusion of the metal atoms and clusters through the
support pores. To date, the effect of sputtering time on the chemical
and physical properties of the formed Pd-NPs deposited on solid
supports has not been reported. Here, the use of the magnetron-
sputtering approach for the deposition of Pd-NPs on commercially
available carbon black is reported. A carbon support was selected
due to its wide variety of applications.37 We disclose herein that the
sputtering approach can be use with advantages to prepare classical
Pd/C catalysts. Moreover, we present the deposition time effect on
1. Introduction
Palladium nanostructures, such as Pd nanoparticles (Pd-NPs),
have been extensively applied in organic transformations involving
dihydrogen (H2).1-11 Efficient industrial implementation of these
catalytic processes requires the use of modern synthetic
methodologies, which allow precise control over the physical (i.e.,
size and shape) and chemical (i.e., well-defined composition)
properties of these nanostructures.12-15 Conventionally, the most
extensively extended approach is the chemical reduction of metallic
salts under non-sustainable conditions (i.e., hazardous reducing
agents and generation of large amount of residues).16-21 The
magnetron-sputtering technique is receiving increasing attention
during the last decade. This technique is a potential candidate for
being considered the most sustainable and efficient method for
generating metal nanostructructures.22-24 Briefly, this technique
involves accelerating ions from an in situ generated plasma towards
high-purity metallic targets, yielding a sputtering beam consisting of
metal atoms and small metal clusters. Stabilization of metal
nanoparticles (M-NPs) occurs when the incident sputtering beam is
directed on the appropriate solid or liquid support.25-26
———
Corresponding author. Tel.: +44-(0)115 -748-4613; fax: +44-(0)115-951-3555; e-mail: Aitor.gualgozalbo@nottingham.ac.uk
Corresponding author. Tel.: +44-(0)115 -748-4613; fax: +44-(0)115-951-3555; e-mail: Jairton.dupont@nottingham.ac.uk

2
Tetrahedron
the size, shape, metal dispersion and surface properties of the Pd-
Table 1. Pd-nanocatalyst supported on carbon black (Pd/C-1 to
ACCEPTED MANUSCRIPT
Pd/C-5) prepared by magnetron-sputtering. Deposition time, metal
NPs catalyst supported on carbon black. The reactivity was evaluated
by comparing the catalytic performance of our catalyst with those
obtained using a reference catalyst (a commercially available Pd/C
catalyst). By increasing the sputtering deposition time our
magnetron-sputtering chamber employing the three dimensions’
constant device (CMS3) allows the production of a series of
palladium nanocatalysts of increasing metal content without size
variations, i.e., avoiding film formation. The catalytic performances
of the Pd-NPs were evaluated in the reduction of the model
substrates nitrobenzene, 1,3-cyclohexadiene and cyclohexene under
4 bar of H2 and compared with a commercially available Pd/C-0
catalyst. The disproportion of 1,3-cyclohexadiene was carried out to
address the heterogeneous nature of the as-prepared catalysts. The
details described herein are complementary to those described in
related studies for the preparation of supported Pd-NPs in other solid
materials by sputtering-deposition.33-35
content, mean diameter (Ø) and metal dispersion. [a]
E. Sample Dep.
Metal
Ø
/
SBET
/
Metal
time/
min
content/
nm[c]
m2 g-1 dispersion
wt. % [b]
/ % [e]
[d]
1
2
3
4
5
Pd/C-1 0.5
Pd/C-2 2.5
Pd/C-3 5.0
Pd/C-4 7.5
Pd/C-5 12.0
0.15±0.01 3.8±1.5 25
0.73±0.01 3.7±1.4 22
1.31±0.01 3.8±1.9 15
1.94±0.01 3.7±1.7 14
2.36±0.01 3.9±1.9 10
-
25.3
22.6
20.4
14.6
[a] Sputtering-deposition conditions: 100 mg of solid support, 50 W
of power, 23 Hz of vibration frequency, 4 × 10-7 mbar vacuum, 4 ×
10-3 mbar Ar, and room temperature (25 ºC); [b] Metal content (wt.
%) determined by ICP-OES; [c] Mean diameter (Ø) and size
distributions determined by TEM analysis; [e] The specific surface
areas were determined by the BET multipoint method using Tristar
3020 Micromeritics equipment; [e] Metal dispersion determined by
H2-chemisorption sing a ASAP 2020 Micromeritics equipment.
Figure 1. Illustration of the magnetron-sputtering chamber
developed by our group for the deposition of metallic nanoparticles
on solid supports. Detailed description is reported elsewhere.33
2. Results and Discussion
Figure 2. TEM images (a and b) and XRD analysis (c and d) of the
sample Pd/C-2.
2.1. Sputter deposition
A series of Pd-nanocatalyst (Pd/C-1 to Pd/C-5) supported on
commercially available carbon black were synthesized by the
magnetron sputtering of Pd-target at 50 W power and with a
frequency of optimized 23 Hz for the vibration of the flask. Five
samples (Pd/C-1 to Pd/C-5) were obtained using deposition times of
0.5 min, 2.5 min, 5.0 min, 7.5 min and 12.0 min, respectively (see
Table 1). ICP-OES analysis revealed that the Pd content increased
with the deposition time. This ratio between the deposition time and
the Pd content is linear up to 7.5 min (samples Pd/C-1 to Pd/C-4)
with an increase of the Pd content in the support of 0.2621 wt. % ×
min-1 (Table 1 and Figure S1). The sample obtained by using a
deposition time of 12 minutes (sample Pd/C-5) displayed a decrease
in the deposition rate after 7.5 min. TEM analysis of the Pd/C-1 to
Pd/C-5 catalysts indicated the formation of very similar small Pd-
nanoparticles (i.e., mean diameter between 3.6 and 3.9 nm) with
narrow size distributions (Figure 2 and Figure S2).
XRD analysis shows the presence of the Pd(0)-fcc planes as a broad
signals which are characteristic small Pd(0)-fcc nanoparticles (Figure
2c and 2d).37 N2-physorption and H2-chemisorption analysis revealed
a decrease in specific surface area as compared to the pure support
(SBET = 30 m2 g-1) and a decrease in the metal dispersion with the
increase of the metal content at longer deposition times (Figure S3,
S4 and Table 1). 38 The same trend was observed for liquid supports,
i.e. the augmentation of sputtering time increases the metal
concentration without changing the metal NPs size.31,39 The support
pores were filled by Pd-NPs, and after longer deposition times, the
surface area was drastically reduced by blockage of the pores, as
well as, the access to the metal sites (i.e., reduced metal dispersion).
XPS spectra at the Pd 3d region for the selected samples of Pd NPs
supported on carbon, Pd/C-2 and Pd/C-5, freshly prepared and after
post-treatment under hydrogenation reaction conditions (i.e., 4 bar
H2 and 75 ºC for 1 h) are displayed in Figure 3a and Figure 3b,

3
respectively. It is possible to observe the presence of two different
Pd-chemical components (Pd(0) and Pd(δ+) species) at the Pd-NPs
surfaces. The components were identified in accordance to the
binding energies reported for similar Pd systems.40-42 The Pd(0)
component appears with a binding energy position around 335.4 eV
and with a 0.1 eV maximum variation around 335.4 eV (i.e., 335.3
eV – 335.5 eV) between different samples. The energy shift of these
values to higher binding energies than those value typically reported
for Pd(0) (i.e., 335.2 eV)40 was already observed in the literature for
Pd/C samples.43 Pd(δ+) component was fixed at a binding energy
value of 1.8 eV higher than the corresponding Pd(0) component of
each case. This component was attributed to the oxidation of the Pd-
NPs surfaces during experimental manipulation. Moreover, the
same samples after post-treatment with H2 displayed lower degree of
oxidation (from 48-65% of Pd(0) before to 90% of Pd(0) after post
reduction). Similar behaviour was observed for the Ru-NPs prepared
by similar sputtering procedures.36
Table 2. Hydrogenation of nitrobenzene catalysed by Pd-
ACCEPTED MANUSCRIPT
nanocatalyst supported on carbon black (Pd/C-1 to Pd/C-5) prepared
by magnetron-sputtering.
Entry[a]
Catalyst
Pd/C-0
Pd/C-1
Pd/C-2
Pd/C-3
Pd/C-4
Pd/C-5
TON[b]
4113
TOF[c]/min-1
35.5
1
2
3
4
5
6
1314
2.1
13 298
7410
141.7
64.8
5004
52.9
4113
55.8
[a] Reaction conditions: Pd/C (10 mg), nitrobenzene (9.1 mmol), 900
r.p.m., 4 bar H2 and 90 ºC; [b] TON defined as the moles of substrate
converted per moles of metal; [c] TOF defined as the moles of
substrate converted per moles of metal and unit of time at the period
of maximum rate of conversion (10-30% conv.).44
Table 3. Hydrogenation of cyclohexene catalysed by Pd-
nanocatalyst supported on carbon black (Pd/C-1 to Pd/C-5) prepared
by magnetron-sputtering.
Entry[a]
Catalyst
Pd/C-0
Pd/C-1
Pd/C-2
Pd/C-3
Pd/C-4
Pd/C-5
TON[b]
4443
TOF[c]/s-1
13.4
1
2
3
4
5
6
Figure 3. XPS measurements at Pd 3d region for selected samples
Pd/C-2 and Pd/C-5. XPS analysis were performed using the (a)
freshly prepared catalysts and (b) after post-treatment under reaction
conditions. The black points represent the experimental points, the
dash black line the Shirley background used, the grey solid line the
fitting performed and the red and blue solid lines represent the Pd(0)
and Pd(δ+) components.
69276
14295
8003
26.3
35.1
10.9
5399
13.3
4423
12.9
A comparison of the two samples revealed that the freshly prepared
sample of Pd/C-2 displayed slightly higher degree of oxidation (65
%) than Pd/C-5 (48 %). Probably the higher degree of oxidation of
sample Pd/C-2 is related to its higher metal dispersion (i.e., higher
number of metal sites exposed). After hydrogen treatment in both
cases the major species are Pd(0).
[a] Reaction conditions: Pd/C (10 mg), cyclohexene (9.9 mmol), 900
r.p.m., 4 bar H2 and 75 ºC; [b] TON defined as the moles of substrate
converted per moles of metal; [c] TOF defined as the moles of
substrate converted per moles of metal and unit of time at the period
of maximum rate of conversion (10-30% conv.).44
Similar trends were observed in the hydrogenation of
nitrobenzene and cyclohexene catalysed by Pd catalysts. The
commercial catalyst produced (Pd/C-0) TON and TOF of the same
magnitude as those of catalysts Pd/C-3 to Pd/C-5 (See Table 2-3 and
Figure S6-S10). The catalysts Pd/C-2 produced higher activity and
productivity than the catalyst with higher metal loadings (Pd/C-3 to
Pd/C-5) and lower metal loadings (Pd/C-1). This behaviour is
attributed to either the higher number of available metal sites in
Pd/C-2 than catalysts with higher metal loadings (Pd/C-3 to Pd/C-
5), and the reduced level of support metal interactions compared to
the catalysts with lower metal content (Pd/C-1). The similar activity
displayed by Pd/C-4 and Pd/C-5 was attributed to the fact that
2.2. Hydrogenation reactions
The catalytic performance of the Pd-nanocatalyst supported on
carbon black (Pd/C-1 to Pd/C-5) prepared by magnetron sputtering
was evaluated and compared with the catalytic performance of
commercially available Pd/C-0 catalyst in the hydrogenation of the
model substrates (nitrobenzene and cyclohexene). The reactions
were performed under solvent-less conditions at constant H2 pressure
of 4 bar. The reaction kinetics were monitored by quantifying the
consumption of H2. Substrate conversions and selectivities were also
determined by GC-analysis of reaction sample aliquots.

4
Tetrahedron
ACCEPTED MANUSCRIPT
Pd/C-4 displayed similar number of active sites to Pd/C-5, a
000) with a drastic reduction of the catalytic activity in the
hydrogenation of cyclohexadiene after successive runs (ca. first run:
24.0 s-1, second run: 16.0 s-1, third run: 12.3 s-1 and fourth run: 9.2 s-
1) with no variation of the product selectivity (ca. 81 % Sel.
cyclohexene, 18-19 % Sel. benzene and 0-1% cyclohexane). The
heterogeneous nature of these catalysts was confirmed by their
activity to the disproportion of 1,3-cyclohexadiene into benzene and
catalyst with higher metal loading but lower surface area and lower
metal dispersion. The remarkable difference of activity and
selectivity displayed for Pd/C-1 in the hydrogenation of cyclohexene
and in the hydrogenation of nitrobenzene was attributed to both the
involvement of different active sites during the hydrogenation steps
and its deactivation during the initial reaction stages of the reaction.
Analogous deactivation behaviours were previously reported in
processes involving similar catalysts and substrates.38,45 It should be
highlighted that catalyst Pd/C-2 displayed comparable performances
(activity and selectivity) in the hydrogenation of nitroaromatics to
anilines to those reported using sub-nanometric Pd clusters on porous
nanorods of CeO2 under similar mild conditions (ca. 80 °C under 5
bar H2), a catalyst reported as one of the most active reported so far.9
The catalytic activity of Pd/C-2 in the hydrogenation of cyclohexene
is higher but of the same order of magnitude than those reported in
the literature for Pd-NPs supported on carbon materials,46 and much
higher (ca. 10-to-100 times) than those reported for Pd-NPs
supported on inorganic oxides and synthesised either by
conventional methods47-49 or by the sputtering approach.33-35
cyclohexene,
a
reaction typically catalysed by metal
surfaces/nanoparticles (See Scheme 1).50
These catalysts offer cheaper, simpler and efficient alternative for
the classical and largely employed systems such as the Lindlar
catalyst.53-54
3. Conclusions
The magnetron-sputtering approach was revealed as one of the
simplest, reliable, fast, clean and cheap methods for the deposition of
palladium nanoparticles (Pd-NPs) on a commercially available
carbon black. Small (ca. 3.7 nm) and uniformly distributed Pd(0)-fcc
nanoparticles with partially oxidised surfaces on the solid supports
were obtained. The linear dependence of the deposition time with the
final metal content is revealed (increases from 0.15 wt. % after 0.5
min to 1.94 wt. % after 7.5 min) without changing the size and shape
of the Pd-NPs. The pores of the support were filled by Pd-NPs, and
after longer deposition times, the surface area was drastically
reduced by blockage of the pore system, and consequently the access
to the metal sites (i.e., reduced metal dispersion). These Pd-NPs
catalyse the hydrogenations of nitrobenzene to aniline, cyclohexene
to cyclohexane and 1,3-cyclohexadiene to cyclohexene with superior
catalytic performance as compared to a commercially available Pd/C
and are comparable to the most active catalysts reported so far.
Indeed, the highest catalytic activity and productivity was obtained
with Pd/C catalyst with palladium content of 0.73 wt%. This
behaviour can be due to the higher number of available metal sites
than the catalysts with higher metal loadings, and the reduced level
of support metal interactions as compared to the catalysts with lower
metal loadings. The heterogeneous nature of these Pd-nanocatalysts
was revealed by the formation of benzene and cyclohexene from
disproportionation of 1,3-cyclohexadienes.
Scheme 1. Hydrogenation and disproportionation of 1,3-
cyclohexadiene catalysed by Pd/C-2. Reaction conditions: Pd/C (10
mg), cyclohexene (9.9 mmol), 900 r.p.m. and 75 ºC.
In the partial hydrogenation of 1,3-cyclohexadiene (See scheme
1), the Pd catalyst supported on carbon black Pd/C-2 displayed
lower cyclohexene selectivity and higher activities than those
reported for Pd-NPs supported on inorganic oxides, i.e., SiO2 and
Al2O3 (ca. TOFs of 1-7 s-1, and 90-96 % cyclohexene selectivity).33-
35
The Pd/C-2 displayed lower catalytic activities in the
hydrogenation of 1,3-cyclohexadiene (24.0 s-1) than for the
hydrogenation of cyclohexene (35.1 s-1). In contrast, Pd-NPs
synthesized by sputtering on SiO2 and Al2O3 displayed much higher
activity in the hydrogenation of 1,3-cyclohexadiene than in the
hydrogenation of cyclohexene.
4. Experimental Section
4.1. General procedures
33-35
All syntheses were performed using standard Schlenk techniques
under argon atmosphere. Chemicals were purchased from Sigma-
Aldrich and purified by standard procedures.55 Carbon black (30 m2
g-1) is a standard material purchased from Micromeritics. Pd/C-0
catalyst Degussa type E101 NO/W with a Pd content of 5 wt. % was
purchased from Sigma-Aldrich. Pd-targets (> 99.99%) were
purchased from AJA INTERNATIONAL, Inc. H2 (> 99.999%), N2
(> 99.999%) and Ar (> 99.999%) were purchased from White-
Martins. ICP-OES analysis for the determination of the Pd content
were carried out after sample digestion by using the Thermo
Scientific™ iCAP™ 7400. X-ray diffraction (XRD) experiments
were performed by using a Philips X’Pert MPD diffractometer with
Bragg–Brentano geometry using a graphite curved-crystal with the
Cu Kα X-ray radiation (1.5406 Å). TEM experiments were
performed on a JEOL – JEM 1200ExII, operating at an accelerating
voltage of 200 kV. Size histograms of the Pd-nanoparticles were
obtained by measuring at least 300 particles. N2 isotherms of the
catalysts, previously degassed at 100 °C under vacuum for 3 h, were
obtained using Tristar 3020 Micromeritics equipment. Specific
Although the higher apparent
reactivity of cyclohexene than 1,3-cyclohexadiene, Pd/C-2 was quite
selective for the partial hydrogenation of 1,3-cyclohexadiene to
cyclohexene (81 % selectivity at >99 % conversion). Palladium
surfaces generally displayed high partial hydrogenation selectivities
in the hydrogenation of 1,3-dienes because the higher affinity of the
diene to the Pd-catalytically active surface sites than the alkene, and
thus, the diene reacts to form the partially hydrogenated product.50
The difference of reactivity between the catalysts on different
supports is attributed to support effects (mainly electronic factors).
XPS analysis of Pd-NPs either on carbon and on SiO2 confirmed that
the latter displayed a higher oxidation degree and hence higher
electrophilic surfaces, which in turn, facilitated the selective
hydrogenation of dienes by increasing the coordination strength to
the metal surface active sites of the diene with respect to the alkene.
Indeed, these behaviours of Pd-NPs dispersed on carbon and metal
oxides and their effect on the catalytic performance were previously
reported in related hydrogenation processes.51-52
A study of the recyclability and reuse of the catalyst Pd/C-2
revealed high productivities (ca. TON of each cycle up to than 15

5
surface areas were determined by the BET multipoint method and
average pore size was obtained by BJH method. H2-chemisorption
analyses were carried out on ASAP 2020 surface area and
porosimetry analyser and using of 30 mg of each Pd-catalysts. The
pre-treatment of the sample consists of the following steps: (a) He
flow at 100 ºC for 30 min, (b) two consecutive evacuations under
vacuum during 15 min at 100 ºC and 350 ºC, respectively, (c) three
cycles of reduction with H2 (pressure of 35 KPa) at 100 ºC for 5 min
and at 350 ºC for 120 min, and (d) two consecutive evacuations
under vacuum at 350 ºC for 120 min and at 100 ºC for 30 min. Leak
test at the temperature of analysis was performed before starting the
analysis. Direct adsorption measurements were made with H2 at 35
ºC and consisted of the determination of the isotherms in the 0.15–60
KPa range (about 5 min per point) separated by an evacuation at the
same temperature for 60 min. X-ray photoelectron spectroscopy
(XPS) measurements were performed using a Kratos AXIS Ultra
DLD instrument. Samples were mounted on the standard Kratos
sample bar using double sided tape (sellotape brand), these were
inserted into the airlock and pumped down to ~ 3 × 10-7 Torr
overnight before transfer into the instrument analysis chamber. The
analysis chamber pressure during the measurements was better than
5 × 10-9 Torr. Wide energy range survey scans were collected using
pass energy 80 eV in hybrid slot lens mode and a step size of 0.5 eV,
high resolution data on the Pd 3d, O 1s and C 1s photoelectron peaks
was collected at pass energy 20 eV over energy ranges suitable for
each peak, and collection times of 5 minutes, step sizes of 0.1 eV.
The charge neutraliser filament was used to prevent sample charging
over the irradiated area. The X-ray source was a mono-chromated Al
K-α emission, run at 10 mA and 12 kV (120W). The data were
captured using Kratos VISIONII software and exported into vms
format for data processing with CASAXPS (Version 2.3.17). The
high-resolution spectra were analysed using a Lorentzian asymmetric
line shape convoluted with a Gaussian function for each chemical
component. The high-resolution data was charge corrected to
adventitious carbon at 284.6 eV. The FWHM value of a given
component of the Pd 3d was constrained to be the same for all the
measurements. The energy range for each ‘pass energy’ (resolution)
was calibrated using the Kratos Cu 2p3/2, Ag 3d5/2 and Au 4f7/2 three-
point calibration method. The transmission function was calibrated
using a clean gold sample method for all lens modes and the Kratos
transmission generator software within Vision II.
constant pressure of 4 bar of H2 and heated at the desired
ACCEPTED MANUSCRIPT
temperature (90 °C for nitrobenzene and 75 °C for cyclohexene and
1,3-cyclohexadiene). The reaction kinetics were monitored by H2
consumption. Samples were taken from the reaction mixture at
regular intervals, and the conversion and selectivity was corroborated
by GC-analysis of the reaction samples using n-heptane as internal
standard. After the desired reaction time, the reactor was cooled to
room temperature and then depressurized. GC analyses were run
with an Agilent Technologies GC System 6820 using a DB-17
column. GC conditions were as follows: injector and detector (FID)
temperature of 260 °C; N2 as carrier (1 mL min−1), column head
pressure of 10 psi and temperature program from 40 °C (10 min) to
250 °C at a heating rate of 10 °C min−1.
Supplementary data
Detailed experimental procedure, sputtering time vs. metal
content, TEM images, size histograms, H2-chemisorption isotherms,
N2-physisorption isotherms, XPS spectra and hydrogenation kinetic
data.
Acknowledgments
We would like to thank TWAS-CNPq, CNPq, CAPES,
FAPERGS, INCT-Catal., Petrobras, EPSRC: LiPPS XPS system,
and EP/K005138/1 ‘University of Nottingham Equipment Account’
for providing financial support for this work.
References and notes
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