Selective hydrogenation of 1,3-butadiene to 1-butene by Pd(0) nanoparticles embedded in imidazolium ionic liquids

Article abstract of DOI:10.1002/adsc.200404313

The reduction of Pd(acac)₂ (acac = acetylacetonate), dissolved in 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMI·PF₆) or tetrafluoroborate (BMI·BF₄) ionic liquids, by molecular hydrogen (4 atm) at 75°C affords stable, nanoscale Pd(0) particles with sizes of 4.9±0.8 nm. Inasmuch as 1,3-butadiene is at least four times more soluble in the BMI·BF₄ than butenes, the selective partial hydrogenation could be performed by Pd(0) nanoparticles embedded in the ionic liquid. Thus, the isolated nanoparticles promote the hydrogenation of 1,3-butadiene to butenes under solventless or multiphase conditions. Selectivities up to 97% in butenes were observed in the hydrogenation of 1,3-butadiene by Pd(0) nanoparticles embedded in BMI-BF₄ under mild reaction conditions (40°C and 4 atm of hydrogen at constant pressure). Selectivities up to 72% in 1-butene were achieved at 99% 1,3-butadiene conversion, 40°C and 4 atm of constant pressure of hydrogen. The amounts of butane (fully hydrogenated 1,3-butadiene) and cis-2-butene products are marginal and the butenes do not undergo isomerisation process, indicating that the soluble Pd(0) nanoparticles possess a pronounced surface-like rather than homogeneous-like catalytic properties.

Full text of DOI:10.1002/adsc.200404313

FULL PAPERS
Selective Hydrogenation of 1,3-Butadiene to 1-Butene by Pd(0)
Nanoparticles Embedded in Imidazolium Ionic Liquids
Alexandre P. Umpierre,a Giovanna Machado,a Gerhard H. Fecher,b
Jonder Morais,c Jairton Duponta,*
a
Laboratoryof Molecular Catalysis, Institute of Chemistry, UFRGS, Av. Bento GonÅalves 9500, Porto Alegre, 91501-970,
RS, Brazil
Fax: (þ55)-51-3316-7304, e-mail: dupont@iq.ufrgs.br
b
Institut für Anorganische und Analytische Chemie, Johannes-Gutenberg Universität, 55099 Mainz, Germany
c
Institute of Physics, UFRGS, Av. Bento GonÅalves 9500, Porto Alegre, 91501-970, RS, Brazil
Received: October 11, 2004; Revised: April 18, 2005; Accepted: April 29, 2005
Abstract: The reduction of Pd(acac)2 (acac¼acetyla- ticles embedded in BMI·BF4 under mild reaction
cetonate), dissolved in 1-n-butyl-3-methylimidazoli- conditions (408C and 4 atm of hydrogen at constant
um hexafluorophosphate (BMI·PF6) or tetrafluoro- pressure). Selectivities up to 72% in 1-butene were
borate (BMI·BF4) ionic liquids, bymolecular hydro-
achieved at 99% 1,3-butadiene conversion, 408C
gen (4 atm) at 758C affords stable, nanoscale Pd(0) and 4 atm of constant pressure of hydrogen. The
particles with sizes of 4.9Æ0.8 nm. Inasmuch as 1,3- amounts of butane (fullyhdyrogenated 1,3-buta-
butadiene is at least four times more soluble in the diene) and cis-2-butene products are marginal and
BMI·BF4 than butenes, the selective partial hydroge- the butenes do not undergo isomerisation process, in-
nation could be performed byPd(0) nanoparticles
dicating that the soluble Pd(0) nanoparticles possess a
embedded in the ionic liquid. Thus, the isolated nano- pronounced surface-like rather than homogeneous-
particles promote the hydrogenation of 1,3-butadiene like catalytic properties.
to butenes under solventless or multiphase conditions.
Selectivities up to 97% in butenes were observed in Keywords: dienes; hydrogenation; ionic liquids; nano-
the hydrogenation of 1,3-butadiene by Pd(0) nanopar- particles; palladium
Introduction
tenes, respectively. Thetrans/cis 2-butenes ratios are the
direct result of the interconversion between the diene
The production of polymer-grade 1-butene through the conformer-adsorbed species on the Pd surface. The
selective hydrogenation of 1,3-butadiene is an impor- trans-2-butene is formed preferentiallysince the S-trans
tant industrial process since even traces of 1,3-butadiene conformer is much more stable than the S-cis conformer.
can poison the olefin polymerization catalysis and con- Moreover, the isomerisation of the monoenes formed is
sequentlyreduce the total polymer production. The hy-
drogenation process for the generation of rich streams in An alternative mechanism, involving the formation of
1-butene can be accomplished bya plethora of palladi- carbenes, has been proposed in cases where the ob-
um catalysts. Supported palladium catalysts such as served ratios of trans/cis-2-butenes are comparable
Pd/SiO2 and Pd/alumina, usuallyin the presence of pro- and n-butane is formed as direct product of the diene hy-
moters or modifiers,[1] are among the most used and in- drogenation.[3]
suppressed in the presence of an excess of the diene .[2]
vestigated catalysts for the partial hydrogenation of 1,3-
Transition metal complexes based on palladium or co-
butadiene. In this respect, the catalytic activity and se- balt, either in homogenous or multiphase conditions, are
lectivitycan be stronglyinfluenced bythe metal disper-
also known to catalyse the partial hydrogenation of 1,3-
sion, the nature of the support and the preparation butadiene with high selectivityin butenes, but onlymod-
method. In particular, in these catalytic processes the se- erate yields in 1-butene were achieved.[4] For these mon-
lectivityin 1-butene is reduced due to the parallel iso-
ometallic catalysts the proposed mechanism involves
merisation of 1-butene to internal butenes and total di- also the formation of a stable p-allyl intermediate (re-
ene hydrogenation, which limit the overall yield in 1-bu- gardless of the H2 cleavage mechanism) through the
À
tene. The most accepted mechanism involves adsorption M H addition to a conjugated diene. The isomerisation
of the butadiene through di-p-coordination. The 1,2- or of the 1-butene formed in the internal butenes is charac-
À
1,4-H addition on the diene produces 1-butene or 2-bu- teristic of the involvement of “homogeneous” M H spe-
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Hydrogenation of 1,3-Butadiene to 1-Butene
FULL PAPERS
uids, a method that was recentlydeveloped for the gen-
eration of stable Ir, Rh and Ru nanoparticles of 2–4 nm
in size.[12] Thus, the treatment of a solution of Pd(acac)2
dissolved in 1 mL of BMI·PF6 with molecular hydrogen
(4 atm, constant pressure) at 758C for 5 minutes affords
a black solution from which a black powder is isolated by
centrifugation (3000 rpm, 15 min, 3 times). The isolated
black powder was washed with methanol, dried under
Figure 1. BMI·BF4 and BMI·PF6 imidazolium ionic liquids.
cies.[5] Therefore, at least in the case of Pd catalysts, the reduced pressure and analysed by X-ray diffraction
product selectivityin the partial hydrogenation of buta- (XRD), X-rayphotoelectron spectroscopy(XPS),
diene can be used as a chemical probe to get some in- transmission electron microscopy(TEM), and energy
sights into the nature of their catalytically active sites, dispersive spectroscopy(EDS).
i.e., if theyare characteristic “homogeneous” (single
site) or “heterogeneous” (multi-site) sites.
The X-raydiffraction patterns could be adjusted to the
predicted lines of the Pd fcc structure (Figure 2). The in-
Among the multiphase catalytic systems, those based dexation of Bragg reflections was obtained bya pseudo-
on Pd(II) compounds dissolved in 1-n-butyl-3-methyli- Voigt profile fitting using the FULLPROF code. The
midazolium hexafluorophosphate (BMI·PF6) or tetra- most representative reflections to Pd(0) were indexed
fluoroborate (BMI·BF4) ionic liquids[6] (Figure 1) yield as closed face-centred packing and the cell unit parame-
butenes in 95% selectivityat 98% butadiene conversion.
The higher selectivityin butenes obtained under multi-
ter obtained was a¼0.38979 nm. The Bragg reflections
at 40.1410, 46.6230, 68.1760, 82.0820, and 86.5790 corre-
phase catalysis compared with those performed in ho- spond to the indexed planes of the crystals of Pd(0)
mogeneous conditions was attributed to the higher solu- (111), (200), (011), (220), (311) and (222).
bilityof butadiene in the ionic phase than that of bu-
The diffraction ring patterns (Figure 3a) from selected
tenes.[7] Moreover, the isomerisation of the 1-butene area diffraction (SAD) confirmed the crystalline nature
formed in 2-butenes occurred even at verylow 1,3-buta-
diene conversions.
of the particles. Moreover, the presence ofPd in the sam-
ple was also confirmed bythe energydispersion spec-
It is clear that both heterogeneous and homogeneous trum (EDS, Figure 3b).
palladium catalysts can promote the partial hydrogena-
The XPS analysis showed the presence of palladium,
tion of 1,3-butadiene to butenes. Moreover, with some fluorine, carbon and a small contribution of phosphorus.
modifications, such as the addition of additives in the It is clear that the Fand P signals indicate that the nano-
case of supported Pd catalysts, or the use of multiphase particles (black powder) contain residues from the ionic
catalysis in the case of Pd complexes, one can improve liquid. It is worth pointing out that the valence band (4d,
the yield in 1-butene. It is expected that soluble transi- 5 s) emission occurs at a binding energyof ca. 0–8 eV,
tion-metal nanoparticles of 1–10 nm in size will exhibit measured with respect to the Fermi level, which is quite
physical-chemical properties intermediate between similar to that of pure Pd. No other impurities were de-
those of the smallest element from which theycan be
composed and those of the bulk material.[8] However,
the use of soluble Pd(0) nanoparticles[9,10] as catalysts
for the hydrogenation of dienes has been only marginal-
lyexplored for cyclohexadiene. [11] It was therefore of in-
terest to check if soluble Pd(0) nanoparticles could per-
form the selective partial hydrogenation of 1,3-buta-
diene. We wish to disclose herein that indeed Pd(0)
nanoparticles of 4.9Æ0.8 nm embedded in BMI·BF4
ionic liquid are highlyefficient multiphase catalysis for
the generation of 1-butene in up to 72% yield from the
partial hydrogenation of 1,3-butadiene.
Results and Discussion
Preparation and Characterisation of the Pd(0)
Nanoparticles
Figure 2. X-raydiffraction pattern of Pd(0) nanoparticles
synthesised from dissolved Pd(acac)2 in BMI·PF6 treated
with molecular hydrogen (4 atm) at 758C for 5 minutes.
The Pd(0) nanoparticles have been prepared bythe sim-
ple reduction of Pd(II) compound dissolved in ionic liq- responding Bragg angles.
The peaks are labelled with the hkl of the planes for the cor-
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Figure 3. a) Selected area diffraction (SAD, left) of Pd(0) nanoparticles synthesised from dissolved Pd(acac)2 in BMI·PF6
treated with molecular hydrogen (4 atm) at 758C for 5 minutes (left) and the simulated rig pattern for Pd(0) (right). b) Energy
dispersion spectrum (EDS) of the sample of Figure 5 confirming the presence of palladium in the sample.
tected within the sensitivityof the technique. Figure 4
shows the XPS signal of the Pd 3d and F 1 s regions (in-
set). The Pd 3d spectrum indicates the presence of two
chemical states of Pd at the nanoparticle surface with
distinct binding energies; the main contribution is relat-
ed to Pd(0) (Pd Pd bonds, Pd5/2 at 335 eV) and the other
À
corresponding to Pd F bonds (Pd5/2 at 336.7 eV). It was
À
À
À
found that the relation between the Pd Pd and the Pd F
areas in the spectrum is about 2.8, which corresponds to
À
À
a 74% contribution of Pd Pd bonds and 26% of Pd F
bonds on the nanoparticle surface. This result is a strong
indication of the effective interaction of ionic liquid with
the metal surface that maybe responsible for the stabi-
lisation of the nanoparticles.
Inasmuch as imidazolium ionic liquids possess no
measurable vapour pressure and a relativelyhigh viscos-
ity(2–3 Poises) the nanoparticleꢁs size and morphology
could be investigated in situ bytransmission electron mi-
croscopy(TEM). Thus, the isolated Pd(0) material was
re-dispersed in the BMI·PF6 ionic liquid and placed as
a thin film in a carbon coated copper grid and analysed
byTEM (Figure 5a). The metal particle size distribution
was estimated from the measurement of around 300 par-
ticle diameters, assuming a spherical shape, found in an
arbitrarilychosen area in enlarged microphotographs.
These particles displaya mono-modal size distribution
Figure 4. X-rayphotoelectron spectra of the of Pd(0) nano-
particles synthesised from Pd(acac)2 dissolved in BMI·PF6
showing the Pd 3d and F 1 s regions (inset) with the fitting re-
sults. The Pd 3d doublet presents two components corre-
sponding to Pd Pd and Pd F bonds, the first being the
most abundant one.
À
À
amounts of BMI·BF4 and BMI·PF6 or under solvent-
free conditions. The use of in situ nanoparticles in the
with an average diameter of (4.9Æ0.8) nm (Figure 5b), ionic liquid is not recommended since it maycontain
which is in good agreement with the mean diameter es- soluble Pd(acac)2 that was not completelyreduced and
timated from the XRD data.
the ionic phase is slightlyacid. The initial temperature
was set at 408C and the hydrogen pressure at 4 atm (con-
stant pressure). The reaction products (Scheme 1) were
monitored byGC and the 1,3-butadiene conversion and
products selectivity, using Pd(0) nanoparticles embed-
Hydrogenation of 1,3-Butadiene
The hydrogenation of 1,3-butadiene was performed ded in BMI·BF4 and under solvent-free conditions are
with the isolated Pd(0) either embedded in different presented in Figures 6–8.
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Figure 5. a) TEM micrograph of Pd(0) nanoparticles synthesised from Pd(acac)2 dissolved in BMI·PF6 treated with molecular
hydrogen (4 atm) at 758C for 5 minutes, supported on a carbon coated grid, and b) the corresponding size distribution histo-
gram.
of the ionic liquid that are mass transfer controlled proc-
esses as observed in various other related studies.[4] In-
deed, the amount of ionic liquid has a strong influence
on the catalytic activity in the hydrogenation of 1,3-bu-
tadiene bythe Pd(0) nanoparticles (Figure 7). In fact
the amount of ionic liquid can be reduced to 5Â10À7
mL without a change in butene selectivity.
Scheme 1. Products resulting from the hydrogenation of 1,3-
butadiene byPd(0) nanoparticles.
The products selectivityis also stronglyinfluenced by
the nature reaction media. The formation of butane is al-
most negligible (less than 2%) in the reactions per-
It is clear that the reaction performed under solvent- formed with the Pd(0) nanoparticles embedded in the
free conditions is much faster than that performed under ionic liquid at any1,3-butadiene conversion whereas
biphasic conditions, i.e., the total consumption of buta- those performed under solvent-free conditions generate
diene takes less than 2 hours using the isolated Pd(0) significant amounts of the alkane even at low 1,3-buta-
nanoparticles whereas almost 6 hours are necessaryin
diene conversions (Figure 8). Noteworthy, 98% selectiv-
the case of the nanoparticles dispersed in the ionic liquid ityin butenes (72% in 1-butene) is attained at complete
(Figure 6).
1,3-butadiene conversion. Moreover, the amount of cis-
This difference is probablyrelated with the typical bi-
2-butene is also negligible in the case of hydrogenation
phasic nature of the reactions performed in the presence using the nanoparticles embedded in the ionic liquid
Figure 6. Activitydata from the hydrogenation of 1,3-butadiene (2.7 g of 1,3-butadiene) at 40 8C and 4 atm catalysed by Pd(0)
nanoparticles (5 mg) embedded in 1Â10À5 mL of BMI·BF4 (left) and under heterogeneous conditions (right). Legend: ( )¼
^
À
1,3-butadiene, (D)¼1-butene, (*)¼trans-2-butene, (r)¼cis-2-butene, (a)¼n-butane.
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Alexandre P. Umpierre et al.
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tion of 1-butene and trans-2-butene in a separate set of
experiments (Figure 10) using the same reaction condi-
tions employed in the hydrogenation of butadiene.
These patterns of selectivity, i.e., negligible formation
of cis-2-butenes and the absence of butenes isomerisa-
tion in the presence of the diene, indicate that ionic liq-
uid-soluble palladium nanoparticles behave as “hetero-
geneous-like” (multisite, Scheme 2) rather than “homo-
geneous-like” (single site) catalysts. The higher selectiv-
ityin butenes attained in the reactions performed with
the Pd(0) nanoparticles embedded in BMI·BF4, com-
pared with those performed under solvent-free condi-
tions can be related to the greater miscibilityof the
1,3-butadiene with the ionic liquid than butenes. Indeed,
1,3-butadiene is at least three times more soluble in
BMI·BF4 than butenes at 408C.
The partial hydrogenation of 1,3-butadiene could also
be performed with the Pd(0) nanoparticles embedded in
BMI·PF6 (Figure 11). However, in this case the forma-
tion of butane is higher (more than 3 times than those
performed byPd(0) embedded in BMI·BF 4) and prob-
Figure 7. Hydrogenation of 1,3-butadiene (2.7 g of 1,3-buta-
diene) at 408C and 4 atm catalysed by Pd(0) nanoparticles
(5 mg) in heterogeneous system and with the nanoparticles
embedded in BMI·BF4.
ablyis a result of the less pronounced difference in the
[6a]
and less than one quarter of the butenes formed under miscibilityof 1,3-butadiene over butenes.
“solvent-free conditions”.
Notewor-
thy, the addition of water to the catalytic system does
Moreover, in the reaction performed with the nano- not cause anysignificant changes in the reaction selec-
particles embedded in BMI·BF4 the formed butenes tivity.
do not undergo isomerisation, i.e., the selectivitydoes
It is worth noting that the recovered Pd(0) ionic liquid
not change with the diene consumption (Figure 9). phase can be reused without anysignificant changes in 1-
This result is in sharp contrast to the catalytic perform- butene selectivity(Figure 12).
ance observed in the same reaction promoted byPd(II) I
Even though the selectivityof this system suffered no
compounds dissolved in imidazolium ionic liquids in appreciable modification after four charges of 1,3-buta-
which the formed 1-butene is isomerised in 2-butenes diene, the catalytic activity was somewhat irreproduci-
even in the earlystages of the process. [7]
ble, possiblydue to expulsion of the catalyst from the re-
Under “solvent-free” conditions the isomerisation of active phase bystirring and adherence of the nanoparti-
the formed butenes onlyoccurs in the absence of the di- cles to the inner walls of the reactor bottle. At 90% 1,3-
ene, i.e., after complete 1,3-butadiene conversion. This butadiene conversion, the turnover frequency(TOF) of
was further corroborated byperforming the hydrogena- the 1,3-butadiene hydrogenation reactions oscillates be-
Figure 8. Selectivitydata from the hydrogenation of 1,3-butadiene (2.7 g of 1,3-butadiene) at 40 8C and 4 atm catalyzed by
Pd(0) nanoparticles (5 mg) embedded in 1Â10À5 mL of BMI·BF4 (left) and under heterogeneous conditions (right). Legend:
(D)¼1-butene, (*)¼ trans-2-butene, (r)¼cis-2-butene, (&)¼n-butane.
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Figure 9. Reaction products selectivityobtained from the hydrogenation of 1,3-butadiene (2.7 g of 1,3-butadiene) at 40 8C and
4 atm catalysed by Pd(0) nanoparticles (5 mg) embedded in 1 Â10À5 mL of BMI·BF4 (left) and under heterogeneous condi-
tions (right). Legend: (D)¼1-butene, (*)¼trans-2-butene, (r)¼cis-2-butene, (&)¼n-butane.
Figure 10. Hydrogenation of 1-butene (left) and 2-trans-butene (right) at 408C and 4 atm catalysed by Pd(0) nanoparticles.
tween 30 hÀ1 and 55 hÀ1. TEM analysis of nanoparticles Conclusion
after the hydrogenation shows significant agglomera-
tion into larger nanoparticles ofabout 20 nm in diameter In summary, we have demonstrated that Pd(0) nanopar-
(Figure 13). This result indicates that the ionic liquid ticles with relativelysmall diameters and narrow size
does not provide an effective protection against agglom- distributions can be prepared bysimple hydrogen reduc-
eration for the Pd(0) nanoparticles under the catalytic tion of Pd(acac)2 dispersed in BMI·PF6 ionic liquid. The
reaction conditions.
XPS analysis showed the effective interaction of ionic
It is interesting to point out that under the same reac- liquid with the metal surface that maybe responsible
tion conditions (1Â10À3 mL of BMI·BF4, 408C, 4 atm for the stabilityof the nanoparticles. The ionic liquid cre-
H2) the selectivityfor butenes, during the hydrogenation
of 1,3-butadiene bythe classical heterogeneous catalyst
Pd/C (5% Degussa), is verylow even at relativelylow
ates an external layer around the metal nanoparticles
that controls the access of the reagents to the catalytical-
lyactive sites as a function of their solubilityin the ionic
substrate conversions (62% and 61% 1,3-butadiene con- layer. Therefore, the primary products (butenes)
version). This result is an indication that the selectivity formed during the hydrogenation of 1,3-butadiene are
for butenes is also related to the nature of the catalysts extracted from the ionic layer by the 1,3-butadiene
precursor and that “ionic-liquid-soluble” Pd nanoparti- (which is at least four times more soluble in the ionic
cles are superior to the classicalheterogeneous Pd/C cat- phase than the butenes). This catalytic system [Pd(0)
alyst.
nanoparticles embedded in ionic liquids] is one of the
most effective for performing the selective hydrogena-
tion of 1,3-butadiene to 1-butene. Most important, we
have demonstrated that the hydrogenation of butadiene
can be used as a chemical probe to check the character-
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Figure 12. Selectivityat 85% conversion in 1,3-butadiene hy-
drogenation under biphasic reaction conditions (1Â10À3 mL
of BMI·BF4, 408C, 4 atm H2).
Scheme 2. Proposed reaction pathways involved in the partial
hydrogenation of butadiene in the catalyst surface through
1,2- and 1,4-additions on S-cis and S-trans conformers of bu-
tadiene leading to different p-allyl intermediates.
Figure 13. TEM micrograph of Pd(0) nanoparticles dispersed
in BMI·PF6 recovered after three charges of 1,3-butadiene.
Figure 11. Reaction products selectivityobtained from the
hydrogenation of 1,3-butadiene (at 85% conversion) by
Pd(0) nanoparticles (5 mg) in different reaction media at
408C and 4 atm.
against aggregation as recentlydemonstrated in the
case of C C coupling reactions promoted bynanoscale
À
palladium catalysts dissolved in functionalized pyridini-
um ionic liquids.[13]
istic behaviour of soluble Pd(0) nanoparticles, i.e., if
theypossess a more pronounced surface-like or single
site-like properties. Although simple 1,3-dialkylimida-
zolium ionic liquids do not provide an effective protec-
tion to the nanoparticles against aggregation under the
catalytic reaction conditions, it can be anticipated that
the use of functionalized imidazolium ionic liquids
mayprovide an effective nanoparticle protection
Experimental Section
Materials
All bench procedures were carried out under Ar using Schlenk
techniques. The ionic liquids BMI·BF4 and BMI·PF6 were pre-
pared according to the procedure described in the literature[14]
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and their puritychecked bythe AgNO 3 test and cyclic voltame-
try. All other chemicals were acquired from commercial sour-
ces. The 1,3-butadiene used was distilled before the hydrogena-
tion reactions. The GC analyses were performed in a Shimadzu
GC 14-B with a 30 m alumina Megabor column using H2 as mo-
bile phase. The hydrogenation reactions products were sepa-
rated under 4 psig and 408C isotherm. Products were identified
bypatterns. The powder XRD analyses were performed in a
Philips XꢁPert MRD using the Bragg-Brentano geometryand
a graphite crystal as monochromator. The chemical analysis
of the nanoparticles was obtained byXPS using the VG ESCA-
LAB MkII, equipped with 150 mm hemispherical analyser and
Al Ka anode X-raysource. The overall resolution was 200 meV.
The TEM analyses were performed in a JEOL JEM 2010 trans-
mission electron microscope operating at 200 kV with nominal
resolution of 0.25 nm. Samples for TEM were prepared bydep-
osition of the Pd(0) nanoparticles dispersed on dichlorome-
thane and a drop of this solution was transferred on a holeycar-
bon grid.
Acknowledgements
Thanks are due to CNPq,CT-PETRO and FAPERGS for par-
tial financial support and to CAPES for a scholarship do
A. P. U.
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Synthesis of the Pd(0) Nanoparticles
The Pd(0) nanoparticles were synthesized by the reduction of
Pd(acac)2 dissolved in BMI·PF6 bymolecular hydrogen. In a
typical experiment, 2 mL of BMI·PF6 were added to a solution
of 30 mg (0.1 mmol) in methanol (ca. 1 mL) in a modified
Fischer–Porter bottle reactor. The formed solution was held
at 1008C for 10 minutes and volatiles were removed under re-
duced pressure. The system was cooled, held at 758C, and H2
(4 atm) was admitted to the reactor bottle for 5 minutes. The
reduction of Pd(acac)2 was followed bythe formationof a black
powder suspension in the ionic liquid. The formed black pow-
der was filtered bycentrifugation (3000 rpm, 15 min, 3 times)
and washed with dichloromethane 2Â10 mL and 5Â10 mL
and dried under reduced pressure. The total yield was 10 mg
(>98% of the initial Pd content). The nanoparticles were an-
alysed by powder X-ray diffraction and transmission electron
microscopy.
[2] a) J. J. Phillips, P. B. Wells, G. R. Wilson, J. Chem. Soc. A
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Hydrogenation Reactions
Hydrogenations experiments were performed in a modified
Fischer–Porter bottle connected to a constant pressure feed
reservoir.
Solvent-Free Conditions: In a typical experiment, 5 mg of
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to the system. The temperature in the active phase was held at
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GC.
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The reactions performed with the nanoparticles dispersed in
the ionic liquids were performed using the same experimental
set-up. In these cases the isolated nanoparticles were directly
dispersed in the desired amount (using a syringe or micro-sy-
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