The generation of palladium silicide nanoalloy particles in a SiCN matrix and their catalytic applications

Article abstract of DOI:10.1039/c1jm13665h

The synthesis, characterization and catalytic studies of single phase palladium silicide nanoalloy particles supported by a polymer derived, non-oxide SiCN matrix (Pd₂Si@SiCN) are reported. Simultaneous chemical modification of a polyorganosilazane as well as its cross-linking was achieved by the use of an aminopyridinato palladium complex at room temperature. Cross-linking takes place with an evolution of hydrogen and increases the ceramic yield by the retention of carbon and nitrogen atoms. Liberation of ligand, as confirmed by ¹H NMR spectroscopy, provides indirect evidence of the transfer of palladium to the nitrogen functions producing metal modified polyorganosilazane whose pyrolysis at 1100 °C under nitrogen atmosphere provides Pd₂Si@SiCN. Powder X-ray diffraction (PXRD) studies confirmed the presence of the hexagonal Pd₂Si phase in the amorphous SiCN matrix. The size of the particles formed seems to depend upon the nature of the solvent used in the cross-linking step. The amount of palladium complex added seems not to affect the size of particles formed but does increase their population density. Pd₂Si@SiCN catalysts were found active for the hydrogenation of ketones. The selectivity of the reaction towards the alcoholic product remains very high. The conversion of the reaction however decreases both with increase in alkyl chain length as well as its branching at alpha carbon. The recyclable Pd₂Si@SiCN could be a suitable choice for catalytic transformations under a harsh chemical environment and at higher temperatures.

Full text of DOI:10.1039/c1jm13665h

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PAPER
The generation of palladium silicide nanoalloy particles in a SiCN matrix and
their catalytic applications
a
b
a
Muhammad Zaheer, G €u nter Motz* and Rhett Kempe*
Received 1st August 2011, Accepted 23rd September 2011
DOI: 10.1039/c1jm13665h
The synthesis, characterization and catalytic studies of single phase palladium silicide nanoalloy
particles supported by a polymer derived, non-oxide SiCN matrix (Pd Si@SiCN) are reported.
2
Simultaneous chemical modification of a polyorganosilazane as well as its cross-linking was achieved
by the use of an aminopyridinato palladium complex at room temperature. Cross-linking takes place
with an evolution of hydrogen and increases the ceramic yield by the retention of carbon and nitrogen
1
atoms. Liberation of ligand, as confirmed by H NMR spectroscopy, provides indirect evidence of the
transfer of palladium to the nitrogen functions producing metal modified polyorganosilazane whose
ꢀ
pyrolysis at 1100 C under nitrogen atmosphere provides Pd Si@SiCN. Powder X-ray diffraction
2
(
PXRD) studies confirmed the presence of the hexagonal Pd Si phase in the amorphous SiCN matrix.
2
The size of the particles formed seems to depend upon the nature of the solvent used in the cross-linking
step. The amount of palladium complex added seems not to affect the size of particles formed but does
2
increase their population density. Pd Si@SiCN catalysts were found active for the hydrogenation of
ketones. The selectivity of the reaction towards the alcoholic product remains very high. The
conversion of the reaction however decreases both with increase in alkyl chain length as well as its
2
branching at alpha carbon. The recyclable Pd Si@SiCN could be a suitable choice for catalytic
transformations under a harsh chemical environment and at higher temperatures.
Introduction
where such robust systems have successfully been used as catalysts
30
for fuel reforming, total oxidation of methane and the decom-
29
Nanoalloys, owing to their improved structural, electronic and
optoelectronic properties as compared to their (metallic) counter-
parts, find intensive applications in many areas of technological
31
position of ammonia. In addition, metal containing SiCN
ceramics have been reported to be selective catalysts in the oxida-
32
tion of alkanes using air as an oxidant. The synthetic strategies for
1
importance. For instance, bimetallic alloy nanoparticles have been
4,5
applied in light emitting diodes (LEDs), data storage devices,
metal containing polymer derived ceramics can broadly be divided
into three categories. Firstly, the chemical modification of orga-
33
2,3
6
and thermoelectric devices. A salient feature of nanoalloy particles
nosilicon polymers by the use of metal powders or by metal
is the superior catalytic performance and their applications, in this
34
oxides; secondly, modification at a molecular level by the use of
35,36
7–12
regard, range from electrochemical fuel cell reactions to various
17,18
and renewable energy production.
metal complexes
followed by its pyrolysis to obtain metal con-
13–16
oxidation reactions
tainingceramics.Thethirdapproachmakesuseofmetalcontaining
37–40
Polymer derived ceramics (PDCs) have been investigated inten-
organosilicon polymers
and their subsequent ceramization. We
19
sively in the past two decades. PDCs based on the SiCN ternary
recently reported a molecular approach utilizing aminopyridinato
system are highly robust materials possessing extraordinary high
22
and oxidation resistance up to 1600 C
transition metal complexes for the chemical modification of poly-
41,32
20,21
temperature properties
ꢀ
organosilazane
(HTT 1800) whose pyrolysis provided metal
23
without showing any prominent mechanical creep. On the
particles containing SiCN ceramics. This synthetic protocol is
advantageousinthesensethatitavoidsentryofanyforeignelement
as the aminopyridinato complexes contain the same elements as
contained by the polysilazane. Such complexes can be synthesized
in good yields and are available for almost all the transition
24
account of their polymer route synthesis, fabrication of fibers,
25
26
films and coatings is facilitated. Introduction of metal not only
27
28
improves the electrical, thermal, and magnetic properties of
thesematerialsbutalsoextendstheirapplicationprofiletocatalysis,
42
elements. Moreover, the dispersion of metal within the ceramic is
assured owing to the covalent linkages of metal with the nitrogen
functionalities of the polysilazane. This molecular approach for the
synthesis of metal containing SiCN ceramics is (here) extended to
the synthesis of so-called intermetallic nanoparticles (nanoalloys).
a
Inorganic Chemistry II, University of Bayreuth, 95440 Bayreuth,
Germany. E-mail: kempe@uni-bayreuth.de
b
Ceramic Materials Engineering, University of Bayreuth, 95447 Bayreuth,
Germany. E-mail: guenter.motz@uni-bayreuth.de
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The aminopyridinato complex of palladium used here generates
palladium silicide nanoparticles bythe chemical modification of the
polysilazane. Moreover, it cross-links the polymer efficiently at
room temperature increasing the ceramic yield by the retention of
carbon and nitrogen atoms within the ceramic. Conventional
synthesis of palladium silicides involves the annealing of palladium
on silicon substrates which, depending upon the stoichiometric
ratio and annealing temperature, generates different silicide phases
Table 1 Designation of the samples synthesized by using different
amounts of palladium complex reacted with HTT 1800, respective
palladium to silicon ratio and palladium loading in resulting ceramics
b
Pd loading
Sample ID
(
Pd complex
(wt% HTT 1800)
Pd/Si
(ratio)
a
CL/FC)
Calculated
Measured
Pd20
Pd40
Pd60
Pd80
Pd100
Pd1000
36.0
18.0
12.0
9.0
7.2
0.2
1/20
1/40
1/60
1/80
1/100
1/1000
8.17
4.86
3.32
2.61
2.09
0.22
6.91
3.36
2.50
1.31
0.74
—
43
(
x y
Pd Si ). Although the growth and structure of palladium silicide
have been studied extensively in the past, there are only a few
44
reportsonthenanosizingofpalladiumsilicides. Herewereporton
the synthesis of palladium silicide nanoparticles and their size
control within a SiCN support and their catalytic applications.
a
Suffixes CL and FC correspond to the cross-linked and ceramic form
respectively. Palladium loading in wt%.
b
Experimental
General remarks
1/80, 0.29 g, 0.62 mmol; Pd/Si 1/100, 0.23 g, 0.5 mmol) in tetra-
hydrofuran (THF) (5 mL) (Table 1). No cross-linking agent was
added as the complex itself acts as a cross-linking agent and
changes the orange solution into a black solid. The solvent was
evaporated under vacuum and the solid obtained was pyrolysed
All reactions were carried out under dry argon using standard
Schlenk and glove box techniques. Solvents were dried and
distilled from sodium benzophenone before use. Deuterated
solvents obtained from Cambridge Isotope Laboratories were
degassed, dried using molecular sieves and distilled prior to use.
n-Butyllithium, 2-amino-4-picoline, chlorotrimethylsilane, ace-
tophenone (ACROS Chemicals), dichloroplatinum(II) (Alfa
Aesar) and polysilazane (HTT 1800, Clariant, GmbH) were used
as received without any further purification.
ꢀ
À1
under nitrogen atmosphere at 1100 C (5 K min ; holding time:
0 min) to get the ceramics.
3
Characterization
Nuclear magnetic resonance (NMR) spectra were recorded using
a Varian INNOVA 400 spectrometer. Chemical shifts are
reported relative to deuterated solvent. Ceramisation was carried
out under nitrogen in a high temperature furnace (Nabertherm
LH 60/14, Nabertherm, Germany). Gas chromatography (GC)
analyses were performed by using an Agilent 6890N gas chro-
matograph equipped with a flame ionization detector (FID) and
an Agilent 19091 J-413 FS capillary column using dodecane as
internal standard. All X-ray powder diffractograms were recor-
Ligand and complex synthesis
The starting material 4-methyl-2-((trimethylsilyl)amino)pyridine
46 47
dichloro(1,5-cyclooctadiene)platinum(II) and complex 2
45
1,
were synthesized following reported methods (Fig. 1).
Cross-linking, metal transfer and pyrolysis
ded by using a STOESTADI-P-diffractometer (CuK
a
radiation,
Polysilazane HTT 1800 (3.218 g) was reacted with palladium
ꢀ
.54178 A) in q–2q-geometry and with a position sensitive
1
aminopyridinato complex 2 (Pd/Si 1/20, 1.16 g, 2.49 mmol; Pd/Si
detector. Transmission electron microscopy (TEM) was carried
out by using a Varian LEO 9220 (200 kV) instrument. The
sample was suspended in chloroform and sonicated for 5 min.
Subsequently a drop of the suspended sample was placed on
a grid (Plano S 166-3) and allowed to dry.
1
/40, 0.581 g, 1.25 mmol; Pd/Si 1/60, 0.38 g, 0.83 mmol; Pd/Si
Elemental analysis was performed by standard protocols
employing digestion in HNO /HCl/H O and inductively
3
2
2
coupled plasma optical emission spectrometry (ICP-OES) using
a Varian, Vista-Pro radial. FT-IR measurements were performed
using a Perkin-Elmer FTIR-Spectrum 100.
Catalytic studies
1
mmol of ketone in toluene (0.4 mL) was taken in a glass tube
along with a magnetic bar and 60 mg of milled ceramics (particle
size: <100 mm) was added. This tube was placed in a Parr auto-
clave under a hydrogen pressure of 40 bar. The reactor was
heated to the respective temperature within 20 min and stirring
Fig. 1 Scheme for the synthesis of Pd
ceramics: (a) synthesis of complex 2 from ligand 1; (b) the polysilazane
HTT 1800) is chemically modified by its reaction with the complex along
2
Si nanoparticles containing SiCN
(
(
400 rpm) was continued at this temperature for 24 hours.
with the liberation of the ligand; (c) metal modified polysilazane 3
Afterwards, reaction mixture was diluted with THF and dodec-
ane as internal standard was added. The conversion and selec-
tivity were determined by GC.
produces dipalladium silicide nanoparticles supported SiCN ceramics
ꢀ
upon pyrolysis at 1100 C under nitrogen atmosphere. n-BuLi: n-butyl-
lithium; cod: 1,5-cyclooctadiene; HTT 1800: polyorganosilazane.
1
8826 | J. Mater. Chem., 2011, 21, 18825–18831
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Results and discussion
Synthesis of palladium complex, metal modified polysilazane and
ceramics
Fig. 1 shows the schematic presentation of the synthesis of the
palladium complex (Fig. 1a), chemical modification of Si–H and
vinyl-silicon groups containing HTT 1800 (Fig. 1b) and the
generation of dipalladium silicide nanoparticles supported by
SiCN ceramics (Fig. 1c). Polysilazane HTT 1800 was reacted
with different amounts of palladium complex 2 (Table 1) to get
the metal modified and cross-linked thermosets 3 whose pyrolysis
ꢀ
at 1100 C provided Pd
2
Si@SiCN.
Complex 2 was reacted with polysilazane HTT 1800 in THF
(
5 mL). Upon mixing of the complex with polysilazane, an
exothermic reaction takes place with effervescence and solution
gradually changes its color until it completely converts into
a black solid. The shape of the solid can be controlled by the
amount of solvent added. With a relatively small amount of
solvent more volume expansion and foaming were observed
which could be avoided by the addition of more solvent. GC
analysis of the gaseous products of the cross-linking reaction
shows predominance of hydrogen.
Fig. 3 FT-IR spectrum of HTT 1800 before and after the addition of
2
complex. The decrease in the intensities of Si–H and CH ]CH- vibra-
tions was observed upon the addition of the palladium complex.
dehydrocoupling mechanism as it will result in the retention of
carbon and nitrogen atoms within the ceramics. The use of free
radical initiators for the initiation of cross-linking could be
avoided by the use of the palladium aminopyridinato complex.
Kinetic studies of metal transfer reaction (cross-linking) were
The Seyferth group had reported on the dehydrocoupling
between Si–H bonds by the reaction of Ru (CO)12 with alkylsilyl
3
1
performed using H NMR. HTT 1800 was reacted with complex
48
hydrides. On the basis of hydrogen evolved during cross-linking
we assume the same kind of dehydrocoupling between Si–H
functions (besides cross-linking via hydrosilylation and vinyl
2
6 6
in deuterated benzene (C D ) and spectra were recorded after
every 2 min (Fig. 2a). The characteristic signals of the complex
gradually decrease in intensities until they are totally absent after
49
polymerization). FT-IR studies of the reaction of HTT 1800
with the palladium complex (Fig. 3) show the decrease in the
intensities of the vibrations characteristic of vinylic (2998–
2
0 minutes of reaction time. At this time, the spectrum of the
reaction mixture shows only the characteristic resonance signals
of the ligand (Fig. 2a and b). Moreover resonance of the –NH–
function, originally absent in the spectrum of the complex, again
appears at 3.89 ppm confirming the evolution of free protonated
ligand in the reaction mixture. This liberation of ligand provides
indirect evidence of the transfer of palladium to the nitrogen
functions of polysilazane most probably due to the availability of
more coordination sites in the polymer. Based upon aforemen-
tioned observations, it may be concluded that the palladium
complex chemically modifies the polysilazane by coordination of
palladium to its nitrogen atoms. The solvent free, metal modified
and cross-linked polysilazane was then shifted to a furnace for
pyrolysis.
À1
À1
À1
3
084 cm ), Si–H (2150 cm ) and N–H (3300–3500 cm ) bonds.
This supports the hydrosilylation and dehydrocoupling cross-
linking mechanisms to be operative and the formation of Pd
amides. Improved yields of the ceramics also support the
Pyrolysis and ceramization
The metal modified cross-linked polymers were heated under
À1
nitrogen atmosphere in a furnace with a heating rate of 5 K min
ꢀ
up to 1100 C to get an amorphous metal containing SiCN
ceramics.
2
Characterization of Pd Si@SiCN
Thermogravimetric analysis (TGA). TGA analysis of the cross-
À1
linked precursors was carried out with a heating rate of 5 K min
ꢀ
up to 1100 C under nitrogen atmosphere (Fig. 4). Major mass
ꢀ
1
Fig. 2 (a) H NMR spectra of the reaction mixture (HTT 1800 and
loss (21–26%) occurs between 100 and 730 C and may be
complex 2 in benzene) at different time intervals; (b) schematic repre-
sentation of metal transfer reaction which produces metal modified
polysilazane (4) by the reaction of palladium aminopyridinato complex 2
with HTT 1800 3. The palladium is transferred to the nitrogen functions
of the polymer with the liberation of protonated ligand 1.
attributed to the loss of gases (methane, ammonia and
5
0
ꢀ
hydrogen). Above 730 C, the observed mass loss was only 1.2–
1.5% giving ceramic yields of 78% (Pd100-FC, curve b) and 73%
(Pd20-FC, curve a). Theoretically speaking, a total yield of 65%
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ꢀ
Fig. 5 Powder XRD of ceramics (pyrolysed at 1100 C under nitrogen
atmosphere) in comparison to the simulated powder XRD pattern of
ꢀ
ꢀ
ꢀ
ꢀ
hexagonal Pd
2
Si, the most intense peaks at 38.1 , 41.4 and 42.4
ꢀ
correspond to (201), (210) and (300) planes. *: reflections at 20.8 , 26.8
ꢀ
and 36.5 may be assigned to quartz.
Fig. 4 TGA analysis of Pd20-FC (8 wt% Pd) in comparison with Pd100-
ꢀ
FC (2 wt% Pd); major mass loss occurs between 100 and 730 C giving
ceramic yields of 78% for Pd100-FC (b) and 73% for Pd20-FC (a).
polymorph (a-Pd Si). The formation of the hexagonal Pd Si
2
2
phase could be the result of the interaction of amorphous SiCN
ꢀ
was expected in the case of Pd20-FC assuming the total loss of
ligand and complete retention of palladium during ceramization.
An increase in yield by 8% suggests that ligand is not totally lost
during ceramization and contributes towards ceramic yield. This
may be attributed to the retention of silicon and palladium atoms
contained by the ligand during pyrolysis. Moreover, the evolu-
tion of hydrogen during cross-linking reaction suppresses the
with palladium at a pyrolysis temperature of 1100 C. In our
32
previous report, formation of the metallic phase instead of
metal silicide phases was confirmed by powder XRD and solid
state copper NMR studies.
In fact, formation of copper silicide requires much higher
53
amount of loaded copper (>80 wt%) within the system which is
very unlikely at a maximal copper loading of 13.7% in the
32
Cu@SiCN system.
ꢀ
emission of methane and ammonia (at 300–500 C) gases
resulting in the retention of carbon and nitrogen atoms. The loss
ꢀ
of oligomers in the temperature regime of 100–300 C is avoided
owing to the efficient cross-linking of polysilazane by the palla-
dium complex. It is evident from TGA data (Fig. 4) that as
expected, ceramic yield decreases with the increase in the amount
of the complex.
Powder X-ray diffraction (Powder XRD). Powder XRD of
palladium containing SiCN ceramics was carried out to confirm
the amorphous nature of the matrix as well as the presence of the
metallic phase. The reflection pattern of the cubic phase of
palladium was totally absent in the diffractograms and reflec-
tions characteristic of the hexagonal phase of Pd Si were
2
observed. Powder XRD data of dipalladium silicide (Pd Si) were
2
51
simulated from the single crystal XRD data and were used as
reference for the interpretation of powder XRD results (Fig. 5).
ꢀ
ꢀ
ꢀ
ꢀ
The peaks at 2q values of 38.1 , 41.4 , 42.4 and 48.5 in Pd20-
FC (8 wt% Pd) can be assigned to the reflections of (201), (210),
(
2
300) and (110) planes of hexagonal Pd Si. With the decrease in
the amount of metal within the support, only the most intense
ꢀ
ꢀ
ꢀ
peaks at 38.1 , 41.4 and 42.4 can be seen in the diffractograms
of all the Pd Si@SiCN composites synthesized. Reflection
patterns corresponding to other silicide phases (PdSi and Pd Si),
as evident from the phase diagram of the Pd–Si system, are not
2
3
52
ꢀ
ꢀ
ꢀ
found in powder XRD. Reflections at 20.8 , 26.8 and 36.5 may
be assigned to quartz. The formation of quartz may arise because
of the exposure of thermosets to air during their transfer to
Fig. 6 TEM micrographs of ceramic materials. (a) SiCN ceramic
without palladium loading does not show any particles; (b) lower loading
of palladium (0.2 wt%, Pd1000-FC) decreases the density of particles
a furnace for pyrolysis. Palladium rich b-Pd
ꢀ
2
Si is stable in the
2
keeping their size in the same regime; (c) Pd Si particles uniformly
temperature regime of 1090–1404 C above which it melts
ꢀ
distributed over Pd20-FC (8 wt% Pd); (d) dipalladium silicide nano-
particles in Pd20-FC with particles size distribution.
congruently and below 1090 C it transforms to its silicon rich
1
8828 | J. Mater. Chem., 2011, 21, 18825–18831
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addition of palladium complex to the polymer no palladium
silicide particles are generated over the ceramic support. The
population density of the particles formed depends upon the
amount of metal complex reacted with the polymer (Fig. 6b)
keeping their size the same (16–18 nm).
Catalytic studies. In the case of palladium based nanoalloys,
55,56
5
4
both unsupported and supported Pd–Ga
have recently been
reported as efficient selective catalysts for semihydrogenation of
alkynes. The alloys of palladium with silicon are worth
mentioning here in this regard as these materials show excellent
catalytic activities for many reactions of industrial impor-
57–59
60
tance.
According to Bartok and co-workers
semi-
hydrogenation of alkynes over Pd–Si alloy provides better
selectivity in comparison to the Pd–Ge and pure palladium
catalysts. Baiker et al. found high conversion and selectivity for
Pd81Si19 alloy in the semihydrogenation of propargyl alcohol and
61,62
phenylacetylene in supercritical carbon dioxide.
silicide phases generated as a result of metal support interactions
in the Pd/SiO system have been reported to be selective catalysts
in semihydrogenation of phenylacetylene to styrene and for
Palladium
2
63
64–66
neopentane isomerization.
The group of Massardier reported
Fig. 7 (a–d) TEM micrographs of Pd20-FC synthesized in hexane
15 mL); a uniform distribution of palladium silicide particles over the
on the catalytic activity of palladium silicides containing Pd/SiC
67
catalysts for methane total oxidation. A promising feature of
(
ceramic has been shown at different magnifications in figures (a) and (b)
while figure (c) shows palladium silicide particles (ꢁ4 to 6 nm) with size
distribution.
palladium silicides is their chemical and electrochemical
68
stability which makes them ideal candidates as anode materials
69,70
for fuel cell applications.
TEM investigations. TEM micrographs of the samples provide
further insight into the microstructure of the supported palla-
dium silicide nanoparticles (Fig. 6 and 7). The size of the particles
generated on the ceramic support depends on the cross-linking
step. The two samples pyrolysed under same conditions but using
different solvents (in the cross-linking step) generate particles
with different sizes. On the other hand, samples with different
loadings of palladium but cross-linked under identical conditions
give the same size of the nanoparticles (Fig. 6b and d). Thus, size
can be controlled in terms of the nature of the solvent used for
the mixing of the palladium complex with polysilazane. Since the
palladium complex is highly soluble in THF, only a small
amount of the solvent (5 mL) was enough for its complete
dissolution. A much faster exothermic reaction takes place upon
the addition of palladium complex solution to the polymer
resulting in an immediate cross-linking along with the chemical
modification of polysilazane. The metal modified polymer upon
its pyrolysis generates palladium silicide particles with an average
size of 18 nm (Fig. 6d) with a uniform distribution over the
surface (Fig. 6c). In the case where hexane was used as solvent,
palladium complex requires a relatively large amount of solvent
Catalytic hydrogenation of ketones. Catalytic hydrogenation of
aromatic ketones to various products (Fig. 8a) was investigated
using the Pd Si@SiCN catalyst system. All the catalysts with
2
(
15 mL as compared to 5 mL of THF in the first approach) for its
dissolution. The nanoalloy particles generated in this case are
–6 nm in size (Fig. 7c) and are homogeneously distributed over
Fig. 8 (a) Schematic representation of catalytic hydrogenation of
ketones to different products; (b) hydrogenation of acetophenone
ꢀ
5
(
2 mmol) with 60 mg of catalyst at 75 C under 20 bar hydrogen for 24
the support with the population density comparable to those
synthesized using THF as solvent (Fig. 7a–d). When the amount
of THF was increased to 15 mL, the cross-linking took place with
a much slower rate but the particles generated were within the
same size regime (ꢁ18 nm). Thus it is the nature of the solvent
and not the extent of dilution which controls the size of the
particles formed. It is evident from Fig. 5a that without the
hours. The conversion decreases with decrease in the amount of palla-
dium contained by the ceramics; (c) hydrogenation of acetophenone
(
2 mmol) using Pd20-FC (120 mg) under 20 bar hydrogen pressure for
4 hours. The conversion increases with temperature keeping the selec-
2
tivity constant; (d) hydrogenation of acetophenone (2 mmol) with the
ꢀ
catalyst Pd20-FC (60 mg) under 20 bar hydrogen pressure at 75 C for 24
hours. The figure shows reusability of the catalyst up to six catalyst runs.
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Table 2 Hydrogenation of ketones using the catalyst Pd20-FC (8 wt%
ꢀ
decrease in activity was observed with an increase in alkyl chain
length and branching at alpha carbon of the ketone.
Pd) at 85 and 50 C; 1 mmol of substrate, 0.4 mL toluene and 60 mg of
catalyst were used under 40 bar hydrogen pressure
ꢀ
ꢀ
50 C
8
5 C
Acknowledgements
Sel
Sel
1
/
Sel
Conversion Sel
1
/
a
b
The authors are grateful to Justus Hermannsd o€ rfer for TEM
analysis, Kathrin Inzenhofer for TGA studies and Dr Wolfgang
Milius for powder XRD measurements. Financial support from
Deutsche Forschungsgemeinschaft (DFG, SPP 1181) is grate-
fully acknowledged. M. Zaheer is thankful to Higher Education
Commission of Pakistan (HEC) and Deutscher Akademischer
Austausch Dienst (DAAD) for the fellowship.
Substrate
Conversion
2
2
Acetophenone
Propiophenone
Valerophenone
Heptanophenone
100
100
100
98
99/1
99/1
99/1
99/1
99/1
99/1
46
48
42
33
11
4
99/1
99/1
99/1
99/1
99/1
99/1
2
2
-Methyl-1-propiophenone 100
,2-Dimethyl-1- 93
propiophenone
a
b
Conversion in mol% units. Sel
and other products respectively.
1 2
and Sel denote selectivity to alcoholic
Notes and references
1
2
3
R. Ferrando, J. Jellinek and R. L. Johnston, Chem. Rev., 2008, 108,
45–910.
Q. J. Sun, Y. A. Wang, L. S. Li, D. Wang, T. Zhu, J. Xu, C. Yang and
Y. Li, Nat. Photonics, 2007, 1, 717–722.
S. Coe, W.-K. Woo, M. Bawendi and V. Bulovic, Nature, 2002, 420,
8
a palladium loading ranging from 2 to 8 wt% (Pd100-FC to
Pd20-FC) show selective hydrogenation of ketones to alcoholic
products. Pd20-FC (8 wt% Pd) shows higher performance
8
M. Wuttig and N. Yamada, Nat. Mater., 2007, 6, 824–832.
00–803.
4
5
(
Fig. 8b) than other ceramics (Pd40-FC, Pd60-FC, Pd80-FC and
D. Alloyeau, C. Ricolleau, C. Mottet, T. Oikawa, C. Langlois,
Y. L. Bouar, N. Braidy and A. Loiseau, Nat. Mater., 2009, 8, 940–
Pd100-FC) and was selected for further studies. The conversion
increases both with the increase in catalyst amount and
temperature (Fig. 8c) but selectivity remains the same. Alkyl
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