Chemistry - A European Journal
10.1002/chem.201702790
COMMUNICATION
The BET measurements were recorded on a Physisorption analyzer
ASAP 2010 from Micromeritics.
In addition, the preparation of the catalysts at different times
using the same conditions give relevant information about the
reproducibility of the method. The urea - d-glucose based
Pd/CNO catalysts were prepared three times at 440 °C by
nozzle and Table 4 shows, that it is possible to reproduce the
catalyst activity using this method.
In conclusion, the reported protocol shows the preparation of a
Pd/CNO catalyst by a simple single step method based on deep
eutectic solvents, to the best of our knowledge, for the first time.
In contrast to the commercial Pd/C, the catalyst activity can be
influenced by many preparation parameters regarding the
desired application field. It has to be investigated, if the
preparation temperature depends on the used substrates as well
and a further characterization of the supporting material is
necessary to understand the preparation mechanism in more
detail.
Activity Test Reactions
In a round-bottom flask, 1 mmol of the 1-dodecene was dissolved in 5 mL
methanol and 25 mg of the different Pd/CNO catalysts were added. The
mixture was stirred at room temperature under hydrogen atmosphere
and the conversion was checked and proved by GC-MS by frequent
sampling for two hours.
To compare the activity of the catalysts, one sample was tested using a
commercial Pd/C catalyst with the same conditions.
Acknowledgements
Financial support of this work by the Bavarian Ministry of
Economic Affairs and Media, Energy and Technology and the
Center of Energy Storage is acknowledged.
Experimental Section
Chemicals
Keywords: deep eutectic solvents • supported metal catalyst
preparation • one step method • palladium
Commercial reagents and used chemicals were purchased from Sigma
Aldrich, Acros, TCI, VWR, Carl Roth, Merck or Alfa Aesar and used
without further purification.
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Flask Method
In a round-bottom flask equipped with a magnetic stirring bar, the DES
used was heated until a clear, homogeneous liquid was formed. In this
solvent a known amount of metal salt for a theoretical 10 w% loading was
dissolved. As soon as the palladium salt was completely dissolved the
mixture was heated under nitrogen atmosphere until 280 °C until a dry
porous material was formed. This material was further pyrolysed in a
muffle furnace at 440 °C under nitrogen atmosphere until a fine black
powder rises.
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A similar method, which is explained in this review is the flame
aerosol technology. A support and dopant precursur are necessary
to prepare supported nanoparticle catalysts. The difference to our
method is that mainly metal oxides are produced, while we use
reductive conditions to obtain the catalyst in metallic form.
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Nozzle Method
In a round-bottom flask equipped with a magnetic stirring bar, the DES
used was heated until a clear, homogeneous liquid was formed. In this
solvent a known amount of metal salt for a theoretical 10 w% loading was
dissolved. As soon as the metal salt was completely dissolved, the
mixture was transferred to a heated nebulization apparatus. By the use of
nitrogen pressure the mixture was sprayed on a heated surface and
further pyrolysed in a muffle furnace under nitrogen atmosphere at
different temperatures until a fine black powder rises.
[
10]
[
[
11]
12]
Characterization
The turnover of the test reactions were determined by GC-MS using a
BPX5 column (SGE, 30 m, I. D. 0.25 mm, film 0.25 µm) connected to a
QP2010 Plus gas chromatograph with a Single Quad MS-detector (both
Shimadzu, Japan) with helium as the carrier gas. 0.5 µL of the diluted
sample was automatically injected via SSL-injector (290 °C) starting at
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-
1
6
2
0 °C for 1 min, then heated to 170 °C at 11 °C min and finally to
2010, 48, 3313-3322.
70 °C at 70 °C min- and held for 3 min.
1
Scanning electron microscopy (SEM) was performed to determine the
morphologies of the supporting material (SE detector), the distribution of
the palladium on the support (BSE detector) and the composition of the
support with the EDX detector. The samples were mounted on carbon
tape and studied using a digital scanning electron microscope (Zeiss,
DSM 940 A, Oberkochen, Germany) and operated in secondary imaging
mode at 20 kV with a working distance of 33.0 mm.
Diffractogram measurements (XRD) were obtained by a general purpose
X-ray diffractometer (Rigaku, MiniFlex 600, Tokyo, Japan) equipped with
a high speed one-dimensional detector (Rigaku, D/teX Ultra, Tokyo,
Japan) and a Kβ foil filter. XRD patterns were recorded over the 2θ range
of 0°-90°, with a step width of 0.02°, a scanning speed of 2°/min and a
CuKα radiation generated at 40 kV and 15 mA. The measurements were
analyzed by the Rigaku PDXL software (Integrated X-ray powder
diffraction software).
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