XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
164
T1: P–31
Pd-containing Si-C-N-O systems prepared by preceramic polymer
route: physicochemical and catalytic properties
Aleksandra Chechelska
1
, Justyna Olejarka
1
, Maria Owińska
1
, Joanna Strzezik
2
,
Mateusz Marzec
3
, Andrzej Bernasik
4
, and Magdalena Hasik
3
1
Faculty of Materials Science and Ceramics, AGH-University of Science and Technology,
Al. Mickiewicza 30, 30-059 Kraków, Poland, e-mail: acheche@agh.edu.pl
2
Faculty of Chemistry, Silesian University of Technology, ul. ks. M. Strzody 9, 44-100 Gliwice,
Poland
3
Academic Centre for Materials and Nanotechnology, AGH-University of Science and Technology,
Al. Mickiewicza 30, 30-059 Kraków, Poland
4
Faculty of Physics and Applied Computer Sciences, AGH-University of Science and Technology,
Al. Mickiewicza 30, 30-059 Kraków, Poland
Since its beginning, more than 40 years ago, polymer-derived ceramics (PDC) has evolved
into a mature field of science. It still, however, offers new possibilities to the researchers. PDC
are prepared by high temperature decomposition (i.e. pyrolysis) of appropriate polymers
containing organic groups in their molecules [1]. Organosilicon polymers, namely:
polycarbosilanes, polysiloxanes and polysilazanes, are the most widely applied precursors to
ceramics. Their pyrolysis leads to SiC, Si–C–O and Si–C–N systems, respectively. Importantly,
in order to get high yields of ceramic materials, cross-linked precursors should be used.
In the present work, Pd-containing Si–C–N–O materials were prepared by pyrolysis of
polysiloxane-silazane networks with incorporated Pd particles. The initial networks were
obtained by cross-linking of poly(methylhydrosiloxane) with 1,3-divinyldisilazane at two molar
ratios of Si–H to Si-vinyl groups equal to 1.5:1 and 6:1. The resulting systems were treated with
palladium(II) acetate solution in THF at room temperature in Ar atmosphere. This led to the
formation of polysiloxane-silazane networks with incorporated Pd particles. They were
pyrolyzed in the quartz tube furnace in the flow of gaseous nitrogen at the temperatures of 380,
550, 700 and 1000°C.
All the obtained materials were characterized by FTIR and XPS spectroscopies, X-ray
diffraction, scanning electron microscopy and elemental analysis. Based on the results of these
studies it was established that in the initial networks silazane moieties were present and
unreacted Si-H groups were preserved. Pd incorporation process was accompanied by the
formation of metallic Pd which occurred due to the reducing properties of Si-H groups
remaining in the systems. The presence of Pd significantly improved the yields of materials
obtained after pyrolysis at various temperatures as compared to the initial networks pyrolyzed at
the same temperatures.
The materials with incorporated Pd particles were applied as catalysts in isopropyl alcohol
conversion. This reaction allows to test the acidic and redox activity of a catalyst [2]. It was
found that all the Pd-containing systems prepared in the work are active in this process. The
prevailing type of activity depends, however, on the temperature at which the sample was
obtained. The initial materials are mainly redox, whereas after pyrolysis they turn into
predominantly acidic catalysts.
Keywords: polysiloxanes; polysilazanes; palladium catalysts
Acknowledgment
The work was financially supported by Polish National Science Center (NCN) project number
014/13/B/ST5/01924
References
[1] P. Colombo, G. Mera, R. Riedel, G. D. Sorarú, J. Am. Ceram Soc. 93 (2010)1805.
[2] W. Turek, A. Krowiak, Appl. Catal. A : General 417–418 (2012) 102.
XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
165
T1: P–32
Comparative studies on incorporation of platinum particles
into polysiloxane networks synthesized in different conditions
Edyta Stochmal
1
, and Anna Gruza
1
1
Faculty of Materials Science and Ceramics, AGH-University of Science and Technology,
Al. Mickiewicza 30, 30-059 Kraków, Poland, e-mail: stochmal@agh.edu.pl
Synthesis of polysiloxane networks with the simultaneous introduction of metallic platinum
was carried out. Metallic Pt particles were created by reduction of platinum ions by the Si-H
groups present in the systems. The products were synthesized and examined for applications as
metallic heterogeneous catalysts.
The statistical copolymer – D
4
/V
4
polysiloxane synthesized by equilibrium cationic ring-
opening polymerization of the corresponding cyclotetrasiloxane monomers was applied for the
cross-linking. The selected – linear (
H
MM
H
) or cyclic (D
4
H
) – hydrosiloxanes of different
molecule geometry as well as different functionality acted as cross-linking agents and as
reducing agents of platinum ions simultaneously. Pt ions were introduced into the reaction
system from PtCl
4
in THF solution. The influence of various synthesis parameters such as the
type of cross-linking agent used, the order of introduction of reagents into the reaction medium,
the amount of platinum introduced, etc. on the physicochemical properties of the products were
tested.
Different analytical methods were applied for the characterization both networks and
platinum species obtained during synthesis. The control of platinum ions reduction was
monitored by UV-vis spectroscopy. The presence of characteristic functional groups (created
during the cross-linking process or participating in it) was examined using IR spectroscopy. The
presence of metallic platinum was explored by X-ray diffraction studies. SEM and TEM
methods were applied for the investigation of platinum particles dispersion. Thermal stability of
products was determined with the application of thermogravimetric analysis. Swelling tests were
performed to compare the cross-linking degree of networks in the obtained products.
As a result of described syntheses, polysiloxane matrices containing platinum metal particles
with the size of a few nanometers were obtained. Better dispersion of metal particles was
achieved for materials obtained using cyclic cross-linking agent. The formation of different
amounts of soluble fractions in the systems depending on the type of cross-linking agent used
has been found. In some cases the formation of polytetrahydrofuran as a by-product has been
also identified [1, 2]. Swelling investigations have shown varying cross-linking degrees of
polysiloxane matrices in the resulting systems, depending on the synthesis parameters (e.g. the
time of synthesis or the order of reagents introduction). The last observation was confirmed
additionaly by the results of thermogravimetric studies – more thermally stable systems were
obtained using a linear cross-linking agent.
Some results of experiments performed were compared with the results obtained for the
similar Pt-containing systems but received using two-step method [3], in which the introduction
of platinum is preceded by the synthesis of the polysiloxane network.
Keywords: polysiloxane networks; platinum; synthesis
References
[1] G. Steiner, C. Zimmerer, Polymer Solids and Polymer Melts - Definitions and Physical Properties,
Springer - Verlag Berlin Heidelberg Eds. K.F.Arnt, M.D. Lechner (2013) 864-870.
[2] J. Turley, Dow Chemical Company, Midland, MI, USA., Private Communication (1965).
[3] E. Stochmal, J. Strzezik, A. Krowiak, J. Appl. Polym. Sci. 133 (2016) 1.
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