Nanoparticles of Palladium in Polyacetylene or Polyaniline Matrix and Their Activity in Model Hydrogenation Reaction
|Andrzej Kosiński , Janusz W. Sobczak , Andrzej Biliński|
Polish Academy of Sciences, Institute of Physical Chemistry, Kasprzaka 52/56, Warszawa 01-224, Poland
In recent years a certain group of polymers with conjugated system of carbon bonds, has attracted the interest in academic and applied research. This is due to the electrical conductivity of those polymers. Its value may vary within over 16 orders of magnitude, from conductivity characteristic of isolators to that of typical metals in process called "doping".
These polymers, called also "synthetic metals", have found many technical applications, such as: rechargeable batteries without heavy metals, antistatic coatings, chemical sensors, light emitting diodes, etc. [1, 2].
Conducting polymers, when properly doped, can be attractive as a host for the catalyst particles since this medium provides an efficient route for the shutting of electronic charge to the catalyst centres. It has been shown that Pd modified polyaniline (PANI) or polyacetylene (PA) exhibits interesting catalytic character in highly selective semihydrogenation of alkyne to alkene CC bonds with a preferential (Z)-hexene stereoselectivity in olefine production. In such system a polymer has a role of "support" for catalytic material [3, 4].
In present work authors concentrated on PANI and PA doped with palladium as catalysis in hydrogenation reaction of alkynes. Polyaniline was doped with H2PdCl4 in H2O solution and polyacetylene, synthetized by Naarmann method, was doped with Pd(NO3)2 in acetonitrile solution.
Samples were examined by X-ray photoelectron spectroscopy (XPS), X-ray Diffraction (XRD), scanning electron microscopy (SEM), and infrared (IR). Catalytic activity was examined in semihydrogenation reaction of hexyne-2.
Both materials were catalytically active and selective in the triple to double CC semihydrogenation. Selectivity of triple CC bond transformed into double bond was over 80%.
The nature of catalytic sites depended on polymer and the procedure of polymer doping. According to the XPS and XRD analysis, Pd in polyaniline appeared mainly in PdCl42- complex with some minor amount of Pd cluster. The influence of moisture on the Pd doped PANI catalysts have been observed. Most active was the catalyst aged in dry atmosphere, during a long and slow process.
In polyacetylene XPS and XRD analysis show three palladium forms: metallic, clusters, and complex form. Form responsible for high selectivity in model hydrogenation reaction are small clusters (less then 1.0 nm). Even small content of metal form of palladium (less then 10%) lowers selectivity of specimen.
 A. MacDiarmid, Synth. Met. 1997, 84, 27.
Presentation: poster at 18th Conference on Physical Organic Chemistry, Posters, by Andrzej Kosiński
See On-line Journal of 18th Conference on Physical Organic Chemistry
Submitted: 2006-05-31 20:31 Revised: 2009-06-07 00:44