Morphology and Conductivity of Polymeric Support as the Key Factors Modifying Catalytic Activity of Keggin Type Heteropo
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Morphology and Conductivity of Polymeric Support as the Key Factors Modifying Catalytic Activity of Keggin Type Heteropolyacids Dispersed in Poly(N-methylpyrrole) and Polypyrrole Matrices J. Strzezik Æ A. Krowiak Æ W. Turek Æ K. Kozieł Æ P. Szperlich
Received: 11 July 2008 / Accepted: 10 September 2008 / Published online: 15 October 2008 Ó Springer Science+Business Media, LLC 2008
Abstract This study concerns investigations of catalytic activity of heteropolyacids: H4SiW12O40 and H5PMo10V2O40 and their cupric and ferric salts deposited on conducting polymer supports: polypyrrole (PPy) and poly(N-methylpyrrole) (PMPy). Redox and acid–base properties of these catalysts were determined using a catalytic test reaction–– conversion of isopropyl alcohol. The results of catalytic studies together with analysis of conductivity and morphology of catalysts show the influence of factors mentioned above on the activity in parallel dehydration and dehydrogenation reactions of isopropyl alcohol. Keywords Heteropolyacids Conducting polymers Heterogeneous catalysis Isopropyl alcohol 1 Introduction The polymer matrix doped with components showing catalytic activity can significantly influence the catalytic J. Strzezik (&) A. Krowiak W. Turek K. Kozieł The Silesian University of Technology, ul. Strzody 9, 44-100 Gliwice, Poland e-mail: [email protected] A. Krowiak e-mail: [email protected] W. Turek e-mail: [email protected] K. Kozieł e-mail: [email protected] P. Szperlich The Silesian University of Technology, ul. Krasin´skiego 8, 40-019 Katowice, Poland e-mail: [email protected]
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properties of the active species [1–3]. The properties of the matrix, which can change the catalytic activity, selectivity and kinetics of the processes are: electric conductivity, heat conductivity, porosity, steric factors, steric hindrance, substituents, vicinity of active centres (heteroatoms and functional groups), degree of crystallinity and the solubility of reactants in the matrix. Most of these factors are linked with each other for example electric conductivity and heat conductivity, steric hindrance and substituents, crystallinity and solubility of reactants [4–6]. High electrical conductivity of the matrix is important, especially in redox reactions. If the active substance, e.g., a heteropolyacid, has two types of centres: redox and acidbase, changes in conductivity of the polymer matrix, which affect mainly redox properties of the catalyst, have an influence on the selectivity of reactions over these catalysts. Changes in electrical conductivity are usually correlated with changes in heat conductivity. Heat conductivity is an important feature of the catalyst, especially in exothermic reactions in the gas phase. If the catalyst (with the matrix) has low heat conductivity it cannot be used in these reactions [7]. Porosity of catalysts has an influence on the diffusion of reactants inside crystallites. It can change the kinetics of the processes (determine whether at a given temperature the
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