화학공학소재연구정보센터
Journal of Catalysis, Vol.147, No.2, 544-551, 1994
Conjugated Polymer-Supported Catalysts - Polyaniline Protonated with 12-Tungstophosphoric Acid
New types of conjugated polymer supported catalysts were prepared from polyaniline and 12-tungstophosphoric acid. Two preparation methods were used : (i) chemical polymerization of aniline in the presence of H3PW12O40 and (ii) protonation of polyemeraldine base with H3PW12O40. UV-VIS, FTIR, and X-ray studies unequivocally prove the protonation of polyaniline with simultaneous incorporation of heteropolyacid (HPA) in the polymer. Molecular dispersion of HPA in polyaniline matrix via a protonation reaction results in effective blocking of acid-base centers since protonation results in the abstraction of the most acidic proton from the molecules of the acid. As a result, in the test reaction of isopropyl alcohol conversion the obtained catalyst exhibits very low acid-base activity and high selectivity (>90% in all cases) towards acetone. Redox activity depends on the preparation method and is higher for the samples prepared through protonation of polyemeraldine base because in this case heteropolyanions are bound only to the surface of the polymer. On the contrary, HPA introduced into the polymer matrix in situ during polymerization is evenly distributed on the surface and in the bulk, and the access of alcohol molecules to those HPA which are located in the bulk is more difficult. Redox activity of the catalyst with HPA distribution limited to the surface of the polymer is comparable to that observed in unsupported H3PW12O40 for the highest obtainable protonation levels and decreases with the decrease of HPA surface concentration. On the other hand, activation energy derived from the Arrhenius plot for the dehydrogenation reaction drops with the decrease of the HPA surface concentration and is ca. 40 kJ/mole in these catalysts as compared to ca. 70 kJ/mole calculated for unsupported H3PW12O40.