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 we re used: (i) chemical polymerization of aniline in the presence of H3P W12O40 and (ii) protonation of polyemeraldine base with H3PW12O40. UV- VIS, FTIR, and X-ray studies unequivocally prove the protonation of po lyaniline with simultaneous incorporation of heteropolyacid (HPA) in t he polymer. Molecular dispersion of HPA in polyaniline matrix via a pr otonation 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 a cid-base activity and high selectivity (>90% in all cases) towards ace tone. Redox activity depends on the preparation method and is higher f or the samples prepared through protonation of polyemeraldine base bec ause in this case heteropolyanions are bound only to the surface of th e 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 compara ble to that observed in unsupported H3PW12O40 for the highest obtainab le protonation levels and decreases with the decrease of HPA surface c oncentration. On the other hand, activation energy derived from the Ar rhenius plot for the dehydrogenation reaction drops with the decrease of the HPA surface concentration and is ca. 40 kJ/mole in these cataly sts as compared to ca. 70 kJ/mole calculated for unsupported H3PW12O40 . (C) 1994 Academic Press, Inc.