Physicochemical and catalytic properties of ployaniline protonated with 12-molybdophosphoric acid

Abstract

Using acid–base-type doping of polyaniline with H₃PMo₁₂O₄₀, two series of catalyst samples were prepared. In series Sl the doping and polymerization were carried out simultaneously, leading to a uniform distribution of the dopant over the whole volume of the polymer. In series SII the doping was achieved by protonation of already formed polyemeraldine base with H₃PMo₁₂O₄₀. Since this process must involve diffusion in the solid matrix, the surface becomes enriched in heteropolyanions (Keggin units) due to their limited diffusivity. The examination of physicochemical properties of the samples by XP, EPR and FTIR spectroscopies indicated that the Keggin units incorporated into the polymer matrix retain their identity and represent catalytically active centres. The insertion of the dopant species increases the electrical conductivity of the polymer by several orders of magnitude. The catalytic activity was tested in ethyl alcohol conversion and both the products of acid–base [C₂H₄ and (C₂H₅)₂O] and redox (CH₃CHO) type reactions were observed. Owing to the surface enrichment of the SII series of catalysts their catalytic activity was much higher than that of samples of the Sl series nominally doped to the same level. In both types of catalysts the selectivity to the redox reaction product (CH₃CHO) was greatly enhanced in comparison with unsupported H₃PMo₁₂O₄₀.