EPR and XPS measurements of polymeric catalysts doped with hereopolyacids in oxygen adsorption studies

The goal of our studies was to determine the nature of interactions between catalytic active samples, such as polypyrrole (PPy) doped with: chloride anions, heteropolyacids such as H ₅ PMo ₁₀ V ₂ O ₄₀ , or H ₄ SiW ₁₂ O ₄₀ , and oxygen particles. In order to reveal the mechanism of the linkage between the catalysts and oxygen we provided the electron paramagnetic resonance (EPR) measurements of synthesized samples in O ₂ and N ₂ flow. Moreover, the X-ray photoelectron spectroscopy (XPS) measurements were performed to show the properties of doped heteropolyacids and the state of nitrogen in polypyrrole matrix. The results of EPR studies of PPy(Cl), PPy(H ₄ SiW ₁₂ O ₄₀ ), PPy(H ₅ PMo ₁₀ V ₂ O ₄₀ ) samples, show that the polypyrrole doped with chloride anions interacts much easier with oxygen than polypyrrole doped with heteropolyacids (in the above given order, of preference with the most active polypyrrole system first). It correlates with XPS results, which show that a molybdenium-vanadium anion is more reduced than a silicon-tungsten one. The redox reactions of heteropolyacids involve the oxidation-reduction of the conjugated polymer chain, leaving no or little place for interactions with oxygen. Polypyrrole doped with H ₄ SiW ₁₂ O ₄₀ shows some oxygen sensitivity as observed in the EPR studies, as opposed to polypyrrole doped with H ₅ PMo ₁₀ V ₂ O ₄₀ , which is in line with the XPS results.