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

Abstract 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.