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Abstract. Various aspects of the problem of reliability of the standards for spin dosimetry in solid samples containing transition metal ions are discussed. A method of preparing standards for d 1 and d 9 ions, based on vanadyl-and copper sulfate, is described. Reference samples with va¡ spin concentration were prepared by uniform distribution of the paramagnetic substance in a diamagnetic, chemically unreactive matrix. The testing of the quality of standards was performed by statistical methods considering the following factors: reproducibility of the average chemical composition between preparafions, macro-and microhomogeneity within preparations and precision of EPR measurements. The statistical analysis proved good quality of the standards produced by the elaborated method except for microinhomogeneity. Several examples ate given to illustrate application of spin dosimetry in catalysis research. E.g., two different centers of reduced vanadium in vanadia-molybdena catalysts, V(IV) stabilized by oxygen vacancies and V(IV) stabilized by Mo(VI) ions, respectively, were identified. The kinetic model of redox processes occurring in V205-MoO3 catalysts upon interaction with oxygen and propylene was proposed. Quantitative determination of isolated Co(II) ions in CoO-MgO solid solutions revealed a strong correlation between the number of these ions and the amount of adsorbed O~ species.

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Undoped and alkali-doped zirconia-supported vanadia catalysts for the oxidative dehydrogenation of propane were prepared by impregnation and characterized by various techniques. The chemical state of surface and bulk vanadium was investigated as a function of the calcination temperature, V2O5 loading, and the nature and content of alkali-metal additives. It is found that on the surface vanadium is present in the form of isolated vanadyl species or oligomeric vanadates, or as nanocrystalline V2O5 and that V5+ and V4+ ions coexist in octahedral and tetrahedral coordination, while within the bulk of zirconia matrix, V4+ ions are stabilized in a V x Zr1 - x O2 solid solution. Presence of the alkali-metal additives and water changes the dispersion of surface vanadium species favoring, in both cases, formation of mononuclear vanadyl surface complexes. Surface heterogeneity plays a vital role for the catalytic performance of V2O5/ZrO2 catalysts in oxidative dehydrogenation of propane. Catalytic properties are related to the nature of VO x surface species and correlates well with their reducibility. The maximum of catalytic activity was observed for catalysts with vanadia content between 3 and 5 mol %, for which octahedral polyvanadate surface species are dominant. It is proposed that the catalytic activity is affected by the nucleophilicity of bridging oxygen in V−O−V entities, modified by the adjacent alkali cations.

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Electron paramagnetic resonance (EPR) spectroscopy, with Cu 21 ions as a paramagnetic probe, was applied to study the process of radical generation in starch and changes occurring in its structure upon thermal treatment and oxidation. Thermally generated radicals in starch containing Cu 21 ions are localized on carbon atoms different from those in the pure starch. EPR signal parameters of the radical species (g av = 2.0047 -2.0049; A av = 0.9 -1.0 mT) suggest a lower number of oxygen atoms in the vicinity of radical centres than that observed in pure starch and weakening of the interaction of the unpaired electron with the nuclear magnetic moment of the b hydrogen (for pure starch g av = 2.0059 -2.0065; A av = 1.2 -1.3 mT). A mechanism of thermal generation of radicals in the native and oxidized starch containing Cu 21 ions was proposed. It consists of breaking of RCO-Cu 21 or RCOO-Cu 21 bonds in the native and oxidized starch, respectively, reduction of Cu 21 to Cu 1 ions and formation of transient RCO. or RCOO. species, active in abstraction of hydrogen from the neighbouring C atom of the glucose unit, at which the unpaired electron became localized.