Yurii D. Perfiliev

Influence of copper and potassium on the structure and carbidisation of supported iron catalysts for Fischer–Tropsch synthesis

This paper addresses the effect of promotion with copper and potassium on the carbidisation kinetics, structure and performance of silica supported iron catalysts for high temperature Fischer–Tropsch synthesis. The promotion with copper and potassium results in the enhancement of iron dispersion. Small hematite nanoparticles were uncovered in the calcined iron catalysts. Activation of the calcined catalysts in carbon monoxide or syngas results in the reduction of hematite to magnetite at 250–300 °C. The magnetite is then carbidised into Hagg iron carbide. The promotion with copper and potassium affects the rate of the iron reduction and carbidisation. Copper strongly enhances both hematite reduction and magnetite carbidisation in carbon monoxide and syngas. The presence of potassium hinders reduction of hematite to magnetite. Much higher reaction rates were observed on copper-promoted catalysts than on the potassium-promoted and unpromoted counterparts while the promotion with potassium had a stronger impact on the selectivity.

Cobalt(II) complexation with small biomolecules as studied by 57Co emission Mössbauer spectroscopy

In the emission (57Co) variant of Mössbauer spectroscopy (EMS), the 57Co radionuclide (with a half-life of 9months) is used that undergoes a nuclear decay 57Co→57Fe via electron capture followed by the emission of a γ-quantum, the energy of which is modified by the chemical state and the close coordination environment of the parent 57Co atom. While EMS has been used largely in materials science and nuclear chemistry, its high sensitivity can also be of great advantage in revealing fine structural features and for speciation analysis of biological complexes, whenever the 57Co2+ cation can be used directly as the coordinating metal or as a substitute for native cobalt or other metal ions. As such EMS applications are yet rare, in order to reliably interpret emission spectra of sophisticated 57Co2+-doped biosystems, model EMS studies of simple cobalt biocomplexes are necessary. In this work, EMS spectroscopic data are analysed and discussed for 57Co2+ complexes with a range of small biomolecules of different structures, including 4-n-hexylresorcinol, homoserine lactone and a few amino acids (spectra measured in rapidly frozen dilute aqueous solutions or in the dried state at T=80K). The EMS data obtained are discussed with regard to the available literature data related to the coordination modes of the biocomplexes under study.

Mössbauer spectroscopic study of transformations of iron species by the cyanobacterium Arthrospira platensis (formerly Spirulina platensis)

In the present paper, Mössbauer spectroscopic studies of dry biomass samples of the cyanobacterium Arthrospira platensis (formerly known as Spirulina platensis) were performed with regard to metabolic iron accumulation. 57Fe Mössbauer parameters of iron in the biomass correspond to ferrihydrite. Spectra of iron hydroxides in A. platensis biomass differ from those of iron complexes with ethylenediaminetetraacetic acid injected to Zarrouk culture medium. The limit of saturation of A. platensis trichomes with iron in the form of ferrihydrite was found to be 5 μg/ml (0.09 μmol/ml) Fe in the culture medium. Conglomerates precipitated in the medium at higher iron concentrations also contain ferrihydrite but the ratio of the crystal lattice forms is different from that in the biomass.