The effect of surface oxidation on the catalytic properties of Ga3Ni2 intermetallic compound for carbon dioxide reduction

Background: In a routine handling of a catalyst material, exposure to air can usually not be avoided. For noble metal catalysts that are resistant to oxidation, this is not an issue, but becomes important for intermetallic catalysts composed of two or more non-noble chemical elements that possess much different standard enthalpies of the oxide formation. The element with higher affinity to oxygen concentrates on the surface in the oxide form, whereas the element with lower affinity sinks into the subsurface region. This changes the number of active sites and the catalytic performance of the catalyst. We have investigated the instability of the surface composition to oxidation of the Ga3Ni2 noble metal-free intermetallic compound, a new catalyst for the CO2 reduction to CO, CH4 and methanol. Methods: The instability of the oxidized Ga3Ni2 surface composition to different heating-annealing conditions was studied by X-ray photoelectron spectroscopy (XPS), used to determine the elemental composition and the chemical bonding in the near-surface region. The dispersion of active sites available for the chemisorption of H-2 and CO on the Ga3Ni2 catalyst surface was determined by H-2 and CO temperature-programmed desorption. CO2 conversion experiments were performed by using the catalyst material reduced in hydrogen at temperatures of 300 and 600 degrees C. Results: XPS study of the Ga3Ni2 surface subjected to different heating-annealing conditions has revealed that the concentration of Ga at the oxidized surface is strongly enhanced and the concentration of Ni is strongly depleted with respect to the values in the bulk. By annealing the surface at 600 degrees C in ultra-high vacuum, the oxides have evaporated and thermal diffusion of atoms near the surface has partially reconstructed the surface composition towards the energetically more favorable bulk value, whereas annealing at a lower temperature of 300 degrees C was ineffective to change the surface composition. Catalytic tests were in agreement with the XPS results, where an increased CO2 conversion for the catalyst reduced with hydrogen at a higher temperature followed an increased Ni/Ga surface concentration ratio. Conclusions: The instability of the active surface chemical composition to oxidation in air must be taken into account when considering noble metal-free intermetallic catalysts as alternatives to the conventional catalysts based on noble metals. Ga3Ni2 and other Ga-Ni intermetallic compounds are good examples of binary intermetallic catalysts, whose catalytic performance is strongly affected by exposure to the air

RESPONSE OF A UTERUS TO IMPACT LOADING DURING PREGNANCY

INTRODUCTION: The improvement of pregnant women's safety in work, leisure and physical activities is an important issue in any society. Impact loading of a pregnant uterus often causes various complications during pregnancy, including a possible unwanted miscarriage. The determination of the vibration frequency of the uterus during pregnancy is relevant for further mathematical-physical interpretation. METHODS: A high-frequency cinematographic recording of a pregnant uterus' response to a defined impact loading was analyzed using a film analyzer. A pregnant uterus, inclusive of the topically relevant organs (5.1 kg), was represented by a pregnant woman in the presence of a gynecologist. The impact load was realized by standing on tiptoe and free fall on the heels. RESULTS: The selected behavioral characteristics of the examined object are as follows: - impulse 2.72 Ns - T – period 0.933 s - amplitude 0.009 m - frequency 1.07 Hz - absorption 6.73 s-1 The real angular frequencies that are necessary for the assessment of the risk frequency zone of vibrations proved to be relevant for further practical interpretation, as well as the viscous absorption coefficient reflecting value changes in the volitional activity of an individual, which can be changed in relation to the perception of external conditions. For this we do not have a correct value. CONCLUSIONS: Regarding the methodological difficulty, the above-mentioned characteristics must be considered limiting. First, it will be made more accurate, and then it will be used in mathematical modeling of the impact loading of a pregnant uterus and will contribute to solving the risky physical routines of pregnant women in the area of sports, leisure and work activities

Complex magnetism of single-crystalline AlCoCrFeNi nanostructured high-entropy alloy

Summary: We have investigated magnetism of the Al28Co20Cr11Fe15Ni26 single-crystalline high-entropy alloy. The material is nanostructured, composed of a B2 matrix with dispersed spherical-like A2 nanoparticles of average diameter 64 nm. The magnetism was studied from 2 to 400 K via direct-current magnetization, hysteresis curves, alternating-current magnetic susceptibility, and thermoremanent magnetization time decay, to determine the magnetic state that develops in this highly structurally and chemically inhomogeneous material. The results reveal that the Cr-free B2 matrix of composition Al28Co25Fe15Ni32 forms a disordered ferromagnetic (FM) state that undergoes an FM transition at TC≈ 390 K. The Al- and Ni-free A2 nanoparticles of average composition Co19Cr56Fe25 adopt a core-shell structure, where the shells of about 2 nm thickness are CoFe enriched. While the shells are FM, the nanoparticle cores are asperomagnetic, classifying into the broad class of spin glasses. Asperomagnetism develops below 15 K and exhibits broken-ergodicity phenomena, typical of magnetically frustrated systems

Genome sequence of a lethal strain of xylem-invading Verticillium nonalfalfae

Verticillium nonalfalfae, a soilborne vascular phytopathogenic fungus, causes wilt disease in several crop species. Of great concern are outbreaks of highly aggressive V. nonalfalfae strains, which cause a devastating wilt disease in European hops. We report here the genome sequence and annotation of V. nonalfalfae strain T2, providing genomic information that will allow better understanding of the molecular mechanisms underlying the development of highly aggressive strains