383 research outputs found
Control of Ni/Ce1-xMxOy catalyst properties via the selection of dopant M = Gd, La, Mg Part 1. Physicochemical characteristics
To elucidate the role of support composition in autothermal reforming of ethanol (ATR of C2H5OH), a series of Ni catalysts (Ni content 2–15 wt.%) supported on different ceria-based oxides (Ce1-xGdxOy, Ce1-xLaxOy and Ce1-xMgxOy; x = 0.1–0.9) were prepared. The synthetized materials were tested in ATR of ethanol at 200–700 °C. It was established that supports themselves show catalytic activity in ATR of C2H5OH and provide 10–15% yield of H2 at 700 °C. Upon the increase of Ni content from 2 to 15 wt.% the temperature of 100% ethanol conversion decreases from 700 tо 300 °С, hydrogen yield increases from 25 to 60%, the inhibition of С2-С3 by-products formation, as well as the promotion of decomposition of acetaldehyde occur. The enhancement of catalyst performance in ATR of C2H5OH has been observed in the next series of supports: Ce1-xMgxOy < Ce1-xGdxOy < Ce1-xLaxOy and with a decrease of x to an optimal value that correlates with the improvement of Ni active component reducibility. At 600 °C on 10Ni/Ce0.8La0.2O1.9 catalyst the H2 yield of 50% was achieved at C2H5OH conversion of 100%. Stable and high performance of developed catalysts in ATR of C2H5OH indicates the promise of their use in the production of hydrogen
Control of Ni/Ce1-xMxOy Catalyst Properties Via the Selection of Dopant M = Gd, La, Mg. Part 2. Catalytic Activity
To elucidate the role of support composition in autothermal reforming of ethanol (ATR of C2H5OH), a series of Ni catalysts (Ni content 2–15 wt.%) supported on different ceria-based oxides (Ce1-xGdxOy, Ce1-xLaxOy and Ce1-xMgxOy; x = 0.1–0.9) were prepared. The synthetized materials were tested in ATR of ethanol at 200–700 °C. It was established that supports themselves show catalytic activity in ATR of C2H5OH and provide 10–15% yield of H2 at 700 °C. Upon the increase of Ni content from 2 to 15 wt.% the temperature of 100% ethanol conversion decreases from 700 tо 300 °С, hydrogen yield increases from 25 to 60%, the inhibition of С2-С3 by-products formation, as well as the promotion of decomposition of acetaldehyde occur. The enhancement of catalyst performance in ATR of C2H5OH has been observed in the next series of supports: Ce1-xMgxOy < Ce1-xGdxOy < Ce1-xLaxOy and with a decrease of x to an optimal value that correlates with the improvement of Ni active component reducibility. At 600 °C on 10Ni/Ce0.8La0.2O1.9 catalyst the H2 yield of 50% was achieved at C2H5OH conversion of 100%. Stable and high performance of developed catalysts in ATR of C2H5OH indicates the promise of their use in the production of hydrogen
Quantum fluctuations of polarons on molecules
The dynamic Jahn-Teller splitting of the six equivalent polarons due
to quantum fluctuations is studied in the framework of the Bogoliubov-de Gennes
formalism. The tunneling induced level splittings are determined to be and for and
, respectively, which should give rise to observable effects in
experiments.Comment: REVTEX 3.0, 13 pages, to be published in Phys. Rev.
Carbonization and Regeneration of Mo/ZSM-5 Catalysts for Methane Dehydroaromatization
The character of carbonaceous deposits formed during methane dehydroaromatization reaction in the presence of Mo/ZSM-5 catalysts was studied by differential thermal analysis. The dependence of the concentration and condensation degree (C/H ratio) of the carbonaceous deposits on the catalyst synthesis conditions (Mo content = 1-10%, Si/Al ratio in the initial H-ZSM-5 = 17-45) and reaction conditions (feed flow
rate = 405-1620 h-1, methane concentration = 90-98%, reaction temperature = 720-780 °C) was investigated.
The oxidative treatment conditions of carbonized Mo/ZSM-5 catalysts providing stable operation of the
catalysts under multiple reaction-oxidative treatment cycles were selected
Structural Changes of Mo/ZSM-5 Catalysts During the Methane Dehydroaromatization
The structure changes of Mo/ZSM-5 catalysts with different Mo content (2 and 10 wt. % Mo) and Si/Al atomic ratio (17, 30 and 45) during the methane dehydroaromatization have been investigated by X-ray powder diffractometry, N2 adsorption and transmission electron microscopy. The treatment of Mo/ZSM-5 catalysts in reducing atmosphere (CH4 or H2) at about 700 oC promotes development of mesoporous system. The pores are open to the exterior of the zeolite grain and have an entrance diameter of ~ 4-10 nm. It is proposed that mesopore formation in Mo/ZSM-5 catalyst is connected with the dealumination of zeolite. The mesopore formation in the parent H-ZSM-5 zeolite by NaOH treatment does not improve the activity of /ZSM-5 catalyst
Deactivation and Regeneration of Mo/ZSM-5 Catalysts for Methane Dehydroaromatization
The methane dehydroaromatization (DHA) was studied over a series of impregnated Mo/ZSM-5 catalysts with different molybdenum contents (1-10 wt.%). It was shown that total methane conversion was decreased by 30% during 12 h of DHA reaction. The benzene formation rate was increased from 0.5 to 13.9 mol C6H6/(gMo·s) when the molybdenum content in the catalyst was lowered from 10 to 1 wt.%. The deactivated Mo/ZSM-5 catalysts were studied by a group of methods: N2 adsorption, XRD, TGDTA, HRTEM and XPS. The content and condensation degree (C/H ratio) of the carbonaceous deposits was found to increase with an increase of either of the following parameters: molybdenum content (1-10 wt.%), reaction temperature (720-780 °C), space velocity (405-1620 h-1), reaction time (0.5-20 h). The stability of Mo/ZSM-5 catalysts in reaction-regeneration cycles was better when the time on stream was shorter. The regeneration conditions of deactivated Mo/ZSM-5 catalysts providing their stable operation under multiple reaction-regeneration cycles have been selected
Observation and Assignment of Silent and Higher Order Vibrations in the Infrared Transmission of C60 Crystals
We report the measurement of infrared transmission of large C60 single
crystals. The spectra exhibit a very rich structure with over 180 vibrational
absorptions visible in the 100 - 4000 cm-1 range. Many silent modes are
observed to have become weakly IR-active. We also observe a large number of
higher order combination modes. The temperature (77K - 300K) and pressure (0 -
25KBar) dependencies of these modes were measured and are presented. Careful
analysis of the IR spectra in conjunction with Raman scattering data showing
second order modes and neutron scattering data, allow the selection of the 46
vibrational modes C60. We are able to fit *all* of the first and second order
data seen in the present IR spectra and the previously published Raman data
(~300 lines total), using these 46 modes and their group theory allowed second
order combinations.Comment: REVTEX v3.0 in LaTeX. 12 pages. 8 Figures by request. c60lon
Theory of Superconducting of doped fullerenes
We develop the nonadiabatic polaron theory of superconductivity of
taking into account the polaron band narrowing and realistic
electron-phonon and Coulomb interactions. We argue that the crossover from the
BCS weak-coupling superconductivity to the strong-coupling polaronic and
bipolaronic superconductivity occurs at the BCS coupling constant independent of the adiabatic ratio, and there is nothing ``beyond'' Migdal's
theorem except small polarons for any realistic electron-phonon interaction. By
the use of the polaronic-type function and the ``exact'' diagonalization in the
truncated Hilbert space of vibrons (``phonons'') we calculate the ground state
energy and the electron spectral density of the molecule. This
allows us to describe the photoemission spectrum of in a wide
energy region and determine the electron-phonon interaction. The strongest
coupling is found with the high-frequency pinch mode and with the
Frenkel exciton. We clarify the crucial role of high-frequency bosonic
excitations in doped fullerenes which reduce the bare bandwidth and the Coulomb
repulsion allowing the intermediate and low-frequency phonons to couple two
small polarons in a Cooper pair. The Eliashberg-type equations are solved for
low-frequency phonons. The value of the superconducting , its pressure
dependence and the isotope effect are found to be in a remarkable agreement
with the available experimental data.Comment: 20 pages, Latex, 4 figures available upon reques
New measurements of thousand-seed weights of species in the Pannonian flora
For understanding local and regional seed dispersal and plant establishment processes and for considering the ecotypes and other forms of specific variability, hard data of locally or regionally measured traits are necessary. We provided newly measured seed weight data of 193 taxa, out of which 24 taxa had not been represented in the SID, LEDA or BiolFlor databases. Our new measurements and formerly published data of locally collected seed weight records together covers over 70% of the Pannonian flora. However, there is still a considerable lack in seed weight data of taxonomically problematic genera, even though they are represented in the Pannonian flora with a relatively high number of species and/or subspecies (e.g. Sorbus, Rosa, Rubus, Crataegus and Hieracium). Our regional database contains very sporadic data on aquatic plants (including also numerous invasive species reported from Hungary and neighbouring countries) and some rare weeds distributed in the southwestern part of the country. These facts indicate the necessity of further seed collection and measurements
Investigating Sub-Spine Actin Dynamics in Rat Hippocampal Neurons with Super-Resolution Optical Imaging
Morphological changes in dendritic spines represent an important mechanism for synaptic plasticity which is postulated to underlie the vital cognitive phenomena of learning and memory. These morphological changes are driven by the dynamic actin cytoskeleton that is present in dendritic spines. The study of actin dynamics in these spines traditionally has been hindered by the small size of the spine. In this study, we utilize a photo-activation localization microscopy (PALM)–based single-molecule tracking technique to analyze F-actin movements with ∼30-nm resolution in cultured hippocampal neurons. We were able to observe the kinematic (physical motion of actin filaments, i.e., retrograde flow) and kinetic (F-actin turn-over) dynamics of F-actin at the single-filament level in dendritic spines. We found that F-actin in dendritic spines exhibits highly heterogeneous kinematic dynamics at the individual filament level, with simultaneous actin flows in both retrograde and anterograde directions. At the ensemble level, movements of filaments integrate into a net retrograde flow of ∼138 nm/min. These results suggest a weakly polarized F-actin network that consists of mostly short filaments in dendritic spines
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