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Frey K.,Free University of Colombia | Frey K.,Institute of Isotope and Surface Chemistry of Hungary | Iablokov V.,Free University of Colombia | Safran G.,Research Institute for Technical Physics and Materials Science | And 5 more authors.
Journal of Catalysis | Year: 2012

Non-stoichiometric Mn-oxides (MnO x and MnO y) were prepared by temperature-programmed oxidation (TPO) of Mn-oxalates, MnC 2O 4·3H 2O and MnC 2O 4·2H 2O. Both oxides provide high specific surface areas (525 m 2 g -1 and 385 m 2 g -1, respectively) and identical CO oxidation reaction rates of 10 -2 molecules nm -2 s -1 (0.017 μmol CO m -2 s -1) at 298 K. A "spinodal" transformation of oxalates into oxides was observed by transmission electron microscopy (TEM). The quantitative evaluation of TPO and temperature-programmed reduction with CO allowed x-values of 1.61, ⋯, 1.67 to be determined for MnO x. The Mn oxidation state in MnO x was found to be 3.4 ± 0.1 by X-ray absorption near-edge structure analysis and X-ray photoelectron spectroscopy. In accordance with the high specific surface area and mixed-type I/IV adsorption isotherms of MnO x, high resolution TEM demonstrated the occurrence of nested micro-rod features along with nanocrystalline particles in the endings of the rods. After CO oxidation MnO and Mn 3O 4 phases were able to be identified in the regions between rods. © 2011 Elsevier Inc. All rights reserved.

Birsa Celic T.,Slovenian National Institute of Chemistry | Rangus M.,Slovenian National Institute of Chemistry | Lazar K.,Institute of Isotope and Surface Chemistry of Hungary | Kaucic V.,Slovenian National Institute of Chemistry | Zabukovec Logar N.,Slovenian National Institute of Chemistry
Angewandte Chemie - International Edition | Year: 2012

Crystal engineering: The synthesis of the known compounds MIL-100(Fe) and MIL-45(Fe) is characterized by spectroscopy. The products are obtained under identical conditions by varying the solvent from pure water to a mixture of water and acetone. The starting solution, the gel, and the final reaction product were characterized by X-ray absorption spectroscopy (see picture). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Firestone R.B.,Lawrence Berkeley National Laboratory | Krticka M.,Charles University | Revay Zs.,Institute of Isotope and Surface Chemistry of Hungary | Revay Zs.,TU Munich | And 2 more authors.
Physical Review C - Nuclear Physics | Year: 2013

Precise thermal neutron capture γ-ray cross sections σγ for 39,40,41K were measured on a natural potassium target with the guided neutron beam at the Budapest Reactor. The cross sections were internally standardized using a stoichiometric KCl target with well-known 35Cl(n,γ) γ-ray cross sections. These data were combined with γ-ray intensities from von Egidy and Krusche to generate nearly complete capture γ-ray level schemes. Total radiative neutron cross sections were deduced from the total γ-ray cross section feeding the ground state, σ0= Σσγ(GS) after correction for unobserved statistical γ-ray feeding from levels near the neutron capture energy. The corrections were performed with Monte Carlo simulations of the potassium thermal neutron capture decay schemes using the computer code dicebox where the simulated populations of low-lying levels are normalized to the measured cross section depopulating those levels. Comparisons of the simulated and experimental level feeding intensities have led to proposed new spins and parities for selected levels in the potassium isotopes where direct reactions are not a significant contribution. We determined the total radiative neutron cross sections σ0 (39K)=2.28±0.04 b, σ0 (40K)=90±7 b, and σ0 (41K)=1.62±0.03 b from the prompt γ-ray data and the γ-ray transition probability Pγ(1524.66)=0.164(4) in the β- decay of 42K in a low-background counting experiment. ©2013 American Physical Society.

Horvath A.,Institute of Isotope and Surface Chemistry of Hungary | Stefler G.,Institute of Isotope and Surface Chemistry of Hungary | Geszti O.,Research Institute for Technical Physics and Materials Science of HAS | Kienneman A.,CNRS The Institute of Chemistry and Processes for Energy, Environment and Health | And 3 more authors.
Catalysis Today | Year: 2011

Ni, NiRh and NiCo catalysts supported on Ce-Zr-oxide synthesised by pseudo sol-gel method have been investigated. Monometallic samples were performed with two different Ce/Zr ratios and by conventional impregnation. BET, XPS, TPR, TPO and TEM were applied for sample characterization and dry reforming of methane was carried out with a feed mixture consisted of CH4/CO 2/Ar = 10/10/80 or CH4/CO2 = 70/30 ratio. Co and Rh containing samples were proved to be stable catalysts, the impregnated Ni catalyst only slightly, while sol-gel Ni samples slowly deactivated during the long term overnight run. The amount of carbon on the sample's surface after catalytic runs varied between 1 and 12 mg C/100 mg of catalyst. The Ni samples prepared by sol-gel and impregnation method had a peak maximum in TPO at 400 °C and 600 °C, respectively. In the case of bimetallic sol-gel samples the carbon that gave TPO peak at 360 °C was slowly transformed to that at 600 °C, showing that after several carbon deposition (dry reforming) and gasification (TPO) cycles structural changes in the catalyst and in the carbon morphology take place and graphitic carbon and nanotube formation become prevailing as was detected by TEM. Upon high temperature pre-treatment and methane dry reforming reaction, alloyed NiRh, NiCo particles and sintered Ni were observed, with the simultaneous presence of carbidic carbon, carbon nanotubes and shell-type graphitic carbon deposition. Support degradation and segregation happened to some extent, but still there was a certain amount of Ni in strong interaction with the support probably still included in the oxide matrix. Broad metal particle size distribution seems to play a role in long term stability. When pure methane was decomposed on Ni catalyst prepared by sol-gel method, the carbonaceous deposit could completely be removed by the subsequent CO2 treatment, emphasizing the active role of Ce-Zr mixed oxide support in gasification of surface coke.

Guczi L.,Institute of Isotope and Surface Chemistry of Hungary | Guczi L.,Institute for Research In Catalysis | Stefler G.,Institute of Isotope and Surface Chemistry of Hungary | Geszti O.,Research Institute for Technical Physics and Materials science | And 4 more authors.
Applied Catalysis A: General | Year: 2010

Methane dry reforming with a mixture of 29% CO2 and 71% CH4 over 8 wt% NiMgAl2O4 in a plug flow reactor with temperature programmed mode has been investigated. It was established that in sequential reactions the catalyst was deactivated due to graphite like carbon deposit measured by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) while by X-ray photoelectron spectroscopy (XPS) only Ni-carbide was observed. The discrepancy found by XPS and TEM can be explained by the different types of carbon species, i.e. it is assumed that after the first reaction mostly carbide is deposited, whereas after several subsequent reactions the carbon on the surface is graphitized forming carbon nanotubes (TEM). Addition of 0.5 wt% gold to NiMgAl2O4 improves the catalytic activity and on gold containing bimetallic catalyst the formation of nanotubes is vanished. The results are interpreted by the formation of non-crystalline NiCx which - depending on the conditions - is transferred to graphitic carbon species. © 2010 Elsevier B.V. All rights reserved.

Guczi L.,Institute of Isotope and Surface Chemistry of Hungary | Beck A.,Institute of Isotope and Surface Chemistry of Hungary | Paszti Z.,Institute for Research In Catalysis
Catalysis Today | Year: 2012

In this contribution the general rules and the exceptions in the area of gold catalysis are discussed in order to establish a correlation between the size of the catalytically active element and its reactivity towards different classes of substrate molecules. The general behaviour of gold is that it is inactive in massive form while it can be used as a highly active catalyst when downsized. Throughout this paper experimental data from different sources are collected to proof that - according to this general behaviour - small molecules (CO, NO, etc.) can be activated only on small nanoparticles or roughened Au(1 1 1) surfaces, whereas Au(1 1 1) single crystals or extended metal films are active in the reaction of large molecules. This observation defines the applicability area of gold nanoparticles and the activity of large gold surfaces, films or single crystals. The above effect can be modulated by interfacial interaction between gold species and active oxide either if gold is deposited directly on them or is supported on inactive oxides (such as model SiO 2/Si(1 0 0) or high surface area amorphous or mesoporous silica) with minute amounts of promoter oxide. The oxide may invoke electronic interaction and simultaneously the defect structure of oxides likely has a key issue in the formation and stabilization of Au nanoparticles. On the other hand, it turned out that in some cases - independently of the interface - the key issue is the available gold area of Au nanoparticles dictating the reaction rate of a substrate. © 2011 Elsevier B.V. All rights reserved.

Guczi L.,Institute of Isotope and Surface Chemistry of Hungary | Guczi L.,Institute of Nanochemistry and Catalysis | Boskovic G.,Institute of Nanochemistry and Catalysis | Kiss E.,University of Novi Sad
Catalysis Reviews - Science and Engineering | Year: 2010

Highly dispersed, oxide-or zeolite-supported bimetallic catalysts are widely used in the catalytic industry, such as in catalytic reforming, nitrogen industry and gas-to-liquid technology. The paper highlights the nano-sized Co-based bimetallic system in terms of correlation between structure and reactivity/selectivity promoted by the second metal. Opposite to the bulk alloys nano-sized bimetallic catalysts are extremely sensitive to the structure, morphology, valence state of the supporting oxide material in which the nano-particles are embedded. In this case, one of the less reducible components, which strongly interact with the supports, may stabilize the second, more noble metals, and thus the latter can be stabilized in highly dispersed state. Conversely, addition of noble metal to the hardly reducible component may facilitate reduction, which causes the retardation of the deactivation process of some hydrocarbon reaction. The future trend is the application of bimetallic nano-particles although careful consideration and experimentation should be taken to elucidate the structure of such type of catalyst. The various effects of Co-based bimetallic particles, such as particle size, metal/support interface, morphology and electronic effects, on the activity/selectivity in given catalytic reactions will be discussed. © Taylor & Francis Group, LLC.

Lazar K.,Institute of Isotope and Surface Chemistry of Hungary
Hyperfine Interactions | Year: 2012

Some applications of Mössbauer spectroscopy are presented with environmental implications. In particular, catalytic processes are discussed with examples for catalyst immobilisation, for removal of contaminants and for decomposition of harmful compounds. Examples are also presented for processes of recycling of end products. © 2011 Springer Science+Business Media B.V.

Kelemen A.,Institute of Isotope and Surface Chemistry of Hungary | Mesterhazy D.,Institute of Isotope and Surface Chemistry of Hungary | Ignatovych M.,Ukrainian Academy of Sciences | Holovey V.,NASU Institute of Physics
Radiation Physics and Chemistry | Year: 2012

This work reports the thermoluminescence characterization of newly synthesized Li2B4O7 (LTB) and LTB:Cu materials of single crystal and glassy structure. The following basic properties were investigated: glow curve, dose response, fading, reproducibility and batch uniformity. The Cu doped samples and the non-doped single crystal gave TL response, while the non-doped glassy LTB did not up to 10kGy. LTB:Cu single crystals showed promising properties. Their glow curve consists of two well separated peaks (at 165°C and 270°C) in the 50-350°C temperature region. The sensitivity of this material is about 5 times higher than that of the TLD-100. The most attractive feature of these LTB:Cu single crystals is their linear dose response in a very wide range: from 0.3mGy to 10kGy. Unfortunately this material is sensitive to light; the fading of irradiated samples is very quick in daylight, but at room temperature and kept in dark the fading of the 270°C peak is less than 6%. © 2012 Elsevier Ltd.

Ignatovych M.,Ukrainian Academy of Sciences | Fasoli M.,University of Milan Bicocca | Kelemen A.,Institute of Isotope and Surface Chemistry of Hungary
Radiation Physics and Chemistry | Year: 2012

Spectrally resolved thermoluminescence (TL) of non-doped and Ag, Cu- and Mn-doped lithium-tetraborate (LTB) single crystals revealed that TL emission bands for differently doped samples proved to be at different wavelengths: 272, 370 and 608nm, respectively. These bands perfectly agree with the photoluminescence (PL) emission bands of Ag+, Cu+ and Mn2+ ions. It strongly points that these dopants are directly involved as recombination centers in the TL process.TL characteristics of non-doped and doped LTB single crystals and the corresponding glassy samples showed that their TL intensities and the structures of the glow curves were apparently different. © 2012 Elsevier Ltd.

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