Papers by András Erdőhelyi
Applied Catalysis B-environmental, Feb 1, 2018
Highlights CO2 reforming of methane was carried out over supported LaNiO3 perovskitetype oxides... more Highlights CO2 reforming of methane was carried out over supported LaNiO3 perovskitetype oxides Supporting LaNiO3 over CeSiO2 significantly decreased the deposition of carbon. High oxygen mobility of CeSiO2 promotes the removal of carbon. Carbon oxidation by the oxygen of ceria inhibited the nickel carbide formation.
Surface Science Letters, Oct 1, 1981
The adsorption and dissociation of CO have been investigated on alumina supported Rh at atmospher... more The adsorption and dissociation of CO have been investigated on alumina supported Rh at atmospheric pressure. The dissociation of CO was detected above 473 K. The carbon formed reacted with Hz eiren at 300-473 K yielding CH 4. A significant aging of surface carbon occurred above 573 K.
Physica Status Solidi B-basic Solid State Physics, Oct 13, 2011
Fe 3 O 4 /Au composite nanoparticles (GoldMag NPs) have received considerable attention because o... more Fe 3 O 4 /Au composite nanoparticles (GoldMag NPs) have received considerable attention because of their advantageous properties arisen from both individual Au and Fe 3 O 4 nanoparticles. Many efforts have been devoted to the synthesis of these composite nanoparticles. Herein, GoldMag NPs were reported to be synthesized by two-step method. Fe 3 O 4 nanoparticles were prepared by co-precipitation and modified by the citric acid, and then citric acid-coated Fe 3 O 4 nanoparticles were used as seeds in sodium citrate solution to reduce the HAuCl 4. The size of obtained nanoparticles was geared from 25 to 300 nm by controlling the concentration of reactants. The GoldMag NPs were characterized by UV-vis spectrometer, dynamic light scattering (DLS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM). The GoldMag NPs showed good superparamagnetism at room temperature and were well dispersed in water with surface plasmon resonance absorption peak varied from 538 nm to 570 nm.
Journal of Molecular Catalysis A-chemical, Nov 1, 2014
ABSTRACT The catalytic activity of Norit supported Cu, Ni and Cu–Ni catalysts was investigated in... more ABSTRACT The catalytic activity of Norit supported Cu, Ni and Cu–Ni catalysts was investigated in the synthesis of dimethyl carbonate (DMC) by the oxidative carbonylation of methanol. Cu/Norit showed the best catalytic activity. The reaction was carried out in a continuous flow system at atmospheric pressure usually at 393 K. The main products were methyl formate, DMC and CO2. The methanol conversion on Cu/Norit achieved in steady state was about 22 % and the DMC yield 13.2 %. Based on the XPS data we can establish that copper reduced to its metallic form during reduction but oxidized in the reaction mixture, and is mostly in the Cu+ state, with some Cu2+. It is possible that the DMC formation rate depends on the surface concentration of oxidized Cu and on the ratio of Cu+ and Cu2+. Based upon the IR measurements adsorbed DMC was found on the surface of the Cu/Norit catalyst during the catalytic reaction. Graphical Abstract
Colloid and Polymer Science, Jan 11, 2006
Nanofilms were prepared by consecutively alternating adsorption of Mg-Al (2:1) layered double hyd... more Nanofilms were prepared by consecutively alternating adsorption of Mg-Al (2:1) layered double hydroxide (LDH) and polysodium 4-styrenesulfonate (PSS). The charge density of oppositely charged materials strongly affect film properties like thickness and ordering. The specific charge of the colloid particles (LDH) and macromolecules was determined with the particle charge detector. The sequential build-up of the thin films was followed by spectrophotometry and X-ray diffraction. The surface morphology of the multilayers was characterized by atomic force microscopy. The influence of the charge density of the applied materials and of the mass ratio of LDH/PSS on the film thickness were studied.
Journal of Catalysis, Jun 1, 1991
The partial oxidation of ethane has been investigated on silica-supported alkali metal vanadate c... more The partial oxidation of ethane has been investigated on silica-supported alkali metal vanadate catalysts in a fixed-bed continuous-flow reactor at 770-823 K using N20 as oxidant. Pulse experiments, temperature-programmed reduction of the catalyst, and catalytic decomposition of N:O and CzHsOH were also carried out. The main products of the oxidation reaction were ethylene, acetaldehyde, CO, and CO 2 . Small amounts of CH4, C2HsOH, C3-, and Cchydrocarbons were also identified. The introduction of water increased the acetaldehyde selectivity but decreased that of ethylene. In the presence of water the acetaldehyde selectivity increased from LiVO3 to RbVO3. Detailed kinetic measurements were carried out on KVO3/SiO2. From the pulse experiments it was inferred that in the oxidation of ethane an intermediate more reactive than C2H 6 is formed for the activation of the catalysts. The temperature-programmed reduction spectra of alkali vanadates show that the onset temperature of the main reduction stage increased, while the extent of the reduction decreased somewhat from Li to Cs. A possible mechanism for the oxidation reaction is discussed.
Journal of Catalysis, May 1, 1994
Journal of Catalysis, Mar 1, 1997
The partial oxidation of methane to formaldehyde was studied on K 2 MoO 4 , deposited on various ... more The partial oxidation of methane to formaldehyde was studied on K 2 MoO 4 , deposited on various supports, in a fixed-bed continuous-flow reactor at 860-923 K using O 2 as oxidant. The catalysts were characterized by Raman and XPS spectroscopies. It was found that the composition of molybdates deposited by impregnation depended sensitively on the pH value of the slurry containing the support. At low pH values a significant amount of K 2 Mo 2 O 7 was formed. The product distribution of the oxidation reaction was markedly influenced by the nature of the support. The highest activity was measured for magnesia-supported catalyst. In this case, however, only the complete oxidation of methane occurred. Formaldehyde, in a larger quantity, was produced on silica-supported catalyst containing a greater amount of K 2 Mo 2 O 7 and on K 2 MoO 4 /ZSM-5. It was observed that at very low oxygen content, ∼0.1%, the reaction pathway of methane conversion was basically different: in this case the main hydrocarbon products were ethylene, ethane, and benzene. Formaldehyde was not detected. A possible mechanism for the reaction of methane is discussed.
Applied Catalysis A-general, Mar 1, 2001
The partial oxidation of methane to formaldehyde or ethane and ethylene was studied on K 2 WO 4 d... more The partial oxidation of methane to formaldehyde or ethane and ethylene was studied on K 2 WO 4 deposited on various supports, on potassium-promoted WO 3 /SiO 2 and for comparison on WO 3 /SiO 2 in a fixed-bed continuous-flow reactor at 860-923 K using O 2 as oxidant. The catalysts were characterised by Raman, XP spectroscopy and TPR method. It was found that the original structure of potassium tungstate remained on K 2 WO 4 /SiO 2 , whereas K 2 W 2 O 7 was very likely formed on K+WO 3 /SiO 2. The main products of the reaction besides the carbon oxides were HCHO on WO 3 /SiO 2 while on K-containing samples mainly the C 2 hydrocarbons were formed. The product distribution of the oxidation reaction was markedly influenced by the nature of the support. The highest activity was measured for alumina-supported catalyst. In this case, however, only traces of partially oxidised products were formed. Formaldehyde, in a larger quantity, was produced on WO 3 /SiO 2 but C 2 in higher selectivity on K 2 WO 4 /SiO 2 was formed. A possible mechanism for the oxidative conversion of methane is also discussed.
Surface Science, Jun 1, 2011
Gold, rhodium and their coadsorbed layers were prepared on titanate nanowires and nanotubes and c... more Gold, rhodium and their coadsorbed layers were prepared on titanate nanowires and nanotubes and characterized by X-ray photoelectron spectroscopy (XPS), low energy ion scattering spectroscopy (LEIS), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM). On titanate nanowire and tube supports the gold 4f 7/2 XP emission appeared after reduction at 83.7 eV and 85.6 eV indicating two different sizes or chemical environments of gold nanoclusters. The titanate nanostructures stabilize the nearly atomically dispersed state of gold (85.6 eV peaks in XPS). Small clusters also developed in rhodium containing samples besides the pure metallic state. Upon CO adsorption on Rh/titanate nanostructures the IR stretching frequencies characteristic of twin form were dominant, whereas bimetallic nanosystems featured a pronounced linear stretching vibration. By performing careful XPS, LEIS and SEM experiments, it was found that, for appropriate Au and Rh coverage, the Au almost completely covers the Rh nanoparticles. CO adsorbed on this surface may induce the surface reconstruction.
Journal of Catalysis, Mar 1, 1986
The hydrogenation of CO2 over Pd supported by A1203, TiO,, SiOt, and MgO has been investigated in... more The hydrogenation of CO2 over Pd supported by A1203, TiO,, SiOt, and MgO has been investigated in a flow technique at 1 and at 9.5 atm. For comparison the hydrogenation of CO was examined under the same experimental conditions. Attention was focused on the identification of surface species formed during the reaction. The hydrogenation of CO1 occurred at a measurable rate above 520 K. It appears that the dispersion of Pd plays a governing role in determining the direction of the Hz + CO2 reaction. On highly dispersed Pd, the main product of the reaction was methane at both pressures while on poorly dispersed Pd the reverse water-gas shift reaction (at 1 atm) or methanol formation (at 9.5 atm) occurred. In situ infrared spectroscopic measurements revealed that multiply bonded CO and formate species were present on the catalyst surface during the reaction at 1 atm. The formation of surface carbon was also detected. From the behavior of surface formate under different conditions it was inferred that it does not play a significant role in hydrocarbon synthesis on Pd catalysts. On the basis of the specific activities, Pd/TiOr proved to be the most effective catalyst for the hydrogenation of COZ. It is proposed that the important step in the methanation of CO* is the dissociation of adsorbed CO. With respect to the high activity of Pd/ TiOz, it is assumed that an electronic interaction operates between TiOz and Pd, influencing the bonding and reactivity of chemisorbed species. As concerns methanol synthesis at 9.5 atm, the results obtained failed to support the idea that methanol is produced in a direct reaction of CO2 and not through formation of CO and its consecutive hydrogenation. o 1986 Academic PWSS, IK. EXPERIMENTAL Methods. Catalytic investigations were carried out in a flow reactor made from an 8-mm-i.d. Pyrex glass tube or, when the total pressure was 9.5 bar, an 8-mm-o.d. stainless-steel tube. The dead volume was filled with glass beads. The reactor was heated by an external oven. No increase in
Catalysis Letters, 1991
ABSTRACT
Acs Symposium Series, May 5, 1993
The partial oxidation of ethane has been investigated on silica-supported M2MoO 4 catalysts (M = ... more The partial oxidation of ethane has been investigated on silica-supported M2MoO 4 catalysts (M = Li, Na, K, Rb, Cs) in a fixed-bed continuous-flow reactor at 770-823 K using N20 as oxidant. Additional measurements included pulse experiments, temperature-programmed reduction of the catalysts, and a study of the catalytic decomposition of NEO and C2HsOH. The numbers of acidic and basic sites have also been determined. Temperature-programmed reduction of the alkali metal molybdates showed that the onset temperature of the reduction decreased from Li to Cs, while the extent of the reduction increased in this sequence. The main products of the oxidation reaction were ethylene, acetaldehyde, CO, and CO2. Small amounts of CH4 and C2HsOH were also identified. The ethane conversion and the rate of the C2H 4 and CH3CHO formation all increased from Li to Cs. Detailed kinetic measurements were carried out on K2MoO4/SiO 2. The activation energy of the ethane consumption was 71 kJ/mol. A possible mechanism for the oxidation reaction is discussed.
Journal of Catalysis, May 1, 1990
The partial oxidation of ethane has been studied on silica-supported V205 catalyst in a fix-bed c... more The partial oxidation of ethane has been studied on silica-supported V205 catalyst in a fix-bed continuous-flow reactor at 775-823 K. The temperature-programmed reduction of V205 was also investigated. Using N20 as oxidant, the main oxidation products were ethylene, acetaldehyde, CO, and CO2. Small amounts of CH4, and C3-and C4-hydrocarbons were also identified. The selectivities for ethylene and acetaldehyde at 823 K were 57.5 and 5.1%, respectively. The introduction of water increased the rate of acetaldehyde and CO formation, but decreased that of ethylene. Kinetic orders were determined for all products. The activation energies for the formation of C2H4, CH3CHO, CO, and CO2 were 47.7, 33.3, 27.9, and 21.5 kcal/mol, respectively. Using 02 as oxidant, the same products were observed, but the conversion was higher and selectivities were lower. The addition of water to the reacting mixture enhanced the selectivity toward ethylene and acetaldehyde formation. A possible mechanism for the oxidation reaction is proposed.
e-Journal of Surface Science and Nanotechnology, 2014
Gold decorated titanate nanowires and nanotubes were investigated by XPS, XRD and HRTEM. XPS and ... more Gold decorated titanate nanowires and nanotubes were investigated by XPS, XRD and HRTEM. XPS and UV-Vis diffuse reflectance results suggested that a certain part of gold underwent an ion exchange process. Higher gold loadings lead to the formation of nanosized-dispersed particles complexed to oxygen vacancies, with a diameter distribution of 1.5-10 nm. Gold additives catalyzed the transformation of the tube structure to anatase. Gold, however, stabilized the wire-like structure up to 873 K.
Applied Catalysis B: Environmental, 2007
ABSTRACT The formation of surface species in the ethanol–water interaction and the reforming of e... more ABSTRACT The formation of surface species in the ethanol–water interaction and the reforming of ethanol have been investigated on Pt/Al2O3 catalysts and for comparison on the support. By means of infrared spectroscopy it was found that on Pt/Al2O3 not only adsorbed ethanol, different types of ethoxy species but also traces of acetaldehyde and a significant amount of acetate groups were detectable on the surface. The latter species were stable even at 700 K. The gas phase analysis of the ethanol-dosed surface showed at higher temperature considerable amount of ethylene in the case of Al2O3 and hydrogen in the case of Pt/Al2O3.In the ethanol + water reaction the selectivity of H2 and CO2 formation at 723 K decreased in time, while that of ethylene increased. This trend was attenuated by increasing the following parameters: water concentration, metal loading and reaction temperature. It was assumed that this behavior of Pt/Al2O3 in the ethanol + water reaction can be attributed to the formation of surface acetate groups which hindered the reaction on the metal, although these species were located rather on the support.
Journal of Coating Science and Technology, 2014
Two different preparation methods were developed to cover successfully multi-walled carbon nanotu... more Two different preparation methods were developed to cover successfully multi-walled carbon nanotubes (MWCNT) with tin-dioxide (SnO2) nanoparticles using SnCl2 2H2O as precursor under different solvent conditions. The applied mass ratios of the components were 1:4, 1:8, 1:16, 1:32 and 1:64, respectively. As-prepared tin-dioxide coverages were characterized by TEM, SEM, SEM-EDX, Raman microscopy, BET and X-ray diffraction techniques. Photocatalytic efficiencies of selected composites were investigated in a self-made photoreactor, equipped with UV-A fluorescence lamps. Photocatalytic degradation of phenol solution was followed by using HPLC. Observations revealed that using hydrothermal method we can easily control the layer of SnO2 nanoparticles on the surface of MWCNTs. Using various solvents SnO2 nanoparticles with different morphologies formed. The nanocomposites have low photocatalytic efficiencies under conditions used generally (when >300 nm).
Journal of Luminescence, 2019
On the effects of milling and thermal regeneration on the luminescence properties of Eu 2þ and Dy... more On the effects of milling and thermal regeneration on the luminescence properties of Eu 2þ and Dy 3þ doped strontium aluminate phosphors Viktor Havasi a , D� avid T� atrai b , G� abor Szab� o b,c , Erika Varga d , Andr� as Erd} ohelyi d , Gy€ orgy Sipos e , Zolt� an K� onya a, f , � Akos Kukovecz a, *
Applied Catalysis B: Environmental, 2016
The photocatalytic transformation of the methane-carbon dioxide system was investigated by in-sit... more The photocatalytic transformation of the methane-carbon dioxide system was investigated by in-situ methods in the present study. Titanate nanotube (TNT) supported gold and rhodium catalysts were used in the catalytic tests. Our main goal was the analysis of the role of the catalysts in the different parts of the reaction mechanism. The catalysts were characterized by X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and diffuse reflectance UV-vis spectroscopy (DR-UV-vis). Photocatalytic tests were performed in a continuous flow quartz reactor equipped with mass spectrometer detector and mercury-arc UV source. Diffuse reflectance infrared spectroscopy (DRIFTS) was used to analyze the surface of the catalyst during photoreaction. Post-catalytic tests were also carried out on the catalysts including XPS, temperature programmed reduction (TPR) and Raman spectroscopy methods in order to follow the changes of the materials. Titanate nanotube can stabilize even the smallest, molecular-like Au clusters which showed the highest activity in the reactions. Approximately 3% methane conversion was reached in the best cases while the carbon dioxide conversion was not traceable. It was revealed that water has a very important role in the oxidation reaction. The main discovered reaction routes are methane dehydrogenation and oxidation, the methyl coupling and the forming of structured carbon deposits on the catalyst surface. The source of the surplus CO can be mostly the reduction of carbon dioxide. During the reduction process photoelectrons and hydrogen ions brings about the CO 2 reduction via CO 2 • − radical anion.
New Horizons in Catalysis, Proceedings of the 7th International Congress on Catalysis, 1981
The synthesis of methane from CO, and H, was investigated on supported Rh catalysts. The adsorbed... more The synthesis of methane from CO, and H, was investigated on supported Rh catalysts. The adsorbed species present on the catalysts were characterized by infrared spectroscopy. The hydrogenation of CO, on RhiAl,O, occurred at a measurable rate above 443 K, yielding exclusively methane. The rate of methane formation on Rh/AI,O, is described by the expression N < ,I4 = 2.69 x 10hexp(-16.200//?1')PA,6i Py$. From a comparison of the specific activities of Rh/Al,O,in the H, + CO, and H, + CO reactions it appears that the hydrogenation of CO, occurs much faster than that of CO. The support exerted a marked influence on the specific activity of Rh. The most effective support was TiO, and the least effective one SiO,. Infrared spectroscopic measurements revealed that linearly bonded CO (perturbed by hydrogen adsorbed on the same Rh atom) and adsorbed formate species were present on the catalyst surface during the reaction. Evidence is presented to show that the surface formate is located not on the Rh, but rather on the support. The formation of surface C was also detected. Its amount slightly increased during the conditioning period and also with temperature elevation. It is proposed that the important steps in CH, formation are the dissociation of CO, promoted by adsorbed hydrogen, the subsequent dissociation of CO into reactive surface carbon, and hydrogenation of the latter. The possible reasons for the different methanation rates of CO, and CO are discussed.
Uploads
Papers by András Erdőhelyi