MTA SZTE Reaction Kinetics and Surface Chemistry Research Group

Szeged, Hungary

MTA SZTE Reaction Kinetics and Surface Chemistry Research Group

Szeged, Hungary
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Xiang C.,Rice University | Cox P.J.,Rice University | Kukovecz A.,Rice University | Kukovecz A.,University of Szeged | And 16 more authors.
ACS Nano | Year: 2013

A thermoplastic polyurethane (TPU) composite film containing hexadecyl-functionalized low-defect graphene nanoribbons (HD-GNRs) was produced by solution casting. The HD-GNRs were well distributed within the polyurethane matrix, leading to phase separation of the TPU. Nitrogen gas effective diffusivity of TPU was decreased by 3 orders of magnitude with only 0.5 wt % HD-GNRs. The incorporation of HD-GNRs also improved the mechanical properties of the composite films, as predicted by the phase separation and indicated by tensile tests and dynamic mechanical analyses. The improved properties of the composite film could lead to potential applications in food packaging and lightweight mobile gas storage containers. © 2013 American Chemical Society.


Ovari L.,MTA SZTE Reaction Kinetics and Surface Chemistry Research Group | Berko A.,MTA SZTE Reaction Kinetics and Surface Chemistry Research Group | Gubo R.,University of Szeged | Racz A.,University of Szeged | And 2 more authors.
Journal of Physical Chemistry C | Year: 2014

The present study focuses on the thermal behavior of continuous rhodium thin films (̃10 nm) deposited on a TiO2(110) substrate at 300 K and covered by a continuous ultrathin gold film (̃1 nm), applying scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and low-energy ion scattering (LEIS) techniques. This arrangement facilitated a rather clear-cut investigation into the effect of the Au cover layer on the well-known encapsulation/decoration of Rh by TiOx, since the contribution of the titania substrate to the XPS and LEIS spectra could be avoided. Upon annealing a monometallic Rh film, the diffusion of Ti and O from the TiO2(110) substrate on top of the Rh film is essentially complete up to 850 K, leading characteristically to the formation of a "pinwheel" encapsulation layer with a TiO1.2 stoichiometry. The dewetting of the Rh film does not take place up to 950 K. Upon annealing of the Rh film in the presence of a continuous Au cover layer, the diffusion/accumulation of O was completely blocked up to 850 K, but metallic Ti was well detectable by XPS. Since LEIS spectra were dominated by the Au peak, and almost no Ti signal was observable up to this temperature, the metallic Ti is mainly stabilized at subsurface positions, probably either at the Rh-Au interface or within the Au film, in any case in contact with Au. The complete separation of O and Ti diffusion in this temperature range can be attributed to the weak interaction between oxygen and gold. Raising the sample temperature up to 930 K induces substantial changes. The diffusion of O is no longer kinetically hindered, and it reacts with a part of the alloyed Ti to form well-separated TiO2 nanoclusters on top of the Au shell. However, no oxygen is stabilized at subsurface sites in the bimetallic film. The rest of Ti alloyed in the subsurface is detectable by STM as ringlike features. The "pinwheel" TiO1.2 encapsulation layer appearing typically on a pure Rh film did not form on the bimetallic Au-Rh film at any of the temperatures investigated. © 2014 American Chemical Society.


Gazsi A.,MTA SZTE Reaction Kinetics and Surface Chemistry Research Group | Schubert G.,MTA SZTE Reaction Kinetics and Surface Chemistry Research Group | Bansagi T.,MTA SZTE Reaction Kinetics and Surface Chemistry Research Group | Solymosi F.,MTA SZTE Reaction Kinetics and Surface Chemistry Research Group
Journal of Photochemistry and Photobiology A: Chemistry | Year: 2013

The effects of Au particles of different sizes were investigated on the photocatalytic decompositions of methanol and ethanol on pure or N-doped TiO2. IR studies revealed that the deposition of Au promoted the dissociation of both compounds during illumination and also resulted in the formation of formate species. Whereas the photo-induced decompositions of methanol and ethanol occurred to only a limited extent on pure TiO2, the deposition of Au, particularly as nanosized particles, markedly enhanced the rate and the extent of the photocatalyzed reactions. An interesting feature of the photodecomposition of methanol was that, besides H2, CO 2 and CO, a significant amount of methyl formate was also produced. Addition of H2O or O2 to the alcohol in both cases decreased the level of CO formed, and in the case of methanol CO was completely eliminated. Au particles on N-doped TiO2 with a lower bandgap catalyzed the photodecompositions of both compounds even in visible light. © 2013 Published by Elsevier B.V.


Mutombo P.,ASCR Institute of Physics Prague | Gubo R.,University of Szeged | Berko A.,MTA SZTE Reaction Kinetics and Surface Chemistry Research Group
Journal of Physical Chemistry C | Year: 2016

The atomic structure of "pinwheel" TiO∼1.2 ultrathin oxide (w-TiO-UTO) layer and its reaction with gold are studied by scanning tunneling microscopy (STM) imaging and density functional theory (DFT) calculations. The UTO film was formed as an encapsulation layer on the top facet (111) of stripe-like Rh nanoparticles supported on a TiO2(110) substrate. For proposing a structural model, the previous STM, photoelectron (XPS), and ion scattering spectroscopy (LEIS) results were also taken into account. DFT calculations were carried out within the generalized gradient approximation (GGA-PBE) in the frame of the Quantum Espresso code. A Rh(111) slab of four layers with a TiO1.14 overlayer and a Rh-Ti-O stacking sequence were used. In the starting model, the ratio between hcp and fcc sites filled with Ti atoms was 1.54 (the same value for O atoms was 2.2) on the top of Rh layers. The simulation of the STM images of the relaxed structure was done following the Tersoff-Hamann approximation. The main structural characteristics obtained experimentally were successfully reproduced in the simulation results: (i) the chemical contrast appeared as a pinwheel structure and (ii) compared with an ideal hexagonal lattice, characteristic local distortions were found in the UTO film. In harmony with the experimental results, the DFT calculations of the adsorption of a single Au atom on a w-TiO-UTO layer indicated that there is a characteristic site preference within the unit cell of the UTO film. This feature was also experimentally demonstrated for the early stage of the deposition of Au at room temperature, suggesting a moderate template effect adjusted by the pinwheel structure. This work demonstrates clearly that the lack of the so-called "nanoholes" does not completely cancel the template effect because the periodic lattice strain in itself substitutes their role. Moreover, the weaker modulation of Au/TiO-UTO bond permits the formation of one atomic layer thick 2D gold nanoparticles at 300 K. © 2016 American Chemical Society.


Gyori Z.,MTA SZTE Lendulet Porous Nanocomposites Research Group | Konya Z.,University of Szeged | Konya Z.,MTA SZTE Reaction Kinetics and Surface Chemistry Research Group | Kukovecz A.,MTA SZTE Lendulet Porous Nanocomposites Research Group | Kukovecz A.,University of Szeged
Applied Catalysis B: Environmental | Year: 2015

In this paper we describe the use of differently sized PbSe quantum dots as photosensitizers for anatase TiO2 nanowires under visible light illumination. After the organometallic synthesis of PbSe quantum dots with three different average diameters (1.8, 2.5 and 4.7nm), the nanocrystals were attached to the surface of nanowires with thioglycolic acid as a linker molecule. These quantum dot decorated nanowires were used as photocatalyst in the methyl orange degradation model reaction with promising results. The best performance achieved was 90% degradation of the initial concentration of methyl orange in six hours over 2.5nm PbSe quantum dot sensitized nanowires using a 40W quartz UV lamp equipped with a 400nm cut-off filter. © 2015 Elsevier B.V.


Gazsi A.,MTA SZTE Reaction Kinetics and Surface Chemistry Research Group | Schubert G.,MTA SZTE Reaction Kinetics and Surface Chemistry Research Group | Pusztai P.,MTA SZTE Reaction Kinetics and Surface Chemistry Research Group | Solymosi F.,MTA SZTE Reaction Kinetics and Surface Chemistry Research Group
International Journal of Hydrogen Energy | Year: 2013

The photo-induced vapor-phase decompositions of formic acid and methyl formate were investigated on pure, N-doped and Au-promoted TiO2. Infrared (IR) spectroscopic studies revealed that illumination initiated the decomposition of adsorbed formate formed in the dissociation of formic acid and located mainly on TiO2. The photocatalytic decompositions of formic acid and methyl formate vapor on pure TiO2 occurred to only a limited extent. The deposition of Au on pure or doped TiO2 markedly enhanced the extent of photocatalytic decomposition of formic acid. The main process was dehydrogenation to give H2 and CO2. The formation of CO occurred to only a very small extent. Addition of O2 or H 2O to the formic acid decreased the CO level from ∼0.8% to ∼0.088%. Similar features were experienced in the photocatalytic decomposition of methyl formate, which dissociated in part to give surface formate. Experiments over Au deposited on N-doped TiO2 revealed that the photo-induced decomposition of both compounds occurs even in visible light. © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights.


Ovari L.,MTA SZTE Reaction Kinetics and Surface Chemistry Research Group | Krick Calderon S.,Friedrich - Alexander - University, Erlangen - Nuremberg | Lykhach Y.,Friedrich - Alexander - University, Erlangen - Nuremberg | Libuda J.,Friedrich - Alexander - University, Erlangen - Nuremberg | And 5 more authors.
Journal of Catalysis | Year: 2013

Near ambient pressure X-ray photoelectron spectroscopy was applied to study the interaction of ethanol (CH3CH2OH) with a well-ordered CeO2(1 1 1) film on Cu(1 1 1) and with a Co/CeO2(1 1 1)/Cu(1 1 1) model catalyst. The oxidation state of the surface and the chemical nature of reaction intermediates were analyzed. At 300 K, the oxidation state of ceria decreased gradually with increasing ethanol pressure. At a constant pressure of 0.1 mbar, the reduction of Ce4+ to Ce3+ increased significantly between 320 and 600 K due to a higher mobility of oxygen or Ce3+ centers at elevated temperatures. The main intermediate, ethoxide, was formed by dissociative adsorption of ethanol at room temperature. No coke formation was observed up to 600 K on CeO2. Upon deposition of metallic cobalt, partial reduction of ceria was observed, leading to the formation of Co2+ sites but still leaving metallic Co in the metal particles. During the reaction of ethanol with the Co/CeO2(1 1 1) model catalyst, the amount of Co2+ decreased drastically with increasing temperature, and at 600 K, the majority of Co was metallic. This process was accompanied by the severe reduction of ceria and the formation of significant carbon deposits. © 2013 Elsevier Inc. All rights reserved.


Toth A.,MTA SZTE Reaction Kinetics and Surface Chemistry Research Group | Halasi G.,MTA SZTE Reaction Kinetics and Surface Chemistry Research Group | Solymosi F.,MTA SZTE Reaction Kinetics and Surface Chemistry Research Group
Journal of Catalysis | Year: 2015

The dehydrogenation of C2H6 and its reaction with CO2 have been investigated on Au deposited on various oxides. Both reactions occurred at relatively high temperatures, above 650 K. Ethylene formed in the dehydrogenation process with high selectivity, 94-98%, on most of the catalysts. The conversion of C2H6 varied with the nature of support and fell in the range of 3-19%. Adding CO2 to C2H6 only slightly influenced the reaction of C2H6 on Au/MgO and Au/Al2O3, but markedly increased the conversion of C2H6 and changed its reaction pathways on Au deposited on n-type TiO2, CeO2 and ZnO. Taking into account the properties of these oxides, we came to the conclusion that their electric behavior and not their defect structure play a dominant role in the enhanced activity of Au deposited on these supports. Based on the different work functions, an electronic interaction between Au particles and these oxides is proposed, which facilitates the formation of reactive negatively charged CO2. © 2015 Elsevier Inc. All rights reserved.


Halasi G.,MTA SZTE Reaction Kinetics and Surface Chemistry Research Group | Bansagi T.,MTA SZTE Reaction Kinetics and Surface Chemistry Research Group | Solymosi F.,MTA SZTE Reaction Kinetics and Surface Chemistry Research Group
Journal of Catalysis | Year: 2015

The effect of illumination on the surface interaction and the reaction between NO + C2H5OH was investigated on Au/TiO2 catalyst. By means of Fourier transform infrared spectroscopy, the formation of absorption bands at ∼2180 and ∼2210 cm-1 was observed. The first was attributed to the NCO species locating on Au particles, and the second one to NCO residing on the TiO2 support. While the thermal reaction between NO and C2H5OH on Au/TiO2 catalyst occurred with measurable rate only at and above 473-523 K, illumination of the system induced the reaction even at room temperature. A fraction of NO was converted into N2O, another one to N2. At the same time, the photo-induced decomposition of C2H5OH also occurred yielding CH3CHO, H2, CO, and CH4. Interestingly, the presence of NO significantly slowed down the rate of the decomposition of C2H5OH. Separate studies revealed that all the products formed in the decomposition of C2H5OH reacted with NO. A mechanism for the photocatalytic reduction of NO with C2H5OH is proposed taking into account the effects of the products of C2H5OH photolysis. Incorporation of N into TiO2, which significantly lowered its band gap, appreciably enhanced the reduction of NO, which occurred even in visible light. © 2015 Elsevier Inc. All rights reserved.


Ferencz Z.,University of Szeged | Erdohelyi A.,University of Szeged | Baan K.,University of Szeged | Oszko A.,University of Szeged | And 7 more authors.
ACS Catalysis | Year: 2014

The effect of the nature of the support and the promotion achieved by a Rh additive on Co-based catalysts in the ethanol steam reforming reaction were studied. The catalysts with 2% Co loading were characterized by temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS). In situ diffuse reflectance Fourier-transform infrared spectroscopy (DRIFTS) identified the surface intermediates formed during the reaction, whereas gas phase products were detected by gas chromatography (GC). Upon heating in hydrogen to 773 K, cobalt could not be reduced to Co0 on alumina, but on silica the reduction was almost complete. On ceria, half of the Co could be reduced to the metallic state. By the presence of a small amount (0.1%) of Rh promoter, the reduction of both cobalt and ceria was greatly enhanced. For Co on the acidic Al2O3 support, the dehydration mechanism was dominant, although on the basic CeO2 support, a significant amount of hydrogen was also formed. Addition of a small amount of Rh as promoter to the Co/CeO2 catalyst resulted in a significant further increase in the hydrogen selectivity. © 2014 American Chemical Society.

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