László Óvári

Determination of acidic centers on supported Mo2C catalysts

Abstract The acidic properties of both HZSM-5 and SiO 2 supported MoO 3 and carburized MoO 3 have been investigated by FTIR spectroscopy. Deposition of Mo caused the consumption of Bronsted acidic OH groups of HZSM-5 as shown by the changes in the ν (OH) region of the spectra and also by pyridine and low temperature CO adsorption measurements. Carburization of the sample did not result in regeneration of acidic OH groups of the zeolite. Mo reacted with OH groups during its deposition on SiO 2 . The results of both pyridine and CO adsorption measurements did not indicate the generation of Bronsted acidic sites on MoO 3 /SiO 2 and carburized MoO 3 /SiO 2 . Lewis acid sites are formed, however, upon the deposition of Mo. Carburization led to stronger Lewis centers, which are probably the active sites—together with the carbide phase—in methane aromatization on MoO 3 /SiO 2 .

A comparative study of the complete oxidation of dimethyl ether on supported group VIII metals

In the study of the interaction of dimethyl ether with alumina-supported platinum metals by means of infrared spectroscopy, methoxy species bonded to the alumina and CO adsorbed on the metals have been detected. The complete oxidation of dimethyl ether in a flow system sets in above 400 K and proceeded to 100% conversion at ~673 K. No or only very slight deactivation was observed in 5 h. The specific activity order of the catalysts is: Ru>Pt>Ir>Pd>Rh.

Probing the interaction of Rh, Co and bimetallic Rh–Co nanoparticles with the CeO2 support: catalytic materials for alternative energy generation

The interaction of CeO2-supported Rh, Co and bimetallic Rh-Co nanoparticles, which are active catalysts in hydrogen production via steam reforming of ethanol, a process related to renewable energy generation, was studied by X-ray diffraction (XRD), high resolution electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and low energy ion scattering (LEIS). Furthermore, diffuse reflectance infrared spectroscopy (DRIFTS) of adsorbed CO as a probe molecule was used to characterize the morphology of metal particles. At small loadings (0.1%), Rh is in a much dispersed state on ceria, while at higher contents (1-5%), Rh forms 2-8 nm particles. Between 473-673 K pronounced oxygen transfer from ceria to Rh is observed and at 773 K significant agglomeration of Rh occurs. On reduced ceria, XPS indicates a possible electron transfer from Rh to ceria. The formation of smaller ceria crystallites upon loading with Co was concluded from XRD and HRTEM; for 10% Co, the CeO2 particle size decreased from 27.6 to 10.7 nm. A strong dissolution of Co into ceria and a certain extent of encapsulation by ceria were deduced by XRD, XPS and LEIS. In the bimetallic system, the presence of Rh enhances the reduction of cobalt and ceria. During thermal treatments, reoxidation of Co occurs, and Rh agglomeration as well as oxygen migration from ceria to Rh are hindered in the presence of cobalt.

Adsorption and switching properties of a N-benzylideneaniline based molecular switch on a Au(111) surface

High resolution electron energy loss spectroscopy has been employed to analyze the adsorption geometry and the photoisomerization ability of the molecular switch carboxy-benzylideneaniline (CBA) adsorbed on Au(111). CBA on Au(111) adopts a planar (trans) configuration in the first monolayer (ML) as well as for higher coverages (up to 6 ML), in contrast to the strongly nonplanar geometry of the molecule in solution. Illumination with UV light of CBA in direct contact with the Au(111) surface (<or=1 ML) caused no changes in the vibrational structure, whereas at higher coverages (>1 ML) pronounced modifications of vibrational features were observed, which we assign to a trans-->cis isomerization. Thermal activation induced the back reaction to trans-CBA. We propose that the photoisomerization is driven by a direct (intramolecular) electronic excitation of the adsorbed CBA molecules in the second ML (and above) analogous to CBA in the liquid phase.

The growth and thermal properties of Au deposited on Rh(111): formation of an ordered surface alloy

Scanning tunnelling microscopy (STM), low energy ion scattering spectroscopy (LEIS), X-ray photoelectron spectroscopy (XPS) and high resolution electron energy loss spectroscopy (HREELS) were applied for studying Au deposited on the Rh(111) surface. Both the deposition of Au at different substrate temperatures (400-800 K) and the effect of annealing Au deposited at 500 K were investigated. Gold deposition at 500 K, investigated by STM and LEIS methods, revealed that up to half monolayer Au the system exhibits clearly layer-by layer growth; however, above this coverage a slight deviation was identified, mainly due to kinetic and morphological effects. A continuous cover layer of Au was formed only above ∼2.5 monolayers (ML). Below this coverage, the pseudomorphic character of the Au overlayer was clearly proven by STM, but this feature disappears at 4 ML coverage. A moderate (5-10%) surface mixing of the two metals was observed only above 600 K, for both annealing the Au layer formed at lower temperatures and performing the deposition at elevated temperatures. Above 600 K a clear step-flow growth mechanism was verified. Depending on the Au coverage, a more extended mixing of the top layer and the sublayer was observed at even higher temperatures. In this case, nano-range ordering of the alloyed layer was detected by STM, where the lateral extension of the uniform commensurate (2 × 1) domains was around 4 × 4 nm2. In this case, the local intralayer mixing of Rh and Au can locally reach a value of 50%. The proposed structural model for the (2 × 1) alloy phase was also corroborated by HREELS investigations on CO adsorption.

Growth of Gold on a Pinwheel TiO∼1.2 Encapsulation Film Prepared on Rhodium Nanocrystallites

Rh nanoparticles of 50-100 nm diameter and 20-40 atomic layer thickness with a (111) flat top facet parallel to the support surface were grown on a TiO2(110) surface via physical vapor deposition (PVD) at room temperature (RT) followed by annealing at 1050 K. These nanoparticles were completely encapsulated by an ordered hexagonal pinwheel TiO∼1.2 ultrathin oxide (w-TiO-UTO) film. STM, XPS, and low energy ion scattering (LEIS) methods were used to characterize the postdeposition of gold and the effects of annealing on the Au/w-TiO-UTO/Rh-particle system. The adlayer exhibits 3D growth and Rh-Au bond formation at 500 K. The 3D Au nanoparticles of 2-3 nm diameter and ∼1 nm height are partially covered by TiOx species at RT and sinter via an Ostwald-ripening in the range of 500-800 K. The adparticles are gradually getting free of TiOx decoration, and at around 900 K they exhibit a double layer height with 2D character. Two different arrangements were found for these Au particles: (i) a compressed Au(111)-(1 × 1) and (ii) a reconstructed Au(111)-(2 × 1), both of them pseudomorphic with the Rh lattice underneath. Above 900 K, the thickness of these 2D particles tends to become a single layer, while they spread out and form a continuous gold layer on the Rh nanoparticles. This behavior indicates a thermally activated replacement of the w-TiO-UTO film by an Au ultrathin layer. The gold layer is stable up to 1000 K, where extended 1D interfaces are formed between gold and w-TiO-UTO layers.

Adsorption and reactions of CH3Cl on Mo2C based catalyst

Abstract The adsorption of CH3Cl on ZSM-5, Mo2C/ZSM-5 and Mo2C/SiO2 was investigated by temperature-programmed desorption (TPD) and Fourier transform infrared spectroscopy (FTIR). The formation of methoxy species was clearly identified on all the three catalysts. Three elementary steps were considered to explain the absorption bands observed in the IR spectra and to describe the reaction products found at higher temperatures: (i) the interaction of CH3Cl with the OH groups of ZSM-5, (ii) dissociation of CH3Cl yielding CH3, and (iii) the elimination of HCl from the adsorbed CH3Cl to give CH2 species. A new finding was the identification of the alkenyl carbocation formed on the Lewis acidic sites of ZSM-5. The decomposition of CH3Cl on ZSM-5 proceeded at 673 K with a high conversion yielding propylene, ethylene, butane, methane and benzene in decreasing selectivities. Deposition of Mo2C on ZSM only slightly modified the catalytic behavior of ZSM-5. Its promoter effect came into prominence on silica surface.

Adsorption geometry of ethyl iodide on clean and oxygen covered Ru(001) surfaces: LEIS, XPS and TDS study

Ion scattering spectroscopy (LEIS) was used in conjunction with temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) for the study of the adsorption of ethyl iodide on clean and oxygen covered Ru(001) surfaces. The data suggest that ethyl iodide forms chemisorbed, physisorbed second (bilayer) and condensed multilayer on clean surface. On oxygen-precovered Ru(001) ethyl iodide molecules bond preferentially to Ru sites but very close to oxygen adatoms holding together by Coulomb forces. # 2003 Elsevier Science B.V. All rights reserved.

Effect of Gold on the Adsorption Properties of Acetaldehyde on Clean and h-BN Covered Rh(111) Surface

Auger electron spectroscopy, high-resolution electron energy loss spectroscopy and temperature programmed desorption methods have been used in order to investigate the adsorption properties and reactions of acetaldehyde on gold decorated rhodium and BN/Rh(111) surfaces. Scanning tunneling microscopy and X-ray photoelectron spectroscopy measurements were carried out to characterize the gold nanoparticles on clean and hexagonal boron nitride (h-BN) covered Rh(111). The adsorption of acetaldehyde was not completely hindered by gold atoms; however, depending on the structure of the outermost bimetallic layer (surface alloy) the dissociation of the parent molecule was suppressed, namely the production of carbon monoxide was inhibited by the gold domains. Our measurements with acetaldehyde on Au/h-BN/Rh(111) confirmed the observation that the lack of suitable adsorption sites eliminates the formation of CO. Nevertheless, increased coverage of gold enhanced the amount of adsorbed aldehyde at low temperature. We may predict that the low reactivity of acetaldehyde on Au/h-BN/Rh(111) significantly determine the ethanol decomposition mechanism on this surface.

The extreme light infrastructure—attosecond light pulse source (ELI-ALPS) project

Globally, large international research infrastructures have over many decades promoted excellence in science and technology. Aligned with the international practice, the Europe Strategy Forum for Research Infrastructures (ESFRI) has developed and keeps updating a roadmap for research infrastructures. The Extreme Light Infrastructure (ELI) is one of the two large scale Laser Research Infrastructures (RI) proposed in the ESFRI Roadmap published in 2006. ELI aims to provide access to some of the most intense world-wide lasers for the international scientific user community, as well as secondary radiation and particle sources driven by them, offering to the users new interdisciplinary research opportunities. ELI is currently implemented as a distributed infrastructure in three pillars: ELI-Beamlines (ELI-BL) in Dolni Břežany, Czech Republic, ELI-Attosecond Light Pulse Source (ELI-ALPS) in Szeged, Hungary and ELI-Nuclear Physics (ELI-NP) in Magurele, Romania. This chapter is devoted to introduce the Hungarian pillar, ELI-ALPS, which will be operational in Szeged in 2018, with the primary mission to provide to the users the highest laboratory spatiotemporal resolution and a secondary mission to contribute to the technological development towards 200 petawatt (PW) lasers for high-field science, which is the ultimate goal of the ELI project. The chapter includes descriptions of the primary and secondary sources, while emphasis is given to selected examples of the scientific case of ELI-ALPS, presenting unique access offered by the technologies to be hosted in the infrastructure.