A comparative study of the thermal stability and reactions of CH2, CH3 and C2H5 species on the Pd(100) surface

Adsorbed CH₂, CH₂ and C₂H₅ moieties were produced on Pd(100) at 90 K by photoinduced dissociation of the corresponding iodo compounds, and their thermal reactions were established.This laboratory is a part of the Center of Catalysis, Surface and Material Science at the University of Szeged.     

Infrared spectroscopic detection of Rh(1) by CO in supported Rh catalyst

The detection limit of Rh(1) in the Rh/Al₂O₃ catalyst in a form of Rh¹(CO)₂ was determined by FTIR spectroscopy. It was demonstrated that at least 0.5 g Rh, corresponding to 0.005 wt% of Rh, can be identified in this way. During synthesis gas conversion the predominant surface species is Rh _x -CO, but a detectable amount of Rh(1) exists on the catalyst up to 473 K.This laboratory is a part of the Center for Catalysis, Surface and Material Science at the University of Szeged.     

All-optical tunable filters built with discontinuity-assisted ringresonators

Numerically simulated performance is presented in a new type of bandstop and bandpass filters, built with discontinuity-assisted ring resonator (DARR)-loaded couplers. The operating characteristic of the bandpass filter is similar to that of a long grating with a centered cavity or a photonic crystal with a defect. The filters are tuned by varying the refractive index or the length of the waveguide forming the ring or the cavity. Selectivity and tuning range are controlled by the coupling coefficient of the couplers, by the order of resonance in the rings, and by the reflection coefficient of the discontinuities. A design procedure and the effect of loss are also presented     

Design of single and coupled microwave meta-material resonators in microsystem technology

In this paper Coupled Triangular Resonators in coplanar waveguide have been studied for S (2–4 GHz) and C (4–8 GHz) Band microwave applications. The peculiarity of the triangular structure to exhibit multiple resonances is usually proposed for dual and three-band purposes, to obtain efficient unit cells for high performance microwave tunable oscillators. One more characteristic of the triangular shape is the meta-material behavior, which allows a significant size decrease of the device. Coupled resonating configurations are proposed in this contribution, to be manufactured in Microsystem Technology by using polymeric layers as spacers between individual resonators organized in a vertical stack. Electromagnetic simulations have been performed to study narrow-band filters characterized by reduced dimensions, low insertion loss and steep band edges. Lumped element models are presented which can be easily implemented in commercial circuital software packages for the design of networks using these resonators.     

Decomposition of Propane and Its Reactions with CO2 Over Alumina-Supported Pt Metals

Propane underwent dehydrogenation and cracking on alumina-supported Pt metals at 823-923 K. Propylene formed with highest selectivity (50-80%) on Pt/Al₂O₃. The deposition of carbonaceous species was observed on every sample, the hydrogenation of which occurred only above 700-750 K with a peak temperature of 900-950 K. The presence of CO₂ basically altered the reaction pathway of propane, and the formation of CO and H₂ came into prominence. The highest specific rates for the production of H₂ and CO were measured for the Ru and Rh catalysts.     

Infrared Study of the NO + CO Interaction over Au/TiO2 Catalyst

It was demonstrated that, in contrast to previous results, an NCO surface complex does form on Au/TiO₂ catalysts in the high-temperature reaction of NO + CO. By means of Fourier transform infrared spectroscopy two new absorption bands at 2285 and 2105-2210 cm^-1, not observed in separate adsorption of reacting gases, were detected during the catalytic reaction. The former is attributed to Au-NCO and the latter to Ti-NCO species. It was assumed that, similar to the case of supported Pt metals, NCO is primarily formed on Au crystallites and then spills over onto titania. This idea was strengthened by the results obtained following the adsorption of HNCO on the catalyst and on the support.     

Dehydrogenation of methane on supported molybdenum oxides. Formation of benzene from methane

The dehydrogenation of methane on MoO₃ supported on various oxides has been investigated under non-oxidizing conditions in a fixed bed, continuous flow reactor. Detailed measurements were performed with MoC₃/SiO₂. The reaction of methane was observed above 923 K after a significant time lag, when a partial reduction of Mo⁶⁺ occurred, the reduced phase being characterized by X-ray photoelectron spectroscopy (XPS). The initial gaseous products are CO₂, H₂O, H₂ and CO. But this stage is followed by the dehydrogenation of methane and coupling of hydrocarbon fragments to various hydrocarbons. A possible pathway of the formation of benzene, the main product of reaction with selectivities ranging from 26 to 56%, is suggested.     

Reactions of adsorbed CH3 species with CO2 on Rh/SiO2 catalyst

Methyl radicals, produced by the high temperature pyrolysis of azomethane, were adsorbed on Rh/SiO₂. The reaction between adsorbed CH₃ and gaseous CO₂ has been followed by determining the intensity changes of the asymmetric stretch of CH₃ and the composition of the gas phase. It was found that adsorbed CH₃ reacts with CO₂ at and above 373 K. It is assumed that similar processes may also take place in the dry reforming of methane, and that they are responsible for the lack of carbon deposition on supported Rh catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Aromatization of ethanol on Mo2C/ZSM catalysts

The reaction of ethanol was investigated on Mo₂C, Mo₂C/SiO₂ and Mo₂C/ZSM-5 catalysts at temperature ranging 573–973 K under atmospheric pressure. Mo₂C and Mo₂C/SiO₂ catalyzed only the decomposition of ethanol to H₂, ethylene, acetaldehyde and different hydrocarbons. The main reaction pathway on pure ZSM-5 is the dehydration reaction yielding ethylene, small amounts of hydrocarbons and aromatics. Deposition of Mo₂C on zeolite greatly enhanced the yield of benzene and toluene by catalyzing the aromatization of ethylene formed in dehydration process of ethanol.     

Improvements in fiber-optic transmission of multicarrier TV signal

When the number of TV channels is high, a significant harmonic and intermodulation distortion arises. These distortions can be reduced by improving the modulation linearity of the laser or by applying a more appropriate modulation method. Both solutions are discussed and evaluated in detail. The linearity has been significantly improved by applying an active matching technique. The improvement achieved by the new driving circuit over the conventional one is 15 dB considering the third harmonic distortion. The sensitivity of QPSK TV transmission to disturbing interferences has been investigated. A so-called group modulation method offers a better approach for optical multicarrier TV transmission