Catalytic reaction of CH4 with CO2 over alumina-supported Pt metals

The dissociation of CH₄ and CO₂, as well as the reaction between CH₄ and CO₂ at 723–823 K have been studied over alumina supported Pt metals. In the high temperature interaction of CH₄ with catalyst surface small amounts of C₂H₆ were detected. In the reaction of CH₄+CO₂, CO and H₂ were produced with different ratios. The specific activities of the catalysts decreased in the order: Ru, Pd, Rh, Pt and Ir, which agreed with their activity order towards the dissociation of CO₂.This laboratory is a part of the Center for Catalysis, Surface and Material Science at the University of Szeged.     

Application of the MIMO Concept in Millimeter-Wave Broadband Wireless Access Networks

In the usual application of Multiple-Input, Multiple-Output (MIMO) and space–time coding (STC) the basis of the operation is a rich-scattering fading channel and a high density of links. In this paper a different situation: cellular millimeter-wave systems are investigated. It is shown that the MIMO concept can also have advantages in this case. Rain-induced fading characteristics and the concept of route diversity are briefly introduced. A route diversity system can be regarded as a parallel MIMO channel. Basic characteristics of these channels including capacity for various cases are investigated. Optimal codes are determined for space-time convolutional coding. Conceptual design of a route-time coding (RTC) system is shown. Simulation results on coding gain, based on empirical rain attenuation data are given.     

Efficient H2 Production from Ethanol over Mo2C/C Nanotube Catalyst

Mo₂C deposited on silica is an effective catalyst for the decomposition of ethanol; the extent of the reaction approached 100% even at 623–673 K. Beside H₂ several C-containing compounds were produced, which caused the low yield of hydrogen. Preparation of Mo₂C by the reaction of MoO₃ with multiwall carbon nanotube, however, dramatically altered the product distribution. The formation of hydrogen came into prominence; about 40% of hydrogen content of ethanol decomposed at 523–723 K has been converted into H₂. Another feature of the Mo₂C/C nanotube is the relatively slow deactivation. Adding water to ethanol further enhanced the hydrogen production.     

A Detailed Experimental Study of the LEO Satellite to Indoor Channel Characteristics

General investigations and results from ratherextensive measurement campaigns are presented tocharacterize the propagation channel of SatellitePersonal Communication Systems; in the measurements the satellite was simulated by a helicopter andmeasurements at S band and L band were made. A newconceptual partitioning of the full link is introduced;the measrement equipment and the environment aredescribed. The major part of the paper deals withpresentation of the measurement results and theiranalyses. Measured and analyzed are average lossincluding satellite elevation and azimuth positiondependence, first-order statistics, Doppler characteristics, andwide-band characteristics. Finally, some rather generalconclusions are drawn.     

Frequency-diversity improvement in n/1 high-capacitydigital microwave radio

Frequency diversity performance of digital microwave radio is investigated. Improvement ratio in n/1 systems is computed, based on the improvement ratio in 1/1 systems and the frequency dependence of the latter. Computed curves showing the dependence of IR on the channel position and of the position of the standby channel are given     

Photocatalytic reaction of H2O+CO2 over pure and doped Rh/TiO2

In the photocatalytic reduction of carbon dioxide to formic acid, formaldehyde and methanol in aqueous suspensions of TiO₂ and Rh/TiO₂, the effects of doping the TiO₂ with W⁶⁺ were investigated.This laboratory is a part of the Center for Catalysis, Surface and Material Science at the University of Szeged.     

Photocatalytic decomposition of formic acid and methyl formate on TiO2 doped with N and promoted with Au. Production of H2

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 H₂O 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.     

Importance of the Electric Properties of Supports in the Carrier Effect

It has long been recognized in heterogeneous catalysis that the efficiency of the catalyst can be markedly increased when supported by certain solids of large surface. Although this observation has been applied very fruitfully in the preparation of catalysts with technical importance, the reason for the carrier effect is still not fully understood. In earlier investigations the effect of support was explained mainly by saying that it stabilizes the state of the active component or that it increases the degree of dispersion and the surface area of the catalyst. There were, however, some observations stating that, besides the above-mentioned factors, there is a chemical interaction between the catalyst and the support which may also play an important role in producing the carrier effect. Therefore Adadurov and co-workers [1] have pointed out that, depending on its atomic radius and valence, the carrier polarizes the molecules of the catalyst, thus considerably altering the properties of the latter. Naturally, this interaction mainly involves those particles of the catalyst which have contact with the support.     

Formation and Migration of NCO Species on Ag/SiO2 Catalyst

The adsorption of HNCO has been investigated on Ag/SiO₂ catalyst by means of FTIR spectroscopy. Adsorption of HNCO on the reduced sample at 190 K produced an absorption band at 2,170 cm⁻¹ attributed to NCO bonded to Ag. Annealing the adsorbed layer under continuous degassing, the 2,170 cm⁻¹ band gradually attenuated and at the same time a spectral feature at 2,300 cm⁻¹ due to Si–NCO developed. From these spectral changes it was inferred that NCO bonded to Ag spilt over onto silica.