Conversion of methane to benzene over Mo2C and Mo2C/ZSM-5 catalysts

The activation and dehydrogenation of CH₂ on Mo₂C and MO₂C/ZSM-5 have been investigated under non-oxidizing conditions. Unsupported Mo₂C exhibited very little activity towards methane decomposition at 973 K. The main reaction pathway was the decomposition of methane to give hydrogen and carbon with a trace amount of ethane. Mixing Mo₂C with ZSM-5 support somewhat enhanced its catalytic activity, but did not change the products of the reaction. A dramatic change in the product formation occurred on partially oxidized Mo2C/ZSM-5 catalyst; besides some hydrocarbons benzene was produced with a selectivity of 70–80% at a conversion of 5–7%. Carburization of highly dispersed MoO₃ on ZSM-5 also led to a very active catalyst: the conversion of methane at the steady state was 5–6% and the selectivity of benzene formation was 85%.This laboratory is a part of the Center for Catalysis, Surface and Material Science at the University of Szeged.     

Conversion of Ethane into Benzene on Re/ZSM-5

The reaction of ethane on pure and Re-containing ZSM-5 has been investigated at 773–973 K. Reaction products were analyzed using gas chromatography. ZSM-5 with Si/Al = 30 exhibited relatively high activity towards dehydrogenation, hydrogenolysis and aromatization of ethane above 773 K, whereas ZSM-5 with Si/Al = 280 showed very low activity. Deposition of 2% Re enhanced the conversion of ethane, the selectivity and the yield of benzene production even on the most effective ZSM-5. Further increase in the Re content did not lead to the improvement of the catalyst. The role of the Re is very likely the activation of ethane and the enhanced production of ethylene. ZSM-5 samples were found to be very active in the aromatization of ethylene, which was only slightly influenced by Re.     

Aromatization of n-hexane on Mo2C catalysts

The deposition-precipitation method was used to prepare gold catalysts based on different supports. Their catalytic activities for combustion of carbon monoxide (CO) and formaldehyde (HCHO) were investigated. All these catalysts showed good activity for the two reactions and the Au/CeO₂-a catalyst exhibited the highest activity for the two reactions. Furthermore, catalysts derived from the as-precipitate hydroxides exhibited higher activity than that from corresponding oxide supports. The BET, XRD, TEM and XPS were carried out. The results indicated that the gold dispersed more homogeneous on the as-precipitate hydroxide supports than that on the corresponding oxide supports.     

Loss and Noise Characteristics of Microwave Direct Modulated Optical Links

Loss and noise figure of optical links transmitting microwave signals —e.g. for remote antennas in wireless communications — are dealt with.Conditions are rather general and include arbitrary matching conditions, shotnoise, and laser relative intensity noise. Specific and somewhat surprisingcharacteristics are derived. Among others, it is shown, that — likepassive, purely microwave systems — noise figure is not proportional toelectrical loss and it can be even lower than loss itself. Optical powershould be as low as possible — this limit is mainly determined by therequired dynamic range of the system. Loss and noise figure were measured inan experimental setup. Results of the measurements proved the theoreticalfindings rather well. Preliminary results on the transmission of 32TCM signalsover the link are briefly presented.     

Effects of the nonlinearity of a Mach-Zehnder modulator on OFDM radio-over-fiber transmission

Radio-over-Fiber (RoF) techniques enable transmission of microwave and millimeter-wave signals for long distances with small loss. Due to the limited signal handling capabilities of electrical/optical components, proper leveling is necessary in order to achieve the highest dynamic range while maintaining distortion at acceptable level. This paper investigates the nonlinear distortion of Orthogonal Frequency-Division Multiplex (OFDM) signals caused by a Radio-over-Fiber stage in the transmission chain if a Mach-Zehnder electro-optical modulator is employed.     

A Comparative Study of the Decomposition of Ethanol on Pt Metals Supported by Carbon

The decomposition of ethanol has been investigated on Pt metals supported by carbon Norit of high surface area. The reaction starts above 450 K and approaches total conversion at 673–723 K. The major products are H₂, CO and CH₄. The selectivity of hydrogen formation on all metals supported by carbon Norit scattered around 30%, and almost ~40% of the hydrogen content of ethanol has been converted to gaseous hydrogen at the total conversion. The order of the efficiency of the metals based on the turnover frequencies is Ru > Pt > Ir > Rh > Pd. An advantageous feature of the Norit-supported Pt metals is that no deactivation occurred at 723 K in 10 h, which is in contrast to the behaviour of Pt/Al₂O₃. The high stability of the catalysts is attributed to the lack of reactive OH groups required for the formation of acetate poisoning the metals. Adding water to ethanol only slightly improved the production of hydrogen.     

A comparative study on the activation and reactions of CH4 on supported metals

The catalytic effects of silica-supported Pt metals were tested and compared in the decomposition of methane and its conversion into higher hydrocarbons. The dissociation of methane is readily measurable at 473–673 K. The rate of initial decomposition at 523 K was the highest on Rh, but it dropped to a low value within a short contact time. The gaseous products were hydrogen and ethane in small, variable amounts. Hydrogen of the carbonaceous species formed in the decomposition led to the production of aliphatic hydrocarbons.This laboratory is a part of the Center for Catalysis, Surface and Material Science at the University of Szeged.     

Realization of true-time delay lines based on acoustooptics

A true-time optical delay line for short radiofrequency (RF) pulses using path length dispersion is proposed. It is an optical implementation of the linear phase-shift theorem of the Fourier transformation. Acoustooptic signal processing is used for conversion into the optical frequency domain and for spatial Fourier decomposition of the pulse. The processing of the pulse is obtained by differentially phase shifting the particular frequency components, followed by a heterodyne reconversion into the RF domain. The optical system is intended to be used for delaying, but also for shaping and filtering of RF pulses, mainly in phased array radar antennas. Theoretical analysis of the system principle is given together with experimental results, demonstrating 2-μs time delay of 0.5-μs-long pulses with maximum optical phase shift of 1.2π. A detailed theoretical and experimental bandwidth analysis is carried out, pointing to the main technical problems and their solutions     

Posterior inferior cerebellar artery aneurysm in the fourth ventricle

We report a patient with a ruptured aneurysm of the choroidal branch of the right posterior inferior cerebellar artery (PICA), lying in and causing an isolated haemorrhage in the fourth ventricle. MRI on the first day after bleeding revealed an abnormal vessel in the fourth ventricle, which was surrounded by a mass of intermediate signal on T1- and T2-weighted images. The aneurysm was clipped via partial splitting of the lower vermis and opening the inferior medullary velum. A postoperative angiogram confirmed complete obliteration of the aneurysm. With PICA aneurysms the rate of intraventricular haemorrhage is high and in most cases due to reflux of blood. If there is an isolated intraventricular haemorrhage, a peripheral PICA aneurysm, lying in or near the fourth ventricle, may be suspected.