Effect of carbon dioxide as oxidant in dehydrogenation of ethylbenzene over alumina-supported vanadium–antimony oxide catalyst

The dehydrogenation of ethylbenzene over alumina-supported vanadium–antimony oxide catalyst has been studied under different atmospheres such as inert nitrogen, steam, oxygen and carbon dioxide as diluent or oxidant. Among them, the addition of CO₂ gave the highest styrene yield (up to 82%) and styrene selectivity (up to 97%) along with stable catalytic performance. Carbon dioxide plays a beneficial role as a selective oxidant in improving the catalytic behavior through the oxidative pathway.     

A sparse preconditioned iterative method for vibration analysis of geometrically mistuned bladed disks

In this paper, the Static Mode Compensation method to predict geometrical mistuning effects on the response of bladed disks is reviewed and its limitations are analyzed. This method proved to be effective only for narrow clusters of modes under localized low rank perturbation. A new algorithm is introduced to address its deficiencies that draws on optimal preconditioned methods for generalized eigenvalue problem featuring sparse matrix vector multiplications, being more attractive under limited memory constraints of multi-millon DOF FEM models. The central idea of the SMC is to correct nominal eigenspace using modal acceleration method. It has been extended here by replacing the quasi-static set of modes with inexact solutions of the linear Jacobi–Davidson correction equations. Some heuristic strategies are discussed to lower the computational effort given the block-circulant structure of the nominal system. Numerical experiments on an industrial scale bladed disk model show that this leads to a very competitive tool. Computational performance and accuracy of both methods is compared in two areas of spectrum. The study demonstrates low accuracy of SMC method in the modal interaction zone, while validating efficiency and accuracy of the new algorithm in both areas.     

Gallium-loaded zeolites for light paraffin aromatization: evidence for exchanged gallium cation active centers

It is shown that certain metal-loaded zeolites (e.g., Ga-MFI) initially prepared as separate metal-containing and zeolite phases are reducible, resulting in solid-state transfer of the metal to the zeolite. The final material is similar to those initially prepared as ‘unsegregated’ by methods such as aqueous impregnation. Reduction occurs either through appropriate pretreatment or onstream in certain hydrocarbon reactions. First, preparation methods leading to one or the other type of material are examined. Then it is shown that reduced catalysts give far higher ratios of dehydrogenation to cracking rates (for alkanes) than either segregated or unsegregated but unreduced systems. The product distributions of the propane reaction at low partial pressure and low conversion are also reviewed, and new data presented for unsegregated, reduced catalysts. There are great differences in the distribution obtained using reduced 1/1 metal/A1 catalysts from corresponding distributions for the H-form zeolites or for segregated systems. The differences suggest a mechanism which may be entirely independent of catalysis by protons.     

Rain rate characteristics in Warsaw and in Dubna

In the years 1985-90, in frames of Intercosmos program, the measurements of 1-min average rain rate were conducted in Dubna (Russia) and in the years 1986–91 in Warsaw (Poland). In Dubna two or three tipping-bucket rain rate gauges were spaced out along the wave propagation experimental path and in Warsaw — five such sensors. Moreover in Warsaw 1-minute rain rate samples were applied for conversion of 1-minute rain rate distribution into 5-minute (10- and 20-minutes) rain rate distributions. The results of measurements and 1-minute rain rate samples conversion are presented in the paper.     

On solvability of a boundary integral equation of the first kind for Dirichlet boundary value problems in plane elasticity

The solution of a Dirichlet boundary value problem of plane isotropic elasticity by the boundary integral equation (BIE) of the first kind obtained from the Somigliana identity is considered. The logarithmic function appearing in the integral kernel leads to the possibility of this operator being non-invertible, the solution of the BIE either being non-unique or not existing. Such a situation occurs if the size of the boundary coincides with the so-called critical (or degenerate) scale for a certain form of the fundamental solution used. Techniques for the evaluation of these critical scales and for the removal of the non-uniqueness appearing in the problems with critical scales solved by the BIE of the first kind are proposed and analysed, and some recommendations for BEM code programmers based on the analysis presented are given.     

Oxygen-free precursor for chemical vapor deposition of gold films: thermal properties and decomposition mechanism

Thermal properties of oxygen-, phosphorus-, and halogen-free dimethylgold(III) diethyldithiocarbamate complex (CH₃)₂AuS₂CN(C₂H₅)₂ (gold, dimethyl(diethylcarbamodithioato -S,S′)-) having excellent storage stability and the mechanism of its decomposition to elemental gold were studied. Saturated vapor pressure was found to be ~10⁻³–10⁻¹ Torr at 50–90°C. Decomposition of the vapor on the surface starts at T = 210°C. The temperature dependence of gas phase composition was studied using the original mass spectrometric technique, it was established that the decomposition of the compound on the surface in vacuum follows three main pathways. Two of them result in the formation of elemental gold, saturated C2–C4 alkanes and (1) protonated ligand or (2) methylated ligand. The third one results in elemental gold and gaseous products: C2–C3 alkylmercaptanes and CH₃SCN(C₂H₅)₂. The formation of gold as a sole solid product within the temperature range 210–240°C was confirmed by X-ray photoelectron spectroscopy analysis. It was shown that the compound exhibits the best combination of volatility, thermal, and storage stability among volatile organogold complexes and thus it may be a promising precursor for obtaining gold films by chemical vapor deposition.     

Li collection experiments on T-11M and T-10 in framework of Li closed loop concept

The concept of a steady state tokamak with plasma facing components (PFC) on the basis of liquid lithium circulation demands the decision of three tasks: lithium injection to the plasma, lithium ions collection before their deposition on the vacuum vessel and lithium returning to the injection zone. Main subject of paper is the investigations of Li collection by different types of limiters intersected the scrape-of-layer (SOL) in T-10 and T-11M tokamaks. For finding solution for this problem in T-11M and T-10, experiments have been applied with Li-, C-rail limiters and ring SS R-limiter-collector (T-11M). The efficiency of Li collection by limiters in T-11M and T-10 tokamaks was investigated by post mortem sample–witness analysis and (T-11M) by the use of the mobile graphite probe (limiter) as a recombination target in the stream of lithium ions. The characteristic depth of lithium penetration in the SOL area of T-11M is about 2 cm and 4 cm in SOL of T-10. The quantitative analysis of the sample–witnesses located on T-11M limiters showed that 60 ± 20% of the lithium injected during plasma operating of T-11M had been collected by limiters. It confirms an opportunity of the lithium ions collection by limiters in tokamak SOL.