Comparison of the catalytic properties of Al‐ZSM‐22 and Fe‐ZSM‐22 in the skeletal isomerization of 1‐butene

The catalytic activities of Al‐ZSM‐22 (Al in the framework) and Fe‐ZSM‐22 (Fe in the framework) were compared in the skeletal isomerization of 1‐butene to isobutene. The catalysts synthesized in the laboratory were characterized by means of XRD, FTIR spectroscopy, SEM and surface area measurements. The activity of the zeolites was investigated using a fixed‐bed microreactor system. Al‐ZSM‐22 demonstrated higher activity in 1‐butene transformation compared to Fe‐ZSM‐22, while the selectivity to isobutene, on the other hand, was higher over Fe‐ZSM‐22. Coke formation was monitored using a microbalance and the results showed that the weight gain of Fe‐ZSM‐22 was slightly higher compared to Al‐ZSM‐22. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the conversion of 1‐butene over Pt‐ZSM5

The conversion of 1‐butene over Pt‐ZSM5 was studied in the presence and absence of hydrogen. In the absence of hydrogen, the catalytic activity of the metal was rapidly poisoned and in the steady state the catalyst showed identical properties as the parent ZSM5. In the presence of hydrogen, the skeletal isomerization of butene was not affected, but the rate of oligomerization/cracking was enhanced. From the by‐products butadiene, propane, ethane and methane, ethane and propane originated mainly from oligomerization/cracking on the acid sites and not from hydrogenolysis on Pt. The contribution of the metal to the overall by‐product formation was small. Thus, an adaptation of the acid rather than of the metal sites is necessary to improve the performance of the bifunctional catalyst. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of the Fuel Type on the Characteristics of Air‐Breathing Engines

Experimental studies of airbreathing engines operating on gaseous and liquid fuels are analyzed. It is shown that, for flight conditions with a Mach number 5 at the ground level, the results on operation and thrust–economic characteristics, which were obtained for hydrogenpowered engines, may be used directly in development of the ducts of hypersonic airbreathing engines operating on liquid organoborn fuels.     

Stereoselective Formation of 1,4‐Anhydro‐2‐C‐carboxytetritols in the Degradation of 1,5‐Anhydroribitol and 1,5‐Anhydroxylitol with Oxygen in Aqueous Alkali

Abstract

In addition to other acid products, degradation of 1,5‐anhydroribitol (5) and 1,5‐anhydroxylitol (6) with oxygen in 1.25 M NaOH produced diastereomeric 1,4‐anhydro‐2‐C‐carboxy‐D‐erythritol (7) and 1,4‐anhydro‐2‐C‐carboxy‐D‐threitol (8) and their enantiomers as major products. However, the ratio of the diastereomers differed for the two reactants. Thus, their formation could not proceed solely by benzilic acid‐type rearrangements through α‐dicarbonyl intermediates as typically proposed for formation of alkyl C‐carboxyfuranosides from alkyl glycopyranosides in similar reactions. The α‐dicarbonyl species that can form from 5 and 6 are identical. Potential mechanisms to account for stereoselective formation of 7 and 8 are presented.     

Modification of the alumina‐supported Mo‐based hydrodesulfurization catalysts by tungsten

The incorporation effect of tungsten as an activity‐promotional modifier into the Ni‐promoted Mo/γ‐Al₂O₃ catalyst was studied. Series of W‐incorporated catalysts with different content of tungsten were prepared by changing the impregnation order of nickel and tungsten onto a base Mo/γ‐Al₂O₃. Catalytic activities were measured from the atmospheric reactions of thiophene hydrodesulfurization (HDS) and ethylene hydrogenation (HYD). The HDS and HYD activities of the WMo/γ‐Al₂O₃ catalysts (WM series) initially increased and subsequently decreased with increasing content of tungsten as compared with those of their base Mo/γ‐Al₂O₃. The maximal activity promotion occurred at the W/(W + Mo) atomic ratio 0.025. For the Ni‐promoted Mo/γ‐Al₂O₃ catalysts, the effect of W incorporation was greatly dependent on the impregnation order of tungsten. The catalysts prepared by impregnating Ni onto the WMo/γ‐Al₂O₃ catalysts showed the same trend of activity promotion as for the WM series, while those by impregnating W onto a NiMo/γ‐Al₂O₃ catalyst resulted in lower activities than their base NiMo/γ‐Al₂O₃ catalyst. To characterize the catalysts, temperature‐programmed reduction and low‐temperature oxygen chemisorption were conducted. The effects of W incorporation on the NiMo‐based catalysts were discussed in reference to those on the CoMo‐based catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

High activity and stability of the Rh‐free Co‐based ex‐hydrotalcite containing Pd in the catalytic decomposition of N2O

The catalytic decomposition of nitrous oxide to nitrogen and oxygen has been studied over calcined hydrotalcite‐like compounds containing different combinations of bivalent (Co, Pd, Mg) and trivalent (Al, La, Rh) cations with carbonate as interlayer anion. The precursors were prepared by co‐precipitation under low supersaturation conditions and characterized by XRD and TG/DSC. The mixed oxides derived after calcination at 723 K were characterized by XRD, N₂ adsorption at 77 K, and XRF. The presence of Rh, La, or Pd in the Co‐based HTlc's improves considerably the catalytic activity. Co–Rh,Al‐HTlc (Co/Rh/Al==3/0.02/1) proved to be a very active catalyst, although the presence of the noble metal Pd in this catalyst ex‐Co,Pd–La,Al‐HT (Co/Pd/La/Al=3/1/1/1) produces a similar catalytic activity to that of Rh‐containing catalyst, both in a N₂O‐containing stream and in one containing also SO₂ and O₂, but with a better performance in stability tests. PdO phase has been identified by XRD as being responsible for the considerable improvement in the activity. The presence of Mg as spinel structure exerts a stabilizing effect in the more active catalysts when mixtures of SO₂ and O₂ are considered. This revised version was published online in July 2006 with corrections to the Cover Date.     

Vapour phase O‐methylation of 2‐naphthol over the solid bases alkali‐loaded silica and Cs‐loaded MCM‐41

O‐alkylation of 2‐naphthol has been investigated in the vapour phase over alkali‐loaded fumed silica and Cs‐MCM‐41. Both SiO₂ and MCM‐41 had low C‐alkylation activities and no O‐alkylation activity. The introduction of alkali ions considerably increases 2‐naphthol conversion with 2‐methoxynaphthalene being the major product. The activity of the catalysts increases with alkali loading and the basicity of the metal (Cs > K > Na > Li). Very high conversion (∼99%) of 2‐naphthol and selectivity (>95%) for 2‐methoxynaphthalene are obtained over Cs‐loaded fumed silica and MCM‐41. A small amount of 1‐methyl‐2‐hydroxynaphthalene is also formed over the Li‐, Na‐ and K‐loaded silica. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of Anions on the Extraction of Lanthanides (III) by N,N′‐Dimethyl‐N,N′‐Diphenyl‐3‐Oxapentanediamide

Abstract

The extraction of microquantities of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y by N,N′‐dimethyl‐N,N′‐diphenyl‐3‐oxapentanediamide (DMDPhOPDA) in 1,2‐dichloroethane from aqueous media containing ClO₄ ^?, PF₆ ^?, (CF₃SO₂)₂N^? anions or by DMDPhOPDA in 1,2‐dichloroethane in the presence of 1‐butyl‐3‐methylimidazolium bis[(trifluoremethyl)sulfonyl]imide ([C₄mim][Tf₂N]) and 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([C₄mim][PF₆]) from HNO₃ solutions has been studied. The effect of HNO₃ concentration in the aqueous phase and that of the extractant concentration in the organic phase on the extraction of metal ions is considered. The stoichiometry of the extracted complexes has been determined. The addition of HPF₆ and (CF₃SO₂)₂NH or their salts to the aqueous HNO₃ or HCl solutions leads to an enchancement of lanthanides (III) extraction by DMDPhOPDA. A considerable synergistic effect was observed in the presence of ionic liquids (IL) in the organic phase containing DMDPhOPDA. This effect is connected with the hydrophobic nature of the IL anion. The distribution of ILs between the equilibrium organic and aqueous phases can govern the extractability of lanthanides (III) in DMDPhOPDA‐IL systems.     

Action of the Coastal 1000‐Ton Surface Explosion on the Environment

Results of experimental investigations of the action of a coastal surface explosion of a 1000ton TNT charge on the environment are presented. Available databases were used, which are generally utilized for predicting ecological consequences of natural and maninduced explosive catastrophes, development of new methods of monitoring and identification of phenomena under consideration, their experimental and mathematical modeling, and testing of the models being developed.     

Prediction of the Elution Profile of Aromatic Compounds in RP‐HPLC

Abstract

An efficient prediction method for the elution profile was used to separate aromatic compounds such as benzene, toluene, chlorobenzene, o‐xylene, and 1,2‐dichlorobenzene by RP‐HPLC. The retention factor and bandwidth were predicted under linear‐gradient condition with the three retention models. The elution profiles were calculated based on the linear and quadratic equations of retention factor, lnk=lnk _w +S?, lnk=L+M?+N?², k=A+B/?, where ? was the vol.% of methanol. The elution profiles were calculated by the Gaussian distribution with obtained retention factor and bandwidth. Two kinds of experiments were performed; one is the isocratic runs to estimate the coefficients of three retention models, and the other is the linear gradient runs that were carried out with same initial mobile phase composition (water/methanol=96/4, vol.%), two final mobile phase compositions (water/methanol=24/76 and 40/60, vol.%), and three gradient times (20, 40, and 60 min). The predicted elution profiles by the three retention models and new prediction method have good agreement with experimental data in the employed gradient conditions. The minimum average errors of calculated and experimental results of aromatic compounds were lower than 3.5% by Bi‐poly equation.     

A Striking Effect of Ionic‐Liquid Anions in the Extraction of Sr2+ and Cs+ by Dicyclohexano‐18‐Crown‐6

Abstract

The nature of the ionic‐liquid (IL) anion has been found to have a remarkable effect on the solvent extraction of Sr²⁺ and Cs⁺ by dicyclohexano‐18‐crown‐6 dissolved in ionic liquids. In particular, the extraction efficiency increases with the hydrophobicity of the IL anion as reflected by the solubility in water of ILs having a common cation. Since a cation‐exchange mechanism is operating in these systems, the influence of the IL anion is in large part attributable to an expected Le Chatelier effect in which a greater aqueous concentration of IL cation, obtained when using an IL anion of lower hydrophobicity, opposes cation exchange. This dependence is opposite to that found for IL cations, indicating a significant advantage of using ILs with hydrophobic anions for cation extraction. Furthermore, the extraction selectivity for Sr²⁺ over Na⁺, K⁺, and Cs⁺ can be significantly improved through the use of hydrophobic anions for the ILs containing 1‐ethyl‐3‐methylimidazolium or 1‐butyl‐3‐methylimidazolium cations.     

Effects of decrease in number of acid sites located on the external surface of Ni‐SAPO‐34 crystalline catalyst by the mechanochemical method

In order to improve shape selectivity of the methanol to ethylene conversion and mitigate coke formation, the acid sites located on the external surface of Ni‐SAPO‐34 crystals were neutralized by the intrinsic mechanochemical method. Ni‐SAPO‐34 crystals were mixed in an agate mortar with basic alkaline or alkaline earth metal oxides supported on microspherical non‐porous silica. Their catalytic performances in methanol conversion were enhanced, especially in the case of BaO‐modified catalyst. The reason was verified by adopting the cracking of t‐butylbenzene, which could not access into the pore channel due to its bulky molecular size. These changes in the reaction performance consistently could be ascribed to the decrease of the acid sites on the external surfaces. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of silver on the catalytic activity of Cu‐ZSM‐5 for NO SCR by propane. Effect of the presence of water and hydrothermal agings

The effect of silver on the activity and hydrothermal stability of Cu‐ZSM‐5 for NOχ reduction with C₃H₈ under oxidizing and wet conditions has been investigated. The addition of silver as a cocation to Cu‐ZSM‐5 catalysts decreases the reversible inhibition by water occurring under catalytic conditions when the temperature does not exceed 773 K. Furthermore, it suppresses the irreversible deactivation observed when the reaction is performed up to 873 K. In effect, the Cu–Ag‐ZSM‐5 solids are more resistant to the dealumination induced by the acids formed by reactions between NO, O₂ and H₂O than the Cu‐ZSM‐5 ones. The presence of silver provides also an higher hydrothermal stability under an (air + 10 vol% H₂O) mixture if the temperature does not exceed 973 K. The catalytic activity and the deactivation behaviour are dependent on the concentration of silver and copper and more especially on the preparation procedure. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of the Location of the Detonation Initiation Point and the Position of the Air–Fuel Cloud on Explosion‐Field Parameters

The effect of the location of the initiation point on explosionfield parameters is studied numerically using as an example the detonation of a stoichiometric mixture of propane with air. The shape of the cloud of the mixture (toroid) and the ratio of its dimensions in calculations are typical of the volumes of air–fuel mixtures formed in accidents. The effect of the initiation point location within the cloud cross section was studied with variation in the position of the lower edge of the cloud above the underlying surface.     

IR study on the reaction path of skeletal isomerization of 1‐butene

The reaction molecularity of the skeletal isomerization on zeolite was deduced from IR spectra of adsorbed butene recorded with heating. Formation of polymeric species from adsorbed butene was observed on ZSM‐5 and beta zeolites, non‐selective catalysts for isobutene production. On the other hand, most of butene molecules adsorbed on ferrierite and clinoptilolite behaved monomolecularly, resulting in complete desorption even at ambient temperature. The exceptional selectivity for isobutene of ferrierite and clinoptilolite was ascribed to the sparse distribution of adsorbed butene molecules, suppressing bimolecular oligomerization and enhancing monomolecular skeletal isomerization. This revised version was published online in July 2006 with corrections to the Cover Date.     

Limits of Increasing the Penetration of Shaped‐Charge Jets by Pulsed Thermal Action on Shaped‐Charge Liners

The effect of preheating of liners on the penetration capability of shaped charges is considered theoretically. It is shown that for a plastically fractured shapedcharge jet, preheating of the liner generally increases the effective jet length and shapedcharge jet penetration. Restrictions on the parameters of preheating of shapedcharge liners due to the possible thermal initiation of the explosive are established. It is noted that excessive weakening of a shapedcharge jet can lead to transition from plastic to volume fracture with a corresponding decrease in shapedcharge jet penetration. The ultimate possibilities of the thermal method for increasing the penetration capability of shaped charges are estimated. Calculation results are compared with available experimental data.     

Triply‐promoted ethene epoxidation: NOx promotion of the Ag‐catalysed reaction in the presence of alkali and chlorine under electrochemical control

Potassium, electrochemically supplied from K β"‐alumina to a silver thin film catalyst in the presence of ppm levels of NO_x, strongly promotes the selectivity of ethene epoxidation. However, in the absence of gaseous NO_x, alkali catastrophically suppresses both activity and selectivity. Addition of surface chlorine via ppm levels of ethylene dichloride further enhances the promotional effect of alkali + NO yielding the highest selectivity of all. The minimum necessary and sufficient conditions for the appearance of NO_x promotion are submonolayer quantities of alkali on the metal surface, and ppm levels of gaseous NO_x. This revised version was published online in August 2006 with corrections to the Cover Date.     

Simulation of the Behavior of Mixtures of Heavy Particles Behind a Shock‐Wave Front

The twodimensional inviscid nonstationary flow behind a shock wave passing through solid uranium dioxide or carbide particles suspended in liquid iron was simulated numerically. Such layers can appear inside planets in the vicinity of the planet's solid core. Shock waves passing in the interior of a planet (resulting from a possible asteroid impact on the planet) can change parameters of the layer. The calculations demonstrated that the local particle massconcentration behind the incident and reflected shock waves increases considerably, which can cause a transition of the layer into a supercritical state and a nuclear explosion inside the planet. The problem was solved taking into account possible particle collisions and their deformation and fission as well as changes in the fields of major thermodynamic parameters inside and outside each particle.