On the preparation and properties of CuZSM-5 catalysts for NO decomposition

Equilibrium exchange isotherms were determined for the exchange of Cu²⁺ with NaZSM-5 at varying Cu(Ac)₂ concentrations in solutions of constant volume and zeolite weight. At low Cu²⁺ levels the solid scavenged all the copper ions. When copper could be detected in the equilibrated solutions, overexchange was observed. The extent of overexchange was higher at pH 6 than at pH 4. These results were analyzed in relation to catalytic activity.On leave from the Central Institute for Chemistry, Hungarian Academy of Sciences, H1525 Budapest, Hungary.     

Characterization of poly(diethoxyphosphazene) by size exclusion chromatography and viscometry

Two samples of poly(diethoxyphosphazene) (PDEP) having very different molecular weights have been studied by viscometry and size exclusion chromatography in THF solution. The results obtained, together with light scattering data of these samples, allow the calculation of the Mark-Houwink constants a=0.65 and K=2.5 10^-4 in THF at 25°C. The method of calculation employed takes into account the great polydispersity of the samples. The characteristic ratio of the unperturbed dimensions was also calculated giving C_n = r²_o/n² 18, a value slightly higher than those previously reported for poly(dihexoxyphosphazene), C_n13 and poly (dichlorophosphazene), C_n13.5.     

Synthesis of new metal-containing side-chain monomers and polymers

New metal-containing vinyl monomers, hexyl-6-oxy-{4-[4-(4-carboxy cyclopentadienyl manganese tricarbonyl phenyl)phenyl]benzoyloxy}methacrylate and hexyl-6-oxy-{4-[4-(4-ferrocenoyl phenyl)phenyl]benzoyloxy}methacrylate, and the corresponding homopolymers and random copolymers with hydroxy monomer hexyl-6-oxy-{4-[4-(4-hydroxyphenyl)phenyl]benzoyloxy}methacrylate were synthesized. The compounds were characterized by¹H NMR; their thermal behavior was investigated by means of differential scanning calorimetry. Monomers and polymers containing the ferrocene unit melt at lower temperatures than those derived from the cyclopentadienyl managanese tricarbonyl moiety. The melting temperatures of the monomers and polymers ranged from 399 to about 515 K, Both monomers and polymers failed to exhibit mesogenic behavior. Values ofM _n,M _w,M _w/M _n, and degree of polymerization were obtained by gel permeation chromatography. TheM _n ranged from 16,500 for the copolymer containing hexyl-6-oxy-{4-[4-(4-ferrocenoyl phenyl)phenyl] benzoyloxy}methacrylate and hydroxy monomer hexyl-6-oxy-{4-[4-(4-hydroxyphenyl)phenyl]benzoyloxy}methacrylate at a 1:3 ratio to 26,000 for the copolymer containing hexyl-6-oxy-{4-[4-(4-carboxy cyclopentadienyl manganese tricarbonyl phenyl)phenyl]benzoyloxy}methacrylate and hydroxy monomer hexyl-6-oxy-{4-[4-(4-hydroxyphenyl)phenyl]benzoyloxy}methacrylate at a 1:3 ratio.M _w/M _n ranged from 1.6 in the case of the copolymer containing hexyl-6-oxy-{4-[4-(4-carboxy cyclopentadienyl manganese tricarbonyl phenyl)phenyl]benzoyloxy}methacrylate and hydroxy monomer hexyl-6-oxy-{4-[4-(4-hydroxyphenyl)phenyl]benzoyloxy}methacrylate at a 1:3 ratio to 2.2 in the case of poly(hexyl-6-oxy{4-[4-(4-carboxy cyclopentadienyl manganese tricarbonyl phenyl)phenyl]benzoyloxy}methacrylate).     

Effects of crystallinity and supermolecular formations on the interfacial shear strength and adhesion in GF/PP composites

Aim of this study was to screen the morphological effects on the interfacial shear strength (i) in glass fibre (GF) reinforced isotactic polypropylene (iPP) model composites. i was determined by a modified single fibre pull-out technique. It was established that the relation between i (5–6 MPa) and the yield stress of the iPP (y30 MPa) is at about 1:6 and that the i values were not influenced by the mophological superstructure set under isothermal crystallization conditions. Increased i was only observed when specimens were produced non-isothermally, by quenching (i9 MPa). This improvement could not be related to thermal shrinkage stresses. The enhancement in i was attributed to better wetting and improved adhesion due to the enlarged amorphous PP (aPP)-phase. A schematic adhesion model considering the wetting behaviour of aPP and iPP was proposed.     

Ultradrawing of “springy” polypropylene films

Summary It is demonstrated that in the process of ultradrawing of semicrystalline polypropylene the morphology of the initial material plays major role. Extremely high draw ratios are obtained (_max50) when drawing hard elastic polypropylene films perpendicular to their initial molecular orientation. This behaviour is explained by the molecular processes of plastic deformation.     

Weak Gel Behaviour of Poly(vinyl alcohol)-Borax Aqueous Solutions

Thermal transition of PVA-borax aqueous gels with a PVA concentration of 60 g/L and a borax concentration of 0.28 M was investigated at temperatures ranging from 15 to 60C using static light scattering (SLS), dynamic light scattering (DLS), and dynamic viscoelasticity measurements. Three relaxation modes, i.e. two fast and one slow relaxation modes, were observed from DLS measurements. Two fast relaxation modes located around 10^–310¹ sec, with one fast mode (_f1) being scattering vector q-dependent and the other fast mode (_f2, with _f2>_f1) being q-independent. The _f1 mode was attributed to the gel mode whilst the _f2 mode could be due to the hydrodynamics of intra-molecular hydrophobic domains formed by uncharged segments of polymer backbones. The slow relaxation mode with relaxation time located around 10¹10³ sec in DLS data was due to the motion of aggregated clusters and was observed only at temperatures above 40C. The amplitude and relaxation time of slow mode decrease as temperature is increased from 40 to 60C. At temperatures below 40C, no slow relaxation mode was observed. The SLS measurements showed PVA-borax-water system had fractal dimensions D _f2.4 and D _f2.0 as temperature was below and above 40C, respectively. The simple tilting test indicated gel behaviour for the PVA-borax aqueous system at temperatures below 40C with a creep flow after a long time exposure in the gravity field. But the dynamic viscoelasticity measurements demonstrated a solution behaviour for PVA/borax/water at temperatures below 40C, the critical gel point behaviour for G() and G() was not observed in this system as those reported for chemical crosslinked gels. These results suggest that the PVA-borax aqueous system is a thermoreversible weak gel.     

Electrodeposition, composition and structure of Zn—Cr alloys

The effect of polyethylene glycol (PEG 1500) as additive and of deposition conditions on Zn—Cr alloy electrodeposition from an acidic sulfate electrolyte at room temperature, without agitation was investigated. PEG polarizes the overall cathodic reaction and inhibits Zn deposition. Cr codeposition with Zn starts at a cathodic potential of about –1,95 V vs Hg/Hg₂SO₄, which is reached at current density of about 20 A dm^–2 in galvanostatic conditions. Zn—Cr alloy coatings containing up to 28 at % Cr were obtained depending on the plating conditions. SEM observations showed an island-like structure, formed by the local growth of crystals, which covered the surface during further deposition. In the first stages of electrodeposition the powder diffraction spectra contain lines of b.c.c. -(Zn,Cr) phase (a 3.02 Å). After 30 s deposition time weak lines of Zn-based phase (a 2.67 Å, c 4.90 Å) appear, and become clearly visible in coatings deposited for 90 s. The average Cr content in the alloy coatings decreases with advancing deposition. The as-plated surface contains C in organic compounds and Zn(OH)₂. After 50 min sputtering, Zn and a mixture of Cr, Cr₂O₃ and Cr₇C₃ were found. The presence of organic C and O, probably from inclusions of PEG, were also detected.     

The application of Taft-Hancock steric constants to the free-radical initiated copolymerization of N-alkylmaleimides with α-methylstyrene

Summary The rates of free-radical initiated alternating copolymerization of -methylstyrene with N-alkylmaleimides (RMI) decrease in the following order: Me>Et>n-Prn-Bun-Hex>iso-Pr>tert-Bu. A linear relationship was established in the plots of log(k_R/k_Me) against polar substituent constants ^*, true steric factors E_S and corrected steric factors E_S ^C. The best fit was obtained in plots of log (k_R/k_Me) against ^* and E_S ^C while a large scattering of results was observed in the plot of log(k_R/k_Me) against E_S.     

Ethynylene-disilanylene copolymers

Polymers of structure (SiR₂SiR₂-C C-SiR₂SiR₂-C C) _n , in which ethynylene units alternate with disilylene units, have been prepared by two routes: (a) condensation of dichlorodisilanes with dilithium derivatives of 1,2-diethynyldisilanes and (b) ring-opening polymerization of strained cyclic disilanylene-acetylnes, (SiR₂SiR₂C C)₂. The polymers display UV absorption near 240 nm indicative of – conjugation between the Si₂ and the C C moieties. Polymers with R=R=n-Bu or R=n-Bu, R=Ph, undergo solid-state transitions to form liquid crystalline mesophases resembling those observed for many poly(silylenes). Single crystals were obtained for the polymer with R=R=CH₃, by precipitation from dilute cyclohexane solution. The solid-state properties and structures of this family of polymers are discussed.This paper was presented at the Second International Topical Workshop, Advances in Silicon-Based Polymer Science.     

Current Waves Generated by Detonation of an Explosive in a Magnetic Field

The structure of the electromagnetic field in detonation of a condensed explosive in a magnetic field is analyzed qualitatively. Propagation of a detonation wave in a magnetic field leads to generation of an electric current in explosion products. The physical reason for current generation is the freezing of the magnetic field into the conducting substance at the detonation front and subsequent extension of the substance and the field in the unloading wave. The structure of the current layer depends on the character of the boundary magnetic fields and conditions on the surface of initiation of the explosive. Detonation of the explosive in an external magnetic field B₀ generates a system of two currents identical in magnitude but opposite in direction. The structure of the arising current and its absolute value are determined by the parameter R₁ = _{0 0}D²t (₀ is the magnetic permeability of vacuum, ₀ is the electrical conductivity of detonation products, D is the detonationfront velocity, and t is the time). The value of the current increases with the detonationwave motion, and the linear current density is limited from above by 2B₀/₀. For R₁ 1, the electric field in the conducting layer is significantly nonuniform; for detonation products with a polytropic equation of state, a region of a constantdensity current is adjacent to thedetonation front. The results of this analysis are important for interpretation of experiments performed and development of new methods for studying the state of the substance in the detonation wave.     

Composition dependence of the oxygen-evolution reaction rate on Ir x Ti1−x O2 mixed-oxide electrodes

Mudcrack-free oxide films of Ir _x Ti_1–x O₂ (0 < x 1) on titanium substrates were obtained, and the effects of the oxide composition on the rate of oxygen-evolution reaction were investigated. At x 0.6, Ir-rich grains appear on the mudcrack-free surface. In the purely single-phase region (0 < x 0.5), the pseudo-capacitive charge is proportional to the surface composition, x _s, and the exchange-current density for the oxygen-evolution reaction increases linearly with x _s at 0.2 x _s 0.5, with an extrapolated intercept at x _s 0.15, below which the oxides are inactive.     

13C NMR chemical shifts of polyisobutylene end groups and related model compounds

Summary The detailed end-structures of CH₃-,-Cl, exo-olefin, endoolefin, and-OH ended polyisobutylenes (PIB) have been characterized by high resolution¹³C NMR spectroscopy. Specifically, the¹³C chemical shifts characteristic of the various carbons in the following structures have been determined: CH₂C(CH₃)₂-CH₂C(CH₃)₃, CH₂C(CH₃)₂CH₂C(CH₃)₂Cl, CH₂C(CH₃)₂CH₂C(CH₃)=CH₂, CH₂C(CH₃)₂CH=C(CH₃)₂, and CH₂C(CH₃)₂CH₂CH(CH₃)CH₂OH. The structure analysis of model compounds was of utmost help in these investigations. The above information is of great value for the identification of terminally functional PIBs and analysis of reaction mixtures.     

Synthesis of ternary Li–Mn–O phase at a temperature of 260 ∘C and electrochemical lithium insertion into the oxide

A lithium–manganese oxide, Li _x MnO₂ (x=0.30.6), has been synthesized by heating a mixture (Li/Mn ratio=0.30.8) of electrolytic manganese dioxide (EMD) and LiNO₃ in air at moderate temperature, 260 C. The formation of the Li–Mn–O phase was confirmed by X-ray diffraction, atomic absorption and electrochemical measurements. Electrochemical properties of the Li–Mn–O were examined in LiClO₄-propylene carbonate electrolyte solution. About 0.3 Li in Li _x MnO₂ (x=0.30.6) was removed on initial charging, resulting in characteristic two discharge plateaus around 3.5V and 2.8V vs Li/Li⁺. The Li _x MnO₂ synthesized by heating at Li/Mn ratio=0.5 demonstrated higher discharge capacity, about 250mAh (g of oxide)^–1 initially, and better cyclability as a positive electrode for lithium secondary battery use as compared to EMD.     

Electrosynthesis of 4,4′-dinitroazobenzene on PbO2 electrodes

Parameters which affect the electrosynthesis of 4,4-dinitroazobenzene from p-nitroaniline on platinum and PbO₂ electrodes were investigated and optimum conditions were determined. Maximum conversion efficiency for electrosynthesis was 95% with a pure -PbO₂ electrode. It was found that the electrocatalytic activity of a PbO₂ electrode depends upon its / ratio and its degree of crystallinity. The effects of the added base and water on the conversion efficiency were also elucidated.     

Hreels study and catalytic significance of low-temperature interaction of isolated carbon atoms with hydrogen on Pt(111)

Isolated atoms of carbon evaporated on to Pt(111) react with hydrogen atT170 K to form methine species, characterized with vibrational modesv(CH) at 2960 and (CH) at 800 cm^–1. The high reactivity ofC _ads is in line with their ability to take part as intermediates in the metanation reaction. CH_ads species are stable up toT 500 K; further heating leads to their dissociation accompanied by H₂ desorption and formation of unreactive graphite-like islands.     

Synthesis and Redox Properties of a π-Conjugated Cyclobutadienecobalt Polymer Containing Ferrocenyl Groups

The reaction of CpCo(PPh₃)₂, in which Cp= ⁵-cyclopentadienyl, with a -conjugated diacetylene, FcCC–o-C₆H₄–CCFc, in which Fc=ferrocenyl, was found to give a cyclobutadienecobalt mononuclear complex, { ⁴-C₄Fc₂(o-FcC₆H₄)₂}CoCp (1), the crystal structure of which was determined by X-ray crystallography. In contrast, the reaction of CpCo(PPh₃)₂ with FcCC–p-C₆H₄–CCFc affords a cyclobutadienecobalt polymer, [p-C₆H₄( ⁴-C₄Fc₂)CoCp] _n (2). The monocobalt complex 1 shows reversible 1e^– and 3e^– redox waves at E ⁰=0.116 and 0.350 V vs Ag/Ag⁺, and the polymer complex 2 shows two chemically reversible redox waves at E ⁰=0.143 and 0.219 V for the oxidation of the ferrocenyl moieties in the cyclic voltammogram. Crystal data are as follows: (1, C₆₅H₄₉CoFe₄), triclinic, space group P\={1} (No. 2), a=13.547(4), b=16.197(4), c=11.763(4) Å, =106.79(2), =97.93(3), =97.12(3), V=2410(1) ų, Z=2.     

Characterization of some organic poly(aminiumphosphate)s

Summary Metachromatic reactions of MB and AO are studied with poly(aminium phosphate)s. The main band() at 665 m and 492 m for MB and AO are shifted to 580 m and 455 m respectively (-bands). The metachromatic values at different concentrations of poly(aminium phosphate)s are also reported. The dye association for MB with these polymer derivatives is investigated conductometrically as well. It is observed that MB can be at the most bind with the phosphate residue of polymer upto 11 molar ratio. The polymeric nature was further established by paper chromatographic technique in Terry's, Ebel's & Pfrengle's solvents.     

Does Density of Cationic Sites Affect Catalytic Activity of Co Zeolites in Selective Catalytic Reduction of NO with Methane?

Selective catalytic reduction of NO with methane (CH₄-SCR) in an excess of oxygen over Co ions located in ZSM-5 of various Si/Al composition and in ferrierite, mordenite, chabazite and beta zeolite was investigated. From the comparison of the dependence of the TOF values per Co ion for NO conversion to N₂ and Co ions distribution among the cationic sites on total Co ion concentration, the catalytic activity of the individual Co ions was estimated. The -type Co²⁺ ions, located in the main channel of mordenite and ferrierite and coordinated above the rectangle of four framework oxygens of the channel wall exhibit the highest activity in these zeolites. On the other hand, the -type Co²⁺ ions coordinated in the plane of four oxygens of the deformed six-member ring located in the channel intersection of ZSM-5 and in channels of beta zeolite control the activity of these Co zeolites. The sequence of activity of Co²⁺ ions in CH₄-SCR of NO was FER Co>ZSM-5 Co>BEA CoZSM-5 CoFER CoMOR CoCHA CoMOR Co. A correlation between the activity of the individual Co ions in CH₄-SCR of NO and a distance between the cationic sites was observed.     

Triggering of Detonation upon Flame Interaction with an Expansion Wave

The transition of a deflagration wave into an abruptly expanding part of a plane channel, where a quasisteady supersonic underexpanded jet of an unburned gas is formed, is studied for a propane–oxygen mixture using schlieren pictures. Two explosioninitiation modes (weak and strong) are registered. In the first case, almost instantaneous onset of the detonation wave occurs when the flame front enters the expanding section; the initial velocity of this wave is approximately 1.5 times the Chapman–Jouguet detonation velocity (D_CJ) and then decreases to a value corresponding to selfsustaining detonation. In the second case, the front velocity gradually increases from 0.4D _CJ to 1.0D _CJ. It is established that the starting pulse triggering the transformation of turbulent combustion to explosion and detonation regimes is generated by interaction of the flame front with expansion waves, which are elements of the structure of the initial section of the jet.     

Simulation of kinetics of nitrogen desorption from Rh(111)

Associative desorption of N atoms from the Rh(111) surface is simulated in the framework of the lattice-gas model. The Arrhenius parameters and nearest-neighbour lateral interaction employed to describe the measured thermal desorption spectra are as follows:v=10¹³ s^–1,E _d=40 kcal/mol, and ₁=1.7 kcal/mol. The results obtained are used to clarify the role of nitrogen desorption in the NO + CO reaction on Rh(111) atT=400–700 K andP _NOP _CO0.01 atm.