Alkylation of benzene with ethane over platinum-loaded zeolite catalyst

Alkylation of benzene with ethane was carried out using various zeolite catalysts at temperature ranges of 400–550°C. Loading of platinum onto zeolite greatly enhanced the yield of ethylbenzene. Among the zeolites tested, H-ZSM5 and H-MCM22 showed catalytic activities. By contrast, mordenite did not yield ethylbenzene. Moderate acid strength distribution is the key factor of zeolite catalysts. Optimum catalyst and conditions for this reaction are as follows. The platinum-loaded H-ZSM5 catalyst containing 6.8 wt% Pt, at a reaction temperature of 500°C, afforded ethylbenzene and styrene formation rates of 14.2 and 0.8 mmolh^–1g-cat^–1, respectively (benzene-based yields 7.3 and 0.4%). In the alkylation of benzene with ethane over platinum-loaded H-ZSM5, ethene was initially formed from ethane over the metallic platinum. Then the alkylation proceeded over the acid sites of H-ZSM5.     

Carbenium ion properties of octene-1 adsorbed on zeolite H-ZSM-5

It is shown that octene-1 adsorbed on zeolite H-ZSM-5 at ambient temperature exhibits carbenium ion properties. Namely: (1) According to²H NMR, the proton of the acidic Al-OH-Si group of the zeolite is transferred into the CH₂= group of the octene-1 molecule. (2) According to¹³C NMR the¹³C label inserted into the terminal CH₂= group of the octene-1 molecule is scrambled over its hydrocarbon skeleton. Thermodynamic and kinetic parameters for carbon scrambling are measured within the temperature range 290–343 K. The zeolite framework is shown to favour the formation of the linear rather than branched carbeniumion.     

Flow-through and flow-by porous electrodes of nickel foam Part III: theoretical electrode potential distribution in the flow-by configuration

This paper deals with the theoretical potential distribution within a flow-by parallelepipedic porous electrode operating in limiting current conditions in a two-compartment electrolytic cell. The model takes into account the influence of the counter-electrode polarization and of the separator ohmic resistance. The results show that the design of the porous electrode requires the knowledge of the solution potential distribution within the whole cell volume.Nomenclature a _c specific surface area per unit volume of electrode - C ₀ entrance concentration (y=0) - C _s exit concentration (y=y ₀) - E electrode potential (= _M – _S ) - E _o equilibrium electrode potential - F Faraday number - i current density - mean mass transfer coefficient - K parameter [a _ea zFi _oa/(_a RT)]^1/2 - L porous electrode thickness - n number of terms in Fourier serials - P specific productivity - Q volumetric flow-rate - mean flow velocity based on empty channel - V constant potential - V _R electrode volume - x thickness variable - X conversion - y length variable - y ₀ porous electrode length - z number of electrons in the electrochemical reaction Greek symbols parameter - parameter - ionic electrolyte conductivity in pores - _S solution potential - _M matrix potential ( _M = constant) - parameter [=n/y ₀ - parameter [=+K] - overpotential Suffices a anodic - c cathodic - eq equilibrium - s separator - S solution     

Water Vapor Sorption on Mesoporous Gamma-Alumina Prepared by the Selective Leaching Method

Water vapor adsorption and desorption properties of mesoporous -alumina prepared by the selective leaching method were investigated. The -alumina was prepared by selective leaching of amorphous silica from calcined kaolinite and mesopores were formed in the inside of the pseudomorph particles of kaolinite. It showed a very narrow unimodal pore size distribution at a radius of 3 nm. The specific surface area and total pore volume measured at –196°C by the BET method using nitrogen gas as adsorbate were around 240 m² g^-1 and 0.7 ml g^-1, respectively. Water vapor sorption isotherm measured at 25°C showed a type IV isotherm and a type H1 hysteresis loop at high partial pressure (P/P₀ region. The steep increase of water adsorption by capillary condensation occurred from around P/P₀=0.8 whereas that of water desorption by evaporation occurred from around P/P₀=0.75. 0These observed P/P₀ values shown were in good agreement with those calculated from the Kelvin equation using the pore radius of 3 nm. The maximum adsorption capacity of water vapor was ca. 600 ml g^-1 at P/P₀ = 0.9 and was larger than that of the commercial -alumina. The statistical thickness of water adsorbed on the surface of the samples calculated from the water adsorption and nitrogen adsorption isotherms of this -alumina was apparently thinner than that of the commercial -alumina and this difference was attributed to the characteristic microtexture of this -alumina. The effects of K₂O and SiO₂ components for the water vapor sorption isotherms of the -alumina were also discussed.     

In-Situ Coating of Zeolite Na-A on Al2O3-SiO2 Glass Fibers

In-situ coating of zeolite Na-A crystals on Al₂O₃-SiO₂ glass fibers was investigated by a low temperature chemical process. The glass fibers were reacted with various concentrations of NaOH solutions at 60–110°C for various times. The surface of glass fibers was first leached by the solution but crystals of zeolite Na-A precipitated on the glass fibers after a certain reaction time because the concentrations of Si and Al components in the solution increased by dissolution of the glass fibers. The precipitated zeolite was identified to be Na-A type but nosean-cancrinite-type phase and/or hydroxysodalite coexisted with zeolite Na-A at longer reaction times. With higher concentration of NaOH solution, the formation rate of zeolite Na-A was faster, the formation temperature was lower and the grain size was smaller ca. 2–3 m. Dense zeolite Na-A coatings were produced when the glass fibers were reacted in 4 M NaOH solution at 60°C for 18 h. The amount of zeolite Na-A formed on the fibers was about 20 mass%.     

Redox chemistry of highly dispersed rhodium in zeolite NaY

NaY zeolite exchanged with [Rh(NH₃)₅Cl]²⁺ ions have been studied using temperature programmed oxidation (TPO), temperature programmed reduction (TPR), and Fourier transformed infrared spectroscopy. The TPO profiles show that ammine ligands in NaY encaged [Rh(NH₃)₅Cl]²⁺ are destroyed above 300 °C, whereas the Rh precursor ion remains intact after calcination at 200 °C. TPR profiles in conjunction with the CO_ads IR spectra show that the reducibility of Rh by H₂ is largely controlled by the concentration of the surface protons, i.e. Rh³⁺+H₂Rh⁺+2H⁺ Rh⁺ + 1/2H₂Rh⁰+H⁺ In the presence of ammonia, the protons are neutralized and Rh³⁺ is reduced to Rh⁰. However, reduction remains incomplete when the concentration of protons is high. The ammonia was provided either by NH₃ admission or by conservation of ammine ligands by controlled calcination. CO adsorption does not lead to reoxidation of Rh⁰ particles to Rh⁺ ions.     

Methanol to Hydrocarbons: Enhanced Aromatic Formation Using Composite Group 13 Oxide/H-ZSM-5 Catalysts

The conversion of methanol to hydrocarbons using composite catalysts comprising physical mixtures of the zeolite H-ZSM-5 with group 13 oxides (-Al₂O₃, -Ga₂O₃, In₂O₃, Tl₂O₃) is reported and discussed. The addition of -Ga₂O₃ at 400 °C gives a marked enhancement in the yield of C₈ and C₉ aromatic compounds, whereas the addition of -Al₂O₃ has no effect and both the In₂O₃/H-ZSM-5 and Tl₂O₃/H-ZSM-5 are inactive. At 300 °C, a marked enhancement in the yield of aromatic hydrocarbons is observed for -Ga₂O₃ and In₂O₃, and a less marked enhancement is observed with Tl₂O₃ and -Al₂O₃. In particular, the addition of In₂O₃ to H-ZSM-5 as a simple physical mixture gives a significant enhancement in catalyst activity at 300 °C. The effect of the Si:Al atomic ratio of H-ZSM-5 is also investigated for the -Ga₂O₃/H-ZSM-5 composite catalysts and the enhancement in aromatic yield is observed with all the ratios investigated but the optimal -Ga₂O₃/H-ZSM-5 ratio is dependent upon the Si:Al ratio. Pretreatment or co-feeding of hydrogen decreases the yield of the aromatic products. The results are explained in terms of an active site formed by the interaction between the oxide and the zeolite.     

Synthesis of New Polyimides from Ru (II) Complex of 2,6-bis [1-(p-dimethylaminophenylimino) Ethyl] Pyridine

Pyridine-based tridentate ligand containing pendant NMe₂ unit was used to prepare novel polyimides via one-stage solution polycondensation due to their stability under a variety of oxidative and reductive conditions. Ru (II) complex of the pydim ligand was synthesized starting from [RuCl₂ (p-cymene)]₂ and 2,6-bis [1-(p-dimethylaminophenylimino) ethyl] pyridine. A series of stable polyimides were synthesized from Ru (II) complex of 2,6-bis [1-(p-dimethylaminophenylimino) ethyl] pyridine (2) and various aromatic dianhyrides had inherent viscosities ranging from 1.31 to 1.55 dL/g and were soluble in polar solvents. The glass transition temperatures were 245–308°C, and the 10% weight loss temperatures were above 482–548°C.     

Fabrication of YSZ electrolyte using electrostatic spray deposition (ESD):I – a comprehensive parametric study

Electrostatic spray deposition (ESD) was applied to fabricate a thin-layer (3 m thickness) yttria-stabilized zirconia (YSZ) electrolyte on a solid oxide fuel cell (SOFC) anode substrate consisting of nickel-YSZ cermet. Reducing the thickness of a state-of-the-art electrolyte, and thereby reducing the cell internal IR drop, is a promising strategy to make the intermediate temperature SOFC (ITSOFC) operating at 600–800 °C possible. About 8 mol% YSZ colloidal solution in ethanol was sprayed onto the substrate anode surface at 250–300 °C by ESD. After sintering the deposited layer at 1250–1400 °C for 17–6 h, the cathode layer, consisting of lanthanum strontium manganate (LSM), was sprayed or brush coated onto the electrolyte layer. Performance tests on the cell were carried out at 800 °C to evaluate the electrolyte layer formed by ESD. With a 97 H₂/3 H₂O mixture and air as fuel and oxidant gas, respectively, open circuit voltage (OCV) was found to be close to the theoretical value.     

Critical solution point and chain dimension of branched-polystyrene solutions

Summary Critical solution point and chain dimension were measured for branched polystyrene(BPS) in solution as a function of molecular weight(M) and compared with those for linear polystyrene(LPS). The critical concentration _c of BPS was quite different from that of LPS at a fixed M, but the same at a fixed overlap-concentration ^*, i.e., plots of _c vs. ^* fall on a single straight line for both BPS and LPS (gf_c ^*). Reduced critical temperature _c defined by gt_c=(–T_c)/ [T_c: critical temperature, : the -temperature] was related to _c as _{c c} ² for BPS, whereas _{c c} for LPS.     

Catalytic conversion of methane to benzene over Mo/ZSM-5

Dehydroaromatization of methane to benzene occurs over a 2 wt% Mo/ZSM-5 catalyst at 700C under non-oxidizing conditions. Following an initial induction period, during which CH₄ reactant reduces the original Mo⁶⁺ ions in the zeolite to Mo₂C and deposition of coke occurs, a benzene selectivity of 70% at a CH₄ conversion of 8–10% could be sustained for more than 16 h. X-ray photoelectron spectroscopy and X-ray powder diffraction measurements indicate that the reduced Mo is highly dispersed in the channels of the zeolite. Initial activation of CH₄ reactant occurs on Mo₂C sites, leading to the formation of C₂H₄ as the primary product. The latter then undergoes subsequent oligomerization reactions on acidic sites of the zeolite to form aromatic products.     

Pulse electrodeposition of titanium on carbon steel in the LiF–NaF–KF eutectic melt

Electrodeposition of titanium was carried out in the K₃TiF₆–LiF–NaF–KF melt using both direct (DC) and unipolar pulse current (PC) techniques. Dense and smooth titanium coatings were obtained by PC plating at 750 °C whereas DC plating led to rough and dendritic deposits. The best results were obtained using a 100C cm^–2 pulse charge and a cathodic current density of 50 and 75mA cm^–2. The cathodic current efficiency was in the range 60–65%. The titanium deposits obtained under such conditions behaved similarly to CP-titanium in NaCl and HNO₃ solutions at room temperature.     

Microcalorimetric studies of ammonia adsorption on γ-Al2O3, HNa-Y zeolite,and H-mordenite

The acidities of-Al₂O₃, HNa-Y zeolite, and H-mordenite have been examined by microcalorimetric measurements of ammonia adsorption at 423 K. The differential heat of adsorption on -Al₂O₃ decreases continuously with ammonia coverage from an initial value of 165 kJ/ mol at low coverages to a value of 70 kJ/mol at higher coverages. The differential heat of adsorption on HNa-Y zeolite shows similar behavior, with a plateau of nearly constant heat at 115 kJ/mol. H-mordenite exhibits a nearly constant heat of adsorption equal to 155 kJ/mol. The results from these microcalorimetric measurements are in agreement with thermogravimetric and temperature-programmed desorption results collected at higher temperatures. Adsorbed ammonia has sufficient mobility at 423 K to equilibrate with the catalyst surface on the time scale of microcalorimetric measurements, and these measurements provide an effective method for quantifying acid site distributions of solid-acid catalysts.     

Chemical Transformations in the Course of Solid-Phase Synthesis of Fibrous Alkali-Free Fluoroamphibole

This paper reports on the results of investigations into the possible chemical transformations occurring in the course of the solid-phase synthesis of fibrous alkali-free fluoroamphibole from synthetic magnesium silicate dihydrate (MSDH) MgO · SiO₂ · 2H₂O in the MSDH–MgF₂–NaCl model system in the concentration range of compositions corresponding to Mg-fluorocupfferite (Mg₇Si₈O₂₂F₂) at temperatures ranging from 60 to 1000°C. It is found that the formation of Mg-fluorocupfferite from MSDH under these conditions is a complex multistage chemical process. In the temperature range 60–700°C, dehydration, dehydroxylation of MSDH, and pyrohydrolysis of fluorides (MgF₂, SiF₄, etc.) proceed near the lower temperature boundary of the fluoroamphibole formation region (T 750°C). These processes result in the formation of compounds containing monomeric and simple polymeric silicon–oxygen anions [SiO₄]^4– and [SiO₃]^2– (forsterite, fluoronorbergite, enstatite, etc.). In the temperature range 850–900°C, the transformation of intermediate compounds leads to the formation of the fluoroamphibole structure. The main elements of this structure are silicon–oxygen anions of the [Si₄O₁₁]^6– type.     

Molybdenum nitride for the direct decomposition of NO

The physico-chemical properties of passivated -Mo₂N have been investigated. The material showed high activities for NO direct decomposition: nearly 100% NO conversion and 95% N₂ selectivity were achieved at 450C. The amount of O₂ taken up by -Mo₂N increased with temperature rise and reached 3133.9 molg^–1 at 450C; we conclude that there formation of Mo₂O_xN_y occurred. This oxygen-saturated -Mo₂N material was catalytically active: NO conversion and N₂ selectivity were 89 and 92% at 450C. We found that by means of H₂ reduction at 450C, Mo₂O_xN_y could be reduced back to -Mo₂N and the oxidation/reduction cycle is repeatable; such a behaviour and the high oxygen capacity (3133.9 molg^–1) of -Mo₂N suggest that -Mo₂N is a promising catalytic material for automobile exhaust purification.     

Comparison of polymerization catalyzed by thesyn andanti diastereomers of [ethylidene(1-η 5-tetramethylcyclopentadienyl)(1-η 5-indenyl)]titanium dichloride and methylaluminoxane

Summary Both the pure anti (1) and an equimolar mixture of1 and the syn (2) diastereomers ofrac-[ethylidene(1- ⁵-tetramethylcyclopentadienyl)(1- ⁵-indenyl)titanium dichloride have been synthesized. The polymerization behaviors of the two systems, activated by methylaluminoxane (MAO), have been compared from -20°C to +25°C. The2/MAO catalyst has about 30% more active species, which polymerizes propylene 20 to 50% faster depending on T _p , undergoes chain transfers less frequently, and produces PP of higher molecular weight than the1/MAO system.See reference 1     

Variable‐temperature IR spectroscopic studies of CO adsorbed on Na‐ZSM‐5 and Na‐Y zeolites

CO interacts with extraframework alkali metal cations (M⁺=) of zeolites to form both M⁺CO and M⁺OC species. By using variabletemperature FTIR spectroscopy, these Cbonded and Obonded species were found to be in a temperaturedependent equilibrium. For the same cation, the difference in interaction energy depends upon the zeolite framework. Thus, for the equilibrium process ZNa⁺=CO ZNa⁺OC, where Z represents the zeolite framework, H ⁰ was found to take the values 3.8 and 2.4 kJ mol^– for CO/NaZSM5 and CO/NaY, respectively. The Cbonded species show always the highest cation–CO interaction energy.     

Origin of rate bistability in Mn–O/Al2O3 catalysts for carbon monoxide oxidation: role of the Jahn–Teller effect

Peculiarities in catalytic activity in carbon monoxide oxidation as well as some structure, electronic and magnetic properties of the three oxide catalysts, Mn³⁺–O/Al₂O₃ (1), Mn³⁺–O–Fe/Al₂O₃ (Mn-substituted spinel, 2) and -Fe₂O₃/Al₂O₃ (3), were studied by kinetic measurements and by Mössbauer spectroscopy. The catalysts 1 and 2 showed a kinetic bistability with a sharp transition towards more reactive state at 200°C (ignition point). In contrast, for catalyst 3, at 200–250°C, the behavior of reaction rate against temperature did not display noticeable hysteresis. On cooling the catalysts 1 and 2, extinction was observed at about 170 and 120°C, respectively, i.e., at 30–80°C lower than the corresponding ignition points. Proximity of activation energy for the high and low activity (15–19 kJ/mol) for both Mn-containing catalysts suggests an increase in the number of active sites at high temperature with no changes in the reaction mechanism. The considerable difference between Mn-containing catalysts 1, 2 and Fe-containing catalyst 3 may be caused by Jahn–Teller (JT) type distortions of the oxygen polyhedron around Mn³⁺. A significant spontaneous axial bond stretching within the local polyhedron seems to diminish Mn–O binding energy, facilitate the participation of surface oxygen species, O_S, in the oxidation of CO by a redox mechanism and promote oxygen vacancies at the surface that would cause considerable effect on the activity. An increase in the width of the counterclockwise hysteresis loop for the catalyst 2 compared to the catalyst 1 indicates that clusters of mixed spinel provide more active sites and more labile O_S species than clusters of the binary Mn oxide.     

Oxidative dimerisation of propene to 1,5-hexadiene on Bi-Zn-O catalysts

The oxidative dimerisation of propene to 1,5-hexadiene has been investigated on Bi-Zn-O catalysts. The Bi₄₈ZnO₇₃ phase, observed in the catalysts calcined at 700 ° C is an active and selective catalyst for the formation of 1,5-hexadiene. The best catalytic performance (1,5-hexadiene selectivity 64%) has been obtained at 525 ° C, with a propene to oxygen ratio of 26, on a catalyst formed by Bi₄₈ZnO₇₃ with a small excess of ZnO.     

Formation and reactions of isocyanic acid during the catalytic reduction of nitrogen oxides

Reactions which can produce and consume isocyanic acid (HNCO) over two types of catalysts active for the reduction of nitrogen oxides have been investigated. More than 1000 ppm HNCO can be produced by the reduction of 3000 ppm NO with H₂/CO mixtures over a Pt/SiO₂ catalyst. Complete hydrolysis of HNCO to ammonia and carbon dioxide occurs if even weakly catalytic materials, such as CeO₂/SiO₂ and BaO/SiO₂, are placed downstream. Isocyanic acid is also involved as an intermediate in the reaction of nitromethane over CoZSM5 and CuZSM5 under the conditions of hydrocarbon SCR. In the initial stages of reaction there is complete conversion through to N₂ with CuZSM5 but the process stops at ammonia with CoZSM5 at temperatures below 350°C. In both cases, but especially with CoZSM5, isocyanic acid becomes observable as the catalyst deactivates during continuous exposure at temperatures below about 290°C. In situ FTIR measurements indicate that deactivation is due to a reaction between isocyanic acid and ammonia which generates cyclic striazine compounds.