Evidence for a high oxygen mobility in Li/MgO

The oxidative properties of Li/MgO in the absence of O₂ were studied at 730° C using C₂H₄ as a reducing agent and a multisectional flow stainless steel tubular reactor. Large amounts of CO and H₂ were determined. It was demonstrated that Li/MgO exhibited a high oxygen mobility. The exchange capacity was (2.4–4.0) × 10²⁰ oxygen atoms per 1 g of the catalyst and the period of oxygen donation was 150 h or more. After the catalyst reduction, its oxygen transfer ability was fully restored by re-oxidation in the stream of air. Oxidation of C₂H₄ to CO and H₂ was accompanied by its decomposition to C and H₂. The ratio H₂/C₂H₄ was found to be 1.91 ± 0.13 independently of the oxidation state of the catalyst, the location of the sampling point along the catalyst bed (and the post-catalytic zone) and the duration of the experiment. The mechanism was discussed.     

Hydrogenation of cyclopentadiene on a nickel catalyst

The hydrogenation of cyclopentadiene on Ni catalyst was carried out with a fixed bed reactor. The initial reaction rates were expressed by the following equations. The activation energies of overall-and surface-reaction rates were, respectively, 1.9 and 6.5 kcal/mol and the heats of adsorption of hydrogen and cyclopentadiene were, respectively, 5.6 and 1.6 kcal/mol. The hydrogenation of cyclopentadiene on Ni catalyst is a consecutive reaction passing through cyclopentene, where the activation energy of the 1st stage is higher than that of the 2nd one, namely, E₁ > E₂. At the lower ratio of P_H/P_C, cyclopentene is produced with 100% selectivity, whereas, increasing P_H/P_C or W/F₀, the selectivity decreases. At the intermediate reaction temperature, there appears the minimum selectivity. This phenomenon is considered to be due to E₁ > E₂.     

Synthesis and Crystal Structure of Two Coordination Polymers Assembled from a Versatile 4-(4-Hydroxypyridinium-1-yl)phthalic Acid

Two coordination polymers, namely, [Ni(L)(C₂H₃N)(H₂O)₅] _n (1), and [Mn(L)(H₂O)₂] _n (2) have been hydro(solvo)thermally synthesized through the reaction of 4-(4-hydroxypyridinium-1-yl)phthalic acid (H₂L) with divalent nickel and manganese salts. As a result of various coordination modes of the versatile 4-(4-hydroxypyridinium-1-yl)phthalic acid, these compounds exhibit structural diversity. Complex 1 exhibits a 3D coordination framework through the rich hydrogen bond. Complex 2 exhibits a 3D coordination network based on layers. These complexes have been characterized by powder X-ray diffractions (PXRD), IR spectroscopy, elemental analysis, thermogravimetry, single-crystal X-ray crystallography and solid UV spectroscopy.     

Methane Aromatization over 2 wt% Mo/HZSM-5 in the Presence of O2 and NO

In the non-oxidative aromatization reaction (temperature = 770 C, flow rate = 34 ml min^-1), 2 wt% Mo/HZSM-5 deactivated after 4 h due to severe coking. We observed that with a suitable amount of O₂ (5.3 vol%) in the methane feed, the catalyst could last for more than 6 h with a ca. 4% yield of aromatics at 770 °C. Depending on the concentration of O₂ or the reaction temperature, there are three reaction zones in the catalyst bed: (i) methane oxidation; (ii) methane reforming; and (iii) methane aromatization. CO and H₂ produced in the first two zones are accountable for stability amelioration of the catalyst. The addition of NO exhibited similar effects on the reaction. Further increase in O₂ (8.4 vol%) or NO (14.2 vol%) concentration would result in CO and CO₂ being the predominant carbon-containing products; C₂H₄ and C₂H₆ were generated in small amounts and no aromatics were detected.     

Fracture behavior of coated/uncoated graphite-epoxy composites

The static delamination behavior of graphite/epoxy composite specimens subjected to mode I tensile opening (using UDCB

1 Uniform double cantilever beam.

specimens), and pure mode II shear loading (using ENF

2 End-notched flexural.

specimens) were studied. The graphite epoxy composites for the study were made from commercially treated fibers, with and without an electropolymerized interlayer. The mode I fracture energy (G_IC) was found to be significantly higher (more than 50 percent) for the coated fibers. However, this improvement was accompanied by a high reduction (more than 3 times) in the mode II fracture energy (G_IIC). This effect is apparently related to poor adhesion between the interlayer and the epoxy resin, which may be corrected by use of a “top layer” of appropriate composition to form chemical bonds between the phases. The fracture toughness (K_IC) of composites made with commercially treated fibers was also evaluated, using double side-notched specimens.     

FTIR investigation of ethylene coordination and polymerization on reduced Cr/SiO2 catalyst

FTIR spectroscopy was applied to study the initial steps of ethylene polymerization on reduced chromia-silica (0.5 wt% Cr/SiO₂). To decrease the speed of the reaction small doses of gas were introduced to the catalyst in each run and C₂D₄ was used to confirm band assignments. At the initial steps of the reaction only ethylene molecules coordinated to probably Cr _A ²⁺ cations were observed. The concentration of such complexes was estimated to be about 50% of the total amount of Cr atoms in the sample. The FTIR spectrum of the polymer formed at the initial doses of C₂H₄ (when [C₂H₄] [Cr]) was found to be slightly different from that formed after excess ethylene was introduced onto the catalyst ([C₂H₄] > [Cr]).     

Photocatalytic Generation of H<Subscript>2</Subscript> Gas from Neat Ethanol over Pt/TiO<Subscript>2</Subscript> Nanotube Catalysts

TiO₂ nanotubes promoted with Pt metal were prepared and tested to be the photocatalytic dehydrogenation catalyst in neat ethanol for producing H₂ gas (C₂H₅OHC₃CHO +H₂). It was found that the ability to produce H₂, the liquid phase product distribution and the catlyst stability of these promoted nano catalysts all depended on the Pt loading and catalyst preparation procedure. These Pt/TiO₂ catalysts with TiO₂ nanotubes washed with diluted H₂SO₄ solution produced 1, 2-diethoxy ethane (acetal) as the major liquid phase product, while over those washed with diluted HCl solution or H₂O, acetaldehyde was the major liquid phase product.     

Thermal decomposition of C2H5I on Ag(111)

The decomposition of C₂H₅I on Ag(111) has been studied using temperature programmed desorption (TPD), work-function change measurements () and X-ray photoelectron spectroscopy (XPS). Adsorption of C₂H₅I at 100 K is mostly molecular with little dissociation. C-I bond cleavage starts around 110 K. Below 1 monolayer coverage, all adsorbed C₂H₅I(a) dissociates to C₂H₅(a) and I(a) during TPD. C₂H₅(a) undergoes only recombination, producing gas phase butane (C₄H₁₀) around 190 K. No C-H or C-C bond cleavage takes place. On D/Ag(111), hydrogenation of C₂H₅(a) to C₂H₅(g) occurs readily between 150 and 220 K.     

Steam reforming of LPG over Ni and Rh supported on Gd-CeO2 and Al2O3: Effect of support and feed composition

The steam reforming of liquefied petroleum gas (LPG) over Ni- and Rh-based catalysts supported on Gd-CeO₂ (CGO) and Al₂O₃ was studied at 750-900 °C. The order of activity was found to be Rh/CGO > Ni/CGO ∼ Rh/Al₂O₃ > Ni/Al₂O₃; we indicated that the comparable activity of Ni/CGO to precious metal Rh/Al₂O₃ is due to the occurring of gas-solid reactions between hydrocarbons and lattice oxygen () on CGO surface along with the reaction taking place on the active site of Ni, which helps preventing the carbon deposition and promoting the steam reforming of LPG.The effects of O₂ (as oxidative steam reforming) and H₂ adding were further studied over Ni/CGO and Ni/Al₂O₃. It was found that the additional of these compounds significantly reduced the amount of carbon deposition and promoted the conversion of hydrocarbons (i.e., LPG as well as CH₄, C₂H₄ and C₂H₆ occurred from the thermal decomposition of LPG) to CO and H₂. Nevertheless, the addition of too high O₂ oppositely decreased H₂ yield due to the oxidizing of Ni particle and the possible combusting of H₂ generated from the reaction, while the addition of too high H₂ also negatively affect the catalyst activity due to the occurring of catalyst active site competition and the inhibition of gas-solid reactions between the gaseous hydrocarbon compounds and on the surface of CGO (for the case of Ni/CGO).     

A comparison of the catalytic performance of the layered oxychlorides of bismuth,lanthanum and samarium in the conversion of methane to ethylene

BiOCl is very efficient as a catalyst for the oxidative coupling of CH₄ to yield C₂ products, conversions of more than 20 percent and ratios of C₂H₄/C₂H₆ from 30 to 60, depending upon the precise conditions, being obtained at ca 700 °C. Its longevity, however, is rather poor: under operating conditions the solid lacks structural stability. Although LaOCl and SmOCl, each of which is isostructural with BiOCl, are inferior catalysts so far as C₂H₄/C₂H₆ ratios are concerned (0.3 to 0.6), they have superior stability. The same is true of the solid-solutions (Bi_0.5,La_0.5) OCl, the structural parameters of which were determined by X-ray powder Rietveld analysis. Both (Bi_0.5, Sm_0.5) OCl and (Bi_0.5, La_0.5) OCl yield C₂H₄/C₂H₆ ratios of close to unity at 700 °C.Paper presented in part at the Royal Society USSR Academy Workshop on Surfaces and Catalysis, Oxford, April 8–10, 1989.     

Minor and trace metal analysis of a solvent-refined coal by flameless atomic absorption

Solvent-refined coal (SRC), THF¹-insoluble SRC, THF-soluble SRC and three of its ‘size-separated’ fractions have been analysed for eleven metallic elements via flameless atomic absorption spectroscopy. Prior to analysis each sample was wet ashed with equal quantities of concentrated H₂SO₄ and 30% H₂O₂. Matrix effects were compensated for by the method of standard additions and deuterium-arc background correction. Mg, Al, K and Fe were found in greatest concentration in all samples. The concentration of Pb and Cd was measurable only in THF-insoluble SRC.     

Synthesis of poly(lactic acid) by heterogeneous acid catalysis from <Emphasis Type="SmallCaps">d</Emphasis>,<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid

Poly(lactic acid) (PLA) is an important polymer because of its significant biocompatibility and biodegradability. Supported H₃PW₁₂O₄₀ (H₃PW) on activated carbon was utilized for the catalytic polymerization of D,L-lactic acid, resulting in blends of PLA. The stability of the polymer was monitored by thermogravimetry (TGA), and the decomposition temperature (T_d) was used to determine the optimal production conditions (i.e., temperature of 180 °C for 15 h; 0.1 wt. % catalyst; 20 wt. % H₃PW/carbon calcined at 400 °C). The best catalyst was reused three times with good activity and recovery (95 %) and was analyzed to confirm the consistency of its Keggin structure, dispersion, and acidity, which are important parameters that affect the catalyst’s activity. The obtained polymer was characterized by gel permeation chromatography (GPC), Fourier-transform infrared spectroscopy (FT-IR), ¹H/¹³C nuclear magnetic resonance (NMR) spectroscopy, specific optical rotation ([α]_D ²⁵), powder X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The average molar mass of the polymer was 17,400 g mol^?1. Blends of poly(lactic acid) with 85 % poly(L-lactic acid) stereospecific isomer were obtained.

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Graphical Abstract Stereoselective synthesis of 85 % PLLA from polymerization of d,l-lactic acid using 12-tungstophosphoric acid supported on carbon as a catalyst

     

Stevensanaloge,Durch Nickelkomplexe Katalysierte Umlagerung Von Triarylphosphoryliden Und Darstellung Sowie Strukturbestimmung Von Phosphorylid-Nickeltricarbonylkomplexen

The Stevens rearrangement of the triarylphosphorusylids R₃ P=CHR′ (III) (R′ = H, CH₃, C₂ H₅) to diarylbenzylphosphines (V) is catalyzed by nickel complexes (e.g., (COD)₂ Ni (I)). Attempts to prepare trimesitylphosphine-methylene result in direct formation of dimesityl (mesitylmethyl) phosphine (XII) — the first recorded direct Stevens rearrangement of a phosphorusylid. Phosphorusylids react with nickeltetracarbonyl without rearrangement to give complexes of the type R₃P=CH_a · Ni(CO)₃ (XIV). The structure of XIV has been established by the IR and NMR spectra and confirmed by an X-ray structural determination.

1 B. L. Barnett and C. Krüger, J. Cryst. Mol. Struct., im Druck.

The ylid is bonded to the nickel through the C-atom with resulting hybridization from sp² towards sp³.     

Oxidative coupling of methane over LaF3/La2O3 catalysts

We studied the oxidative coupling of methane over the LaF₃/La₂O₃ (5050) catalyst. The catalyst was found active even at 873 K. At 1023 K, the C₂ yield was 12.7% at 26.0% CH₄ conversion and 49.1% C₂ selectivity. It was found to be stable and had a lifetime not less than 50 h at 1023 K. The catalyst was effective in C₂H₆ conversion to C₂H₄. XRD results indicated that the catalyst was mainly rhombohedral LaOF. It is suggested that the catalyst has ample stoichiometric defects and generates active oxygen sites suitable for methane dehydrogenation.     

A Fourier-transform infrared spectroscopic study of the adsorbed species from perdeuteroethene on a deuterium-exchanged Pt-on-silica catalyst

Fourier-transform infrared spectroscopy has been applied to study the adsorption and deuteration of perdeuteroethene (C₂D₄) at 298 K on a deuterium-exchanged Pt/SiO₂ catalyst. The spectra show absorptions associated with- and di--bonded (C₂D₄) and with (CCD₃), and a trace of (CCD₂H), ethylidyne surface species. These were identified by comparison with the closely-corresponding pattern of absorptions from the adsorption of C₂H₄. They are also correlated with previous spectroscopic results from C₂D₄ adsorption on Pt single-crystals and from analogous ligands in organometallic compounds. Deuteration of the initially-adsorbed species gives only gas-phase C₂D₆ and a trace of C₂D₅H.     

Coatings of Conducting Polymers for Corrosion Protection of Mild Steel

The investigation of electrochemical behavior of different conducting polymers, polythiophene (PTh), polypyrrole (PPy) and polyterthiophene (PTTh) on a mild steel (MS) electrode were done. Moreover, the combinations of the conducting polymers PTh and PPy was investigated. The synthesis of all polymeric coatings was done by the cyclic voltammetry technique. The electrochemical impedance spectroscopy (EIS) measurements were used to evaluate the corrosion performance of coated mild steel by different polymers in 0.5 M of different acid solutions (HCl, HClO₄, H₂ C ₂ O ₄, H₃PO₄ and HNO₃). The protection of all polymeric coatings against corrosion of the substrate was promising and the bilayer coating PPy/PTh gave the best protection efficiency in all used acids. The order of efficiency for the different coatings in HCl and HNO₃ solutions was MS/PPy/PTh > MS/PPy > MS/PTTh > MS/PTh but the order in HClO₄, H₃PO₄ and H₂ C ₂ O ₄ solutions was MS/PPy/PTh > MS/PTTh > MS/PPy > MS/PTh.     

Complex-radical copolymerization of <Emphasis Type="Italic">N-</Emphasis>vinyl pyrrolidone with isostructural analogs of maleic anhydride

Radical copolymerizations of N-vinyl-2-pyrrolidone (VP) with isostructural analogs of maleic anhydride (MA), such as citraconic anhydride (CA) and N-substituted maleimides [maleimide (MI), N-ethylmaleimide (EMI) and N-phenylmaleimide (PhMI)] were studied. Compositions of copolymers synthesized in a wide range of monomer feed ratios were determined by alkali titration (for anhydride copolymers), FTIR and ¹H NMR spectroscopy using 1495 and 630 cm^-1 (for VP-MI), 1289 and 1225 cm^-1 (for VP-EMI) and 1050 and 3067 cm^-1 (for VP-PhMI) analytical bands and integral areas of CH₂ (pyrrolidone ring) and CH (MI), CH₃ (EMI) and CH= (benzene ring in PhMI) groups, respectively. Electron-donor VP monomer was found to have substantially different reactivities in the radical copolymerization with MA, CA and N-substituted (H, C₂H₅ and phenyl) malemides as electron-acceptor comonomers. Effects of H-bonding and N→O=C coordination on the monomer reactivity ratios were evaluated. Tendency to alternation of the monomer pairs increases in the order of VP–MA > VP–CA > VP-MI > VP-PhMI > VP-EMI. Structure-thermal property-relationship for the synthesized copolymers was also studied.     

A polymeric amine–copper(II) complex as catalyst for the hydrolysis of 1,2,2-trimethylpropyl methylphosphonofluoridate (soman) and bis (1-methylethyl) phosphorofluoridate (DFP)

The Cu (II) complex of poly-4-vinylpyridine, quaternized with 19 mol % ethyl bromide and 36 mol % 4-chloromethyl-4′-methyl-2,2′-bipyridine, was examined as a catalyst for the hydrolysis of the toxic organophosphorous compounds bis (1-methylethyl) phosphorofluoridate ( 1 ,

1 Registry no.: 1 , 55-91-4; 2 , 96-64-0.

DFP) and 1,2,2-trimethylpropyl methylphosphonofluoridate ( 2 , soman). Studies were carried out at 25.0 and 37.0°C for both substrates in MOPS buffer at pH 7.0. In the presence of 7.31 × 10^?3 M catalyst at 25.0°C, soman is hydrolyzed with a first-order rate constant of 0.019 min^?1 (t_1/2 = 37.5 min), whereas DFP hydrolyzes with a rate constant of 0.011 min^?1 (t_1/2 = 63.8 min). For soman, this represents a 14-fold increase over the uncatalyzed rate in the same buffer. Other studies examined the effect of a strongly sorptive polymeric resin on catalysis by this copper-containing polymer and found a dramatic decrease in the hydrolysis rate of soman in the presence of the polymeric sorbent.     

Fischer-Tropsch reactor selection

A comparison of slurry versus fixed-bed reactor design principles for methanol and Fischer-Tropsch distillate production.Notation a gas-liquid interfacial area, m^–1 - CCat catalyst concentration, kg mole/m³ - C _HG hydrogen concentration in gas phase, kg mole/m³ - C ^* _HL hydrogen concentration, liquid, in equilibrium with gas, kg mole/m³ - C _HL hydrogen concentration in the liquid phase, kg mole/m³ - D I.D. of reactor, m - GHSV Gas hourly space velocity, Nm³ (H₂ + CO)/[h · m³ reactor volume], (reactor volume is expanded slurry height times cross section area) - H solubility coefficient of hydrogen =C _HG/C ^* C _HL - l Inlet ratio of CO/H₂ - k _L liquid side mass transfer coefficient, m/s - k _H effective reaction rate constant for hydrogen consumption, s^–1 (note that to agree with space velocity in Nm³/[s · kgCat],k _H =k _H ·CCat wherek _H is in m³/[kg · s] - L Length of expanded slurry bed, m - P pressure, kPa - r rate of hydrogen consumption,r =k _H ·C _HL, kg moles/[m³ · s] - SV Space velocity in actual m³ inlet gas/[s · m³] - T temperature, K - U Usage ratio of CO/H₂ - X _H hydrogen fractional conversion per pass (IfU=l,X _H =X _CO) - contraction factor, = [m³/s(X _{H 2+CO} = 1)-m³/s(inlet)]/[m³/s(inlet)] - * contraction factor modified for H₂ conversion, * = · (1 +U)/(1 +l) - _L fractional liquid hold-up     

Effect of processing conditions on unsupported Ni-based catalysts for graphitic-nanofibre formation

Graphitic nanofibres (GNFs) were successfully synthesised at low temperatures (below 400 °C) using NiO powder as the catalyst precursor and a H₂/C₂H₄ gas mixture with a high yield, around . The yield was found to vary with temperature with the optimum yield at 500 °C. XRD patterns confirm that during GNF formation the NiO was reduced forming either metallic Ni and or Ni₃C phase. TEM study confirmed the formation of a graphitic phase in the form of GNFs and that the diameter was dependent on the synthesis temperature, varying from 500 nm to 20 nm. The sample surface area was found to increase from 49 to 252 m² g⁻¹, with lowering of the synthesis temperature.