Presence Of Ether Research Articles

Hydrogen production from ethanol for PEM fuel cells. An integrated fuel processor comprising ethanol steam reforming and preferential oxidation of CO

The aim of the work was to study the performance of ceria catalysts to convert ethanol to hydrogen in a combined system including ethanol steam reforming and PROX. The roles of the active oxide component, partially reduced ceria, and the metal component, Pt, in the ethanol steam reforming mechanism were investigated by diffuse reflectance infrared spectroscopy (DRIFTS) carried out under steady state reaction conditions. The main mechanism was found to proceed by (1) dissociative adsorption of ethanol to ethoxy species; (2) dehydrogenation of ethoxy species to adsorbed acetaldehyde; (3) oxidation of acetaldehyde species by ceria OH groups to acetate; (4) acetate demethanation to CH 4 and carbonate species; (5) carbonate decomposition to CO 2; and presumably (6) CH 4 decomposition steps. Though Pt improved the initial ethanol conversion rate by facilitating hydrogen transfer and demethanation steps, the Pt–ceria interface was quickly lost to the buildup of carbon-containing species, thus hindering the Pt from effectively demethanating the acetate intermediate. Unpromoted ceria, though less active, was a significantly more stable catalyst. The steps for the PROX reaction in the presence of acetaldehyde were found to include: (1) decomposition of acetaldehyde leading to CO and methane; (2) hydrogenation of acetaldehyde producing ethanol; and (3) oxidation of the CO.

O‐Acylated 2‐Phosphanylphenol Derivatives – Useful Ligands in the Nickel‐Catalyzed Polymerization of Ethylene

AbstractThe title ligands were prepared by O‐acylation of 2‐diphenylphosphanyl‐4‐methylphenol (1) or directly by double lithiation of 2‐bromo‐4‐methylphenol and stepwise coupling with ClPPh2 and ClP(O)Ph2 or RC(O)Cl (R = Me, tBu, Ph, 4‐MeOC6H4) to afford diphenylphosphinate 2 and carboxylic esters 3a–d. X‐ray crystal structure analyses of 3b–d show conformations in which the P‐phenyl substituents are rotated away from the ester group and the C(O)O π planes are nearly perpendicular to the phenol ring π plane. O‐Acylated phosphanylphenols 2 and 3a–d form highly active catalysts with Ni(1,5‐cod)2 (as does 1) for polymerization of ethylene, whereas phosphanylphenyl ethers do not give catalysts under the same conditions. The reason is the cleavage of the O‐acyl bond upon heating with nickel(0) precursor compounds in the presence of ethylene. The precursors are P‐coordinated Ni0 complexes, which are formed at room temperature, such as 4d obtained from 3d and Ni(cod)2 (in a 2:1 molar ratio), and characterized by multinuclear NMR spectroscopy. Upon heating in the presence of ethylene, the precatalysts are activated. Catalysts 2Ni and 3a–dNi convert ethylene nearly quantitatively, 2Ni slowly, and 3a–dNi rapidly, into linear polyethylene with vinyl and methyl end groups, and in the latter case, C(O)R end groups are also detectable. This proves insertion of Ni0 into the O–C(O)R bond of 3a–d ligands for formation of the primary catalyst. Termination of the first chain growing cycle by β‐hydride elimination changes the mechanism to the phosphanylphenolate–NiH initiated polymerization providing the main body of the polymer. A small retardation in the ethylene consumption rate with 3a–dNi catalysts relative to that observed for 1Ni and stabilization of the catalyst, which gives rise to reproducibly high ethylene conversion, is observed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The Effect of nitric oxide on the photocatalytic oxidation of small hydrocarbons over titania

The catalytic UV photo-oxidation of NO in the absence and presence of ethane, ethene, propane, propene, and n-butane over TiO2 in the presence of excess oxygen was studied in the temperature range 21–150°C. It was confirmed in our system that in the absence of hydrocarbon NO was photocatalytically oxidised by oxygen to NO2 over TiO2 and was strongly absorbed. Both NO and hydrocarbon could be simultaneously photo-converted with the conversion varying considerably with both NO and hydrocarbon concentration and the nature of the hydrocarbon. In some instances the presence of NO in the feed gas enhanced hydrocarbon oxidation via reactions involving NO2 that is a powerful oxidant. The extent of this effect depended on the relative strengths of adsorption on TiO2 of the reactants and products. To reduce surface coverage of hydrocarbon most reactions were run at 150°C, and it was shown that at this temperature NOx adsorbed on titania could be reduced by photogenerated hydrocarbon surface species to N2O and N2 under these conditions. The formation of N2 was confirmed using 15NO with helium as carrier gas. By contrast, at room temperature in the presence of propene NO was converted to NO2.

Redox-Regulated Ethylene Binding to a Rhenium-Thiolate Complex

The influence of oxidation state on the reversibility of carbon-sulfur bond forming reactions between ethylene and [Re(DPPBT)(3)](n+) (n = 0, +1, +2; DPPBT = 2-diphenylphosphinobenzenethiolate) has been investigated. For the neutral complex [Re(DPPBT)(3)], no reaction with ethylene is spectroscopically detectable consistent with the determined equilibrium constant, K(1), of (1.9 +/- 0.4) x 10(-11) M(-1). Oxidation by one electron to [Re(DPPBT)(3)](+) yields a stable complex that rapidly and reversibly binds ethylene with electrochemically determined constants of k(f) = (1.2 +/- 0.2) x 10(-1) M(-1) s(-1), k(r) = (3.0 +/- 0.4) x 10(-2) s(-1), and K(2) = 4.0 +/- 0.8 M(-1). C-S bond formation/cleavage can be regulated by ethylene concentration, and the system is stable to multiple cycles of nitrogen/ethylene purges. Further oxidation to the dication in the presence of ethylene by chemical or electrochemical methods stabilizes the C-S bond, K(3) = (2.5 +/- 0.9) x 10(9) M(-1), and the dithioether product has been characterized by X-ray crystallography. The large differences in K as a function of charge permit the controlled binding and release of ethylene as a function of applied potential.

Establishment of a plant regeneration system from callus of Dendrobium cv. Serdang Beauty

An in vitro propagation protocol was established for the Dendrobium Serdang Beauty orchid. The propagation protocol utilized calli tissues that were successfully initiated from protocorm-like bodies (PLBs) explants, while the leaf and root tip explants died. The percentage of protocorm-like bodies explants responding to calli formation was 100% in all tested levels of IAA, IBA and NAA auxin treatments. The highest amount of calli (49.59 gram) proliferated on MS medium containing 1.5 mg/L IBA. These calli successfully regenerated on media supplemented with either KIN or BAP cytokinins and combined treatments of KIN and IAA (4 mg/L) or NAA (1.5 mg/L). However, media supplemented with only 1 mg/L KIN was sufficient to produce significantly high percentage of plantlet formation (80%), high number of planlets per explant (4-5 plantlets) and high mean fresh weight per plantlet (11.128 g). These plantlets were acclimatized on all tested media and obtained satisfactory rate of plantlet survival (80-100%), mean number of leaves per plant (4-6 leaves), and mean leaf length (4 - 5 cm). Among these media, charcoal was considered the most economical and available material in the local market. During the development of this protocol, substantial necrosis of calli were observed when cultures were treated with 2,4-D and BAP. It was proposed that the presence of ethylene within the cultures, which is known to be emitted by plant growth regulators into the micro-climate of in vitro culture vessels, is the determining factor of a suitable plant growth regulator for the survival and growth of the Dendrobium Serdang Beauty calli cultures in our study.

A Straightforward Synthesis of 2,3,4,5-Tetrasubstituted Tetrahydrofuran Derivatives

A concise synthesis of 2,3,4,5-tetrasubstituted tetrahydrofurans starting from furan via 7-oxabicyclo[2.2.1]hept-5-ene-2,3-diol (2,3-dihydroxy-7-oxanorbomene) derivatives is reported. The key step of these transformations was the sequence ring-opening metathesis-cross metathesis (ROM-CM) reactions of the oxabicyclic compounds in the presence of ethylene and using commercially available 2nd generation Hoveyda-Grubbs catalyst.

Molecular Chemistry in a Zeolite: Genesis of a Zeolite Y-Supported Ruthenium Complex Catalyst

Dealuminated zeolite Y was used as a crystalline support for a mononuclear ruthenium complex synthesized from cis-Ru(acac)2(C2H4)2. Infrared (IR) and extended X-ray absorption fine structure spectra indicated that the surface species were mononuclear ruthenium complexes, Ru(acac)(C2H4)2(2+), tightly bonded to the surface by two Ru-O bonds at Al(3+) sites of the zeolite. The maximum loading of the anchored ruthenium complexes was one complex per two Al(3+) sites; at higher loadings, some of the cis-Ru(acac)2(C2H4)2 was physisorbed. In the presence of ethylene and H2, the surface-bound species entered into a catalytic cycle for ethylene dimerization and operated stably. IR data showed that at the start of the catalytic reaction, the acac ligand of the Ru(acac)(C2H4)2(2+) species was dissociated and captured by an Al(3+) site. Ethylene dimerization proceeded approximately 600 times faster with a cofeed of ethylene and H2 than without H2. These results provide evidence of the importance of the cooperation of the Al(3+) sites in the zeolite and the H2 in the feed for the genesis of the catalytically active species. The results presented here demonstrate the usefulness of dealuminated zeolite Y as a nearly uniform support that allows precise synthesis of supported catalysts and detailed elucidation of their structures.

New polymers by copolymerization of olefins with bio oil components

AbstractOleic acid methyl ester can be converted by metathesis reaction in the presence of ethene into 1‐decene and 9‐decenoic acid methyl ester. Both components are suitable comonomers for the synthesis of polyolefin specialties by copolymerization with ethene or propene. For this copolymerization, metallocene/methylaluminoxane catalyst or other single‐site catalysts are more active than classical Ziegler‐Natta catalysts because they insert higher amounts of longer‐chain α‐olefins or olefins with polar groups. The microstructure of these copolymers can be tailored in a great variety using metallocene complexes with different symmetries.

Dinuclear Ruthenium Ethylene Complexes: Syntheses, Structures, and Catalytic Applications in ATRA and ATRC Reactions

The complexes [(p-cymene)Ru(μ-Cl)3RuCl(C2H4)(PR3)] (PR3 = PPh3, Pn-Bu3) were synthesized by reaction of [(p-cymene)RuCl(μ-Cl)]2 with the respective phosphine ligand in the presence of ethylene. Structurally related complexes containing the tricyclopentylphosphine (PCyp3) or the isobutylphobane ligand (phobane = 9-phosphabicyclo[3.3.1]nonane) were obtained by reaction of [(arene)RuCl(μ-Cl)]2 (arene = p-cymene, 1,3,5-i-Pr3C6H3) with 2 equiv of [(arene)RuCl2(PCyp3)] or [(arene)RuCl2(isobutylphobane)] in the presence of ethylene. The structures of the dinuclear complexes [(p-cymene)Ru(μ-Cl)3RuCl(C2H4)(PPh3)] and [(1,3,5-i-Pr3C6H3)Ru(μ-Cl)3RuCl(C2H4)(isobutylphobane)] as well as of the mononuclear precursors [(p-cymene)RuCl2(isobutylphobane)], [(1,3,5-i-Pr3C6H3)RuCl2(isobutylphobane)], and [(p-cymene)RuCl2(PCyp3)] were determined by single-crystal X-ray analyses. Kinetic analyses of the atom transfer radical addition reaction of CCl4 to styrene revealed that the catalytic activity of the dinuclear complexes was strongly dependent on the nature of the phosphine ligand but only slightly affected by the nature of the arene ligand. Addition of Mg to the reaction mixture was found to increase the lifetime of the catalyst significantly. With Mg as the cocatalyst, mixed-valence Ru(II)−Ru(III) complexes of the general formula [(arene)Ru(μ-Cl)3RuCl2(PR3)] were found to be equally potent catalyst precursors when compared to the Ru(II)−Ru(II) complexes [(arene)Ru(μ-Cl)3RuCl(C2H4)(PR3)].

Factors affecting product distributions in ethylene/styrene copolymerization by (aryloxo)(cyclopentadienyl)titanium complexes‐MAO catalyst systems

AbstractEthylene/styrene copolymerizations using Cp′TiCl2(O‐2,6‐iPr2C6H3) [Cp′ = Cp* (C5Me5, 1), 1,2,4‐Me3C5H2 (2), tert‐BuC5H4 (3)]‐MAO catalyst systems were explored under various conditions. Complexes 2 and 3 exhibited both high catalytic activities (activity: 504–6810 kg‐polymer/mol‐Ti h) and efficient styrene incorporations at 25, 40°C (ethylene 6 atm), affording relatively high molecular weight poly (ethylene‐co‐styrene)s with unimodal molecular weight distributions as well as with uniform styrene distributions (Mw = 6.12–13.6 × 104, Mw/Mn = 1.50–1.71, styrene 31.7–51.9 mol %). By‐productions of syndiotactic polystyrene (SPS) were observed, when the copolymerizations by 1–3‐MAO catalyst systems were performed at 55, 70 °C (ethylene 6 atm, SPS 9.0–68.9 wt %); the ratios of the copolymer/SPS were affected by the polymerization temperature, the [styrene]/[ethylene] feed molar ratios in the reaction mixture, and by both the cyclopentadienyl fragment (Cp′) and anionic ancillary donor ligand (L) in Cp′TiCl2(L) (L = Cl, O‐2,6‐iPr2C6H3 or N=CtBu2) employed. Co‐presence of the catalytically‐active species for both the copolymerization and the homopolymerization was thus suggested even in the presence of ethylene; the ratios were influenced by various factors (catalyst precursors, temperature, styrene/ethylene feed molar ratio, etc.). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4162–4174, 2008

Metallocenes in ethylene polymerization studied by cyclic and differential pulse voltammetry

The relationship between redox characteristics and catalytic activity in ethylene polymerization, with methylaluminoxane (MAO) as the cocatalyst, was evaluated for a series of homogeneous metallocenes (Cp2ZrCl2, (MeCp)2ZrCl2, (nBuCp)2ZrCl2, (iBuCp)2ZrCl2, (tBuCp)2ZrCl2, Cp2TiCl2, Cp2HfCl2, Et(Ind)2ZrCl2, Et(IndH4)2ZrCl2 and MeSi2(Ind)2ZrCl2). Catalytic activity is discussed in terms of the coordination sphere and metal center of the metallocene and compared with their electrochemical behavior in the presence of ethylene and MAO. The resulting polyethylenes were analyzed by GPC. The catalytic activity in the ethylene polymerization reaction is discussed in terms of half-life (t1/2) and electrochemical gap of the metallocene species.

Growth of aligned carbon nanotube arrays on metallic substrate and its application to supercapacitors

Aligned carbon nanotube arrays (ACNTAs) with lengths up to 150 μm were fabricated on metallic alloy (Inconel 600) substrates by pyrolysis of iron (II) phthalocyanine (FePc) in the presence of ethylene (C 2H 4). The as-grown ACNTAs, formed by aligned multi-walled carbon nanotubes with high purity, were characterized by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and Raman spectroscopy techniques. The ACNTAs were used directly as electrode materials in supercapacitors with (Et) 4NBF 4 + propylene carbonate (PC) as electrolyte, and their electrochemical properties were investigated. A rectangular-shaped cyclic voltammetry (CV) curve was observed even at a sweep rate of 1000 mV s −1. The specific capacitance measured at 1000 mV s −1 was about 57 % (47 F g −1) of that obtained at 1 mV s −1 (83 F g −1), and an equivalent series resistance (ESR) of 0.55 Ω was measured for the ACNTA and activated carbon pair electrodes embedded in a coin cell. The results indicated that the ACNTAs could be a promising candidate as electrode materials in supercapacitors.

Combustion of methane, ethane and propane and of mixtures of methane with ethane or propane on Pd/γ-Al2O3 catalysts

The influence of adding ethane or propane in the feed during catalytic combustion of methane on Pd(2 wt.%)/γ-Al 2 O 3 catalyst was investigated. The addition of ethane or propane inhibits the ignition of methane. Palladium particles sinter during reaction. Palladium seems to be slightly less oxidized in presence of ethane or propane. Catalytic combustion of methane on a Pd(2 wt.%)/γ-Al 2 O 3 catalyst (♢, dotted line). Effect of the addition of increasing concentrations of ethane (500 (♦), 1000 (■), 1500 (▴) and 2000 ppm (●)) on the conversion of methane (solid lines). In a first step, the catalytic combustion of methane, ethane and propane on a Pd(2 wt.%)/γ-Al 2 O 3 catalyst was investigated. The order of reactivity of these three gases is propane > ethane > methane. In a second step, the influence of adding ethane or propane in the feed during the catalytic combustion of methane was studied. At low temperature, the addition of ethane or propane inhibits the ignition of methane. This inhibition could be explained by a competition for the surface oxygen species on the surface of palladium. At high temperature, the same competitive effect would explain the inhibition observed at high ethane concentration. In the presence of propane, a thermal effect seems to have an important role. This effect is minor in the presence of ethane. In all cases, palladium particles sinter during reaction and their surface is more oxidized after test than before running the reaction. However, when ethane or propane is added in the methane feed, palladium seems to be slightly less oxidized than in the presence of pure methane. In this last case the sintering effect seems to be more pronounced. The migration of oxygen species from the bulk seems to play an important role in the oxidation of palladium. These results support previous studies using H 2 -assisted methane combustion. Implications of the presence of ethane and propane in the combustion of natural gas are also discussed.

Characterization of Na +-β-zeolite supported Pd and PdAg bimetallic catalysts using EXAFS, TEM and flow reactor

Flow reactor studies of the selective hydrogenation of acetylene in the presence of ethylene have been performed on Na + exchanged β-zeolite supported Pd, Ag and PdAg catalysts, as an extension of our previous batch reactor studies [W. Huang, J.R. McCormick, R.F. Lobo, J.G. Chen, J. Catal. 246 (2007) 40–51]. Results from flow reactor studies show that the PdAg/Na +-β-zeolite bimetallic catalyst has lower activity than Pd/Na +-β-zeolite monometallic catalyst, while Ag/Na +-β-zeolite does not show any activity for acetylene hydrogenation. However, the selectivity for the PdAg bimetallic catalyst is much higher than that for either the Pd catalyst or Ag catalyst. The selectivity to byproduct (ethane) is greatly inhibited on the PdAg bimetallic catalyst as well. The results from the current flow reactor studies confirmed the pervious results from batch reactor studies [W. Huang, J.R. McCormick, R.F. Lobo, J.G. Chen, J. Catal. 246 (2007) 40–51]. In addition, we used transmission electron microscope (TEM), extended X-ray absorption fine structure (EXAFS), and FTIR of CO adsorption to confirm the formation of Pd–Ag bimetallic alloy in the PdAg/Na +-β-zeolite catalyst.

Methane activation over Ag-exchanged ZSM-5 zeolites: A theoretical study

Methane activation catalyzed over Ag-exchanged ZSM-5 zeolites was investigated by using the density functional theory (DFT) with a cluster model. Two different pathways were taken into account in this work: the “alkyl” and the “carbenium” pathways. The activation barriers obtained are 34.09 and 66.63 kcal/mol for the “alkyl” and the “carbenium” pathway, respectively. The calculated results show that the activation barrier of the “alkyl” pathway is smaller than that of “carbenium” pathway. Consequently, the “alkyl” pathway is the preferential reaction pathway. A new mechanism of methane conversion in the presence of ethene was proposed. In the catalytic cycle, the initial step of methane activation proceeds with the “alkyl” pathway and the Ag + cation acts as an acceptor of the methyl group, then ethene reacts with the Ag +CH 3 − group to form propene. In addition, it is found that the Ag + cations play an important role in the methane activation, compared with the reaction of methane activation over H-ZSM-5.

Photochemical behaviour of 5-formyl and 5-acetyl uracils in the presence of ethene

Atypically for uracils, 5-formyl and 5-acetyl uracils react photochemically with excess ethene to produce non-acylated cyclobutane adducts whose formation can be explained by a novel, tandem [2+2] cycloaddition/Norrish-I α-cleavage process.

Effect of ethylene, 1-MCP, ABA and IAA on break strength, cellulase and polygalacturonase activities during cotton leaf abscission

Organ abscission in higher plants has invariably been characterized by higher activities of cell wall hydrolases in the abscission zone of the abscising organ, which facilitates degradation of middle lamella and loosening of cell wall of separation layers. The plant hormone ethylene has been implicated in the induction and progression of the abscission process. In the present study, we have measured activities of cellulase and polygalacturonase (PG) in the abscission zone of cotton (Gossypium hirusutum var RST-39) leaf explants in the presence of ethylene. The effects of abscisic acid (ABA) and indole acetic acid (IAA) were monitored to elucidate the role of other phytohormones in the process of abscission. A several fold increase in cellulase and PG activities and decrease in break strength were observed in the LAZ of ethylene-treated explants. The increase in enzyme activities and decrease in break strength were strongly suppressed in the presence of 1-methylcyclopropene (1-MCP) and IAA. ABA alone was found to stimulate enzyme activities and decrease the break strength though not to the extent of ethylene. 1-MCP pretreatment of ABA and ethylene-treated explants showed significant inhibition in enzyme activities. It is concluded that cotton leaf abscission is ethylene regulated and characterized by increased activities of cellulase and PG in its abscission zone. ABA can induce abscission. However, it appears that ABA induced abscission may be mediated through ethylene.

Practical Synthesis of Functionalized 2‐Thioxoimidazolidine Derivatives

High‐yielding syntheses of an unpublished series of 2‐thioxo‐imidazolidin‐4‐ones 6 bearing an N‐ethoxycarbonyl and amidyl moieties an N1 and C5, respectively, are reported. These derivatives were obtained by intramolecular cyclization of 3‐ethylhydrazinoacetate 3,4‐dihydro maleimides 4 in the presence of ethyl or phenylisothiocyanate 2 under neutral conditions.

Propene Production from Ethene and Methane Using Silver- and Proton-exchanged Zeolite Catalysts

Two new methods for the catalytic synthesis of propene using solid acid catalysts are presented. The first approach is a new method for the activation of methane, involving conversion of methane to propene over silver-exchanged zeolite in the presence of ethene. In the second method, ethene conversion proceeds directly and selectively over proton-exchanged zeolite under the control of a molecular sieving effect.The heterolytic dissociation of methane over silver cationic clusters (Agn+) in Ag+-exchanged zeolites, leading to the formation of silver hydride (Agn-H) and CH3δ+ species, which reacts with ethene to form propene around 673 K. Using 13C-labeled methane as a reactant, propene is shown to be a primary product from methane and ethene. Thus, a significant proportion of propene was singly 13C-labeled (13CC2H6).Under these reaction conditions, H+-exchanged zeolites, such as H-ZSM-5 do not catalyze the methane conversion, only ethene being converted into higher hydrocarbons, such as propene. Ethene is selectively converted to propene over SAPO-34 at 723 K with a yield of 52.2% and selectivity of 73.3% at ethene conversion of 71.2%. The high and selective propene yields achieved over SAPO-34 can be attributed to a shape selectivity effect of the small-pore SAPO-34.

코로나/촉매 일체형 시스템의 탈질특성에 관한 연구

This study was carried out to investigate the reaction characteristics of corona/catalyst hybrid <TEX>$DeNO_x$</TEX> process. The experiments were performed by using the multi-staged pin-to-hole type corona reactor which is enable to control the pin-to-hole gap and to insert the catalyst. Also, used for this study, were catalysts which commercially used Pt, Pd and <TEX>$TiO_2$</TEX>, and oxygen and hydrocarbon (<TEX>$C_2H_4$</TEX>) as reagents. In the syn-gas test, at high temperatures in the range of <TEX>$100{\sim}200^{\circ}C$</TEX>, the corona-only <TEX>$DeNO_x$</TEX> process did not reduce the <TEX>$NO_x$</TEX> concentration effectively. However in the presence of ethylene and oxygen as reagents, the <TEX>$NO_x$</TEX> removal efficiency was better at these high temperatures than corona-only <TEX>$DeNO_x$</TEX> process. In addition, coronal catalyst hybrid process with <TEX>$TiO_2$</TEX> showed more efficiency of <TEX>$NO_x$</TEX> removal than Pt and Pd catalyst, because the <TEX>$TiO_2$</TEX> catalyst was more active than Pt and Pd catalyst to converse the <TEX>$NO_2$</TEX> to <TEX>$HNO_3$</TEX>. Furthermore, at the condition of real diesel exhaust gas, the <TEX>$DeNO_x$</TEX> efficiency of corona/catalyst hybrid process was not good at higher reaction temperature and plasma density.