Presence Of Thiophene Research Articles

Tailoring the pore size of zeolite Y as the support of diesel aromatic saturation catalyst

The molecular dimensions of typical aromatics and sulfur-containing compounds in diesel cuts were simulated. A pore configuration design was proposed for sulfur-tolerant metal catalyst. Modified zeolite Y with and without the presence of mesopores were used as a catalyst support. Pyrene and naphthalene were used as the model compounds for hydrogenation. Sulfur tolerance of the catalyst was investigated with naphthalene hydrogenation in the presence of thiophene. It was demonstrated that the generation of mesopores in zeolite Y can enhance the activity of pyrene hydrogenation, but lower the tolerance to thiophene.

Characterization and Catalytic‐Hydrogenation Behavior of SiO2‐Embedded Nanoscopic Pd, Au, and Pd–Au Alloy Colloids

Colloids embedded in a silica sol-gel matrix were prepared by using fully alloyed Pd-Au colloids, and pure Pd and Au colloids stabilized with tetraalkylammonium bromide following a modified sol-gel procedure with tetrahydrofuran (THF) as the solvent. Tetraethoxysilicate (TEOS) was used as the precursor for the silica support. The molar composition of the sol was TEOS/THF/H2O/HCl = 1:3.5:4:0.05 for the bimetallic Pd-Au and TEOS/THF/H2O/HCl = 1:4.5:4:0.02 for Pd and Au monometallic systems. After refluxing, the colloid was added as a 4.5 wt % solution in THF for Pd-Au, 10.2 wt % solution in THF for Pd and 8.4 wt % solution in THF for Au at room temperature. The gelation was carried out with vigorous stirring (4 days) under an Ar atmosphere. Following these procedures, bimetallic Pd-Au-SiO2 catalysts with 0.6 and 1 wt % metal, and monometallic Pd- and Au-SiO2 catalysts with 1 wt % metal were prepared. These materials were further treated following four different routes: 1) by simple drying, 2) in which the dried catalysts were calcined in air at 723 K and then reduced at the same temperature, 3) in which they were directly reduced in hydrogen at 723 K, and 4) in which the surfactant was extracted using an ethanol-heptane azeotropic mixture. The catalysts were characterized by nitrogen adsorption-desorption isotherms at 77 K, H2 chemisorption measurements, solid-state 1H, 13C, 29Si-CP/MAS-NMR spectroscopy, powder X-ray diffraction (XRD), small angle X-ray scattering (SAXS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and 197Au Mössbauer spectroscopy. The physical characterization by a combination of these techniques has shown that the size and the structural characteristics of the Pd-Au colloid precursor are preserved when embedded in an SiO2 matrix. Catalytic tests were carried out in selective hydrogenation of 3-hexyn-1-ol, cinnamaldehyde, and styrene. These data showed evidence that alloying Pd with Au in bimetallic colloids leads to enhanced activity and most importantly to improved selectivity. Also, the combination of the two metals resulted in catalysts that were very stable against poisoning, as was evidenced for the hydrogenation of styrene in the presence of thiophene.

Hydrogenation of benzene over ruthenium-exchanged montmorillonite in the presence of thiophene

Ruthenium-exchanged montmorillonite with different loading of ruthenium have been prepared and used for hydrogenation of benzene at 400–600 psi (27.6–41.4 bar) and 80 °C with or without the presence of thiophene. Preparation of the catalysts by ion-exchange process ensures a high dispersion of metal ions into the montmorillonite matrix. The catalytic reactions have been carried out in a PAAR autoclave reactor in the liquid phase. Under the experimental conditions of 500 psi (34.5 bar) hydrogen pressure and 100°C temperature, the benzene is completely hydrogenated. Further modifications of the catalysts with Cu(I) and Cu(II) ions have been attempted to improve the sulfur tolerance of the catalysts. Both, impregnation of Cu(II) salt on the montmorillonite and addition of CuI to the reaction mixture significantly improves the sulfur tolerance of the Ru ion-exchanged montmorillonite, thus, providing a new approach for developing sulfur-tolerating hydrogenation catalysts.

Biphasic hydroformylation of olefins by the new binuclear water soluble rhodium complex [Rh(μ-Pz)(CO)(TPPTS)] 2

The new water-soluble rhodium complex [Rh(μ-Pz)(CO)(TPPTS)] 2 ( I) with TPPTS tris- meta-sulfonatophenylphosphine and Pz = pyrazolate ligand, has been synthesized by the reaction of the rhodium precursor [Rh(acac)(CO) 2] with TPPTS and pyrazol in aqueous solution under inert atmosphere and characterized by FT-IR, UV–vis, 1H NMR, 31P{ 1H} NMR. This complex ( I) shows high solubility and stability in water for long periods of time as demonstrated by UV–vis studies. The new rhodium complex was used as catalyst precursor during the two-phase catalytic hydroformylation of different olefins under the following reactions conditions: 373 K, 4981.3 kPa (CO/H 2 = 1:1), 600 rpm and S/ C = 100/1, obtaining as reaction order: 1-hexene > styrene > allylbenzene > 2,3-dimethyl-1-butene > cyclohexene. The catalytic activity of the complex ( I) in the equimolar and real mixture of olefins with or without the presence of thiophene was also studied and practically no change in the total conversion to aldehydes was observed. This experiments shows that the binuclear complex ( I) is resistant to possible sulphur poisons present in refinery cuts.

Synthesis and Electrochromic Properties of a Symmetric Polythiophene Derivative: Decanedionic Acid Bis‐(2‐thiophene‐3‐yl‐ether)ester and its Copolymer with Thiophene

Here we describe the electrochemical homopolymerization and copolymerization of decanedionic acid bis‐(2‐thiophene‐3‐yl‐ ether)ester (DATE) in the presence of thiophene. Tetrabutylammonium tetrafluoroborate (TBAFB) was utilized as the supporting electrolyte in acetonitrile (ACN)/borontrifloride ethylether (BFEE) solvent mixture (8:2D, v/v). Electrochemical homopolymerization of DATE and copolymerization with thiophene were studied by cyclic voltammetry (CV). Conducting polymers were characterized by Fourier Transform Infrared (FT‐IR) and Thermal Analyses. The morphologies of electrochemically synthesized P(DATE) and P(DATE‐co‐Th) thin films were analyzed by Scanning Electron Microscopy (SEM). Electrical conductivities were measured by the four‐probe technique. Spectroelectrochemical behaviors of P(DATE) and P(DATE‐co‐Th) films were investigated by UV‐Vis Spectrophotometer. Homopolymer revealed color changes between brownish yellow and blue, whereas copolymer revealed changes between orange and blue in reduced and oxidized states respectively. Switching ability of the polymers was investigated via kinetic study upon measuring the % transmittance (%T) at the maximum contrast point. Results implied that copolymerization is a valuable approach to achieve the desired electrochromic properties.

Micro- and nanopatterns of polythiophene covalently bound to silicon

Abstract Micro- and nanopatterns of polythiophene covalently bound to Si(111) have been generated from the photoelectrochemical oxidation of silicon surfaces patterned with thiophene-terminated decyl and decyl monolayers in the presence of thiophene. The procedure used for the attachment of these organic monolayers on silicon involved either UV photolithography or a highly diluted mixture of precursor alkenes. To cite this article: B. Fabre and D.D.M. Wayner, C. R. Chimie 8 (2005).

Characterization of Conducting Copolymers of Succinic Acid Bis‐(‐4‐pyrrol‐1‐yl‐phenyl) Ester and Thiophene via Pyrolysis Mass Spectrometry

In this work, a direct pyrolysis mass spectrometry technique was applied to characterize a conducting copolymer of succinic acid bis‐(4‐pyrrol‐1‐yl‐phenyl) ester (SM) and thiophene prepared by electrochemical polymerization. Thermal degradation behavior of both components was quite similar to those of the corresponding homopolymers, PSM, and polythiophene PTh. Yet, detection of oligomers and mixed dimers of both monomers in the high temperature pyrolysis mass spectra confirmed the formation of a copolymer. Furthermore, evolution of SM monomer in the temperature range where the fragments, due to the thermal degradation of PTh chains, have been detected. Also, the generation of dimer of thiophene in the temperature range, where the fragments associated with PSM have been observed, pointed out the presence of thiophene and SM units along the PTh and PSM chains. However, as thermal stabilities of PTh and PSM chains were nearly identical to the corresponding homopolymers, it may be concluded that the presence of other monomer or low molecular weight oligomers along the chains of each component did not significantly affect the thermal characteristics.

Synthesis and characterization of a bifunctional amido-thiophene monomer and its copolymer with thiophene and electrochemical properties

A bifunctional amido-thiophene namely hexamethylene (bis-3-thiophene acetamide) (HMTA) was synthesized by the reaction of 3-thiophene acetic acid with hexamethylene diamine. Copolymerization in the presence of thiophene was achieved electrochemically in tetrabutylammonium tetrafluoroborate/acetonitrile (TBAFB/AN). Spectroelectrochemical analysis of the resulting copolymer [P(HMTA-co-Th)] reflected electronic transitions at 505 nm, 740 nm and ∼1000 nm, revealing π to π* transition, polaron and bipolaron band formation respectively. Switching ability was evaluated by a kinetic study via measuring the transmittance (% T) at the maximum contrast. Dual type polymer electrochromic devices (ECDs) based on P(HMTA-co-Th) and poly(ethylene dioxythiophene) (PEDOT) have been constructed. Spectroelectrochemistry, switching ability and stability of the devices were investigated by UV–vis spectroscopy and cyclic voltammetry. These devices exhibit low switching voltages (between 0.0 V and +1.6 V), short switching times with reasonable switching stability under atmospheric conditions.

Synthesis, characterization, and electrochromic properties of conducting poly(hexanedioic acid bis-(2-thiophen-3-yl-ethyl ester) and its copolymer with thiophene

Hexanedioic acid bis-(2-thiophen-3-yl-ethyl) ester (HABTE) was synthesized via the reaction of 3-thiophene ethanol with adipoyl chloride. Resulting monomer was electrochemically homopolymerized in the presence of tetrabutylammonium tetrafluoroborate as the supporting electrolyte, in acetonitrile/borontrifloride ethylether solvent mixture (8:2, v/v). Copolymerization in the presence of thiophene was achieved in TBAFB/AN. Resulting homo and copolymers were characterized via CV, FTIR, DSC, TGA, SEM, and UV–vis Spectroscopy. Spectroelectrochemistry analysis of homopolymer, P(HABTE), reflected electronic transitions at 385, ~600, and ~900 nm, revealing π–π* transition, polaron, and bipolaron band formation, respectively. Switching ability of the homopolymer was evaluated by a kinetic study upon measuring the % T at the maximum contrast point, indicating that PHABTE is a potential material for electrochromic devices.

Conducting polymers of terepthalic acid bis-(2-thiophen-3-yl-ethyl) ester and their electrochromic properties

Terepthalic acid bis-(2-thiophen-3-yl-ethyl)ester (TATE) was synthesized through the reaction of 2-thiophen-3-yl-ethanol and terepthaloyl chloride. Homopolymer of TATE was synthesized via potentiostatic and potentiodynamic methods by using tetrabutylammonium tetrafluoroborate (TBAFB) as the supporting electrolyte in dichloromethane/borontrifluoride ethylether solvent mixture (DM/BFEE) (8:2, v/v). Copolymerisation of TATE with thiophene was achieved in DM/BFEE solvent mixture (8:2, v/v) by using TBAFB as the supporting electrolyte in the presence of thiophene. The chemical structure of monomer is characterised via NMR and FTIR. Both homopolymer (PTATE) and copolymer P(TATE- co-Th) were characterised by various techniques including cyclic voltammetry, FTIR, scanning electron microscopy and UV–VIS spectroscopy. Conductivities of samples were measured by four probe technique. Optoelectrochemical analysis indicates that the homopolymer and copolymer have an electronic band gap, measured as the onset of the π-to-π* transition, as 2.17 and 2.00 eV, respectively.

Thiophene derivatives as effective inhibitors for the corrosion of steel in 0.5 M H 2SO 4

The inhibition of the corrosion of the steel in 0.5 M H 2SO 4 by thiophene compounds is studied by weight loss and electrochemical polarisation. The results obtained reveal that these compounds are very efficient inhibitors. The inhibition efficiency increases with the increase of inhibitor concentration to reach 98% at 5×10 −3 M for the 2-ethylamine thiophene. Potentiodynamic polarisation studies clearly reveal that the presence of thiophenes does not change the mechanism of the hydrogen evolution reaction and they act essentially as cathodic inhibitors. The temperature effect on the corrosion behaviour of steel is studied in the range from 298 to 353 K without and with thiophene at 10 −3 M. The inhibitors 2-ethylamine thiophene and 3-ethylamine thiophene adsorb on steel according to Frumkin isotherm model.

A water‐dispersible conducting nanocomposite from suspension polymerisation of thiophene in presence of N‐vinylcarbazole

AbstractThe polymerisation of a mixture of thiophene and N‐vinylcarbazole was achieved in aqueous suspension in the presence of nanodimensional alumina and FeCl3 as oxidant. The resultant composite was found to contain both polythiophene (PTP) and poly(N‐vinylcarbazole) (PNVC) components even after reflux in benzene, which would remove any PNVC homopolymer. The presence of the individual polymer components was endorsed by FTIR spectroscopic analyses. Thermogravimetric analyses showed that the overall stabilities of the composite and the corresponding homopolymers were in the order: PTP–Al2O3 > PTP > PTP–PNVC–Al2O3 > PNVC. Differential thermal analyses studies showed the manifestation of two different exotherms corresponding to the presence of two different polymeric constituents in the PTP–PNVC–Al2O3 composite. Differential scanning calorimetry studies revealed two glass‐transition temperatures (Tg) suggesting the presence of two polymeric moieties in the PTP–PNVC composite. Scanning electron micrographs of the PTP–Al2O3 and PTP–PNVC–Al2O3 composites showed distinctive morphological patterns. Transmission electron microscopic images of the composite revealed that the average particle size varied between 20 and 80 nm. DC conductivities of the composites were of the order of 10−6 S cm−1. Copyright © 2003 Society of Chemical Industry

Organometallic Precursor Route to Carbon Nanotubes

AbstractFor Abstract see ChemInform Abstract in Full Text.

Carbon Nanotubes from Organometallic Precursors

AbstractFor Abstract see ChemInform Abstract in Full Text.

Electrocopolymerization of Indole and Thiophene: Conductivity-Peak Current Relationship and In Situ Spectroelectrochemical Investigation of Soluble Co-Oligomers

Electropolymerization of indole (IN) in the presence of thiophene (Th) was followed by in situ and ex situ spectroelectrochemical studies. A correlation between absorbance (390 nm) and charge (at 600 mV) values indicated that oligomeric species were formed in solution, and similar results were found with in situ measurements. The increase in conductivity by the incorporation of Th into polyindole was about 60 times for a feed ratio n IN / n Th =1: 10 and 19 times for n IN / n Th =1: 1. Similar effects were also observed during in situ spectroelectrochemical measurements of copolymer formation. It was also found that the cyclic voltametry peak potentials for the electrogrowth of copolymer films were closely correlated to the conductivities of the corresponding films (measured separately by four-point probe method), thereby allowing us to use the peak potential currents to predict the final copolymer film conductivities during the electrochemical growth process. The T g value of the polymer also increased with the incorporation of Th. The results strongly suggest that IN and Th copolymerize on the electrode surface as well as in solution.

Catalytic desulfurization of thiophene on H-ZSM5 using alkanes as co-reactants

Propane, n-hexane, n-decane, and hydrogen were used as co-reactants in the desulfurization of thiophene catalyzed by H-ZSM5 at 673 K. These co-reactants lead to hydrogen-rich intermediates, which are required for the removal of unsaturated fragments formed in thiophene decomposition reactions. Thiophene desulfurization rates increased with increasing alkane chain size, suggesting that the availability of hydrogen-rich intermediates increases with increasing alkane reactivity. Desulfurization rates with alkane co-reactants were significantly higher than those achieved with hydrogen. Sulfur is predominately removed as hydrogen sulfide (>80% S-selectivity) in the presence of alkane co-reactants, but much lower hydrogen sulfide selectivities were obtained when hydrogen was used and when thiophene decomposed in the absence of any co-reactants. The presence of thiophene did not alter the nature of the cracking, dehydrogenation, oligomerization, and cyclization pathways typical of alkane reactions or the overall rates of propane conversion on H-ZSM5. The selectivity for alkane conversion to aromatics, however, increased when alkane reactions occur concurrently with thiophene desulfurization, indicating that thiophene-derived intermediates contribute to the formation of aromatics by scavenging alkene intermediates formed from the alkane co-reactants. The higher alkene/alkane ratios observed during alkane reactions in the presence of thiophene are consistent with the scavenging of hydrogen-rich intermediates by thiophene-derived species via reactions that form aromatic molecules containing carbon atoms from both alkane and thiophene reactants.

Carbon nanotubes from organometallic precursors.

Multiwalled as well as single-walled carbon nanotubes are conveniently prepared by the pyrolysis of organometallic precursors such as metallocenes and phthalocyanines in a reducing atmosphere. More importantly, pyrolysis of organometallics alone or in mixture with hydrocarbons yields aligned nanotube bundles with useful field emission and hydrogen storage properties. By pyrolysis of organometallics in the presence of thiophene, Y-junction nanotubes are obtained in large quantities. The Y-junction tubes have a good potential in nanoelectronics. Carbon nanotubes prepared from organometallics are useful to prepare nanowires and nanotubes of other materials such as BN, GaN, SiC, and Si(3)N(4).

Hydrogenation of toluene over β-Mo 2C in the presence of thiophene

Unsupported β-Mo 2C have been synthesized by temperature programmed reaction in CH 4/H 2 mixtures and characterized by XRD, XPS and BET measurements. These solid compounds have been tested for the hydrogenation of toluene at 3.0 MPa with or without thiophene in a fixed bed reactor. Their activities have been compared to those of a reference catalyst 1 wt.% Pt/γ-Al 2O 3. β-Mo 2C hydrogenates toluene and shows a deactivation during the first stages of the reaction at 150 °C. With 50 ppm thiophene the 1% Pt/γ-Al 2O 3 deactivates rapidly and totally after exposure of six sulfur atoms on each Pt. β-Mo 2C shows a high activity at 200 °C which reflects a good tolerance to sulfur in the first stages of the reaction but then deactivates quite linearly with time. It seems that one sulfur atom titrates one surface molybdenum atom. Characterization of the spent catalysts show that the bulk structure is retained. XPS results reveal that the surface is sulfided (as a carbosulfide and/or MoS 2). This surface transformation is believed to be responsible for the deactivation of the catalysts as these phase sites are inactive for toluene hydrogenation.

Organometallic precursor route to carbon nanotubes

Abstract Multi-walled as well as single-walled carbon nanotubes are conveniently prepared by the pyrolysis of organometallic precursors, such as metallocenes and phthalocyanines, in a reducing atmosphere. Pyrolysis of organometallics alone or in mixture with hydrocarbons also yields aligned nanotube bundles with useful field emission properties. By pyrolyzing organometallics in the presence of thiophene, Y-junction nanotubes are obtained in large quantities. The junction nanotubes have a good potential in nanoelectronics. Carbon nano-tubes prepared from organometallics are useful for preparing nanowires and nanotubes of materials such as BN, GaN, SiC, and Si3N4.

Sulfur-Tolerant Pt-Supported Zeolite Catalysts for Benzene Hydrogenation: I. Influence of the Support

Benzene hydrogenation was investigated over a series of Pt-supported MOR and LTL zeolites in the presence of varying thiophene concentrations. Higher activity and a higher sulfur resistance were observed for Pt supported on partially alkali-exchanged zeolites compared to completely alkali-exchanged and purely acidic zeolites. This is attributed to the contribution of catalytically active sites on the metal and on Brønsted acid sites in the vicinity or at the perimeter of the metal particles. Increasing temperature and hydrogen partial pressure increased the sulfur tolerance of the catalysts. Although the deactivation of Pt by thiophene during benzene hydrogenation was higher for Pt/KH-LTL compared to Pt/NaH-MOR, the higher overall hydrogenation activity for benzene in the presence of thiophene was observed for Pt/KH-LTL. This is attributed to the high Pt dispersion and the closer vicinity of Pt and Si(OH)Al groups in LTL. As a consequence, the benzene hydrogenation route on Brønsted acid sites with spillover of hydrogen from Pt is more effective on Pt/KH-LTL than on Pt/NaH-MOR.