Selective hydrogenation of styrene: Poisoning effect of thiophene

The poisoning effect of thiophene on a commercial selective hydrogenation Pd/Al₂O₃ catalyst, using the styrene hydrogenation to ethylbenzene as a test reaction, has been studied. It was found that the addition of thiophene to the reactants modifies the electronic properties of Pd and also prevents (within certain limits) the catalyst from a subsequent poisoning when a second amount of thiophene is added. These modifications on Pd electronic state have been followed by X-ray photoelectron spectroscopy, and the poison addition has been studied by IR spectroscopy.     

吡啶改性Pd/SiO2催化剂用于H2和O2直接合成H2O2

引言过氧化氢(H2O2)是一种理想的绿色氧化剂,广泛应用于化学品合成、纺织、造纸、环保、食品、医药、冶金和农业等领域[1]。目前,蒽醌法[2-5]是工业上生产H2O2的主要方法。20世纪40年代,德国I.G.Farbenindustrie首先采用蒽醌法(又称Riedl-Pfleiderer法)工业化生产过氧化氢。该方法首先将2-烷基蒽醌(通常是2-乙基蒽醌)溶解于合适的有机溶剂中,溶液中的2-烷基蒽醌经催化剂催化加氢,被还原成蒽氢醌或5,6,7,8-四氢蒽氢醌,再经空气氧化得到蒽醌或四氢蒽醌和     

Studies of molybdena-alumina catalysts. X. temperature programmed desorption of H2S and thiophene

Temperature programmed desorption (TPD) and reduction (TPR) studies were carried out on H₂S and thiophene adsorbed on Mo/Al₂O₃ and CoMo/Al₂O₃ catalysts. Freshly sulfided and pyridine poisoned catalysts were run. For sulfided catalysts, the major products of desorption of thiophene were thiophene and butene, leaving a carbonaceous residue. Subsequent TPR in H₂ effected complete removal of the residue with formation of H₂S, thiophene and butene. The residue appeared to consist of an easily reactive thiophene polymer and a less-reactive, sulfur-containing coke. Runs on poisoned catalysts showed less adsorption but product profiles were similar, showing that the adsorption characteristics of the remaining sites were not significantly altered.     

Unterschiede in der Totaloxidation organischer Verbindungen an heterogenen Platin- und Palladiumkatalysatoren

Differences in the Total Oxidation of Organic Compounds on Heterogeneous Pt- and Pd-Catalysts The catalytic oxidation of selected organic compounds was studied on supported Pd and Pt catalysts and on massive wires. Unfunctionalized (Decane), unsaturated (dodecene, benzene), oxygen containing (1-octanol, formaldehyde, acetone, n-butylacetate, formic acid), nitrogen containing (aniline, pyridine), sulfur containing (thiophene) and chlorinated (1,2-dichloroethane) hydrocarbons were used as model compounds. The relative activity of the metals for oxidation of the various compounds was determined from the turnover frequencies. While platinum is more active for the oxidation of the unfunctionalized, aromatic and chlorinated compounds, palladium is more active for nitrogen and sulfur containing compounds and for formic acid. No specificity is found for alkenes and compounds with a lower oxygen content. In the presence of octane, the unreactive pyridine is much more effectively oxidized than pyridine alone. There are distinct differences for the oxidation of octane/pyridine mixtures on bimetallic, mixed and pure Pt- and Pd-catalysts. The bimetallic catalyst and the pure Pt-catalyst dominate with respect to conversion and selectivity. The oxidation of linear alkanes on Pt correlates with the boiling point. Pd catalyzes the oxidation of lower hydrocarbons (< C₅) better, while higher hydrocarbons ( > C₅) are better oxidized by Pt.     

Selective hydrogenation of cyclopentadiene over supported metal catalysts

The selective hydrogenation of cyclopentadiene to cyclopentene has been studied in the liquid phase using Pd and Pd Me/Al₂O₃ bimetallic catalysts (Me = Mn, Ni, Co, W). The highest activity was obtained with Pd Co and Pd W/Al₂O₃. For these catalysts, no hydrogen or CO chemisorption was detected although Pd could be seen by XPS at 335·8 eV; it is considered that new species, more active for the selective hydrogenation of cyclopentadiene, appeared at the catalyst surface. The sulfur resistance towards thiophene has also been studied. It was observed that the highest sulfur resistance is coincident with the highest activity. XPS analysis shows that the poisoning species is thiophene adsorbed on the catalyst surface.     

The treatment of binary VOC mixtures by adsorption and oxidation using activated carbon and a palladium catalyst

The adsorption of binary thiophene‐containing mixtures on activated carbon and their subsequent desorption and oxidation over a Pd/CeO₂/Al₂O₃ catalyst has been studied as a model for the treatment of dilute VOC streams by intermittent accumulation and combustion. When adsorbed together, cyclohexene and thiophene have similar breakthrough times with little tendency for one to displace the other. However the adsorption of thiophene continues beyond that of diethylamine in mixtures while thiophene is itself displaced by methylmethacrylate. Oxidation of the binary mixtures is controlled by that of thiophene which requires temperatures somewhat above 300 °C for complete removal. Combustion of the other VOCs proceeds in parallel with thiophene although they react at much lower temperatures when alone. Both components of the mixtures can be removed by a system in which the VOCs are accumulated on carbon and then undergo temperature programmed desorption in air onto Pd/CeO₂/Al₂O₃ held at 350 °C. However it is not possible to operate with the adsorbent and catalyst together since desorption then occurs before the catalyst reaches working temperature. © 2002 Society of Chemical Industry     

Surface synthesis of thiophene

A cyclization reaction has been observed in which thiophene is produced from acetylene and sulfur co-adsorbed on the Pd(111) surface. As in the case of acetylene trimerization to benzene the reaction yielding thiophene can proceed via an intermediate species of stoichiometry C₄H₄. The ability of the reaction intermediate to extract sulfur from the surface varies between the two phases of adsorbed sulfur that can exist on the Pd(111) surface.     

Acetonylacetone conversion on AlPO4–cesium oxide (5–30 wt%) catalysts

The effect of hydrogen spillover over Pd/SiO₂ + USY on pyridine chemisorbed on acid sites of USY zeolite was investigated. According to FTIR measurement, pyridine adsorbed on Lewis acid sites migrated to Brønsted acid sites under hydrogen-flowing atmosphere. The rate of migration was drastically promoted by physically mixed Pd/SiO₂ catalysts. This suggests that spilt-over hydrogen enhance the migration of pyridine adsorbed on Lewis acid sites.     

Aromatic sulfur‐nitrogen extraction using ionic liquids: Experiments and predictions using an a priori model

The tie‐line composition of three quaternary system namely 1‐ethyl‐3‐methylimidazolium acetate ([EMIM][OAc]) ([EMIM][OAc]) (1) + thiophene (2) + pyridine (3) + toluene (4), 1‐ethyl‐3‐methylimidazolium ethylsulphate ([EMIM][EtSO₄]) (1) + thiophene (2) + pyridine (3) + toluene (4), 1‐ethyl‐3‐methylimidazolium methylsulphonate ([EMIM][MeSO₃]) (1) + thiophene (2) + pyridine (3) + toluene (4) were experimentally determined at 298.15 K. The measured tie‐line data were successfully correlated with the nonrandom two liquid and UNIversal QUAsiChemical model prediction which gave less than 1% root mean square deviation (RMSD). [EMIM][MeSO₃] looks to be a promising solvent for the simultaneous separation having distribution ratios less than unity for both thiophene and pyridine. The quantum chemical‐based conductor like screening model for real solvent (COSMO‐RS) model was then used to predict the tie‐line composition of quaternary systems. COSMO‐RS gave the RMSD for the studied systems to be 8.41, 8.74, and 6.53% for the ionic liquids, respectively. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4806–4815, 2013     

Quantum chemical studies on the simultaneous interaction of thiophene and pyridine with ionic liquid

The simultaneous interaction of thiophene and pyridine with different ionic liquids:1‐butyl‐1‐methylpyrrolidinium tetrafluoroborate([BPYRO][BF₄]),1‐butyl‐1‐methylpyrrolidinium hexafluoro‐phosphate ([BPYRO][PF₆]), 1‐butyl‐4‐methylpyridinium tetrafluoroborate ([BPY][BF₄]), 1‐butyl‐4‐methylpyridinium hexafluorophosphate ([BPY][PF₆]) and 1‐benzyl‐3‐methylimidazolium tetrafluoroborate ([BeMIM][BF₄]) were investigated using quantum chemical calculations. A three‐tier approach comprising of partial charges, interaction energies and sigma profile generation using conductor‐like screening model for real solvents (COSMO‐RS) was chosen to study the systems. A quantitative attempt based on the CH‐π interaction in ionic liquid; thiophene–pyridine complexes gave the interaction energies of ILs in the order: [BPY][BF₄] > [BPYRO][PF₆] > [BeMIM][BF₄] > [BPY][PF₆] > [BPYRO][BF₄]. An inverse relation was observed between the activity coefficient at infinite dilution predicted via COSMO‐RS–based model and interaction energies. The dominance of CH‐π interaction was evident from the sigma profiles of ionic liquid together with thiophene and pyridine. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Synthesis,structures, and density functional theory computational study of thiophene‐containing and fluorodecorated imine‐linked polymers

A new series of extended–conjugated and thermally stable thiophene‐containing imine‐linked polymers were synthesized via a Schiff‐base condensation reaction between aryl aldehydes and 2,6‐diaminopyridine building blocks. The backbones of the polymers were functionalized with phenyl, fluorosubstituted phenyl, thienyl, and pyridyl aromatic rings. The successful synthesis was confirmed with spectrochemical characterization techniques, including IR, ¹H‐NMR, ¹³C‐NMR, and elemental analyses. The electronic properties of the polymers were investigated with ultraviolet–visible (UV–vis) absorption spectroscopy; the properties were collected experimentally and calculated with density functional theory (DFT) in the gas phase. The maximum absorption calculated from DFT was higher than the experimental values by about 60 nm; this was attributed to the absence of the solvent effect in the DFT case. The frontier molecular orbital ((HOMO) highest occupied molecular orbital and (LUMO) lowest unoccupied molecular orbital), optical band gap (E_g), and total energy (E_T) values of the optimized structures were calculated. Apparently, there was a significant relation between the number of thiophene rings and the resulting E_g and E_T values. As the number of thiophene rings in the polymer chain increased, E_g and E_T decreased, and the thermal stability of the polymers increased. E_g and the absorption band edges were determined experimentally from the UV–vis and transmittance spectra, respectively. Poly(terthienyl–azomethine–pyridine–azomethine), with the highest thiophene content, had the lowest experimental and calculated E_g values (2.10 and 2.63 eV, respectively). In contrast, upon fluorination, poly[(2,5‐dithienyl–1,4‐difluorobenzene)–azomethine–pyridine–azomethine] exhibited the highest E_g (2.81 eV) and absorption band edges (2.94 eV), whereas the thermal stability decreased to 250 °C. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44331.     

Synthesis, electropolymerization, and photoelectrochemical characterization of 2,7-di(thiophen-2-yl)-N-methylcarbazole

A new copolymer derived from 2,7-carbazole with thiophene is reported. This copolymer was obtained through the synthesis of 2,7-dibromo-N-methyl carbazole and 2-bromothiophene using a Kumada-type reaction to bond both rings and using two different kinds of Pd catalysts, [Pd(OAc)₂] and [Pd(PPh₃)₄], with significant differences in their yields. The trimer that was obtained was subsequently electropolymerized using cyclic voltammetry, and the photoelectrochemical properties were determined. Polymerization using electrochemistry showed that the trimer contains two types of possible bonds for the formation of the macromolecule, which led to the formation of two distinctly different materials. The obtained materials exhibit promising photoelectric responses suggesting that they both can be explored in the designing of photovoltaic cells.     

Benzene Formation During the Oxidation of Cyclohexene in the Presence and Absence of Thiophene over a Supported Palladium Catalyst

The catalytic oxidations of cyclohexene and thiophene, singly and together, have been studied over a Pd/CeO₂/Al₂O₃ monolith catalyst. On a freshly reduced sample, the oxidation of cyclohexene on its own commences below 100°C with benzene as the major product over a considerable temperature range, even when O₂ is in large excess. Benzene is still produced when cyclohexene and thiophene are co-oxidised and the reaction exhibits oscillations, associated with accumulation and removal of sulfur, at high conversions. The oxidation of thiophene is self-poisoned to some degree and sulfur accumulated during it considerably reduces the activity of the catalyst for the subsequent oxidation of cyclohexene. However, the maximum yield of benzene remains high.     

Thermodynamic properties of 1‐ETHYL‐3‐methylimidazolium methanesulphonate with aromatic sulphur,nitrogen compounds at T = 298.15–323.15 K and P = 1 bar

This work investigates the ability of 1‐ethyl‐3‐methylimidazolium methanesulphate ([EMIM][MeSO₃]) as a green and tuneable solvent for denitrification and desulphurisation studies. Experimental density, surface tension and refractive index data have been measured for the following systems: [EMIM][MeSO₃] (1) + pyridine (2), [EMIM][MeSO₃] (1) + pyrrole (2), [EMIM][MeSO₃] (1) + quinoline (2), [EMIM][MeSO₃] (1) + indoline (2), [EMIM][MeSO₃] (1) + thiophene (2) and [EMIM][MeSO₃] (1) + water (2) over the entire mole fraction of [EMIM][MeSO₃] at T = 298.15–323.15 K and P = 1 bar. Further from experimental density, surface tension and refractive index, coefficient of thermal expansivity, excess molar volume, deviation of surface tension and refractive index deviation were also calculated. It was found that the heteroaromatic nitrogen/sulphur compounds are completely miscible in [EMIM][MeSO₃]. The surface tension values were found to increase while the refractive index decreases with increasing mole fraction of [EMIM][MeSO₃]. The experimental values for surface tension increased in the order: pyridine > thiophene > pyrrole > indoline > quinoline > water and for refractive index: pyridine > pyrrole > indoline > quinoline > thiophene > water. It was found that the composition of [EMIM][MeSO₃] has a greater influence than temperature in deciding the surface, optical and thermodynamic properties for similar molecular interaction such as IL–thiophene and IL–pyrrole than dissimilar molecules such as IL–water. Further quantum chemical‐based COSMO‐RS tool was used to estimate the activity coefficient at different composition. © 2012 Canadian Society for Chemical Engineering     

Poisoning and Regeneration of an Ni/SiO2 Catalyst

The poisoning effect of thiophene during the hydrogenation of styrene on an Ni/SiO₂ catalyst, and the regenerating role of both pure hydrogen and 2-butyne in the presence of hydrogen on the poisoned catalyst, were studied. The treatments induced the elimination of sulfur and promoted an important recovery of the catalytic activity and selectivity. XPS analyses show that the sulfur species adsorbed during the catalyst poisoning is thiophene. Part of the sulfur remained irreversibly adsorbed after the regeneration treatments carried out at 473 K; a modification on the adsorbed sulfur electronic state was detected, which can be ascribed to thiophene hydrogenolysis induced by the regenerating temperature. © 1997 SCI.     

The effect of N-containing compounds on oxidative desulphurization of liquid fuel

The oxidative removal of organic sulfur compounds from model fuel with H₂O₂ over Ti-containing molecular sieves in the presence of N-containing compounds had been studied. The effect of the types and amounts of nitrides on oxidative desulphurization were investigated. It has been shown that pyridine and pyrrole have adverse impact on the oxidation of thiophene and lead to the decrease of corresponding removal rate. The pyridine has stronger influence than pyrrole. Quinoline and indole have no impact on the final removal rate of thiophene. However, the two kinds of nitrides, as well as carbazole, have obvious impact on the oxidation removal of benzothiophene and 4,6-dimethyl dibenzothiophene. The effect of nitrides on oxidative desulphurization can be attributed to the strong adsorption of nitrides and their oxidized products on the active sites of catalysts. For pyridine and quinoline, which are basic nitrides, their adsorptions on catalysts are even stronger than that of sulfides.     

Nitrogen Tolerant Hydrodesulfurization Catalysts Based on Rh and Ru Promoted Mo/Al2O3

Rh and Ru promoted Mo/Al₂O₃ catalysts were tested in HDS of thiophene in the presence of different amounts of pyridine and compared with CoMo/Al₂O₃. The Rh and Ru promoted catalysts were more nitrogen tolerant and in the presence of pyridine showed higher HDS activities than CoMo/Al₂O₃. This was explained by higher C–N bond hydrogenolysis activity and high nitrogen tolerance of the free Rh and Ru sulfides in the promoted catalysts.     

Environmental remediation from thiophene solution by photocatalytic oxidation using a Pd/ZrO2–chitosan nanocomposite

A modified sol–gel technique was used to prepare ZrO₂ nanoparticles through impregnation of ZrO₂ with Pd and/or chitosan (CS). The composite photocatalyst of Pd/ZrO₂ was characterized by XRD, TEM, UV–vis, Pl, and BET and the photocatalytic activity was investigated under visible light irradiation by using a thiophene solution as a model pollutant. The results revealed the influence of the type and amount of the catalyst where CS can effectively prevent the agglomeration of ZrO₂ nanoparticles. UV–vis spectroscopic investigation indicated also that the ability of the composite to absorb visible light is greatly improved. The catalyst was reproducible without significant loss in its activity during the first five cycles.     

DRIFT study of CO chemisorption on organometallics-derived Pd/MgO catalysts: the effect of chlorine

Magnesia-supported palladium catalysts were prepared from chemical vapour deposition (CVD) of [Pd(C₃H₅)(C₅H₅)] and incipient wetness impregnation of [Pd(C₃H₅)Cl]₂ and [Pd(acac)₂]. DRIFT spectroscopy of adsorbed CO on prereduced catalysts indicates that the electronic state of metal particles depends on the preparation methodology and markedly on the organometallic precursor. Inn-heptane reforming at 500°C, the highest activity and selectivity were shown by the CVD-based system. Chloride ions deriving from the impregnation solvent exchange with surface hydroxyls. Acidic Mg-Cl sites are thus formed, which induce a beneficial effect on the catalytic properties. The reforming activity collapsed when a chlorine-containing precursor was used, due to a partial coverage of the palladium surface with chemisorbed chlorine atoms.     

The effect of sulfur compound on the hydrogenation of tetralin over a Pd–Pt/HDAY catalyst

A composite metal catalyst with a Pd/Pt of 4:1 and an H-form dealuminated Y zeolite support for the hydrogenation of tetralin was investigated. The materials were characterized by XRD, NH₃-TPD, N₂ adsorption, TPR and FTIR. The activity for the hydrogenation of tetralin was investigated with a high-pressure fixed-bed continuous-flow reactor operating at 4.0 MPa. The thiotolerance was tested with feeds containing 200 ppm sulfur in the form of 4,6-dimethyldibenzothiophene and thiophene, respectively. It was found that thiophene was more effective for deactivating the catalyst than the former one. The diffusion barrier of the pores for the sulfur compound is likely the major reason for the different deactivation rate of catalysts. The products other than decalins were mainly decalin isomers and ring-opened products. Selectivity of cracking products for the feed with thiophene was lower than that for the other feed, while that of ring-opened and ring-contracted products with the two feeds was similar.