Photo‐induced protonation and conductivity of polyaniline/poly(ethylene glycol) and polyaniline/[poly(ethylene glycol)‐grafted polyaniline] composites

Composites of polyaniline in its emeraldine base form (PANI‐EB) and photo‐acid generators (PAG) show an increase in conductivity upon photo‐irradiation due to the protonation of PANI‐EB. Such materials may be utilized to fabricate conducting patterns by photo‐irradiation. However, the conductivity obtained by direct irradiation of PANI‐EB/PAG composites was normally quite low (<10^?3 S/cm) due to aggregation of highly loaded PAG. In this work, poly(ethylene glycol) (PEG), which is a proton transfer polymer, was added to PANI‐EB/PAG. Results showed that addition of low M_w (550) PEG significantly enhance the photo‐induced conductivity. Conductivities as high as 10^?1–10⁰ S/cm were observed after photo‐irradiation. This conductivity is comparable to that of PANI‐salt synthesized by oxidizing aniline in the presence of an acid. High M_w (8000) PEG is much less effective than PEG 550, which is attributed to its lower compatibility with PANI. PEG‐grafted PANI (N‐PEG‐PANI) was also studied as an additive. Composites of PANI‐EB and N‐PEG‐PANI showed conductivity as high as 10² S/cm after treatment with HCl vapor. The photo‐induced conductivity of the N‐PEG‐PANI/PANI‐EB/PAG composite reached 10^?2–10^?1 S/cm. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Acid-treated bentonite-supported Ni catalysts via rapid microwave-assisted drying for nitrobenzene hydrogenation

Acid-treated bentonite-supported Ni catalysts were prepared using a microwave-assisted drying process, characterized and used for the hydrogenation of nitrobenzene to aniline. Microwave-assisted drying of the catalyst reduced the drying time from 3?h with a traditional heating method to 10?min; after drying by microwave irradiation, the acid-treated bentonite-supported Ni catalysts were more stable due to a smaller crystallite size, a higher dispersion of metallic Ni and stronger interactions between Ni and the acid-treated bentonite support than the traditional drying method. Catalytic studies conducted at 300°C with a nitrobenzene liquid hourly space velocity of 3.6?mL?g^?1?h^?1 and a H₂ gas hourly space velocity of 4,800?mL?g^?1?h^?1 indicated that the catalyst prepared using the microwave heating method maintained a nitrobenzene conversion of >99.9% with an aniline selectivity >93% during a 60-h reaction. In addition, the catalyst dried using a traditional method only functioned for 16?h.     

Removal of diazinon by various advanced oxidation processes

Diazinon is a widely used organophosphorus insecticide that is an important pollutant in aquatic environments. The chemical removal of diazinon has been studied using UV radiation, ozone, Fenton's reagent, UV radiation plus hydrogen peroxide, ozone plus hydrogen peroxide and photo‐Fenton as oxidation processes. In the photodegradation process the observed quantum yields had values ranging between 2.42 × 10^?2 and 6.36 × 10^?2 mol E^?1. Similarly, the ozonation reaction gave values for the rate constant ranging between 0.100 and 0.193 min^?1. In the combined systems UV/H₂O₂ and O₃/H₂O₂ the partial contributions to the global oxidation reaction of the direct and radical pathways were deduced. In the Fenton's reagent and photo‐Fenton systems, the mechanism of reaction has been partially discussed, and the predominant role of the radical pathway pointed out. Additionally, the rate constant for the reaction between diazinon and the hydroxyl radicals was determined, with the value 8.4 × 10⁹ L mol^?1 s^?1 obtained. A comparison of the different oxidation systems tested under the same operating conditions revealed that UV radiation alone had a moderate oxidation efficiency, which is enhanced in the case of ozone, while the most efficient oxidant is the photo‐Fenton system. Copyright © 2007 Society of Chemical Industry     

Studies on the reduction of nitrobenzene to aniline catalysed by pd(acac)2-pyridine system

The complex, bis(acetylacetonato)palladium(II) in pyridine, is used as a homogeneous catalyst for the conversion of nitrobenzene to aniline. From a study of various operational parameters the optimum reduction was found to occur at 1 atm pressure and at room temperature in petroleum ether (b.p. 100–120°C) solvent, yielding 90% of aniline on input nitrobenzene basis. The complex [Pd¹¹(acac)H(C₆H₅NO₂)Py] was isolated under similar experimental conditions and was characterised by elemental analysis, magnetic, thermal and spectral studies. Formation of a phenylnitrene metal complex has been suggested as a hypothetical intermediate in the reduction process.     

Preparation of mono(dimethylglyoxime)(triphenylphosphine)-halogenocobalt(I) complexes and their application as homogeneous catalysts in reduction of aromatic nitrocompounds

The complexes [Co(I)(DMGH)(PPh₃)X].C₂H₅OH (X? Cl/Br) have been prepared and characterised by elemental analysis, infrared and electronic spectral studies and magnetic measurements. These compounds have been used as homogeneous catalysts for the reduction of nitrobenzene at atmospheric and higher pressures. From a study of various operational parameters, it has been observed that the reduction at atmospheric pressure was only possible in a basic ethanolic medium and resulted in 64% of azobenzene on input nitrobenzene basis whereas at higher pressure (4.2 × 10³ kN/m²), 60% of aniline on the same basis could be obtained in neutral ethanolic medium. The optimum conditions were established both under normal pressure and under high pressure.     

Performance and Economic Assessment of the Treatment of Phenol with TiO2 Photocatalysis,Photo‐Fenton,Biological Aerated Filter,and Wetland Reactors

The performance and economic cost of the removal of phenol with TiO₂ photocatalysis, photo‐Fenton reactions, biological aerated filter (BAF), and constructed wetland (CW) reactors has been studied. The BAF achieved complete removal with a maximum phenol concentration of 200 mg·L^?1. The BAF‐CW combination provided a phenol‐free effluent with a maximum phenol concentration of 650 mg·L^?1. In both cases, a complete detoxification of the treated water was achieved at the concentrations studied. The efficiency of TiO₂ photocatalysis was limited to concentrations below 50 mg L^?1 to minimize removal reduction and toxicity of the intermediates. Photo‐Fenton was more efficient, but also more expensive because of the high cost of H₂O₂. The photo‐Fenton‐BAF combination is proposed to be the most suitable one.     

On the Mechanism of the Oxidative Amination of Benzene with Ammonia to Aniline Over NiO/ZrO2 as Cataloreactant

The kinetics of the semi-batch oxidative synthesis of aniline under atmospheric pressure using DuPont’s NiO/ZrO₂ cataloreactant was studied in a microreactor flow set-up equipped with a calibrated online mass spectrometer. It was found that the reaction temperature is a crucial parameter for the selectivity to aniline. At 590 K, exclusively aniline was formed, whereas at higher temperatures the decomposition of benzene into C-1 fragments led to the formation of toluene and benzonitrile. TPO experiments carried out in the same reactor subsequent to isothermal aniline synthesis allowed us to derive the degree of coking and the degree of NiO reduction.     

Thin‐Film Catalytic Coating of a Microreactor for Preferential CO Oxidation over Pt Catalysts

Different Pt‐based catalyst layers have been prepared and tested in a stacked foil microreactor for CO oxidation and preferential oxidation of CO in presence of hydrogen. The reactions were performed on Pt without support by impregnation of a pre‐oxidized microstructured metal plate, Pt/Al₂O₃ and Pt/CeO₂ based on sol methods as well as Pt/nano‐Al₂O₃, a combined method of sol‐gel and nanoparticle slurry coating. The ceria based sol‐gel catalyst was much more active for CO oxidation than alumina based sol‐gel catalysts at low temperature. However, total oxidation was only obtained at higher temperature on the alumina based catalysts. The combined method seems to have advantages in terms of less internal mass transfer limitation when trying to increase the catalyst coating thickness based on sol‐gel approaches due to no reduction of CO selectivity up to 300 °C reaction temperature. Experiments on CO oxidation with the Pt/CeO₂ catalyst have been conducted in an oxygen supply microreactor to evaluate the catalyst performance under sequential oxygen supply to reaction zone (CO excess).     

Hydrogenation of Nitrobenzene with Supported Transition Metal Catalysts in Supercritical Carbon Dioxide

Transition metal catalysts such as Pd, Pt, Ru, and Rh supported on carbon, silica and alumina have been examined for the hydrogenation of nitrobenzene (NB) in supercritical carbon dioxide (scCO₂) and in ethanol. The order of hydrogenation activity is Pt>Pd>Ru, Rh in scCO₂ and in ethanol. The effectiveness of the support is C>Al₂O₃, SiO₂ for either Pt or Pd in scCO₂. For all the catalysts, higher selectivity to aniline has been obtained in scCO₂ compared with ethanol. Hydrogenation of nitrobenzene catalyzed with Pd/C and Pt/C catalysts was successfully conducted in scCO₂ with a 100% yield to aniline at a lower reaction temperature of 35 °C. The product aniline (organic phase) can be easily separated from the side‐product water (aqueous phase), solvent (scCO₂), and catalyst (solid) by a simple phase separation process. The hydrogenation of NB is a structure‐sensitive reaction in ethanol as well as in scCO₂ except for a few Pt/C catalysts in which the degree of metal dispersion is small (<0.08).     

Homogeneous catalysis of the reduction of nitrobenzene by bromotris(triphenylphosphine) copper (I)

Homogeneous reduction of nitrobenzene by hydrogen in presence of complex [Cu^IBr(PPh₃)₃] as catalyst has been investigated. From a study of various operational parameters, it has been observed that maximum reduction occurred at 2.5 × 10³ kPa pressure and at 473–513 K and resulted in 75% aniline, 10% azobenzene, 2% nitrosobenzene in ethanol, and 70% aniline, 5% azobenzene, 7% nitrosobenzene in dimethylformamide, calculated on the basis of input nitrobenzene. In an attempt to elucidate the reduction mechanism two new intermediates, [CuHPPh₃Br]₂ (I) and [(C₆H₅N=NC₆H₅)Cu₂(PPh₃)₄Br₂] (II), have been isolated and characterised by elemental analysis, spectral, thermal, magnetic and p.m.r. studies.     

High trans,trans Conjugated Linoleic Acid-Rich Triacylglyceride Production by Photo-Irradiation

Recent studies have shown that a 20 % trans,trans conjugated linoleic acid (CLA)‐rich soy oil significantly reduces heart disease and diabetes risk factors in obese rats. Furthermore, trans,trans‐CLA has been reported to have superior anti‐carcinogenic activity than other CLA isomers. Therefore, a more concentrated source of trans,trans‐CLA oil would be highly desirable. The objectives of this study were to (1) determine the yield of trans,trans‐CLA isomers resulting from photo‐irradiation of Tonalin^® (BASF Global, Florham Park, NJ, USA) and identify trans,trans‐CLA positional isomers; and (2) derive a mathematical model of kinetics of trans,trans‐CLA TAG formation from Tonalin^®. Fifty‐five percent trans,trans‐CLA rich oil was obtained in about 140 min when Tonalin^® was photo‐isomerized with 0.35 % iodine, which is almost three times more than is possible with photo‐isomerized soy oil. Photo‐isomerization of Tonalin^® requires about 2 h, compared to 12 h for photo‐isomerization of soy oil. This reaction is a first‐order reversible reaction with the forward rate constant (k_f) = 13.17 × 10^?3min^?1 and backward rate constant (k_b) = 5.334 × 10^?3min^?1. The major isomers identified were trans‐9,trans‐11‐ and trans‐10,trans‐12‐CLA.     

Electrically controllable perchlorate removal based on poly(aniline‐co‐o‐aminophenol) doped with p‐toluene sulfonate

Poly(aniline‐co‐o‐aminophenol) (PANOA) was synthesized via electrochemical copolymerization of o‐aminophenol and aniline using p‐toluene sulfonate (TSA^?) as the counterion. The redox transformation of PANOA is accompanied by the exchange of anions into and out of the copolymer, and the feasibility of perchlorate (ClO₄^?) removal via an electrically switched ion exchange process was evaluated in this study. The results of electrochemical quartz crystal microbalance (EQCM), electrochemical impedance spectroscopy (EIS), and Fourier transform infrared spectroscopy (FTIR) demonstrated the successful release of TSA^? upon reduction and uptake of ClO₄^? upon reoxidation of the copolymer. Also, in this work, the possible ion‐exchange mechanism of PANOA was proposed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41895.     

Manipulation of polymer layer characteristics by electrochemical polymerization from mixtures of aniline and ortho‐phenylenediamine monomers

The influence of adding ortho‐phenylenediamine (OPDA) during the polymerization of aniline on the characteristics of the resulting polymer film was examined. When using a platinum electrode, the deposits were obtained from solutions containing 0.1 mol dm^?3 aniline and 1, 5, or 10 mmol dm^?3 OPDA. The deposits were also prepared from solutions containing 0.5 mol dm^?3 aniline and 5, 10, or 50 mmol dm^?3 OPDA. In both cases, 3 mol dm^?3 phosphoric acid solution was used as a supporting electrolyte. The characteristics of the obtained layers were investigated through the catalytic effect of different polymer layers on hydroquinone/quinone (H₂Q/Q) test redox system. The results obtained confirm the earlier established catalytic effect on the potential of the redox reaction by shifting it to more reversible values. However, as the concentration of OPDA was increased, the resulting limiting current decreased, thus indicating in the presence of OPDA a lower population of the available active centers necessary for the catalytic reaction to proceed. The influence of OPDA on polymer characteristics was also studied by using scanning electron microscopy as well as electrochemical impedance spectroscopy. The polymer was synthesized on a stainless steel electrode (13% Cr) from a solution containing 0.5 mol dm^?3 aniline and 5, 10, or 50 mmol dm^?3 OPDA. The layers were tested in chloride‐containing solutions by monitoring the open circuit potential. The results obtained suggest that, by increasing the concentration of OPDA, the time of OCP in the passive region of stainless steel is prolonged. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of conducting poly(aniline‐co‐diaminodiphenylsulfone) copolymers

Polyaniline, poly(aniline‐co‐4,4′‐diaminodiphenylsulfone), and poly(4,4′‐diaminodiphenylsulfone) were synthesized by ammonium peroxydisulfate oxidation and characterized by a number of techniques, including infrared spectroscopy, ultraviolet–visible absorption spectroscopy, ¹H‐NMR, thermogravimetric analysis, and differential scanning calorimetry. These copolymers had enhanced solubility in common organic solvents in comparison with polyaniline. The conductivities of the HCl‐doped polymers ranged from 1 S cm^?1 for polyaniline to 10^?8 S cm^?1 for poly(4,4′‐diaminodiphenylsulfone). The copolymer compositions showed that block copolymers of 4,4′‐diaminodiphenylsulfone (r₁ > 1) and aniline (r₂ < 1) formed and that the reactivity of 4,4′‐diaminodiphenylsulfone was greater than that of aniline. The results were explained by the effect of the ? SO₂? group present in the polymer structure. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2337–2347, 2003     

A robust mixed‐conducting multichannel hollow fiber membrane reactor

To accelerate the commercial application of mixed‐conducting membrane reactor for catalytic reaction processes, a robust mixed‐conducting multichannel hollow fiber (MCMHF) membrane reactor was constructed and characterized in this work. The MCMHF membrane based on reduction‐tolerant and CO₂‐stable SrFe_0.8Nb_0.2O_3‐δ (SFN) oxide not only possesses a good mechanical strength but also has a high oxygen permeation flux under air/He gradient, which is about four times that of SFN disk membrane. When partial oxidation of methane (POM) was performed in the MCMHF membrane reactor, excellent reaction performance (oxygen flux of 19.2 mL min^?1 cm^?2, hydrogen production rate of 54.7 mL min^?1 cm^?2, methane conversion of 94.6% and the CO selectivity of 99%) was achieved at 1173 K. And also, the MCMHF membrane reactor for POM reaction was operated stably for 120 h without obvious degradation of reaction performance. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2592–2599, 2015     

Destruction of chlorinated organics by hydrotreatment using Ru/TiO2 catalyst

Catalytic hydrodechlorination reactions of p‐chloro‐m‐cresol (PCMC) and p‐chloroaniline (PCA) were investigated in a slurry reactor using a Ru/TiO₂ catalyst. The organic reaction intermediates, m‐cresol and aniline, were further converted into methylcyclohexanol and cyclohexylamine respectively. Kinetics of PCMC hydrogenation was studied over the ranges in temperature, 323–373 K, H₂ partial pressure, 0.34–1.38 MPa, PCMC concentration, 3.5–14 mM and catalyst loading, 0.1–2 kg/m³. The reaction orders with respect to PCMC and H₂ were evaluated as 0.5 and 0.8 respectively. It was found that aniline hydrogenation is the rate‐determining step in the hydrotreatment of PCA. Kinetics of aniline hydrogenation was studied at 343 and 363 K over the ranges in H₂ partial pressure, 0.34–1.38 MPa, aniline concentration, 5.4–21.5 mM and catalyst loading, 0.1–0.6 kg/m³. The reaction orders with respect to aniline and H₂ were found to be 1.3 and 1.0 respectively. © 2012 Canadian Society for Chemical Engineering     

Preparation and catalytic efficiency of mixed noble metal catalysts on electrochemically activated carbon fibre supports

Mixed noble metal catalytic systems were prepared on electrochemically activated PAN-based carbon fibre supports through a procedure of repetitive cation exchange between the acidic (-OOOH and-OH) groups of the electrooxidized carbon surface and noble metal salts and subsequent cathodic reduction of the exchanged noble metal ions to the metallic state.The whole investigation was carried out for the binary system Ag-Pd. The catalytic efficiency of palladium deposited on silver is more pronounced compared to a Pd-deposition obtained after only one Pd²⁺-exchange procedure and subsequent cathodic reduction, whereas an inhibition of the catalytic activity of palladium is noticed when it is covered by silver deposition. The catalytic efficiency of the obtained mixed noble metal catalysts was studied by means of hydrogen-adsorption and absorption profiles in H₂SO₄, the electroreduction of nitrobenzene in aqueous methanolic H₂SO₄ solutions and the hydrogenation reaction of nitrobenzene to aniline in methanolic solutions. The study was completed by impedance spectroscopic measurements at the potential of hydrogen evolution in H₂SO₄ solutions.Mixed Ag-Pd systems are even more stable than double Pd-Pd depositions on activated carbon fibre supports, as shown by the fact that they retain their mechanical stability and catalytic activity even after prolonged storage in aqueous or methanolic solutions, as well as after ultrasonic treatment.     

Synthesis of p‐aminophenol from the hydrogenation of nitrobenzene over metal–solid acid bifunctional catalyst

BACKGROUND: A single‐step conversion of nitrobenzene (NB) to p‐aminophenol (PAP) through catalytic hydrogenation is a widely used synthesis route for PAP. The main shortcoming of this route is the use of sulfuric acid for rearrangement of the phenylhydroxylamine (PHA) intermediate. In this paper, S₂O₈^2?/ZrO₂ (PSZ) solid acid and Pt‐S₂O₈^2?/ZrO₂ (Pt‐PSZ) bifunctional catalysts were prepared for the synthesis of PAP in non‐acid medium. RESULTS: Calcination temperature has a substantial effect on the acidity, structure and activity for PHA rearrangement of PSZ. The highest PAP yield was 33.8% over PSZ calcined at 823 K when the reaction was carried out in water at 423 K. A high PAP yield of 23.9% was achieved by a single‐step reaction of nitrobenzene over Pt‐PSZ bifunctional catalysts. CONCLUSION: PSZ solid acid exhibits high activity for PHA rearrangement. Perfect tetragonal ZrO₂ and much stronger acid sites play important roles in catalytic activity. Inhibiting the hydrogenation activity by reducing the amount of Pt loading on Pt‐PSZ can improve the competition of PHA rearrangement on acid sites with hydrogenation of PHA on metal active sites, resulting in better selectivity to PAP. Copyright © 2008 Society of Chemical Industry     

Scale-up of a fixed bed electrochemical reactor consisting of parallel screen electrode used for p-aminophenol production

The behavior of a fixed bed consisting of amalgamated copper screens has been investigated for the electrolytic reduction of nitrobenzene to p-aminophenol under potentiostatic condition (controlled potential). The preparative electrolysis of nitrobenzene was carried out using supporting electrolytes consisting of 2 M H₂SO₄ in a solution of 50% 2-propanol/50% water (v/v). The criterion for scale-up (?_n) was determined through application of one-dimensional model. The polarization curves that describe the reduction of nitrobenzene to p-aminophenol were obtained experimentally by using a pilot scale for different nitrobenzene concentrations and flow rates of catholyte.It was found that the effectiveness factor (?_n) increases with increasing flow rate, and decreasing nitrobenzene concentration. An optimum thickness of bed equal to 0.6 cm was obtained, in which the effectiveness factor not less than 0.588, to ensure a well distribution of current and potential.     

Preparation and characterization of Ni-B/SiO2sol amorphous catalyst and its catalytic activity for hydrogenation of nitrobenzene

Supported Ni-B/SiO₂sol amorphous alloy catalyst was prepared by a sol-gel and impregnation-chemical reduction method, and the effects of the tetraethyl orthosilicate (TEOS) and ammonia ratio, and the nickel loading amount on the nitrobenzene hydrogenation were also investigated. The results showed that Ni-B amorphous alloy catalyst supported on the silica sol increased the specific surface area of catalysts, improved the catalytic activity of Ni-B amorphous alloy catalyst, and the Ni species on the surface existed in the form of Ni²⁺. The optimal TEOS and ammonia ratio and nickel loading amount was 1.0 and 10%, respectively, and when using this optimal Ni-B/SiO₂sol catalyst, the nitrobenzene conversion was 99.9% with an aniline selectivity of 99.8%, and after 5 recycles, the Ni-B/SiO₂sol maintained a good stability.