Hydrierung von p‐Nitrophenol zu p‐Aminophenol als Testreaktion für die katalytische Aktivität von Pt‐Trägerkatalysatoren

The hydrogenation of p‐nitrophenol (PNP) to p‐aminophenol (PAP) using NaBH₄ as a reducing agent was studied as a test reaction for determining the catalytic activity of supported Pt catalysts. The initial reaction rate, which is accessible within less than 10 minutes via online UV‐vis spectroscopy at room temperature, ambient pressure and in water as a solvent, was used as measure for the catalytic activity. For three Pt catalysts supported on porous SiO₂, porous glass and Al₂O₃, respectively, significant differences in the catalytic activity were observed. However, especially in case of very active catalysts, limitations of the reaction by internal or external mass transfer have to be considered.     

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     

A new catalytic process for high‐efficiency synthesis of p‐xylene by methylation of toluene with CH3Br

A new catalytic process for p‐xylene synthesis from the methylation of toluene with CH₃Br was proposed. CH₃Br was prepared from the catalytic bromination of natural gas (CH₄), by using H₂O + HBr + O₂ as mediator over supported Rh catalyst. The methylation conditions were investigated using HZSM‐5 or modified HZSM‐5 catalyst. Under optimal reaction conditions, p‐xylene selectivity is up to 93%, and p‐xylene yield is more than 21% at 673 k over the Si—P modified HZSM‐5 catalyst. Compared to the processes using MeOH or dimethyl carbonate (DMC) as methylation agent, this new process is very attractive in an economic standpoint since CH₄ is much cheaper than MeOH and DMC. In addition, the process has other advantages, such as mild reaction conditions, simple operation, high‐product yield, and so on. It is predicted that the process has good industrial potential for para‐xylene production. © 2012 American Institute of Chemical Engineers AIChE J, 59: 532–540, 2013     

Copolymerization of propylene with p‐allyltoluene using metallocene catalysts

Copolymerization of propylene with p‐allyltoluene (p‐AT) was performed using two metallocene catalysts, rac‐ethylenebis(indenyl)zirconium dichloride and rac‐dimethylsilylenebis[1‐(2‐methyl‐4‐phenylindenyl)]zirconium dichloride. The effects of the polymerization conditions, such as the amount of p‐AT in the feed and polymerization temperature, on the properties of the copolymers and the activity of the catalysts were investigated. With increasing p‐AT feed, the incorporation of p‐AT increased, but the activity of the metallocene catalyst, the melting temperature (T_m) and the number‐average molecular weight of the copolymers decreased. Higher polymerization temperature tended to enhance the activity of the metallocene catalyst and the incorporation of p‐AT. The copolymers produced using the two metallocene catalysts were characterized with ¹H NMR, ¹³C NMR and differential scanning calorimetry; the results showed that the copolymers had a random structure. Copyright © 2006 Society of Chemical Industry Society of Chemical Industry     

Selectivity engineering in the O‐ versus C‐alkylation of p‐cresol with cyclohexene over sulfated zirconia

Solid acids are more widely used as heterogeneous catalysts, because they are eco‐friendly. This paper reports the results for the Friedel‐Crafts alkylation of p‐cresol with cyclohexene using solid acids sulfated zirconia, 20% w/w dodecatungstophosphoric acid (DTP) supported on K10 clay and ZnCl₂/K10 (Clayzic). This reaction gave substantial amount of 1‐cyclohexyloxy‐4‐methyl benzene (O‐alkylated product) and 4‐cyclo‐hexyl‐4‐methyl phenol (C‐alkylated product). Both products are of commercial importance as perfume and insecticide respectively. Sulfated zirconia catalyst was shown to be better than others studied in terms of activity and selectivity to the O‐alkylated product. The kinetics were studied with sulfated zirconia as catalyst where the rate determining step was the surface reaction between chemisorbed cyclohexene and p‐cresol from the liquid phase within pores according to the Eley‐Rideal mechanism. The production of O‐alkylated p‐cresol is favoured at lower temperatures and C‐alkylated product at higher temperatures. The best operating temperature is 353 K. The activation energies for O‐ and C‐alkylation are 72.68 and 118.28 kj/mol, respectively.     

Insights into Supported Copper(II)‐Catalyzed Azide‐Alkyne Cycloaddition in Water

Cross‐linked polymeric ionic liquid material‐supported copper (Cu‐CPSIL), imidazolium‐loaded Merrifield resin‐supported copper (Cu‐PSIL) and silica dispersed CuO (CuO/SiO₂), were prepared and proved to be efficient catalysts for the one‐pot synthesis of 1,4‐disubsituted‐1,2,3‐triazoles by the reaction of alkyl halides with sodium azide and terminal alkynes in water at room temperature. Moreover, these supported copper catalysts were recovered quantitatively from the reaction mixture by simple filtration and reused for five consecutive recycles without significant loss of catalytic activity. Among the three immobilized copper catalysts, Cu‐CPSIL exhibited excellent catalytic activity for the reaction of aliphatic bromides, sodium azide and terminal alkynes. The differences in the catalytic performances of the catalysts could be ascribed to the copper dispersion and the interaction between copper and the supports. In addition, water was used as the reaction media and the proton provider, the latter was found to be very important for the reaction. The XPS results suggested that the supported Cu(II) catalysts were reduced to catalytic Cu(I) species via alkynes homocoupling reaction. By means of IR and ESI‐MS studies, a possible mechanism of cycloaddition based on the reduction of Cu(II) to Cu(I) species was proposed.     

Synthesis and characterization of new polyamides containing p‐phenylenediacryloyl moieties in the main chain

Six new polyamides 8a–f containing p‐phenylenediacryloyl moieties in the main chain were prepared by the direct polycondensation reaction of bis(p‐amidobenzoic acid)‐p‐phenylene diacrylic acid 6 with 1,4‐diphenylene diamine 7a , 1,3‐diamino toluene 7b , 1,5‐diamino naphthalene 7c , 4,4′‐diamino diphenyl ether 7d , 4,4′‐diamino diphenyl sulfone 7e , and 3,3′‐diamino diphenylsulfone 7f by using thionyl chloride, N‐methyl‐2‐pyrolidone, and pyridine as condensing agents. These new polymers 8a–f were obtained in high yield and inherent viscosity between 0.35–0.65 dL/g. The resulting polyamides were characterized by elemental analysis, viscosity measurements, thermal gravimetric analysis (TGA and DTG), solubility test, FTIR and UV–vis spectroscopy. Diacid acid 6 as a new monomer containing p‐phenylenediacryloyl moiety was synthesized by using a three‐step reaction. First, p‐phenylenediacrylic acid 3 was prepared by reaction of terephthal aldehyde 1 with malonic acid 2 in the presence of pyridine, then diacid 3 was converted to p‐phenylenediacryloyl chloride 4 by reaction with thionyl chloride. Finally, bis(p‐amidobenzoic acid)‐p‐phenylene diacrylic acid 6 was prepared by the condensation reaction of phenylenediacryloyl chloride 4 with p‐aminobenzoic acid 5 . © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Study on liquid‐phase hydrogenation of paranitrotoluene over Ru‐based catalysts

This paper presented a study on the role of yttrium addition to Ru‐based catalysts for liquid phase paranitrotoluene hydrogenation reaction. An impregnation‐precipitation method was used for preparation of a series of yttrium doped Ru/NaY catalysts with yttrium content in the range of 0.0026–0.0052 g/g. Properties of the obtained samples were characterized and analyzed by X‐ray diffraction (XRD), H₂‐TPR, Transmission electron microscopy (TEM), ICP atomic emission spectroscopy, and Nitrogen adsorption‐desorption. The results revealed that catalytic activity of NaY supported Ru catalysts increased with the yttrium content at first, then decreased with the further increase of yttrium content. When yttrium content was 0.0033 g/g, a Ru‐Y/NaY² catalyst showed the most excellent performance of paranitrotoluene hydrogenation reaction (paranitrotoluene conversion and the selectivity toward P‐methyl‐cyclohexylamine reached 99.9 % and 82.5 %, respectively). In addition, to compare with the performance of Ru‐Y/NaY catalysts, the active carbon supported Ru catalysts were prepared using the same method in view of its higher surface area and adsorption capacity. Finally, the effect of solvent on the reaction over Ru‐Y/NaY² catalyst has been investigated, it was found that the best performance of paranitrotoluene hydrogenation reaction took place in protic solvents (isopropanol and ethanol). This was mainly ascribed to their polarity and hydrogen‐bond accepting capability.

     

Preparation,characterization, and adsorption performance of p‐hydroxybenzoic acid imprinted polymer and selective catalysis of toluene to para‐chlorotoluene

A p‐hydroxybenzoic acid surface molecularly imprinted polymer (p‐HB– S MIP) with si lica microspheres as a supporting matrix was prepared by the adoption of the surface molecular imprinting technique with acrylamide ( AM) as a functional monomer, ethylene glycol dimethacrylate as a crosslinker, and azoisobutyronitrile as an initiator. The p‐HB–SMIP was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetry. Interactions between the functional monomer and template were observed with UV–visible spectroscopy of the solutions of these components as well. The results indicate that a 1:2 molecular complex was formed between p‐hydroxybenzoic acid (p‐HB) and AM. A kinetic binding study showed that p‐HB–SMIP reached saturation adsorption after about 1 h, and the pseudo‐second‐order model fitted the adsorption kinetics data. Static adsorption experiments revealed that the Freundlich equation fitted the adsorption isotherm data. The thermodynamics parameters (with positive values of enthalpy and entropy and negative values of Gibbs free energy) indicated that the binding system for p‐HB–SMIP was endothermic and entropy was gained and was spontaneous. Selective experiments showed that p‐HB–SMIP had a high affinity and excellent recognition selectivity for the template p‐HB. p‐HB–SMIP was further investigated by the catalysis of toluene to para‐chlorotoluene. The catalytic reaction results showed that the conversion of toluene was 85.5% and the molar ratio of para‐chlorotoluene to o‐chorotoluene was 1.38; this was higher than that of traditional catalysts. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40118.     

Bi2O3 nanoparticles incorporated porous TiO2 films as an effective p‐n junction with enhanced photocatalytic activity

Porous TiO₂ films decorated with Bi₂O₃ nanoparticles are fabricated via alkali‐hydrothermal of titanium (Ti) plate by varying the reaction time. The amorphous TiO₂ is transformed into anatase after annealing the films at 500°C in air. The p‐type Bi₂O₃ nanoparticles are successfully assembled on the surface of porous n‐type TiO₂ films through the ultrasonic‐assisted successive ionic layer adsorption and reaction (SILAR) technique to form Bi₂O₃/TiO₂ nanostructure by the two cycles. The obtained Bi₂O₃/TiO₂ films are consisted of a well‐ordered and uniform porous structure with an average pore diameter of about 100‐200 nm containing homogeneously dispersed Bi₂O₃ nanoparticles of ~5 nm diameter. Moreover, the resultant composites present excellent photocatalytic performance toward methyl blue (MB) degradation under UV and visible light irradiation, which could be mainly ascribed to the enhanced light adsorption capacity of unique composite structure and the formation of p‐n heterojunctions in the porous Bi₂O₃/TiO₂ films. This research is helpful to design and construct the highly efficient heterogeneous semiconductor photocatalysts.     

Oxidation of p‐Cresol to p‐Hydroxybenzaldehyde with Molecular Oxygen in the Presence of CuMn‐Oxide Heterogeneous Catalyst

A high‐yield synthesis of p‐hydroxybenzaldehyde from p‐cresol and molecular oxygen was achieved over a CuMn‐oxide supported carbon catalyst. The reaction parameters such as pressure, stirring speed, reaction temperature, solvent, and the amount of sodium hydroxide in the reaction media were optimized. As a result, a high conversion of p‐cresol (99%) and a high selectivity to p‐hydroxybenzaldehyde (96%) were realized at the same time. Catalyst separation and recycling tests clearly showed that the reaction proceeded on the heterogeneous catalyst but not on dissolved species.     

Synthesis and light‐emitting properties of a novel π‐conjugated poly[di(p‐phenyleneethynylene)‐alt‐ (p‐phenylenecyanovinylene)] containing n‐octyloxy side branches

A novel π‐conjugated poly[di(p‐phenyleneethynylene)‐alt‐(p‐phenylenecyanovinylene)] having n‐octyloxy side chains (PPE‐C₈PPE‐PPV) was prepared by polymerization of the monomer DEDB with BCN. Chemical structure of the polymer obtained was confirmed by ¹H NMR, FTIR, and EA. PPE‐C₈PPE‐PPV had a molecular weight enough to fabricate the electroluminescent (EL) device, and showed a good organosolubility, excellent thermal stability, and film‐forming property. In UV absorption and PL spectra in film it showed a maximum at 430 and 543 nm, respectively, which appeared 5 and 41 nm longer wavelengths than that of the solution, respectively. HOMO, LUMO energy levels and band gap were determined to be ?5.70, ?3.29, and 2.41 eV, respectively. Two EL devices with low‐work function cathodes were fabricated with the structures of ITO/PEDOT/PPE‐C₈PPE‐PPV/cathodes (LiF/Al and Mg:Ag/Ag). The both devices exhibited a bright green light emission at 545 nm and the maximum luminescence of 197 cd/cm² (LiF/Al) and 158 cd/cm² (Mg:Ag/Ag). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Improving the Stability and Ethanol Electro‐Oxidation Activity of Pt Catalysts by Selectively Anchoring Pt Particles on Carbon‐Nanotubes‐Supported‐SnO2

To improve the stability and activity of Pt catalysts for ethanol electro‐oxidation, Pt nanoparticles were selectively deposited on carbon‐nanotubes (CNTs)‐supported‐SnO₂ to prepare Pt/SnO₂/CNTs and Pt/CNTs was prepared by impregnation method for reference study. X‐ray diffraction (XRD) was used to confirm the crystalline structures of Pt/SnO₂/CNTs and Pt/CNTs. The stabilities of Pt/SnO₂/CNTs and Pt/CNTs were compared by analyzing the Pt size increase amplitude using transmission electron microscopy (TEM) images recorded before and after cyclic voltammetry (CV) sweeping. The results showed that the Pt size increase amplitude is evidently smaller for Pt/SnO₂/CNTs, indicating the higher stability of Pt/SnO₂/CNTs. Although both catalysts exhibit degradation of electrochemical active surface area (EAS) after CV sweeping, the EAS degradation for the former is lower, further confirming the higher stability of Pt/SnO₂/CNTs. CV and potentiostatic current–time curves were recorded for ethanol electro‐oxidation on both catalysts before and after CV sweeping and the results showed that the mass specific activity of Pt/CNTs increases more than that of Pt/SnO₂/CNTs, indicating that Pt/CNTs experiences more severe evolution and is less stable. The calculated area specific activity of Pt/SnO₂/CNTs is larger than that of Pt/CNTs, indicating SnO₂ can co‐catalyze Pt due to plenty of interfaces between SnO₂ and Pt.     

Reaction between methanol and acetic acid catalyzed by SiO2‐supported V‐P‐O catalyst in oxygen atmosphere

SiO₂‐supported V‐P‐O catalysts prepared by the incipient‐wetness impregnation method beginning with ammonium metavanadate and phosphoric acid were used in the catalytic reaction between methanol and acetic acid in an oxygen atmosphere. The SiO₂‐supported V‐P‐O catalysts were composed of VOPO₄ and (VO)₂P₂O₇ phases. Both the acidic and alkaline sites were co‐present in the catalysts. The vanadium species catalyzed the oxidation of methanol to formaldehyde. The V‐P‐O(20–30 wt%)/SiO₂ catalysts with a P/V mole ratio of 2:1 exhibited higher catalytic activity for the formation of acrylic acid and methyl acrylate with a total selectivity of ～28 % at 380 °C. The acid sites of the catalysts also catalyzed the formation of methyl acetate with a selectivity of ～65 %. Methanol can be an alternative to formaldehyde for the synthesis of both acrylic acid and methyl acrylate through the aldol condensation reaction.     

Effect of Catalyst Supports on Water‐Gas Shift Reaction at Ultrahigh Temperatures Using Syngas

Monometallic and bimetallic catalysts (Pt, Ni, and Pt‐Ni) with single support (Al₂O₃, TiO₂) and composite support (CeO₂/Al₂O₃, CeO₂/TiO₂) were prepared and tested for water‐gas shift reaction in a tubular quartz reactor. Syngas and steam with different steam‐to‐carbon ratios served as feedstock. The operating pressure was fixed while the reaction temperature was varied. The measured results indicated that the monometallic Ni/Al₂O₃ catalyst exhibits the lowest CO conversion and H₂ yield as compared with other catalysts. About the same CO conversion can be obtained from Pt and Pt‐Ni catalysts with single or composite support. However, higher H₂ yield can be achieved from the TiO₂‐supported catalyst compared with those supported by Al₂O₃. The experimental data also indicated that good thermal stability can be reached for the Pt‐based catalysts studied.     

Study of Methanol‐tolerant Oxygen Reduction Reaction at Pt–Bi/C Bimetallic Nanostructured Catalysts

The nanostructured platinum–bismuth catalysts supported on carbon (Pt₃Bi/C, PtBi/C and PtBi₃/C) were synthesised by reducing the aqueous metal ions using sodium borohydride (NaBH₄) in presence of a microemulsion. The amount of metal loading on carbon support was found to be 10 wt.‐%. The catalyst materials were characterised by X‐ray diffraction (XRD), X‐ray fluorescence (XRF), transmission electron microscope (TEM) and electroanalytical techniques. The Pt₃Bi/C, PtBi/C and PtBi₃/C catalysts showed higher methanol tolerance, catalytic activity for oxygen reduction reaction (ORR) than Pt/C of same metal loading. The electrochemical stability of these nano‐sized catalyst materials for methanol tolerance was investigated by repetitive cycling in the potential range of –250 to 150 mV_MSE. Bi presents an interesting system to have a control over the activity of the surface for MOR and ORR. All Pt–Bi/C catalysts exhibited higher mass activities for oxygen reduction (1–1.5 times) than Pt/C. It was found that PtBi/C catalyst exhibits better methanol‐tolerance than the other catalysts.     

Effect of Nickel Addition on Ceria‐Supported Platinum Catalysts for Medium‐Temperature Shift Reaction in Fuel Processors

Medium‐temperature shift reaction (MTS, 280–340 °C) has received much attention for use in fuel processors. In this study, bifunctional Pt‐Ni/CeO₂ catalysts were prepared by different Pt (0.1–0.5 %) and Ni (5–20 %) loadings, and investigated for MTS reaction. X‐ray diffraction, N₂ adsorption and temperature‐programmed reduction tests were used to characterize the prepared samples. The results showed that Pt‐Ni bimetallic catalysts have higher CO conversion in comparison to Pt/CeO₂ monometallic catalyst. Furthermore, the sequential synthesis method of Pt and Ni impregnation was preferred to the simultaneous one, which is due to the better Pt dispersion on catalytic surface. Steam to carbon ratio variations study showed the maximum CO conversion to be in the range of 4.5.     

Immobilized fenton‐like ionic liquid: Catalytic performance for oxidative desulfurization

MCM‐41‐supported Fenton‐like ionic liquid catalysts were synthesized by the grafting method and applied in the removal of sulfur compounds in model oil. The structure and property of the catalysts were characterized by Fourier transform infrared spectra, X‐ray diffraction, diffuse reflectance spectra, transmission electron microscopy, thermogravimetric and differential scanning calorimetry, and N₂ adsorption‐desorption. Results suggested that Fenton‐like ionic liquid was supported on mesoporous material MCM‐41. Different desulfurization systems were studied. The results indicated that at room‐temperature (30°C) for 1 h, MCM‐41‐supported Fenton‐like ionic liquid in extraction combined with catalytic oxidative desulfurization (ECODS) system showed a high catalytic activity with H₂O₂ as the oxidant, and [Omim]BF₄ as the extractant. Different factors, such as temperature, the amount of H₂O₂, solvent, and different sulfur‐containing compounds for sulfur removal were investigated. Through the gas chromatography‐mass spectrometer (GC‐MS) analysis, dibenzothoiphene sulfone was proved to be the only product of dibenzothiophene oxidizing reaction. Furthermore, the process of ECODS was confirmed by GC‐MS results. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4696–4704, 2013     

Aerobic Oxidation of Benzylic Alcohols in Water by 2,2,6,6‐Tetramethylpiperidine‐1‐oxyl (TEMPO)/Copper(II) 2‐N‐Arylpyrrolecarbaldimino Complexes

Novel copper(II) 2‐N‐arylpyrrolecarbaldimine‐based catalysts for the aerobic oxidation of benzylic alcohols mediated by the 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) radical are reported. The catalytic activity for both synthesized and in situ made complexes in alkaline water solutions was studied revealing high efficiency and selectivity (according to GC selectivity always >99%) for both of these catalytic systems. For example, quantitative conversion of benzyl alcohol to benzaldehyde can be achieved with the in situ prepared bis[2‐N‐(4‐fluorophenyl)‐pyrrolylcarbaldimide]copper(II) catalysts in 2 h with atmospheric pressure of O₂ at 80 °C. Interestingly, these catalysts can utilize dioxygen as well as air or hydrogen peroxide as the end oxidants, producing water as the only by‐product.     

Liquid‐phase hydrogenation of cinnamaldehyde over Cu‐Au/SiO2 catalysts

The synthesis, characterization, and application of silica‐supported Cu‐Au bimetallic catalysts in selective hydrogenation of cinnamaldehyde are described. The results showed that Cu‐Au/SiO₂ bimetallic catalysts were superior to monometallic Cu/SiO₂ and Au/SiO₂ catalysts under identical conditions. Adding a small amount of gold (6Cu‐1.4Au/SiO₂ catalyst) afforded eightfold higher catalytic reaction rate compared to Cu/SiO₂ along with the high selectivity (53%, at 55% of conversion) toward cinnamyl alcohol. Characterization techniques such as x‐ray diffraction, H₂ temperature‐programmed reduction, ultraviolet‐visible spectroscopy, transmission electron microscopy, Fourier‐transform infrared spectra of chemisorbed CO, and x‐ray photoelectron spectroscopy were employed to understand the origin of the catalytic activity. A key genesis of the high activity of the Cu‐Au/SiO₂ catalyst was ascribed to the synergistic effect of Cu and Au species: the Au sites were responsible for the dissociative activation of H₂ molecules, and Cu⁰ and Cu⁺ sites contributed to the adsorption‐activation of C?C and C?O bond, respectively. A combined tuning of particle dispersion and its surface electronic structure was shown as a consequence of the formation of Au‐Cu alloy nanoparticles, which led to the significantly enhanced synergy. A plausible reaction pathway was proposed based on our results and the literature. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3300–3311, 2014