A recoverable catalyst Co(salen) in zeolite Y for the synthesis of methyl N-phenylcarbamate by oxidative carbonylation of aniline

A green process for the synthesis of methyl N-phenylcarbamate (MPC) by the oxidative carbonylation of aniline was studied. In this process, Co(salen) complexes were successfully encapsulated in zeolite Y by a flexible ligand method. The heterogeneous catalysts were characterized by AAS, BET, IR, TGA, XRD and XPS. The catalytic activities of the encapsulated catalysts and their homogeneous analogues were examined in the oxidative carbonylation of aniline to MPC. Under the conditions of aniline (11 mmol), encapsulated catalyst (0.5 g), KI (0.365 g), CO/O₂ ratio 9:1, 4 MPa, 170 °C, 3 h, Co(salophen)(OH)₂–Y catalyst shows the highest activity with the conversion of 67.1% and the selectivity of 77.3%. Co(salophen)(OH)₂–Y could be recycled at least five times and no significant loss of catalytic activity was observed.     

碱式氯化铜对氧化羰基合成碳酸二乙酯催化活性的影响

引言 碳酸二乙酯(diethyl carbonate, 简称DEC)作为一种绿色化学品,是重要的有机合成中间体,具有很高的工业应用价值.近年研究表明,碳酸二乙酯可以作为汽油和柴油机燃料的含氧添加剂,替代传统的添加剂甲基叔丁基醚(MTBE),提高汽油的燃烧性能.DEC作为MTBE的替代品之一比碳酸二甲酯与乙醇更具有竞争优势[1],具有潜在的应用前景.     

Electro-oxidation of methanol on mixed catalysts based on platinum and organic metal complexes in acidic media

New electro-catalysts were developed based on platinum and organic metal complexes for methanol oxidation reaction (MOR) in acidic media. As complexes nitrogen containing ligands such as N,N′-bis(salicylidene)ethylenediamine (salen), N,N′-bis(salicylidene)phenylenediamine (salophen), N,N′-mono-8-quinolyl-o-phenylenediamine (mqph) and N,N′-bis(anthranilidene)ethylenediamine (anthen), coordinated to V, Mn, Fe, Co, Ni, Cu, Mo, Pd and Sn were synthesized and tested. Mixture of platinum tetraammine complex with one of the organic metal complexes with 50/50 mixing ratio was supported on carbon powder, and heat-treated at 400-700 °C in argon atmosphere. Powder, thus obtained was put on a glassy carbon disk electrode, and tested for electrochemical MOR in sulfuric acid solutions. Among catalysts tested, Fe(salen), VO(salen), Ni(mqph) or Pd(mqph) turned out to be good co-catalysts mixed with Pt for MOR. Compared with platinum-ruthenium alloy catalysts, the new catalysts showed very promising catalytic ability. It is inferred that after the heat treatment, the organic complex catalyst played a role in mitigating CO poisoning on Pt surface.     

Effect of SSIE structure of Cu-exchanged β and Y on the selectivity for synthesis of diethyl carbonate by oxidative carbonylation of ethanol: A comparative investigation

Cu-exchanged β and Y catalysts were investigated by oxidative carbonylation of ethanol in the gas-phase reaction. Cuβ catalyst has shown better catalytic selectivity for oxidative carbonylation of ethanol to diethyl carbonate (DEC), without the principal by-product 1,1-diethoxyethane (DEE) for CuY catalysts. In order to investigate the effect of zeolite structure on the selectivity for products, computational analysis of molecular dimensions and diffusion parameters of DEC and DEE within Cuβ and CuY catalysts zeolite framework has been performed using molecular mechanics and quantum mechanics methods. The computational analysis results are in good agreement with the experimental results to some extent. DEC having a kinetic diameter of 3.663 Å and the lowest energy barrier was formed preferentially over both zeolites. However, the DEE molecule was not detected among the products over Cuβ because of its greater kinetic diameter 6.059 Å and higher energy barrier. The special architecture of β zeolite did not allow the diffusion of DEE molecules through its pores. The formation of the higher sterically hindered DEE over CuY catalyst could be explained by involvement of the outer surface.     

Synthesis of diethyl carbonate by catalytic alcoholysis of urea

The production of diethyl carbonate (DEC) from urea and ethanol was investigated in a batch process. The catalytic activities of many metal oxides were evaluated, the influences of various operation conditions on the DEC yield were explored, and the catalytic mechanism was also analyzed. Among the tested catalysts, ZnO showed the best catalytic activity toward DEC synthesis. The optimum reaction conditions were as follows: ethanol/urea molar ratio of 10, catalyst concentration of 6%, reaction temperature of 463 K, reaction time of 5 h and the reaction pressure of 2.5 MPa, respectively. The highest DEC yield was 14.2%. The reaction of producing N-ethyl ethyl carbamate (N-EEC) was the main side reaction in this process, which consumed both ethyl carbamate and DEC. It is necessary to remove DEC from the reactor as quickly as possible.     

Synthesis of carbon nanotubes by catalytic conversion of methane: Competition between active components of catalyst

Catalytic growth of carbon nanotubes from methane was studied as competitive catalytic process in situ of both oxidative (partial oxidation) and non-oxidative (pyrolysis) conversion. Ni and Fe may act as either competing or cooperative catalyst components in the process of carbon nanotubes growth. The competition between Ni and Fe in the process of carbon nanotube growth on Ni-Fe based stainless steel alloy during partial oxidation of methane results in suppression of Ni catalytic activity in favor of Fe. The discrimination is so strong that iron is segregated from Ni-Fe based stainless steel alloy leaving characteristic Ni-enriched corrosion caverns. Interaction between Ni and Fe during non-oxidative conversion, in contrast to the oxidative conversion, leads to cooperative effect; the activity of bimetallic catalyst increases as compared with monometallic one. Depending on particular catalyst bed composition, the nanotubes of various morphologies may occur. In particular, the use of perovskite-type catalyst for partial oxidation of methane leads to formation of “olive-branch”-like peculiar carbon nanostructures.     

Experimental, kinetic and 2-D reactor modeling for simulation of the production of hydrogen by the catalytic reforming of concentrated crude ethanol (CRCCE) over a Ni-based commercial catalyst in a packed-bed tubular reactor

Mechanistic kinetic models were formulated based on Langmuir-Hinshelwood-Hougen-Watson and Eley-Rideal approaches to describe the kinetics of hydrogen production by the catalytic reforming of concentrated crude ethanol over a Ni-based commercial catalyst at atmospheric pressure, temperature range of 673-863 K, ratio of weight of catalyst to the molar rate of crude ethanol 3472-34722 kg cat s/kmol crude in a stainless steel packed bed tubular microreactor. One of the models yielded an excellent degree of correlation, and was selected for the simulation of the reforming process which used a pseudo-homogeneous numerical model consisting of coupled material and energy balance equations with reaction. The model was solved using finite elements method without neglecting the axial dispersion term. The crude ethanol conversion predicted by the model was in good agreement with the experimental data (AAD%=4.28). Also, the predicted concentration and temperature profiles for the process in the radial direction indicate that the assumption of plug flow isothermal behavior is justified within certain reactor configurations. However, the axial dispersion term still contributed to the results, and thus, cannot be neglected.     

Synthesis,characterization and assessment of poly(urethane-co-pyrrole)s derived from castor oil as anticorrosion coatings for stainless steel

Electrically conductive and organic-solvent soluble poly(urethane-co-pyrrole)s (CPUPYs) were prepared by oxidative polymerization of pyrrole with a hydroxyl-terminated polyurethane prepolymer in the presence of ceric (IV) ammonium nitrate. Direct electrodeposition of CPUPYs from their appropriate solvent on the surface of stainless steel working electrode by continuous cycling potential between −0.8 and 1.8 V vs. Ag/AgCl with a scan rate of 0.03 V/s led to smooth, strongly adhered and insoluble coatings. All materials were characterized by conventional spectroscopic methods, and their physical and viscoelastic properties were evaluated. The corrosion protection properties of the CPUPYs-coated stainless steels were measured by Tafel polarization and electrochemical impedance spectroscopy. A substantial lower corrosion current, higher corrosion potential and higher charge transfer resistance values of CPUPYs-coated steels were recorded and comparisons were made with those properties of bare steel as well as parent polyurethane and neat polypyrrole-coated stainless steel. Excellent anticorrosive efficacy of newly developed CPUPYs-coated steel was achieved.     

Hydrogen production from oxidative steam reforming of ethanol in a palladium-silver alloy composite membrane reactor

In this investigation, we studied the oxidative steam reforming reaction of ethanol in a Pd-Ag/PSS membrane reactor for the production of high purity hydrogen. Palladium and silver were deposited on porous stainless steel (PSS) tube via the sequential electroless plating procedure with an overall film thickness of 20 μm and Pd/Ag weight ratio of 78/22. An ethanol-water mixture (n_water/n_ethanol = 1 or 3) and oxygen (n_oxygen/n_ethanol = 0.2, 0.7 or 1.0) were fed concurrently into the membrane reactor packed with Zn-Cu commercial catalyst (MDC-3). The reaction temperatures were set at 593-723 K and the pressures at 3-10 atm. The hydrogen flux in the permeation side increased proportionately with increasing pressure; however, it reduced slightly when increasing oxygen input. This is probably due to the fast oxidation reaction that consumes hydrogen before the onset of the steam reforming reaction. The effect of oxygen plays a vital role on the ethanol oxidation steam reforming reaction, especially for a Pd-Ag membrane reactor in which a higher flux of hydrogen is required. The selectivity of CO₂ increased with increasing flow rate of oxygen, while the selectivity of CO remained almost the same.     

A new type of catalyst PdCl2/Cu-HMS for synthesis of diethyl carbonate by oxidative carbonylation of ethanol

A new type of catalyst, PdCl₂/Cu-HMS, for diethyl carbonate (DEC) synthesis by oxidative carbonylation of ethanol in the gas-phase reaction was investigated. The modified support Cu-HMS which was synthesized using the neutral templating pathway at the room temperature kept its mesoporous structure even after it was calcined repeatedly at 550 °C for 3 h to remove the template. From XRD, XPS and ICP analysis, it can be concluded that copper incorporated into HMS frame and was highly dispersed in the frame of silica. Notably, the degree of order of mesoporous molecular sieves was improved in a certain extent after PdCl₂ was loaded on Cu-HMS samples. The PdCl₂/Cu-HMS catalyst exhibited excellent selectivity for DEC. The catalytic reaction mechanism was illuminated by the interaction between Pd²⁺ loaded on the surface and Cu²⁺ in Cu-HMS frame.     

Corrosion of similar and dissimilar metal crevices in the engineered barrier system of a potential nuclear waste repository

Crevice corrosion is considered possible if the corrosion potential (E_corr) exceeds the repassivation potential for crevice corrosion (E_rcrev). In this study, potentiodynamic polarization and potentiostatic hold were used to determine the E_rcrev of similar and dissimilar metal crevices in the engineered barrier system of the potential Yucca Mountain repository in 0.5 M NaCl, 4 M NaCl, and 4 M MgCl₂ solutions at 95 °C. The results were compared with data previously obtained using crevices formed between Alloy 22 and polytetrafluoroethylene. It was observed that, except for Type 316L stainless steel, all other metal-to-metal crevices were less susceptible to crevice corrosion than the corresponding metal-to-polytetrafluoroethylene crevices. Measurements of galvanic coupling were used to evaluate the crevice corrosion propagation behavior in 5 M NaCl solution at 95 °C. The crevice specimens were coupled to either an Alloy 22 or a Titanium Grade 7 plate using metal or polytetrafluoroethylene crevice washers. Crevice corrosion of Type 316L stainless steel propagated without repassivation. For all the tests using a polytetrafluoroethylene crevice washer, crevice corrosion of Alloy 22 was initiated at open circuit potential by the addition of CuCl₂ as an oxidant, whereas no crevice corrosion of Alloy 22 was initiated for all the tests using Alloy 22 or Titanium Grade 7 metals as crevice washer. However, crevice corrosion propagation was found to be very limited under such test conditions.     

Metal dependent control of cis-/trans-1,4 regioselectivity in 1,3-butadiene polymerization catalyzed by transition metal complexes supported by 2,6-bis[1-(iminophenyl)ethyl]pyridine

Fe(III), Cr(III), Fe(II), Co(II) and Ni(II) chloride complexes supported by 2,6-bis[1-(iminophenyl)ethyl]pyridine have been synthesized and characterized along with single crystal X-ray diffraction. These complexes, in combination with MAO, have been examined in butadiene polymerization. The catalytic activity and regioselectivity are strongly controlled by metal center and cocatalyst (MAO/Co ratio dependent in the case of Co(II) complex). The activity decreases in the order of Fe(III) > Co(II) > Cr(III) ≈ Ni (II) complexes, in consistent with the space around the metal center. Polybutadiene with different microstructure content, from high trans-1,4 units (88-95% for iron(III) and Cr(III)), medium trans-1,4 and cis-1,4 units (55% and 35%, respectively, for iron(II)) to high cis-1,4 units 79% for Co(II) and 97% for Ni(II) can be easily achieved by varying of the metal center. In addition, mechanism speculation is also presented to elucidate the dependence of catalytic behaviors on metal and cocatalyst.     

Inhibitory effect of non-ionic surfactants of the TRITON-X series on the corrosion of carbon steel in sulphuric acid

The corrosion inhibition characteristics of non-ionic surfactants of the TRITON-X series, known as TRITON-X-100 and TRITON-X-405, on stainless steel (SS) type X4Cr13 in sulphuric acid were investigated by potentiodynamic polarisation measurements. It was found that these surfactants act as good inhibitors of the corrosion of stainless steel in 2 mol L⁻¹ H₂SO₄ solution, but the inhibition efficiency strongly depends on the electrode potential. The polarisation data showed that the non-ionic surfactants used in this study acted as mixed-type inhibitors and adsorb on the stainless steel surface, in agreement with the Flory-Huggins adsorption isotherm. Calculated ΔG_ads values are −57.79 kJ mol⁻¹ for TRITON-X-100, and −87.5 kJ mol⁻¹ for TRITON-X-405. From the molecular structure it can be supposed that these surfactants adsorb on the metal surface through two lone pairs of electrons on the oxygen atoms of the hydrophilic head group, suggesting a chemisorption mechanism.     

Poly(N-ethylaniline) coatings on 304 stainless steel for corrosion protection in aqueous HCl and NaCl solutions

Poly(N-ethylaniline) (PNEA) coatings were grown by potentiodynamic synthesis technique on 304 stainless steel (SS) alloy from 0.1 M of N-ethylaniline (NEA) in 0.3 M oxalic acid solution. Characterization of adhesive and electroactive PNEA coatings was carried out by cyclic voltammetry, FT-IR spectroscopy and scanning electron microscopy (SEM) techniques. The protective properties of PNEA coatings on SS were elucidated using linear anodic potentiodynamic polarization, Tafel and electrochemical impedance spectroscopy (EIS) test techniques, in highly aggressive 0.5 M HCl and 0.5 M NaCl solutions. Linear anodic potentiodynamic polarization test results proved that PNEA coating improved the degree of protection against pitting corrosion in HCl and NaCl solutions. Tafel test results showed that PNEA coating appears to enhancement protection for SS in 0.5 M NaCl and 0.5 M HCl solutions. However, according to long-term EIS results, PNEA coating is better for the protection of SS electrodes during the long immersion period in NaCl compared to that in HCl medium.     

Blends of poly(2,5-dimethoxy aniline) and fluoropolymers as protective coatings

This work presents the study of blends formed by a substituted polyaniline (PAni), poly(2,5-dimethoxy aniline) (PDMA), and the fluoropolymers poly(vinylidene fluoride) (PVDF) and poly(tetrafluoroethylene-co-vinylidene fluoride-co-propylene) (co-PTFE). PDMA was electrochemically synthesized from monomer 2,5-dimethoxy aniline (DMA) onto stainless steel surfaces. The polymers and the ternary blends were dissolved in N,N-dimethyl formamide and were deposited onto polished stainless steel plates. Thermal analysis (differential scanning calorimetry (DSC) and thermogravimetric analysis (TG)) and atomic force microscopy (AFM) were used in order to evaluate the properties of the materials. Ternary blends with good adhesion properties and thermal stability (with degradation over 400 °C) were obtained. Porous morphology with indication of PVDF enrichment on surface was observed. Preliminary open circuit potential (OCP) test showed an increase in this potential in the blends, compared with uncoated stainless steel. Therefore, blends with phase separation and very promising new protective properties were produced. Co-PTFE guarantees good adhesion, PDMA the special corrosion protection, and both fluoropolymers contribute to the large thermal stability.     

Evaluation of the corrosion resistance of Ni-Co-B coatings in simulated PEMFC environment

The corrosion resistance behavior of Ni-Co-B coated carbon steel, Al 6061 alloy and 304 stainless steel was evaluated in simulated proton exchange membrane fuel cell (PEMFC) environment. The phase structure of the NiCoB based alloy was determined by Rietveld analysis. The PEMFC environment was constituted of 0.5 M H₂SO₄ at 60 °C and the evaluation techniques employed included potentiodynamic polarization, linear polarization resistance, open circuit potential measurements and electrochemical impedance spectroscopy. The results showed that in all cases the corrosion resistance of the Ni-Co-B coating was higher than that of the uncoated alloys; about two orders of magnitude with respect to carbon steel and an order of magnitude compared to 304 stainless steel. Except for the uncoated 304 type stainless steel, the polarization curves for the coated specimens did not exhibit a passive region but only anodic dissolution. The corrosion potential value, E_corr, was always nobler for the coated samples than for the uncoated specimens. This was true for the stainless steel in the passive region, but in the active state for the carbon steel and Al 6061 alloy. The corrosion of the underlying alloy occurred due to filtering of the solution through coating defects like microcracks, pinholes, etc. During the filtering process the E_corr value of the coating decreased slowly until it reached a steady state value, close to the E_corr value of the underlying alloy.     

Ethanol steam reforming reactions over Al2O3 · SiO2-supported Ni-La catalysts

Nickel-based catalysts supported on Al₂O₃ · SiO₂ were prepared with modification of the second metal involving La, Co, Cu, Zr or Y, of which the catalytic behaviors were assessed in the ethanol steam reforming reaction. Activity test indicated that addition of La resulted in higher selectivity of hydrogen and lower selectivity of carbon monoxide, compared with Co-doped nickel catalyst. Influences of lanthanum amounts on catalytic performance were studied over 30NixLa/Al₂O₃ · SiO₂ (x = 5, 10, 15), and characterizations by XRD, TPR and XPS indicated that low amount of lanthanum additives (5%) was superior to inhibit the crystal growth of nickel as well as beneficial to the reduction of nickel oxide. Finally 100 h test for the optimal catalyst 30Ni5La/Al₂O₃ · SiO₂ indicated its good long-term stability to provide high hydrogen selectivity and low carbon monoxide formation, as well as good resistance to coke deposition at low temperature.     

甲醇氧化羰基化合成碳酸二甲酯催化剂研究进展

碳酸二甲酯(DMC)是一种重要的绿色有机合成中间体。在合成DMC的方法中,甲醇氧化羰基化法对设备腐蚀小、原料易得、产物易分离,有着诱人的工业化前景。文中介绍了该反应中所使用的Co、Pd、Cu和Au这4类催化剂的结构特点和催化性能,比较了不同催化剂在氧化羰基化中的催化效果。为了进一步提高催化剂的活性、选择性、减少其腐蚀性,开发出性能更好的工业催化剂,可以通过研究催化反应机理,并通过添加助剂和载体来实现。其中无卤铜系催化剂是今后羰基化合成DMC的重要研究方向。     

Poly(pyridine-2,5-diyl)–CuCl2 catalyst for synthesis of dimethyl carbonate by oxidative carbonylation of methanol: catalytic activity and corrosion influence

A -conjugated polymer, poly(pyridine-2,5-diyl) (PPy) was investigated as a support for CuCl₂ in the synthesis of dimethyl carbonate by oxidative carbonylation of methanol. The PPy–CuCl₂ adduct had high catalytic activity which was comparable to that of the homogeneous CuCl₂ catalyst. The adduct caused corrosion of stainless-steel vessels only to minor extent, compared with the homogeneous CuCl₂ catalyst. This PPy–CuCl₂ catalyst was easily recycled by filtration and showed a similar catalytic activity in the third time use. The presence of the -conjugated system in PPy, through which electrons can move, may bring about the high catalytic activity for the oxidative carbonylation of methanol, which involves Cu(II)/Cu(I) redox processes.     

Cracking of n-dodecane during supercritical state on HZSM-5 membranes

In the new generation of aircraft, jet fuel will serve as both an energy source and a heat sink for cooling through endothermic fuel reactions. Catalytic cracking of hydrocarbon fuel has proved to be potential for endothermic reaction. For this application, we have prepared ZSM-5 membranes as catalyst on the surface of stainless steel by secondary growth method. An optimized activation procedure of ZSM-5 membrane for catalytic cracking reaction is established by combining the results of catalytic reaction with thermal analysis (TGA and DSC). Taking n-dodecane as a model compound, the influence of silica alumina ratio (SAR = nSiO₂/Al₂O₃) of initial gel on the activity of hydrocarbon cracking reaction were studied. The results also demonstrate that the conversion of catalytic cracking reaction is much higher than that of pyrolysis during supercritical state. In addition, hydrogen molar ratio in gas production decreases with increasing the reaction temperature. Besides that, the optimum temperature for coke removal and the reduction of zeolite catalysts is between 550 °C and 600 °C.