Oxidation of CO and hydrocarbons over perovskite-type complex oxides

The catalytic activity of perovskites M^IM^IIO₃ (M^I=La; M^II=Co, Mn, Cr, Al, Ni, and V) and M^ICoO₃ (M=Y, Nd, Sm, and Er) in the oxidation of CO, propylene, and ethylbenzene was investigated. The highest activity was observed for the M^ICoO₃ catalysts with perfect perovskite structure. The nature of the rare-earth element has no influence on the catalytic activity. Deformation of the octahedral coordination of the metal was found for the less active catalysts. The interaction of gases (CO, CO+air) with the catalyst surface was investigated. The more active catalysts adsorb a greater amount of O₂, and the adsorption occurs in the temperature region of the oxidation reaction. The activities of the perovskite- and spinel-type catalysts were compared under similar conditions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 698–701, April, 1999.     

Synthesis of hetero binuclear macrocyclic CoV complex bonded to chemically modified alumina support for oxidation of cyclohexane using oxygen

A binuclear complex M_A^IIM_B^IVL²⁺ [with M_A^II = Co^II and M_B^IV = V^IV] has been synthesized with a macrocyclic ligand prepared by condensing 2 equiv. of 2,6-diformyl-4-methylphenol with 2 equiv. of 1,2-phenylenediamine. This has been immobilized on a carbamate-modified alumina support by covalently binding it to the surface. The TGA analysis of the final catalyst showed that it is thermally stable up to 251 °C and it has been shown that it serves as a catalyst for oxidation of cyclohexane forming cyclohexanone and cyclohexanol in the ratio of 14:1 as identified by the GC/MS analysis.     

Selektivitätssteigerung katalytischer bestimmungsverfahren—extraktionskataly-metrische molybdänbestimmung

To increase the selectivity of catalytic methods, a solvent extraction and catalytic determination have been combined. By means of the determination of molybdenum based on the catalytic oxidation of 1-naphthylamine by bromate, it is shown that by selection of a suitable extraction system the catalyst can be determined directly in the organic extract. The catalytic activity of different complexes of molybdenum was tested and for an analytical application the extraction of molybdenum as oxinate was chosen. The method enables molybdenum to be determined down to 2.7 × 10^?9M. The relative error of the determinations is 10%. 10^?4M V, 2 × 10^?4M Cr, 5 × 10^?5M W and 10^?2M Mn, Ni, Cu, Co, Fe, Mg, Zn, Cd, Al and Pb cause no interference. The method has been used for the determination of molybdenum in sea-water.     

Polymerization kinetics of octene-1 catalyzed by metallocene methylaluminoxane investigated with attenuated total reflectance fourier transform infrared (ATR-FT-IR) spectroscopy

The kinetic parameters have been measured for octene-1 solution polymerization at 120°C catalyzed by zirconocene with the cocatalyst methylaluminoxane. The polymerizations were performed in an attenuated total reflectance (ATR) reaction cell. The progress of the reactions were followed by observing the disappearance of octene-1 using the 910 cm^?1 band measured by FT-IR spectroscopy. The dependence of the reaction rate, R_p, on catalyst concentration and cocatalyst/catalyst ratio was examined. The catalyst deactivation mechanism was studied by fitting the experimental data to mathematical models involving second-order propagation and either first or second order catalyst deactivation. Second-order catalyst deactivation provided a much better fit. The calculated deactivation rate constant, k_d, is 21 (Ms)^?1. This model is used to determine the propagation rate constant for Al/Zr = 4 × 10³ as k_p = 19.9 (M s)^?1. A decrease in Al/Zr = 3 × 10² lowered the propagation rate constant, k_p, to 9.6 (M s)^?1 indicating that less than 50% of the initial Zr is active at this Al/Zr ratio.     

有机/无机复合载体负载复合催化剂用于乙烯聚合时有机载体的作用

采用溶胶-凝胶法,将苯乙烯-丙烯酸(P(S-co-AA))共聚物包覆在以硅胶/MgCl2为载体的TiCl3催化剂(M-1催化剂)上,负载(n-BuCp)2ZrCl2后制得TiCl3/(n-BuCp)2ZrCl2复合催化剂,研究聚合物载体P(S-co-AA)在复合催化剂乙烯聚合中的作用.前期实验结果表明有机载体P(S-c...     

Novel neodymium (III) isopropoxide‐methylaluminoxane catalyst for isoprene polymerization

A novel catalyst composed of neodymium (III) isopropoxide [Nd(OiPr)₃] and methylaluminoxane (MAO) was examined in isoprene polymerization. The Nd(OiPr)₃‐MAO catalyst proved to be highly effective in heptane even at low [Al]/[Nd] ratios (ca. 30) to give polyisoprene that possessed high cis‐1,4 stereoregularity (> ca. 90%), a high number‐average molecular weight (M_n ～10⁵), and relatively narrow molecular weight distributions (M_w/M_n = 1.9–2.8). The catalyst activity increased with an increasing [Al]/[Nd] ratio from 10 to 80 as well as temperature of aging and polymerization from 0 to 60 °C. The polymerization proceeded in the first order with respect to the monomer concentration. Aliphatic solvents (heptane and cyclohexane) achieved a higher yield and M_n of polymer than toluene as a solvent. The M_w/M_n ratio remained around 2.0, and the gel permeation chromatographic curve was always unimodal, indicating that this system is homogeneous and involves a single active site. The microstructure of polyisoprene was determined by IR, ¹H NMR, and ¹³C NMR. The cis‐1,4 contents of the final polymers stayed in the range of 90–92%, regardless of reaction conditions, indicating the high stability of stereospecificity of the catalyst. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1838–1844, 2002     

Catalyst Design for Methacrolein Oxidation to Methacrylic Acid

Heteropoly compounds (HPCs) with the general formula CsMHPVMo₁₁O₄₀are prepared and tested as catalysts. The influence of elements entering the formula on the catalyst properties is studied: Cs defines the acidity and specific area, V controls the selectivity, and the transition metal M defines the mobility of oxygen in the bulk and the catalyst activity. The mechanism of methacrolein oxidation over HPCs is investigated. Using the response method and mass spectrometry of the reaction mixture, it is shown that only the catalyst oxygen atoms take part in the formation of methacrylic acid and that the transport of active oxygen to adsorbed methacrolein plays a key role in the oxidation process. A correlation between the HPC activity and the redox ability of the metal cation M ⁿ⁺ M ^{n+ i} (i= 1 or 2) is found. New catalysts for methacrolein oxidation to methacrylic acid are developed on the basis of this correlation. These are the salts of PVMo-poly acid with Cs, Cu, and the transition metal M as cations. These catalysts are more active (a conversion of up to 91%) and selective (up to 98%) compared to conventional catalysts for methacrolein oxidation to methacrylic acid.     

Preparation of ultra high molecular weight amorphous poly(1‐hexene) by a Ziegler–Natta catalyst

High molecular weight polymers such as poly (α‐olefin)s play a key role as drag‐reducing agents which are commonly used in pipeline industry. Heterogeneous Ziegler–Natta catalyst system of MgCl₂.nEtOH/TiCl₄/donor was prepared using a spherical MgCl₂ support and utilized in synthesis of poly(1‐hexene)s with a viscosity average molecular weight (M_v) up to 3.5 × 10³ kDa. The influence of effective parameters including Al/Ti ratio, polymerization temperature, monomer concentration, effect of alkylaluminus type on the productivity, and molecular weight of the products was evaluated. It was suggested that the reactivity of the Al‐R group and the bulkiness of the cocatalyst were correlated to the performance of the Ziegler–Natta catalyst at different polymerization time and temperatures, affecting the catalyst activity and M_v of polymers. Moreover, bulk polymerization method leads to higher viscosity average molecular weights, revealing the remarkable effect of polymerization method on the chain microstructure. Fourier transform infrared, ¹³C Nuclear magnetic resonance spectra, and DSC thermogram of the prepared polymers confirmed the formation of poly(1‐hexene). The properties of the polymers measured by vortex test showed that these polymers could be used as a drag‐reducing agent. Drag‐reducing behaviors of the polymers exhibited a dependence on the M_v of the obtained polymers that was changed by variation in polymerization parameters. Copyright © 2016 John Wiley & Sons, Ltd.     

Cooperative effect through different bridges in nickel catalysts for polymerization of ethylene

A series of mononuclear (M₁ and M₂) and dinuclear (C₁–C₆) Ni α‐diimine catalysts activated by modified methylaluminoxane were used in polymerization of ethylene. Catalyst C₂ bearing the optimum bulkiness showed the highest activity (1.6 × 10⁶ g PE (mol Ni)^?1 h^?1) and the lowest short‐chain branching (32.5/1000 C) in comparison to the dinuclear and mononuclear analogues. Although the mononuclear catalysts M₁ and M₂ polymerized ethylene to a branched amorphous polymer, the dinuclear catalysts led to different branched semicrystalline polyethylenes. Homogeneity and heterogeneity in the microstructure of the polyethylene samples was observed. Different trends for each catalyst were assigned to syn and anti stereoisomers. In addition, thermal behavior of the samples in the successive self‐nucleation and annealing technique exhibited different orders and intensities from methylene sequences and lamellae thickness in respect of each stereoisomer behavior. Higher selectivity of hexyl branches obtained by catalyst C₂ showed a cooperative effect between the centers. The results also revealed that for catalysts C₅ and C₆, selectivity of methyl branches led to very high endotherms and crystalline sequences with melting temperatures higher than that of 100% crystalline polyethylene indicating ethylene/propylene copolymer analogues. For catalysts C₃ and C₄, more vinyl end groups were a result of the long distance between the Ni centers. Kinetic profiles of polymerization along with a computational study of the precatalysts and catalysts demonstrated that there is a direct relation between rate constant, energy interval of catalyst and precatalyst, and interaction energy of Et···methyl cationic active center (Et···MCC or π–Comp.). Based on this, narrow energy interval (activation energy) of precatalyst and catalyst leads to fast and higher activation rate (catalyst M₂), and strong interaction of ethylene and catalyst leads to high monomer uptake and productivity (catalyst C₂). Moreover, theoretical parameters including electron affinity, Mulliken charge on Ni, chemical potential and hardness, and global electrophilicity showed optimum values for C₂.     

Synthesis and dilute solution properties of branched poly(benzyl methacrylate) using na-clay supported aqueous-phase catalysis

The supported aqueous-phase catalysis (SAPC) using hydrated interface has been used to synthesize branched polymers (star and graft) of benzyl methacrylate (BnMA) via atom-transfer radical polymerization (ATRP) in the presence of Na-clay supported catalyst in anisole at ambient temperature. The propagation of star poly(BnMA)s using diPENDTA-Br₆, as hexa-functional initiator is confined at the hydrated interface between the support and the liquid medium as evident from the obtained polymers that are catalyst contamination-free, and exhibited moderately narrow molecular weight distributions (M_w/M_n ≤ 1.33). The hexa-functionality of synthesized stars is verified by ¹H NMR, the measurement of their intrinsic viscosity ([η]), and radius of gyration (R_g). The polymerization was also recycled up to 5 times to produce star PBnMAs with high initiator efficiency. The star polymers prepared using hydrated Na-clay supported is compared with star prepared using covalent silica supported catalyst system. The star polymer obtained from covalently supported catalyst gave broad M_w/M_n and poor initiator efficiency. The polystyrene-graft-PBnMA (PS-g-PBnMA) copolymer is also prepared using hydrated Na-clay supported catalyst system in anisole at ambient temperature. The graft-copolymer had narrow M_w/M_n and was confirmed using ¹H NMR and atomic force microscopy. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2225–2237     

Solving the loss of orthogonality during the polyaddition of α‐azide‐ω‐alkyne monomers catalyzed by Cu(PPh3)3Br: Application to the synthesis of high‐molar mass polytriazoles

Polyaddition of an α‐azide‐ω‐alkyne monomer by Cu(PPh₃)₃Br catalyzed 1,3‐dipolar cycloaddition was thoroughly studied as a model system to investigate the orthogonality of this click chemistry process. Indeed, loss of chain‐end functionality and occurrence of side reactions have a tremendous impact on the molar mass of polymers obtained by step growth polymerization. Particularly, SEC, ¹H, and ³¹P NMR experiments have highlighted the occurrence of a Staudinger side‐reaction between azide chain‐ends and PPh₃ from the copper(I) catalyst that dramatically alters M_n of the resulting polytriazoles. A significant enhancement of M_n could be achieved by using an alternative catalyst and optimized experimental conditions, that is, dilution and reaction time. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2470–2476, 2010     

Synthesis of sugar‐based macromolecules via sono‐ATRP in miniemulsion

Ultrasound‐mediated atom transfer radical polymerization (sono‐ATRP) in miniemulsion media is used for the first time for the preparation of complex macromolecular architectures by a facile two‐step synthetic route. Initially, esterification reaction of sucrose or lactulose with α‐bromoisobutyryl bromide (BriBBr) is conducted to receive multifunctional ATRP macroinitiators with 8 initiation sites, followed by polymerization of n‐butyl acrylate (BA) forming arms of the star‐like polymers. The brominated lactulose‐based molecule was examined as an ATRP initiator by determining the activation rate constant (k_a) of the catalytic process in the presence of a copper(II) bromide/tris(2‐pyridylmethyl)amine (Cu^IIBr₂/TPMA) catalyst in both organic solvent and for the first time in miniemulsion media, resulting in k_a = (1.03 ± 0.01) × 10⁴ M^?1 s^?1 and k_a = (1.16 ± 0.56) × 10³ M^?1 s^?1, respectively. Star‐like macromolecules with a sucrose or lactulose core and poly(n‐butyl acrylate) (PBA) arms were successfully received using different catalyst concentration. Linear kinetics and a well‐defined structure of synthesized polymers reflected by narrow molecular weight distribution (M_w/M_n = 1.46) indicated 105 ppm wt of catalyst loading as concentration to maintain controlled manner of polymerization process. ¹H NMR analysis confirms the formation of new sugar‐inspired star‐shaped polymers.     

Anodic stripping determination of mercury in air with a glassy carbon electrode

A technique for stripping determination of mercury traces in air employing a glassy carbon electrode is described. The sample is passed at 2 liters min^?1 for 2 hr through an absorber containing 0.2 M potassium permanganate and 10% $\text{w}\text{v}$ sulfuric acid (1:1). After reduction with hydroxylamine hydrochloride, the determination is carried out in 0.12 M potassium thiocyanate at pH 2.0 ± 0.2 in the presence of 0.2 ppm of cupric ions. Calibration curves were found to be linear in the range 20 ppb-1 ppm Hg(II) in the cell. The accuracy of the method was tested over simulated samples and it was found to be better than 95%; the relative standard deviation was 5% or less. The limit of detection of mercury in air was approximately 10 μg m^?3.     

Atom transfer radical polymerization of n-octyl acrylate under microwave irradiation

The atom transfer radical polymerization (ATRP) of n-octyl acrylate (OA) was successfully carried out using ethyl-2-bromobutyrate as an initiator, and CuBr/2,2^′-bipyridine (bpy) as a catalyst under microwave irradiation (MI) at 76.8 °C. The polymerization of n-octyl acrylate under MI showed linear first-order rate plots, a linear increase of the number-average molecular weight M_n with conversion, and low polydispersities, 1.1<M_w/M_n<1.4, where M_w is weight-average molecular weight. The ATRP of n-octyl acrylate is well controlled. Under the same experimental conditions, the apparent rate constant, k_p^app, under MI is larger apparently than that under conventional heating. In addition, the effects of concentration of catalyst and other factors on polymerization are reported.     

Cobalt‐Catalyzed,Aminoquinoline‐Directed C(sp2)H Bond Alkenylation by Alkynes

A method for cobalt‐catalyzed, aminoquinoline‐ and picolinamide‐directed C(sp²)? H bond alkenylation by alkynes was developed. The method shows excellent functional‐group tolerance and both internal and terminal alkynes are competent substrates for the coupling. The reaction employs a Co(OAc)₂?4 H₂O catalyst, Mn(OAc)₂ co‐catalyst, and oxygen (from air) as a terminal oxidant.     

Cobalt‐Catalyzed,Aminoquinoline‐Directed C(sp2)?H Bond Alkenylation by Alkynes

A method for cobalt‐catalyzed, aminoquinoline‐ and picolinamide‐directed C(sp²) H bond alkenylation by alkynes was developed. The method shows excellent functional‐group tolerance and both internal and terminal alkynes are competent substrates for the coupling. The reaction employs a Co(OAc)₂⋅4 H₂O catalyst, Mn(OAc)₂ co‐catalyst, and oxygen (from air) as a terminal oxidant.     

Synthesis, structural characterization and selectively catalytic properties of metal-organic frameworks with nano-sized channels: A modular design strategy

Modular design method for designing and synthesizing microporous metal-organic frameworks (MOFs) with selective catalytical activity was described. MOFs with both nano-sized channels and potential catalytic activities could be obtained through self-assembly of a framework unit and a catalyst unit. By selecting hexaaquo metal complexes and the ligand BTC (BTC=1,3,5-benzenetricarboxylate) as framework-building blocks and using the metal complex [M(phen)₂(H₂O)₂]²⁺ (phen=1,10-phenanthroline) as a catalyst unit, a series of supramolecular MOFs 1-7 with three-dimensional nano-sized channels, i.e. [M¹(H₂O)₆]·[M²(phen)₂(H₂O)₂]₂·2(BTC)·xH₂O (M¹, M²Co(II), Ni(II), Cu(II), Zn(II), or Mn(II), phen=1,10-phenanthroline, BTC=1,3,5-benzenetricarboxylate, x=22−24), were synthesized through self-assembly, and their structures were characterized by IR, elemental analysis, and single-crystal X-ray diffraction. These supramolecular microporous MOFs showed significant size and shape selectivity in the catalyzed oxidation of phenols, which is due to catalytic reactions taking place in the channels of the framework. Design strategy, synthesis, and self-assembly mechanism for the construction of these porous MOFs were discussed.     

Regulation of Molecular Weight Characteristics and Microtacticity of Polyhexene Produced over Highly Active Supported Titanium–Magnesium Catalysts

The data on the effect of polymerization temperature of 1‐hexene within the 30–70 °C range in the presence of a highly active supported titanium–magnesium catalyst on molecular weight characteristics and microtacticity of polyhexene, with cocatalyst composition being additionally varied (AlEt₃ or Al(i‐Bu)₃), in the absence and presence of an external stereoregulating electron‐donating compound and hydrogen, are reported. Polymerization conditions, making it possible to specifically regulate molecular weight and molecular weight distribution of polyhexene over a broad range ((M_w = 7 × 10⁴–2.2 × 10⁶ g mol⁻¹; M_w/M_n = 3.7–33) and regulate isotacticity of polyhexene (content of mmmm pentads from 56% to 96%), while retaining high catalyst activity, are determined.     

Microwave‐improved polymerization of ϵ‐caprolactone initiated by carboxylic acids

The ring‐opening polymerization of ε‐caprolactone (ε‐CL), initiated by carboxylic acids such as benzoic acid and chlorinated acetic acids under microwave irradiation, was investigated; with this method, no metal catalyst was necessary. The product was characterized as poly(ε‐caprolactone) (PCL) by ¹H NMR spectroscopy, Fourier transform infrared spectroscopy, ultraviolet spectroscopy, and gel permeation chromatography. The polymerization was significantly improved under microwave irradiation. The weight‐average molecular weight (M_w) of PCL reached 44,800 g/mol, with a polydispersity index [weight‐average molecular weight/number‐average molecular weight (M_w/M_n)] of 1.6, when a mixture of ε‐CL and benzoic acid (25/1 molar ratio) was irradiated at 680 W for 240 min, whereas PCL with M_w = 12,100 and M_w/M_n = 4.2 was obtained from the same mixture by a conventional heating method at 210 °C for 240 min. A degradation of the resultant PCL was observed during microwave polymerization with chlorinated acetic acids as initiators, and this induced a decrease in M_w of PCL. However, the degradation was hindered by benzoic acid at low concentrations. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 13–21, 2003     

Catalytic oxidation of unsymmetrical dimethylhydrazine on Pt/SiO<Subscript>2</Subscript>

Specific features of oxidation of unsymmetrical dimethylhydrazine on a Pt-containing catalyst were studied. The temperature dependence of the unsymmetrical dimethylhydrazine conversion was determined, and the main intermediate and final reaction products were identified. Platinum behaves in the process as a multifunctional catalyst participating in dehydrogenation, hydrogenolysis, and oxidation. A new method was suggested for detecting unsymmetrical dimethylhydrazine in air. It consists in catalytic conversion of unsymmetrical dimethylhydrazine and detection of the nitrogen dioxide formed with semiconductor gas sensors. The method was successfully used for detecting unsymmetrical dimethylhydrazine in air at concentrations in the range 0.1–10 mg m^–3.