Organometallics in ethylene polymerization with a catalyst system TiCl4/Al(C2H5)2Cl/Mg(C6H5)2: 1. Suspension polymerization process

Suspension polymerization of ethylene with the catalyst system TiCl₄/Al(C₂H₅)₂Cl/Mg(C₆H₅)₂, at different molar ratios Mg/Ti and Al/Ti, was studied. The transition metal compounds in the catalyst complex formed in this system were found to consist only of Ti(II) and Ti(III), without free Ti(IV); but even with a Ti(II) content of 30% the catalyst was highly active. The influence of the molar ratio cocatalyst/catalyst (Al/Ti and Mg/Ti) on the catalyst activity and on the polyethylene molecular weight was studied, together with the reduction of TiCl₄ by Al(C₂H₅)₂Cl and Mg(C₆H₅)₂ in the reduction step. The polymer yield increased to some limiting molar ratio Mg/Ti and to some limit ratio Al/Ti and further increase of organometal concentration in the system has practically no influence on the catalyst productivity. Dependence of the polyethylene molecular weight on the molar ratios Mg/Ti and Al/Ti was observed, proving the presence of chain transfer reactions with organometallics.     

Organometallics in ethylene polymerization with a catalyst system TiCl4/Al(C2H5)2Cl/Mg(C6H5)2: 2. Polymerization process in pseudo-solution

A study has been made of ethylene polymerization in pseudo-solution with a catalyst system TiCl₄/Al(C₂H₅)₂Cl/Mg(C₆H₅)₂ in the presence of hydrogen as a regulator of polyethylene molecular weight. The polymerization process in pseudo-solution by adjustment of hydrogen makes it possible to produce polyethylene having a wide range of molecular weights. For this purpose melt indices between 0°–50°C/min are desirable and these values are not reached with a suspension type of ethylene polymerization with a catalyst system TiCl₄/Al(C₂H₅)₂Cl/Mg(C₆H₅)₂. The effect of the molar ratio cocatalyst/catalyst (Al/Ti and Mg/Ti) on the catalyst activity and on the polyethylene molecular weight was studied, together with the content of hydrogen as a regulator of the molecular weight. The catalyst productivity increased to some limiting molar ratio Mg/Ti and Al/Ti and further increase of organometallics in the catalyst system did not influence the polymer molecular weight. In the case of ethylene polymerization with this catalyst combination in the presence of hydrogen, some activation of the catalyst was observed. Two mechanisms, which may account for the activation effect of the hydrogen are discussed.     

Organically templated Np(IV) coordination polymer with in situ formed oxalate anion (ImidazoleH)[Np(C2O4)(CH3SO3)3(H2O)2]

The reaction of Np(V) methanesulfonate solution with imidazole led to the in situ formation of oxalic acid and the reduction of Np(V) to Np(IV). As a result, the novel organically templated organic polymer, (ImidazoleH)[Np(C₂O₄)(CH₃SO₃)₃(H₂O)₂], was formed. The structure consists of infinite chains of [Np(C₂O₄)(CH₃SO₃)₃(H₂O)₂]⁻ and imidazolium cations. The crystal structure is confirmed by IR and UV–vis spectroscopic data. This complex is the first example of structurally characterized 1:1 An(IV) oxalate.     

Influence of the Type of Reducing Agent (H2, CO, C3H6 and C3H8) on the Reduction of Stored NOX in a Pt/BaO/Al2O3 Model Catalyst

In this investigation, a comparative study for a NO _X storage catalytic system was performed focusing on the parameters that affect the reduction by using different reductants (H₂, CO, C₃H₆ and C₃H₈) and different temperatures (350, 250 and 150 °C), for a Pt/BaO/Al₂O₃ catalyst. Transient experiments show that H₂ and CO are highly efficient reductants compared to C₃H₆ which is somewhat less efficient. H₂ shows a significant reduction effect at relatively low temperature (150 °C) but with a low storage capacity. We find that C₃H₈does not show any NO _X reduction ability for NO _X stored in Pt/BaO/Al₂O₃ at any of the temperatures. The formation of ammonia and nitrous oxide is also discussed.     

Transmission electron microscopy characterization of nanostructured carbon derived from Cr3C2 and Cr(C5H7O2)3

The preparation, characterization and comparison of nanostructured carbons derived by direct chlorination of Cr₃C₂ and Cr(C₅H₇O₂)₃ are reported in this work. Cr₃C₂ precursor was treated at 400 and 900 °C with a reaction time of 1 h. The nanostructure of the products has been characterized in some detail by means of transmission electron microscopy and associated techniques, such as electron energy-loss and X-ray energy dispersive spectroscopies and high-angle annular dark field imaging. Remains of Cr₃C₂ encapsulated in an amorphous carbon shell were observed at 400 °C, whereas carbon with higher ordering degree was produced at 900 °C. In the latter case, the sample can be described as a continuous variation from poorly-stacked graphene-like carbon to graphitic agglomerates. Remains of the reaction by-product, CrCl₃, are detected in the carbon particles, forming monolayers intercalated inside the graphitic agglomerates and amorphous nanoparticles. As a comparison, carbon samples derived from Cr(C₅H₇O₂)₃ were prepared at 300 and 900 °C. They mainly consist of highly disordered carbon, with local graphite-like stacking in the sample prepared at 900 °C.     

Solid state studies of the C60. 2(CH3)CCl3 solvate

At room temperature, the hexagonal C₆₀. 2(CH₃)CCl₃ solvate (a = 10.13(1) Å, c = 10.84(1) Å), made of alternating layers of C₆₀ and solvent molecules, forms with a negative excess volume, and its desolvation enthalpy is virtually the same as the sublimation enthalpy of the pure solvent. Crystallographic and calorimetric studies vs temperature indicate that hexagonal C₆₀. 2(CH₃)CCl₃ changes at 211.7 K (1.3 kJ mol⁻¹ of solvate) into an intermediate triclinic phase which transforms at 189.7 K (4.1 kJ mol⁻¹ of solvate) into another triclinic phase.A crystallographic analysis in the series of hexagonal C₆₀. 2 YCCl₃ solvates (Y = H, Cl, Br, CH₃) reveals that: (i) the change in the unit-cell volume values is due to a change in axis c whose value depends on the size of Y, (ii) the molar volume of the solvates depends linearly on the molar volume of the solvents.Ageing studies at room temperature show that C₆₀. 2(CH₃)CCl₃ loses its solvent molecules within a few days or a few months, depending on storage conditions.     

Ethylene polymerization using nickel α-diimine complex supported on SiO2/MgCl2 bisupport

Nickel α-diimine complex [C₆H₅-NC(CH₃)C(CH₃)N-C₆H₅]NiCl₂ was impregnated on SiO₂/MgCl₂ bisupport, and ethylene polymerizations were carried out with alkylaluminum compounds as cocatalyst. Branched polyethylenes were prepared when heptane is used as solvent. Polymerization conditions such as modified method of bisupport, cocatalyst, Al/Ni ratio, temperature and nickel concentration had a pronounced effect on catalytic activity and properties of polyethylenes. The activity of 2.9×10⁵ g PE mol Ni h⁻¹ was obtained in the presence of AlEt₂Cl as well as the bisupport without AlEt₃ modification, Al/Ni ratio 80, nickel concentration 0.12 mmol/l and temperature 14 °C. Branching degree of polyethylenes increased with temperature, and molecular weight, melting point and crystallinity of polyethylenes decreased correspondingly. Polymerization temperature had a pronounced effect on branches distribution of polyethylenes. Content of methyl branch increased sharply with temperature, but long branches dropped quickly.     

A new type of supramolecular assembly consisting of crown ether complex cation and a polyoxometalate anion: Synthesis and crystal structure of [Na(C20H24O6)(CH3CN)2]2[Mo6O19] · 4CH3CN

A novel supramolecular assembly consisting of sodium-dibenzo-18-crown-6(DB18C6) complex cation [Na(C₂₀H₂₄O₆)(CH₃CN)₂]²⁺ and isopolyanion [Mo₆O₁₉]²⁻ has been demonstrated in the 3D structure of [Na(C₂₀H₂₄O₆)(CH₃CN)₂]₂[Mo₆O₁₉] · 4CH₃CN (1). Weak intermolecular forces (C–HO hydrogen bonds) between isopolyanion and crown ether play a significant role in the construction of supramolecular framework in the crystal structure of 1. Compound 1 has been characterized in the solid state by single crystal X-ray diffraction, IR, CHN analysis, and TGA.     

The effect of synthesis gas composition on the Fischer–Tropsch synthesis over Co/γ-Al2O3 and Co–Re/γ-Al2O3 catalysts

The Fischer–Tropsch synthesis over Co/γ-Al₂O₃ and Co–Re/γ-Al₂O₃ was investigated in a fixed-bed reactor at 20 bar and 483 K using feed gases with molar H₂/CO ratios of 2.1, 1.5 and 1.0 simulating synthesis gas derived from biomass. With lower H₂/CO ratios in the feed, the CO conversion and the CH₄ selectivity decreased, while the C₅₊ selectivity and olefin/paraffin ratio for C₂–C₄ increased slightly. The water–gas shift activity was low for both catalysts, resulting in high molar usage ratios of H₂/CO (close to 2.0), even at the lower inlet ratios (i.e. 1.5 and 1.0). For both catalysts, the drop in the production rate of hydrocarbons when shifting from an inlet ratio of 2.1 to 1.5 was significant mainly because the H₂/CO usage ratio did not follow the change in the inlet ratio. The hydrocarbon selectivities were rather similar for inlet H₂/CO ratios of 2.1 and 1.5, while significantly deviating from those for an inlet ratio of 1.0. With the studied catalysts, it is possible to utilize the advantages of an inlet ratio of 1.0 (higher selectivity to C₅₊, lower selectivity to CH₄, no water–gas shifting of the bio-syngas needed prior to the FT reactor) if a low syngas conversion is accepted.     

Adsorption and interaction of NO, C3H6 and O2 on Pt, Zr, Nb-MCM-41—FTIR study

Adsorption of NO, O₂ and C₃H₆ on the MCM-41 matrices with Nb and Zr loaded with Pt has been studied by the FTIR spectroscopy to characterize these materials as catalysts in the selective reduction of NO with propene. Two types of the catalysts have been studied differing by the methods of Zr and Nb introduction: either by one-pot (group 1) or by post-synthesis impregnation (group 2) and hence by the location of Nb and Zr in the framework (group 1) or extra framework (group 2). It has been found that the positions of these metals in the MCM-41 matrix determine the platinum dispersion, acidic–basic properties and influence the interaction of NO + O₂ + C₃H₆ with the catalyst surfaces. The fact that the Pt dispersion is much higher in group 2 materials has been revealed by results of XRD patterns and TEM images. According to the explanation proposed, the presence of Lewis acid–base pairs in the group 2 of catalysts has strongly activated chemisorption of propene, whereas Lewis basicity, characterized by 2-PrOH dehydrogenation on the samples containing transition metals introduced during the synthesis (group 1), has enhanced chemisorption of nitrite species on platinum. It has been proved that nitrite species have not been stored on Pt/Zr/MCM-41 samples, whereas they have been stabilized on Pt/Zr/Nb/MCM-41 containing BrØnsted acidic centres.     

New ferrocene-derived hydroxymethylphosphines: FcP(CH2OH)2 [Fc=(η-C5H5)Fe(η-C5H4)] and the dppf analogue 1,1-Fc[P(CH2OH)2]2 [Fc=Fe(η-C5H4)2]

Reactions of the ferrocene-phosphines FcPH₂ and 1,1^′-Fc^′(PH₂)₂ with excess formaldehyde gives the new hydroxymethylphosphines FcP(CH₂OH)₂ 1 and 1,1^′-Fc^′[P(CH₂OH)₂]₂ 2, respectively. Phosphine 1 is an air-stable crystalline solid, whereas 2 is isolated as an oil. Reaction of 1 with H₂O₂, S₈ or Se gives the chalcogenide derivatives FcP(E)(CH₂OH)₂ (E=O, S or Se), whilst reaction of 2 with S₈ gives 1,1^′-Fc^′[P(S)(CH₂OH)₂]₂, which were fully characterised. Phosphine 1 was also characterised by an X-ray crystal structure determination.     

Polymerization of 1,3-butadiene with VO(P204)2 and VO(P507)2 activated by alkylaluminum

The oxovanadium phosphonates (VO(P₂₀₄)₂ and VO(P₅₀₇)₂) activated by various alkylaluminums (AlR₃, R = Et, i-Bu, n-Oct; HAlR₂, R = Et, i-Bu) were examined in butadiene (Bd) polymerization. Both VO(P₂₀₄)₂ and VO(P₅₀₇)₂ showed higher activity than those of classical vanadium-based catalysts (e.g. VOCl₃, V(acac)₃). Among the examined catalysts, the VO(P₂₀₄)₂/Al(Oct)₃ system (I) revealed the highest catalytic activity, giving the poly(Bd) bearing M_n of 3.76 × 10⁴ g/mol, and M_w/M_n ratio of 2.9, when the [Al]/[V] molar ratio was 4.0 at 40 °C. The polymerization rate for I is of the first order with respect to the concentration of monomer. High thermal stability of I was found, since a fairly good catalytic activity was achieved even at 70 °C (polymer yield > 33%); the M_n value and M_w/M_n ratio were independent of polymerization temperature in the range of 40-70 °C. By IR and DSC, the poly(Bd)s obtained had high 1,2-unit content (>65%) with atactic configuration. The 1,2-unit content of the polymers obtained by I was nearly unchanged, regardless of variation of reaction conditions, i.e. [Al]/[V], ageing time, and reaction temperature, indicating the high stability of stereospecificity of the active sites.     

Effect of Ti5Si3 on wear properties of Ti3Si(Al)C2

Near-fully dense Ti₃Si(Al)C₂/Ti₅Si₃ composites were synthesized by in situ hot pressing/solid–liquid reaction process under a pressure of 30 MPa in a flowing Ar atmosphere at 1580 °C for 60 min. Compared to monolithic Ti₃Si(Al)C₂, Ti₃Si(Al)C₂/Ti₅Si₃ composites exhibit higher hardness and improved wear resistance, but a slight loss in flexural strength (about 26% lower than Ti₃Si(Al)C₂ matrix). In addition, Ti₃Si(Al)C₂/Ti₅Si₃ composites maintain a high fracture toughness (K_IC = 5.69–6.79 MPa m^1/2). The Ti₃Si(Al)C₂/30 vol.%Ti₅Si₃ composite shows the highest Vickers hardness (68% higher than that of Ti₃Si(Al)C₂) and best wear resistance (the wear resistance increases by 2 orders of magnitude). The improved properties are mainly ascribed to the contribution of hard Ti₅Si₃ particles, and the strength degradation is mainly due to the lower Young's modulus and strength of Ti₅Si₃.     

Samarium Coordinated Polymer: Structural, Vibrational and Thermal Studies of [Sm2(C3H2O4)3(H2O)6]n

The title compound, [Sm₂(C₃H₂O₄)₃(H₂O)₆]_, was investigated by X-ray diffraction. It crystallizes in the monoclinic space group C2/c with cell parameters a = 17.1650(8) ?, b = 12.3010(5) ?, c = 11.1420(4) ?, β = 127.5161(10)°, Z = 4 and V = 1866.04(14) ?³. The Sm atom lies on a two-fold axis and has nine-coordination with six oxygen atoms from carboxylate groups and three water molecules. The compound forms a layer-type polymeric structure. The layers are formed by samarium and one independent malonate group to give a three-dimensional framework. The extensive network of hydrogen bonds and bridge bonds observed in this structure enhances the structural stability. The thermal dehydration of the compound was investigated by thermogravimetric analysis.     

The Synthesis and Characterization of Triorganotin Carboxylates of 2-Mercapto-4-methyl-5-thiazoleacetic Acid: X-ray Crystal Structures of Polymeric Me3Sn[O2CCH2(C4H3NS)S]SnMe3 and Ph3Sn[O2CCH2(C4H3NS)S]SnPh3

The triorganotin carboxylates of 2-mercapto-4-methyl-5-thiazoleacetic acid (1), R₃Sn[O₂CCH₂- (C₄H₃NS)S]SnR₃ (R=Me 2, n-Bu 3, Ph 4 PhCH₂ 5), have been synthesized and characterized by IR, ¹H and ¹³C NMR spectroscopy. Among them, complexes 2 and 4 were also characterized by X-ray crystallography diffraction analysis, which revealed that both 2 and 4 showed a one-dimensional polymeric structure in which the geometries of the tin atoms are different: one was a distorted tetrahedron and the other was trigonal bipyramidal with the axial positions occupied by oxygen atoms.     

Stabilized β-Bi2O3 nanoparticles from (BiO)4CO3(OH)2 precursor and their photocatalytic properties under blue light

Stabilized tetragonal Bi₂O₃ nanoparticles (β-Bi₂O₃) were obtained by annealing treatments of amorphous Bi-based precursors, obtained by chemical precipitations, at temperatures between 350 and 450?°C. The formation of the stabilized β-Bi₂O₃ phase was possible by using (BiO)₄CO₃(OH)₂ while other precursors such as amorphous bismuth carbonate ((BiO)₂CO₃) and amorphous basic bismuth nitrate (Bi₆O₆(OH)₂(NO₃)₄·2H₂O) led to the formation of the thermodynamically stable monoclinic α-Bi₂O₃ and Bi₅O₇NO₃ phases. The Bi-based precursors were prepared by the chemical precipitation method at room temperature in ethylenediamine-solvent varying the HNO₃/Bi³⁺ molar ratio (10, 26 and 56). The physicochemical properties of the three as-prepared amorphous precursors and the formed-after-calcination β-Bi₂O₃, α-Bi₂O₃ and Bi₅O₇NO₃ phases were analyzed by X-ray diffraction, scanning electron microscopy, thermogravimetry, X-ray photoelectron spectroscopy (XPS), FTIR analysis, diffuse reflectance spectroscopy and surface area by BET method. The photocatalytic activity of all annealed solids containing the β-Bi₂O₃ phase was tested in the photodegradation of the indigo carmine (IC) dye under specific blue light. A schematic diagram of the Bi₂O₃ phases obtained as a function of the annealing conditions and initial amorphous precursor is proposed and explained in terms of the amount of CO₃^2-, NO₃^- and amine (ENH₂²⁺ ? ENH⁺) ions present in each bismuth precursor.     

Transesterification of triglycerides with methanol over thermally treated Zn5(OH)8(NO3)2×2H2O salt

Methanolysis of natural oil, i.e. castor oil and triacetin, a model compound for the transesterification of triglycerides in biodiesel production was studied under atmospheric pressure at temperature of 50-60 °C. As-received zinc hydroxy nitrate Zn₅(OH)₈(NO₃)₂×2H₂O (Zn-5) and samples obtained by thermal treatment of Zn-5 for 2 h in the temperature range of 105-300 °C were used as the catalysts. The catalysts were characterized by thermogravimetric (TG) analysis, X-ray powder diffraction (XRD), infrared spectroscopy (FTIR), nitrogen sorption (BET) and scanning electron microscopy (SEM). The effect of thermal treatment of Zn-5 salt on the activity and reusability in methanolysis of triglycerides was studied. During thermal treatment of as-received Zn-5 salt a gradual decomposition via various hydroxy nitrates intermediates such as Zn₅(OH)₈(NO₃)₂ and Zn₃(OH)₄(NO₃)₂ to ZnO occurred. This was accompanied by significant morphological and textural changes. Plate-like particles of Zn-5 salt reorganized into spherically shaped particles of ZnO. Moreover, decrease in specific surface area and porosity occurred. In methanolysis of both triglycerides, the activity of Zn-catalysts gradually decreased as the temperature of thermal treatment increased and the activity of ZnO, a final product of thermal decomposition was very low. The most active was as-received Zn-5 salt and its morphological/chemical properties did not change during methanolysis reaction performed at temperature of 50-60 °C. Moreover, the activity of original Zn-5 salt was fully restored after methanol/THF washing of spent catalysts. The activity of as-received Zn-5 catalyst was preserved under successive use in catalytic tests. The activity of thermally treated Zn-5 salt (at 140 °C) did not restore after methanol/THF washing and during subsequent use of Zn-5-140 catalyst its activity successively decreased.     

Kinetics of Polyurethane Formation in Polymerization Reactions Using the Organometallic Diol (η5-C5H4CH2CH2OH)2Mo2(CO)6

Summary The kinetics of the dibutyltin diacetate (DBTA) – catalyzed polymerization reactions of (η⁵-C₅H₄CH₂CH₂OH)₂Mo₂(CO)₆ with Hypol 2000 (an isocyanate-terminated polyether prepolymer) and with 1,4-butanediol were studied, as were the kinetics of a copolymerization involving (η⁵-C₅H₄CH₂CH₂OH)₂Mo₂(CO)₆ and PEG-1000 (a poly(ethylene glycol)) with Hypol 2000. The purpose was to determine if (η⁵-C₅H₄CH₂CH₂OH)₂Mo₂(CO)₆ appreciably affected the overall rate of the polymerization reaction and if it changed the mechanism of the reaction. The kinetics were analyzed with a fitting program, which allowed extraction of the rate constants for the individual elementary steps in the mechanism. The results showed that (η⁵-C₅H₄CH₂CH₂OH)₂Mo₂(CO)₆ does not significantly alter the timescale of the reaction and that the same reaction mechanism is likely used as with the 1,4-butanediol and PEG-1000. There are some differences in the rate constants of the elementary steps, but these differences can be attributed to the increased steric crowding caused by the bulkier (η⁵-C₅H₄CH₂CH₂OH)₂Mo₂(CO)₆ diol. The effect of the (η⁵-C₅H₄CH₂CH₂OH)₂Mo₂(CO)₆ on the polymers’ physical properties was also investigated. As is the case with other segmented polyurethanes, the hydrogen bonding index (HBI) and the relative amount of soft segments of the (η⁵-C₅H₄CH₂CH₂OH)₂Mo₂(CO)₆-containing polyurethane correlate in a general way with the physical properties of the polymer.     

Effect of potassium hydrogen phthalate (C8H5KO4) on the one-step electrodeposition of single-phase CuInS2 thin films from acidic solution

The effect of potassium hydrogen phthalate (C₈H₅KO₄) as a special additive on the one-step electrodeposition of single-phase CuInS₂ thin films from acidic solution (pH 2.5) was investigated in detail. The XRD, SEM and UV-vis-NIR characterization confirms that the addition of an adequate concentration of C₈H₅KO₄ (23 mM) to the electrolytic bath containing 12.5 mM Cu²⁺, 10 mM In³⁺, 40 mM S₂O₃²⁻ and 100 mM LiCl can contribute greatly to the controllable growth of pure chalcopyrite CuInS₂ films with uniform surfaces and an ideal band gap of approximately 1.54 eV. Complexation studies of C₈H₅KO₄ with Cu²⁺ and In³⁺ in electrolytic solutions indicated that C₈H₅KO₄ can complex Cu²⁺ more strongly than In³⁺ and move the electrode potentials of Cu²⁺ and In³⁺ near each other as determined by polarization analysis. Furthermore, the potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) analysis performed in a series of solution systems revealed a three-step reaction mechanism for CuInS₂ deposition and considerable adsorption of C₈H₅O₄⁻ and Cu(C₈H₅O₄)⁺ to the cathode surface. This deposition shows that the synergetic effects of complexation and adsorption originated from the additive on the Cu²⁺ electro-reduction, thus promoting the co-deposition of copper, indium and sulfur in the form of single-phase CuInS₂.     

Electrochemical characterization of self-assembly process of nano-scaled polyoxomolybdate (NH4)42[Mo72Mo60O372(CH3COO)30(H2O)72]·ca.300H2O

Cyclic voltammetry and electrochemical admittance were used to characterize the self-assembly process of nano-scaled spheres of polyoxomolybdate (NH₄)₄₂[Mo^VI₇₂Mo^V₆₀O₃₇₂(CH₃COO)₃₀(H₂O)₇₂]·ca.300H₂O·ca.10CH₃COONH₄) or {Mo₁₃₂}. Cyclic voltammetry indicated that the self-assembly process could be detected after 8 h and completed after one day. Electrochemical admittance showed that the molybdenum species in the CH₃COONH₄-CH₃COOH buffer (pH 4.46) were totally different from those in the pure (NH₄)₆Mo₇O₂₄ solution (pH 5.54) and the (NH₄)₆Mo₇O₂₄ solution (pH 4.21) acidified by hydrochloric acid. However, the molybdate species in the latter two solutions should be mixtures of non-protonated and/or protonated [Mo₇O₂₄]⁶⁻ and [Mo₈O₂₆]⁴⁻ anions. Detailed analysis of admittance results could support the existence of the molybdate species related to the {Mo^VI₆} fragment which was one of the components of {Mo₁₃₂} clusters. Admittance results on the self-assembly process were coincident with those from cyclic voltammetry.