Novel Type of Metal-Containing Polyimides for the Heck and Suzuki–Miyaura Cross-Coupling Reactions as Highly Active Catalysts

Novel palladium (II)-containing polyimides with exceptional catalytic properties for the Heck and Suzuki–Miyaura cross-coupling reactions were prepared from Pd(II)--bis(imine) complex and the corresponding dianhyrides. The glass transition temperatures (T _g ) of the polymers ranged from 169 to 241°C. The temperatures at which 10% weight loss occurred in air ranged from 415 to 579°C. Polyimides based on the palladium (II) complex were tested for catalytic activity in the Heck coupling reaction between styrene and several aryl halides and the Suzuki coupling reaction between phenylboronic acid and several aryl halides. The negative effects (e.g., expense, low reaction rates, air-sensitivity) experienced by using phosphines, particularly electron-rich phosphines, as catalysts in large scale applications is overcome by using polymer supported catalysis.     

Suzuki–Miyaura cross-coupling reactions catalyzed by efficient and recyclable Fe3O4@SiO2@mSiO2–Pd(II) catalyst

In this study, a novel Pd(II) complex functionalized core–shell magnetic mesoporous catalyst (Fe₃O₄@SiO₂@mSiO₂–Pd(II)) was synthesized by a simple cost effective procedure. It was characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, vibrating sample magnetometer, and nitrogen physical adsorption. The Fe₃O₄@SiO₂@mSiO₂–Pd(II) catalyst offered high surface area and exhibited excellent activity towards Suzuki–Miyaura cross-coupling reaction of halides with aryl boronic acids in ethanol in air. The Fe₃O₄@SiO₂@mSiO₂–Pd(II) catalyst was stable, reusable, and conveniently recovered by applying an external magnetic field. Moreover, it provided 91% conversion after the sixth catalytic run. The Fe₃O₄@SiO₂@mSiO₂–Pd(II) catalyst examined in this study combined both the efficiency of a homogeneous catalyst and the durability of a heterogeneous catalyst. The results revealed that the Fe₃O₄@SiO₂@mSiO₂–Pd(II) catalyst is promising as a candidate for various Pd-based catalytic applications.     

Oxidative Dehydrogenation of Ethylbenzene to Styrene with Carbon Dioxide over Fe2O3/TiO2–ZrO2 Catalyst: Influence of Chloride

This study was undertaken to know the influence of chloride ions in TiO₂–ZrO₂ mixed oxide and to explore chloride containing Fe₂O₃/TiO₂–ZrO₂ catalyst for oxidative dehydrogenation of ethylbenzene to styrene utilizing carbon dioxide as a soft oxidant. The TiO₂–ZrO₂ mixed oxide was synthesized by a co-precipitation method. Over the calcined support, a nominal 15 wt.% Fe₂O₃ was deposited by a wet impregnation method. The prepared catalysts were characterized using X-ray diffraction, temperature programmed desorption of NH₃ and CO₂, scanning electron microscopy and BET surface area methods. The catalytic activity measurements were made in a fixed-bed microreactor under normal atmospheric pressure. Characterization studies reveal that chloride ions exhibit a strong influence on the physicochemical and catalytic properties of the titania–zirconia composite oxides. The impregnated iron oxide was found to be in a highly dispersed form over the TiO₂–ZrO₂ support and influenced greatly on its acid–base properties. The chloride containing Fe₂O₃/TiO₂–ZrO₂ catalyst exhibited better activity and selectivity. The order of activity on various samples was found to be Fe₂O₃/TiO₂–ZrO₂ (chloride) > TiO₂–ZrO₂ (chloride) > TiO₂–ZrO₂.     

Preparation and Characteraction of New Magnetic Co–Al HTLc/Fe3O4 Solid Base

Novel magnetic hydrotalcite-like compounds (HTLcs) were synthesized through introducing magnetic substrates (Fe₃O₄) into the Co–Al HTLcs materials by hydrothermal method. The magnetic Co–Al HTLcs with different Fe₃O₄ contents were characterized in detail by XRD, FT-IR, SEM, TEM, DSC, and VSM techniques. It has been found that the magnetic substrates were incorporated with HTLcs successfully, although the addition of Fe₃O₄ might hinder the growth rate of the crystal nucleus. The morphology of the samples showed the relatively uniform hexagonal platelet-like sheets. The grain boundaries were well defined with narrow size distribution. Moreover, the Co–Al HTLcs doped with magnetic substrates presented the paramagnetic property.     

Mn3O4@ZnO Core–Shell Nanocomposite: Synthesis and Characterization

Nano-sized single-phase Mn₃O₄@ZnO core–shell nanocomposite was prepared via a simple one-pot sequential polyol using triethylene glycol as a high boiling point solvent as well as a reducing agent. The presence of both Mn₃O₄ and ZnO was confirmed with X-ray diffractometry. Infrared measurements proved the presence of triethylene glycol on the surface of Mn₃O₄@ZnO core–shell. The average particle size is between 8 and 13 nm. Reference intensity ratios method calculations showed that the weight percentage of phases were found as 54.7 % ZnO and 45.3 % Mn₃O₄. The lower Tc maybe explained by interface effects and dominant ZnO shell in magnetic properties of core–shell nanocomposite.     

Structure-activity Relation of Fe2O3–CeO2 Composite Catalysts in CO Oxidation

A series of Fe₂O₃–CeO₂ composite catalysts were synthesized by coprecipitation and characterized by X-ray diffraction (XRD), BET surface area measurement, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Their catalytic activities in CO oxidation were also tested. The Fe₂O₃–CeO₂ composites with an Fe molar percentage below 0.3 form solid solutions with the CeO₂ cubic fluorite structure, in which the doped Fe³⁺ initially substitutes Ce⁴⁺ in fluorite cubic CeO₂, but then mostly locate in the interstitial sites after a critical concentration of doped Fe³⁺. With an Fe molar percentage between 0.3 and 0.95, the Fe₂O₃–CeO₂ composites are mixed oxides of the cubic fluorite CeO₂ solid solution and the hematite Fe₂O₃. XPS results indicate that CeO₂ is enriched in the surface region of Fe₂O₃–CeO₂ composites. The Fe₂O₃–CeO₂ composites have much higher catalytic activities in CO oxidation than the individual pure CeO₂ and Fe₂O₃, and the Fe_0.1Ce_0.9 composite shows the best catalytic performance. The structure-activity relation of the Fe₂O₃–CeO₂ composites in CO oxidation is discussed in terms of the formation of solid solution and surface oxygen vacancies. Our results demonstrate a proportional relation between the catalytic activity of cubic CeO₂-like solid solutions and their density of oxygen vacancies, which directly proves the formation of oxygen vacancies as the key step in CO oxidation over oxide catalysts.     

Heterogeneous Fe3O4@chitosan-Schiff base Pd nanocatalyst: Fabrication,characterization and application as highly efficient and magnetically-recoverable catalyst for Suzuki–Miyaura and Heck–Mizoroki C–C coupling reactions

An environmentally friendly palladium-based catalyst supported on magnetite nanoparticles was successfully prepared. FT-IR, XRD, VSM, SEM, EDS and TGA studies have been used to characterize the nanocatalyst. The catalytic activity of the as-prepared catalyst was evaluated as a heterogeneous catalyst for the Suzuki–Miyaura carbon–carbon cross-coupling reaction of aryl halides and phenylboronic acid. Furthermore, it was found that the catalyst showed a high activity for the Mizoroki–Heck reaction of aryl halides and n-butyl acrylate. Interestingly, the novel catalyst could be recovered in a facile manner from the reaction mixture and recycled consecutive five runs without any significant loss in activity.     

Palladium Nanoparticles Supported on Poly(2-hydroxyethyl methacrylate)/KIT-6 Composite as an Efficient and Reusable Catalyst for Suzuki–Miyaura Reaction in Water

Pd nanoparticle-poly(2-hydroxyethyl methacrylate)/KIT-6 (Pd-PHEMA/KIT-6) composite was fabricated through in situ polymerization method and was evaluated as a novel heterogeneous catalyst in Suzuki–Miyaura cross coupling reactions of aryl halides and phenylboronic acid in an aqueous medium. The catalyst was characterized by XRD, FT-IR, UV–Vis, TG, BET, and TEM techniques. The results revealed that the supported catalyst Pd-PHEMA/KIT-6 exhibited excellent catalytic activity for the coupling of aryl iodides, aryl bromides, and aryl chlorides. This heterogeneous catalyst could be reused at least nine times without any decrease in activity.     

Phase equilibria and stability of intermediate phases in the Sm2O3–BaO–Fe2O3 system

Phase equilibria in the ½ Sm₂O₃–BaO–½ Fe₂O₃ system were systematically studied at 1100°C in air. Two individual compounds: Sm_1.875Ba_3.125Fe₅O_15-δ and Ba₃SmFe₂O_7.5+δ have been detected in the studied system at 1100°C in air. One more complex oxide with double perovskite structure SmBaFe₂O_5+w has been obtained under reduced oxygen partial pressure. Thermodynamic stability of SmBaFe₂O_5+w and its thermal stability in metastable state in air were determined. The subsolidus phase diagram for the ½ Sm₂O₃ – BaO – ½ Fe₂O₃ system at 1100°C in air has been constructed.     

Fabrication of graphene nanosheet (GNS)–Fe3O4 hybrids and GNS–Fe3O4/syndiotactic polystyrene composites with high dielectric permittivity

Graphene nanosheet–Fe₃O₄ (GNS–Fe₃O₄) hybrids were obtained by a one-step solvothermal reduction of iron (III) acetylacetonate [Fe(acac)₃] and graphene oxide (GO) simultaneously, which had several advantages: (1) the Fe₃O₄ nanoparticles were firmly anchored on GNS surface even after mild ultrasonication; (2) the loading amount of Fe₃O₄ nanoparticles could be effectively controlled by changing the initial feeding weight ratio of Fe(acac)₃ to GO; (3) the Fe₃O₄ nanoparticles were homogeneously distributed on the GNS surface without much aggregation. Composites based on syndiotactic polystyrene (sPS) and GNS–Fe₃O₄ were prepared by a solution-blending method and the electric and dielectric properties of the resultant GNS–Fe₃O₄/sPS composites were investigated. The percolation threshold of GNS–Fe₃O₄ in the sPS matrix was determined to be 9.41 vol.%. Slightly above the percolation threshold with 9.59 vol.% of GNS–Fe₃O₄, the GNS–Fe₃O₄/sPS composite showed a high dielectric permittivity of 123 at 1000 Hz, which was 42 times higher than that of pure sPS. The AC electrical conductivity at 1000 Hz increased from 3.6 × 10⁻¹⁰ S/m for pure sPS to 2.82 × 10⁻⁴ S/m for GNS–Fe₃O₄/sPS composite containing 10.69 vol.% of GNS–Fe₃O₄, showing an obvious insulator-semiconductor transition.     

Influence of Mn and Fe Addition on the NO x Storage–Reduction Properties and SO2 Poisoning of a Pt/Ba/Al2O3 Model Catalyst

This work deals with the effect of Mn or Fe addition on the NO _x storage–reduction properties of a Pt/Ba/Al₂O₃ model catalyst. NO _x storage capacity, SO₂ poisoning and regeneration and NO _x removal efficiency under rich/lean cycling conditions are studied. Fe addition to Pt/Ba/Al₂O₃ leads only to a small increase of NO _x storage capacity, and more interestingly, to a better sulfur removal due to the inhibition of bulk barium sulfate formation. Unfortunately, the NO _x storage property cannot be fully recovered. Moreover, Fe addition results in a decrease in the NO _x removal efficiency. Mn addition also improves the NO _x storage capacity, but no significant influence on the sulfur elimination is observed. Mn-doped catalyst does not improve the NO _x removal efficiency, but NH₃ selectivity is found to drastically decrease at 400 °C, from 20 to 3%. In addition, the NO _x conversion can be improved at higher H₂ concentration in the rich pulse, always keeping NH₃ selectivity at low level.     

Citrate-Nitrate Synthesis and the Electrophysical Properties of Ceramics in the K2O–TiO2–Fe2O3 System

Glass Physics and Chemistry - This paper presents a study of the electrically conductive properties of ceramics based on phases crystallizing in the K2O–Fe2O3–TiO2 system, when using...     

Preparation and structural properties of Fe3O4–polyimide hybrid nanocomposites

Polyimide films in which magnetic Fe₃O₄ nanoparticles are uniformly distributed are prepared. Before the preparation of the Fe₃O₄–polyimide composites, pure magnetite nanoparticles (Fe₃O₄) have been synthesized in water by co-precipitation (from ferric chlorides). Its surface was firstly modified with the 3-aminopropyl triethoxysilane. The prepared polyimide–Fe₃O₄ nanocomposite films were characterized for their structure, morphology, and thermal behavior employing Fourier transform infrared spectroscopy, scanning electron micrograph, X-ray diffraction, and thermal analysis (DTA/TGA/DSC) techniques.     

Magnetic,luminescent and core–shell structured Fe3O4@YF3:Ce3+,Tb3+ bifunctional nanocomposites

Bifunctional magnetic–luminescent nanocomposites with Fe₃O₄ nanoparticles as the cores and YF₃:Ce³⁺,Tb³⁺ as the shells were synthesized by a facile direct precipitation method. Transmission electron microscopy (TEM) images revealed that the obtained bifunctional nanocomposites had a core–shell structure, in a spherical shape with a size ranging from 160 to 220 nm, and the shell thickness of about 25 nm. The X-ray diffraction (XRD) patterns showed that a cubic spinel structure of Fe₃O₄ core and an orthogonal phase of YF₃ shell were obtained. Photoluminescence (PL) spectra confirmed that the nanocomposites displayed a strong green light emission. Magnetic measurements indicated that the obtained bifunctional nanocomposites exhibited a stronger magnetic behavior at room temperature. Therefore, the bifunctional nanocomposites are expected to develop many potential applications in biomedical fields.