Manganese ferrite nanoparticles synthesized through a nanocasting route as a highly active Fenton catalyst

Spinel ferrite MnFe₂O₄ nanoparticles were synthesized by means of a nanocasting technique using a low-cost mesoporous silica gel as a hard template. The magnetic nanoparticles, of <10 nm diameter and with a surface area of around 100 m²/g, were tested as a heterogeneous Fenton catalyst for the decomposition of hydrogen peroxide under neutral and basic conditions. This catalyst shows a much higher activity than previous heterogeneous catalysts reported in the literature, which is mainly ascribed to its small particle size. Furthermore, the magnetic catalyst can be easily separated from the reaction medium by means of an external magnetic field. The effects of residual silica and the purity of the catalyst (hematite formation) on catalytic activity have been studied and correlated. The results obtained show this catalyst to be a suitable candidate for the removal of pollutants in wastewaters by means of the Fenton heterogeneous reaction.     

Preparation of supported Pt(0) nanoparticles as efficient recyclable catalysts for hydrogenation of alkenes and ketones

A magnetically recoverable Pt(0) catalyst was prepared by in situ H₂ reduction of Pt²⁺ species bound to an amino modified silica-coated magnetic nanoparticles. Compared to ordinary silica (maximum uptake Pt 0.03 wt%), the amino-functionalized silica surfaces were loaded with 1.95 wt% of metal. The supported Pt(0) nanoparticles exhibit high catalytic activity in the hydrogenation of alkenes and ketones under solventless mild reaction conditions. Partially hydrogenated products could also be isolated. The magnetic property of the catalyst grants a fast and efficient product isolation compared to traditional methods used in heterogeneous systems that generally make use of time- and solvent-consuming procedures.     

Preparation of supported Pt(0) nanoparticles as efficient recyclable catalysts for hydrogenation of alkenes and ketones

A magnetically recoverable Pt(0) catalyst was prepared by in situ H₂ reduction of Pt²⁺ species bound to an amino modified silica-coated magnetic nanoparticles. Compared to ordinary silica (maximum uptake Pt 0.03 wt%), the amino-functionalized silica surfaces were loaded with 1.95 wt% of metal. The supported Pt(0) nanoparticles exhibit high catalytic activity in the hydrogenation of alkenes and ketones under solventless mild reaction conditions. Partially hydrogenated products could also be isolated. The magnetic property of the catalyst grants a fast and efficient product isolation compared to traditional methods used in heterogeneous systems that generally make use of time- and solvent-consuming procedures.     

Molybdenum Schiff Base Complex Covalently Anchored to Silica-Coated Cobalt Ferrite Nanoparticles as a Novel Heterogeneous Catalyst for the Oxidation of Alkenes

Abstract  

Silica-coated cobalt ferrite nanoparticles were prepared and functionalized with Schiff base groups to yield immobilized bidentate ligands. The functionalized magnetic nanoparticles were then treated with Mo (O₂)₂(acac)₂, resulting in the novel immobilized molybdenum Schiff base catalyst. The as-prepared catalyst was characterized by X-ray powder diffraction, transmission electron microscopy, vibrating sample magnetometry, thermogravimetric analysis, Fourier transform infrared, and inductively coupled plasma atomic emission spectroscopy. The immobilized molybdenum complex was shown to be an efficient heterogeneous catalyst for the oxidation of various alkenes using t-BuOOH as oxidant. This catalyst, which is easily recovered by simple magnetic decantation, could be reused several times without significant degradation in catalytic activity.     

Synthesis of dimethyl carbonate from ethylene carbonate and methanol using immobilized ionic liquid on amorphous silica

Ionic liquid immobilized on mesoporous amorphous silica was prepared from the coupling of 1-(triethoxysilylpropyl)-3-n-alkyl-imidazolium halides with tetraethyl orthosilicate (TEOS) through template-free condensation under strong acidic conditions. The immobilized 1-n-butyl-3-methyl imidazolium bromide ionic liquid on amorphous silica (BMImBr-AS) was characterized by EA, N₂ adsorption, FT-IR, ¹³C NMR and ²⁹Si NMR. The immobilized amount of IL was 1.27 mmol/g-SiO₂ and surface area was 652 m²/g with bimodal distribution of pores. The average pore diameter was 3.3 and 24.6 nm, respectively. The silica-supported ionic liquids were proved to be an effective heterogeneous catalyst for the synthesis of dimethyl carbonate (DMC) from transesterification of ethylene carbonate (EC) with methanol. High temperature, high carbon dioxide pressure, and longer reaction time were favorable for the reactivity of BMImBr-AS. The catalyst can be reused for the reaction up to three consecutive runs with a slight decrease of its catalytic activity.     

Zn-VCO3 hydrotalcite: A highly efficient and reusable heterogeneous catalyst for the Hantzsch dihydropyridine reaction

The Zn-VCO₃ hydrotalcite was found to be an excellent solid catalyst for the one-pot synthesis of triphenylpyridine-3,5-dicarboxamide via Hantzsch reaction of acetoacetanilide, ammonium hydroxide and various aromatic aldehydes. The combinatorial syntheses were achieved for the first time using hydrotalcite as a heterogeneous catalyst. The catalyst was active for the Hantzsch reaction in water at 60 °C. The products were isolated in good yields (85–93%) with short reaction times (2–3 h). The resulting substituted dihydropyridines were characterized and confirmed by ¹H and ¹³C NMR, FTIR, and HRMS spectral data and the solid catalyst was characterized by XRD, BET, SEM and TEM. The newly synthesized heterogeneous solid catalyst offers simple means for recovery and the isolated catalyst was reused for five rounds for the synthesis of compound 4a, without significant loss of catalytic activity. For all the other reactions carried out with the recycled catalyst, results were similar to with the fresh catalyst.     

Au anchored to (α-Fe2O3)-MCM-41-HS as a novel magnetic nanocatalyst for water-medium and solvent-free alkyne hydration

A novel catalytic system based on Au nanoparticle functionalized magnetic mesoporous silica was prepared as (α-Fe₂O₃)-MCM-41-HS-Au. This material was obtained through the reaction of ordered mesoporous silica-coated magnetic nanoparticles (α-Fe₂O₃)-MCM-41, (3-mercaptopropyl) trimethoxysilane (MPTMS) and HAuCl₄. This catalyst was extensively characterized by various techniques such as SEM, TEM, XRD, EDX, IR and N₂-sorption isotherm. Very uniform dispersion and ordered mesopores of (α-Fe₂O₃)-MCM-41-SH (about 2–3 nm) causes Au nanoparticles to be distributed very finely on the pore surfaces, resulting in a very useful and robust magnetically recyclable catalyst for water-medium and solvent-free alkyne hydration.     

Supported imidazole as heterogeneous catalyst for the synthesis of cyclic carbonates from epoxides and CO2

Imidazole anchored onto a silica matrix, by means of a propyl linkage, is found to be an effective heterogeneous catalyst for the synthesis of cyclic carbonates from epoxides and CO₂ in near quantitative yield. The versatility of this catalyst is demonstrated by using different substrates (epichlorohydrin, propylene oxide, butylene oxide and styrene oxide) for this cycloaddition reaction. These CO₂ insertion reactions were typically carried out in the temperature range of 343 to 403 K at 0.6 MPa CO₂ pressure under solvent-free conditions. Several spectroscopic methods were used to characterize the catalyst and study the integrity of the fresh and spent catalysts.     

Magnetically separable Pt catalyst for asymmetric hydrogenation

A magnetic Pt/SiO₂/Fe₃O₄ catalyst consisting of chirally modified platinum supported on silica coated magnetite nanoparticles was prepared using an easy synthetic route and successfully applied for the enantioselective hydrogenation of various activated ketones. The magnetic catalyst modified with cinchonidine showed a catalytic performance (activity, enantioselectivity) in the asymmetric hydrogenation of various activated ketones in toluene comparable to the best known Pt/alumina catalyst used for these reactions. The novel catalyst can be easily separated from the reaction solution by applying an external magnetic field and recycled several times with almost complete retention of activity and enantioselectivity.     

Magnetically retrievable nanoscale nickel ferrites: An active photocatalyst for toxic dye removal applications

Nickel ferrite (NiFe₂O₄) nanoparticles were synthesized through the sol-gel auto-combustion method using urea and glycine as mixed fuel. The prepared nanoparticles were investigated for their structural, optical, and magnetic characterizations. Rietveld refined X-ray diffraction (XRD) patterns revealed the development of single-phase cubic spinel. The crystallite size was calculated by using Modified Scherrer's method and the W-H plot was found in the order of 26.6 nm and 25.4 respectively which are nearly the same. The infrared spectrum showed the typical characteristic absorption bands in the range of 400 cm^-1 to 600 cm^-1 belonging to cubic spinel structure. Scanning electron microscopy images showed the spherical nature of the nanoparticles along with agglomeration to some extent. As per the optical study, the prepared nanoparticles have an optical bandgap of 2.59 eV. The magnetic properties were studied through the M − H hysteresis curve showing superparamagnetic nature, the value of saturation magnetization (M_s), coercivity (H_c) was observed 46.20 emu/gm, and 383.2 Oe respectively. The photocatalytic activity of nickel ferrite was studied based on the degradation of methylene blue (MB) dye as a model compound, where the result showed that prepared nanoparticles possessed a good photocatalytic activity against dye degradation. Up to four times catalyst exhibits nearly the same reutilization.     

The generation of hydroxyl radicals by hydrogen peroxide decomposition on FeOCl/SBA‐15 catalysts for phenol degradation

Iron oxychloride (FeOCl) supported on mesoporous silica (SBA‐15), as a Fenton‐like solid catalyst for phenol degradation, showed supreme activity for production of hydroxyl radical (HO·) by H₂O₂ decomposition, and the generation capacity was comparable to the conventional Fenton reagent (Fe²⁺+H₂O₂). The structure of FeOCl was characterized with spectroscopies. The generation of HO· species during the reaction was detected using 5,5‐dimethyl‐1‐pyrroline N‐oxide trapped electron paramagnetic resonance. Furthermore, the kinetics in detail was driven for the creation and diffusion of HO· by H₂O₂ decomposition over FeOCl, which follows a first‐order rate through a two‐step reaction. With the combination of the catalyst structure and kinetic parameters, the plausible mechanism for H₂O₂ decomposition during the oxidative degradation of phenol was rationalized. As a Fenton‐like solid catalyst, FeOCl/SBA‐15 is a promising alternative for the removal of low‐level organic contaminates from water. © 2014 American Institute of Chemical Engineers AIChE J, 61: 166–176, 2015     

Characterizations of TiO2/SiO2/Ni–Cu–Zn Ferrite Composite for Magnetic Photocatalysts

The TiO₂/SiO₂/Ni–Cu–Zn ferrite composite for magnetic photocatalysts with high photocatalytic activity is successfully prepared in this study. The composite are composed of spherical or elliptical Ni–Cu–Zn ferrite nanoparticles about 20–60 nm as magnetic cores, silica as barrier layers with thickness of 15 nm between the magnetic cores and titania shells with thickness approximately 1.5 nm. Photodegradation examination of TiO₂/SiO₂/ Ni–Cu–Zn ferrite composite was carried out in methylene blue (MB) solutions illuminated under a Xe arc lamp with 35 W and color temperature of 6000 K. The results indicated that about 47.1% of MB molecules adsorbed on the TiO₂/SiO₂/Ni–Cu–Zn ferrite composite within 30 min mixing due to it higher pore volume of 0.034 cm³/g, and after 6 h Xe lamp irradiation, 83.9% of MB 16.1% was photodegraded. Compared with the TiO₂ /Ni–Cu–Zn ferrite composite, the TiO₂/SiO₂/Ni–Cu–Zn ferrite composite with silica barrier layer prohibited the photodissolution and enhanced the photocatalytic ability. The magnetic photocatalyst shows high photocatalytic efficiency that the apparent first‐order rate constant k_obs is 0.18427 h^?1, and good magnetic property that the saturation magnetization (M_s) of is 37.45 emu/g, suggesting the magnetic photocatalyst can be easily recovered by the application of an external magnetic field.     

Amino Functionalized Nano Fe3O4@SiO2 as a Magnetically Green Catalyst for the One-Pot Synthesis of Spirooxindoles Under Mild Conditions

(3-Aminopropyl)-triethoxysilane attached to Fe₃O₄@SiO₂ nanoparticles has been characterized by powder X-ray diffraction, vibrating sample magnetometer, scanning electronic microscope, transmission electron microscope, energy dispersive X-ray, thermal gravimetric analysis, and Fourier transform infrared spectroscopy. The prepared nanoparticles employed as a heterogeneous catalyst in the synthesis of spirooxindoles derivatives in one-pot four-component reactions of isatin, methyl cyanoacetate or malononitrile, hydrazine hydrate, and ethyl acetoacetate. Amino-functionalized magnetic nanoparticles showed high catalytic activity in mild reaction conditions and excellent yields of products in short reaction times. Also, this nanocatalyst can be easily recovered by a magnet and reused for subsequent reactions for at least 5 times without noticeable loss in catalytic activity.     

RETRACTED ARTICLE: Optimization of Biodiesel Production Using a Magnetically Stabilized Fluidized Bed Reactor

A biodiesel production process using magnetically stabilized fluidized bed reactor (MSFBR) has been developed based on the refined cottonseed oil. The reactant flow rate and magnetic field intensity effects on the nanometer magnetic catalyst behavior in the column were investigated. Orthogonal experiments (L₄(2)³) were applied to optimize the best transesterification reaction conditions. Reaction temperature, methanol to oil molar ratio, and reactant flow rate were the main factors to influence transesterification conversion efficiency. These three factors chosen for the present investigation were based on the results of single-factor tests. The optimum transesterification reaction conditions of cottonseed oil were determined in MSFBR as follows: methanol to oil molar ratio 8:1, 40 cm³ min⁻¹ reactant flow rate, 225 Oe magnetic field intensity and reaction temperature of 65 °C, the conversion efficiency reached 97% in 100 min. The cold filter plugging point and kinematic viscosity of cottonseed oil biodiesel were higher than that described by Chinese specifications of biodiesel because of the special fatty acid profiles of cottonseed oil. The activity stability of the nanometer magnetic solid catalyst in MSFBR was much better than that in the autoclave stirred reactor (ASR).     

“Cat in a bag” recycling of dendrimer encapsulated Au nanoparticles by use of dialysis membrane bag in the reduction of 4-nitrophenol: proof of heterogeneous catalysis

Generation 4 PAMAM-NH₂ dendrimers were used as template to synthesize Au₁₃- and Au₁₀₀-dendrimer-encapsulated nanoparticles (Au-DENs) with an average diameter of 2.1 ± 0.3 and 3.1 ± 0.5 nm respectively. Au-DENs were characterized using various techniques. Catalytic recycling of Au-DENs using a dialysis membrane bag in the reduction of 4-NP is presented. The reduction process was primarily monitored by UV–vis spectroscopy at around λ 400 nm. The catalyst was found to exhibit a very good activity and stability even after more than 3 catalytic reaction cycles without any leaching, confirming that the reduction of 4-NP is purely a heterogeneous reaction.     

A new reactor coupling heterogeneous Fenton‐like catalytic oxidation with membrane separation for degradation of organic pollutants

BACKGROUND: There is growing interest in employing heterogeneous Fenton‐like catalysts in slurry to obtain higher activity. However, fine size particles create problems associated with recovery from the treated water. Therefore, it is highly desirable to develop a novel Fenton‐like process that not only has high degradation efficiency of organic pollutants, but also allows for easily reusing the catalysts. RESULT: A new reactor was investigated by coupling the heterogeneous Fenton‐like oxidation with membrane separation. Results showed that the FeY catalyst could be almost filtrated by a submerged micro‐filtration membrane in the reactor to continuously activate H₂O₂. For a FeY dose of 1 g L^?1 and a residence time of 120 min, the degradation efficiency of AO II reached 97%. CONCLUSIONS: In the new reactor, degradation of AO II occurred continuously and efficiently without an additional FeY separation process. The treatment capacity of this FeY catalyst for wastewater containing 100 mg L^?1 AO II in the reactor was estimated to be 82 times that of a reactor in which the catalyst could not be reused. The distinguishing technical feature of this reactor was the reuse of the Fenton‐like catalyst. Copyright © 2011 Society of Chemical Industry     

Heterogeneous Catalytic Polymerization of Ethylene in Microtubular Reactor Systems

The feasibility of using a microtubular reactor for heterogeneous polymerization of ethylene was investigated experimentally. Chemically inert polymer tubing of 800–2300 μm in inner diameter was fabricated and used as a polymerization reactor. Nonporous silica nanoparticles with a diameter of 400 nm were synthesized and used as support for the high‐activity rac‐ethylene(indenyl)₂ZrCl₂ catalyst with methylaluminoxane as cocatalyst and toluene as diluent. Large‐diameter microtubular reactors were also successfully used to conduct heterogeneous polymerization of ethylene in continuous reaction operations. High initial catalyst activity was obtained and the overall polymerization activity per volume or reactor length was quite high. No particle fragmentation occurred and the polymer particles were covered with small subgrains or nanofibrils with a diameter of 30 nm.     

Ferromagnetically modified zeolite catalysts for liquid-phase High–Throughput Experimentation

A novel method for the separation of heterogeneous catalysts from liquid-phase reactions in High–Throughput Experimentation (HTE) libraries was developed based on a magnetic recuperation procedure. Ferromagnetic iron nanoparticles were introduced in a set of zeolite structures by means of aqueous impregnation of an iron precursor, followed by reduction in H₂. The obtained magnetic zeolites can be efficiently stirred in the catalytic reaction mixture using conventional magnetic stirring bars and they are automatically separated by depositing on the magnetic bar when the stirring is stopped. Characterization techniques demonstrated that the iron nanoparticles are distributed on the external surface of the zeolites, where the interference with the catalytic active sites is limited. Catalytic tests of a High-Throughput library of 10 wt. % Fe magnetic zeolites, performed using the liquid-phase benzylation of toluene with benzyl alcohol as test reaction, showed that the modified catalysts can be very easily and efficiently separated from the reaction mixture while they retain similar activity and selectivity to that of the unmodified samples.     

Catalytic performance of zinc containing ionic liquids immobilized on silica for the synthesis of cyclic carbonates

Cycloaddition of carbon dioxide and epoxides was investigated using zinc halide based Lewis acidic ionic liquids (ILs) as catalysts. ILs such as 1-butyl-3-methylimidazolium bromide (BMImBr), 1-butylpyridinium bromide (BPyBr), tetra-n-butylammonium bromide (TBABr) were mixed with zinc halide and supported on silica gel to produce heterogeneous catalysts. Catalytic reaction tests demonstrated that the incorporation of zinc ions can significantly enhance the catalytic activity of the silica-supported ILs for the cycloaddition of CO₂ to epoxides in solvent-free conditions. BPyBr-ZnCl₂/SiO₂ showed the highest propylene carbonate yield of 98% when the reaction was carried out with 0.5 g of catalyst at 120 °C at 1.89 MPa of CO₂ pressure for 4 h. The immobilized zinc containing IL catalyst could be reused for at least four cycles without any considerable loss of its activity.     

Fibrous material based on a combination of poly(acrylic acid‐co‐hydroxyethyl methacrylate) with iron ions as a heterogeneous Fenton catalyst for dye oxidative decomposition

The Fenton method has been used to remedy dye wastewater because hydroxyl radicals generated from the Fenton reaction can oxidize the dye into small molecules. In comparison with a homogeneous reaction, a heterogeneous reaction with a solid material as a catalyst is a more appropriate alternative for dye wastewater treatment. Because of the large specific surface area and excellent applicability, a novel fibrous material based on a combination of functional polymer with iron ions was designed in this study and used as a heterogeneous catalyst for dye wastewater treatment by the Fenton method. The fibrous material was found to have good catalytic activity for the oxidative decomposition of a variety of dyes and good reusability; additionally, the fibrous material could remove the dye to a greater extent and leave fewer iron ions in the treated wastewater than a homogeneous Fenton catalyst such as iron(II) chloride (FeCl₂). What is more, the fibrous material could adsorb the residual iron ions from the treated wastewater and make these iron ions take part in the next catalyzation. The previous results make us believe that the prepared fibrous material might be used to create a green approach for dye wastewater treatment. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44875