Catalysts For Oxidation Reactions Research Articles

Preparation of thin film gold based catalysts for oxidation reactions in liquid and gas phases

This work deals with the preparation of gold on titania catalysts to make catalytic films in the less than 100nm thickness area and its comparison with usual powder catalyst in catalytic oxidation reactions in gas and liquid phases. Titania was coated on glass plates with different thicknesses, but with ultra-low surface roughness (<5Å). Gold deposition was performed with usual chemical method for catalysts preparation, that is deposition–precipitation with urea. Transmission electron microscopy showed that planar samples are decorated with a high quantity (>10wt.% with respect to TiO2) of gold nanoparticles smaller than 2.5nm, with a narrow size distribution. Activity in CO oxidation demonstrates the catalytic behavior of the planar samples, although they are less active than powder catalyst because of the different geometries of the reactors and catalysts. In contrast, their catalytic performances in liquid phase, benzyl alcohol oxidation, are comparable. These results validate the concept that gold planar catalysts prepared by chemical methods can present similar catalytic behavior as real powder gold catalysts. Such planar catalysts could be useful for bridging the material gap between real and model catalysts in advanced techniques, such as scanning tunnelling microscopy and spectroscopy or high-pressure photoelectron spectroscopy.

Comparison of Porous Iron Trimesates Basolite F300 and MIL-100(Fe) As Heterogeneous Catalysts for Lewis Acid and Oxidation Reactions: Roles of Structural Defects and Stability

Two porous iron trimesates, namely, commercial Basolite F300 (Fe(BTC); BTC = 1,3,5-benzenetricarboxylate) with unknown structure and synthetic MIL-100(Fe) (MIL stands for Material of Institut Lavoisier) of well-defined crystalline structure, have been compared as heterogeneous catalysts for four different reactions. It was found that while for catalytic processes requiring strong Lewis acid sites, Fe(BTC) performs better, MIL-100(Fe) is the preferred catalyst for oxidation reactions. These catalytic results have been rationalized by a combined in situ infrared and 57Fe Mossbauer spectroscopic characterization. It is proposed that the presence of extra Bronsted acid sites on the Fe(BTC) and the easier redox behavior of the MIL-100(Fe) could explain these comparative catalytic performances. The results illustrate the importance of structural defects (presence of weak Bronsted acid sites) and structural stability (MIL-100(Fe) is stable upon annealing at 280 °C despite Fe3+-to-Fe2+ reduction) on the catalytic...

A recyclable polymer anchored copper(II) catalyst for oxidation reaction of olefins and alcohols with tert-butylhydroperoxide in aqueous medium

Abstract A new reusable polymer anchored Cu(II) complex was synthesized which can acts as an efficient heterogeneous catalyst for oxidation of olefins and alcohols with tert -butylhydroperoxide (TBHP) in aqueous medium. The present catalyst well oxidized styrene and other olefins to their allylic products and alcohols were converted to their corresponding aldehydes in good-to-moderate yields. This catalyst can be easily recovered by filtration and recycled without significant loss of its catalytic performances.

テトラフェニルポルフィリンコバルト(II)触媒のシリカ被覆およびその酸化反応特性

テトラフェニルポルフィリンコバルト(II)触媒のシリカ被覆およびその酸化反応特性

Preparation and characterization of Fe-doped TiO2 nanoparticles as a support for a high performance CO oxidation catalyst

A simple method is described for the preparation of Fe-doped TiO2 nanoparticles (Ti1−xFexO2) that can be used as a high performance support material for a CO oxidation catalyst. The method allows one to fabricate Ti1−xFexO2 with uniform sizes and shapes. Microstructural studies using XRD, Raman spectroscopy and EPR analyses indicate that the Fe dopant is substitutionally incorporated by replacing Ti4+ cations. Electrochemical results indicate that, when a small amount of Fe molecules (less than 8 atomic%) are incorporated into a TiO2 structure, the support material has greatly improved redox characteristics. This suggests that an Fe-doped TiO2 support enhances both the release and uptake of oxygen atoms from the catalysts, thus resulting in a high catalytic activity in CO oxidation reactions. The results confirmed that a Au catalyst supported on Fe-doped TiO2 containing a 6 atom% Fe dopant showed an outstanding oxidation performance. The findings reported herein represent an innovative route to designing high performance catalysts for oxidation reactions.

Nitrogen‐Doped Carbon Nanotubes as a Highly Active Metal‐Free Catalyst for Selective Oxidation

Catalytic reactions are generally carried out on supported metals or oxides, which act as an active phase and require impregnation and thermal treatment steps. During tests, the metal or oxide nanoparticles could be further sintered, which would induces deactivation. Direct incorporation of the active phase into the matrix of a support could be an elegant alternative to prevent catalyst deactivation. Here, we report that nitrogen-doped carbon nanotubes (N-CNTs) can be efficiently employed as a metal-free catalyst for oxidative reactions that allow the selective transformation of the harmful, gaseous H(2)S into solid sulfur. The catalyst exhibits a high stability during the test at high space velocity. The macroscopic shaping of the catalyst on the silicon carbide foam also increases its catalytic activity by improving the contact between the reactants and the catalyst. Such macroscopic shaping allows the avoidance of problems linked with transport and handling of nanoscopic materials and also reduces the pressure drop across the catalyst bed to a large extent.

ChemInform Abstract: Metal—Organic Frameworks as Heterogeneous Catalysts for Oxidation Reactions.

AbstractReview: 91 refs.

Use of immobilized transition metal complexes as recyclable catalysts for oxidation reactions with hydrogen peroxide as oxidant

A tetradentate Schiff base (teta), obtained from triethylenetetramine and salicylaldehyde, has been covalently bonded to divinylbenzene cross-linked chloromethylated polystyrene. This chelating ligand, abbreviated as PS-teta (PS = polymeric support), reacts with metal chlorides (Cu2+, Co2+, and Ni2+) in methanol to give polymer-bound transition metal complexes, PS-Cu(II)teta/(Cat-1), PS-Ni(II)teta/(Cat-2), and PS-Co(II)teta/(Cat-3), formation of which has been established by various physiochemical methods and spectroscopic techniques. The catalytic potential of these materials has been tested for the oxidation of various alkenes, alkanes, alcohols, and thioethers in the presence of 30% H2O2 as an oxidant. At the same time, these catalysts are very stable and could be reused in oxidation reactions for more than five times without noticeable loss of their catalytic activity.

Platinum Ruthenium Nanotubes as Methanol Oxidation Reaction Catalysts

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ChemInform Abstract: Synthesis of Catalytically Active Ruthenium Complexes with a Remote Chiral Lactam as Hydrogen‐Bonding Motif.

AbstractA novel ruthenium complex is prepared and tested as chiral catalyst in oxidation reactions.

Metal–organic frameworks as heterogeneous catalysts for oxidation reactions

In this Perspective, we describe the use of metal–organic frameworks (MOFs) as heterogeneous catalysts for oxidations using hydroperoxides or molecular oxygen. These two types of oxidants fulfill the requirements of green chemistry in terms of environmental benignity and sustainability. For the sake of clarity and to illustrate the possibilities of using MOFs as oxidation catalysts, we have constrained ourselves to present the results obtained for the oxidation of cycloalkanes, oxidation of benzylic positions, oxidation of cycloalkenes and aerobic oxidation of alcohols. The use of MOFs as catalysts for enantioselective oxidations has been dealt with in a separate section in which the peculiarity of the required oxidants and the advantages of having homo chiral MOFs have been discussed. The key features of MOFs as catalysts, the similarities with inorganic porous solids and future developments in this field have been discussed in separate sections.

Preparation of ultra low loaded Au catalysts for oxidation reactions

Cyanide leaching was used to obtain Au/SiO2 catalysts with very low gold loadings. A number of catalysts with a nominal 5 wt% target loading were prepared using impregnation and deposition precipitation techniques and these were found to be active catalysts for the solvent-free aerobic oxidation of benzyl alcohol. Exposure of these catalysts to a basic solution of NaCN for 10 min leached gold from the materials to give very pale pink catalysts which were found to contain just 0.06 wt% Au. The concentration of Au removed from the catalyst was constant regardless of the length of NaCN exposure. When the cyanide leached materials were employed for benzyl alcohol oxidation under the same conditions as the unleached parent catalysts, the conversions were identical. However, when the catalytic activity was normalised to the Au content (determined by ICP analysis) the TOFs were much higher for the NaCN treated catalysts (> 400,000 h(-1)). These results clearly demonstrate that NaCN leaching is an effective route to the development of catalysts containing very low gold content, whilst maintaining high activity. The leached materials were found to comprise metallic Au nanoparticles. The successful utilisation of ultra low loaded Au catalysts for selective oxidation, where the majority of the Au present is active and 98% of the spectator Au is removed, makes the industrial application of such materials more economically viable. Information obtained through the identification of these active structures using state of the art techniques may provide useful insights into how the reaction proceeds on the Au surface.

The reaction mechanism of the high temperature ammonia oxidation to nitric oxide over LaCoO 3

Perovskites are promising catalysts for oxidation reactions. Good NO selectivity is reported for the oxidation of ammonia into nitric oxide over LaCoO 3. More interestingly over this catalyst very little N 2O is produced, which makes it a potential candidate for industrial ammonia oxidation. In order to further develop perovskite catalysts, an understanding of the reaction mechanism is necessary. Steady-state, TAP and oxygen exchange experiments over LaCoO 3 have been carried out. A reaction mechanism that describes the product distribution (NO, N 2O and N 2) as a function of the oxidation degree of the catalyst has been proposed. The reaction proceeds by a Mars and Van Krevelen mechanism. NO and N 2O are formed through parallel routes from ammonia via surface nitroxyl (HNO) species. Formation of nitrogen occurs through at least three routes. Decomposition of both reaction products NO and N 2O leads to N 2, the latter decomposition being the fastest. The third route to N 2 consists of the reaction of adsorbed ammonia with short-lived oxygen surface species, such as peroxide or superoxide species.

Synthesis, Analysis and Possibility Application of Cyclic and Linear Forms of Poly(Aspartic Acid) Synthesized Under Microwave Irradiation

In this paper a new original method of synthesis of poly(aspartic acid) (PAA) from aspartic acid (AA) or maleic anhydride under microwave irradiation is presented. The syntheses carried out mainly without the catalyst, received higher yield in comparison for conventional method. PAA has been characterized by nuclear magnetic resonance (1H NMR, 13C NMR), infrared spectroscopy (FT-IR) and termogravimetric analysis (Tg). Obtained polymer we used for several diversified applications, such as, medicine, agriculture and catalyst for oxidation reactions.

New Catalysts Based on Poly(aspartic acid) for Oxidation Reaction

In the current work we describe synthesis of novel poly(D, L-aspartic acid) catalysts for oxidation reactions. The catalysts were prepared by a three-step reaction procedure. First, poly(D, L-aspartic acid) (PAA) was synthesized by polycondensation reaction D, L-aspartic acid with propylene carbonate under microwave irradiation. In the second stage, poly(aspartic acid) sodium salt (PAA-Na) was obtained during the reaction of hydrolysis of cyclic forms of PAA in water solutions of sodium. The last stage of catalysts synthesis were reaction of poly(aspartic acid) sodium salt with cobalt or copper acetate. FTIR, 1H NMR, SEM, SEM-EDS, and SIMS were employed for characterization of the obtained catalysts were employed for characterization of the obtained catalysts. Oxidation reactions of some compounds were carried out on synthesized catalysts at atmospheric pressure in the presence of molecular oxygen. As the main products epoxides and ketone were obtained with very high yield and selectivity.

Zeolite-encapsulated M(Co, Fe, Mn)(SALEN) complexes modified glassy carbon electrodes and their application in oxygen reduction

Zeolite-encapsulated transition metal complexes of SALEN [N, N′-bis(salicylidene) ethylenediamine] have been used as catalysts of oxidation reactions of hydrocarbons with oxidants including dioxygen. But in these processes molecular oxygen as oxidant did not show good activity compared with other oxidants such as TBHP, PhIO and H 2O 2. In order to evaluate the catalytical effect of the hybrid materials on the process of activating molecular oxygen, zeolite-encapsulated M(Co, Fe, Mn)(SALEN) complexes modified glassy carbon electrodes [M(SALEN)/Y/GCEs (M = Mn, Fe, Co)] were prepared and used as electrocatalysts of oxygen reduction reaction (ORR). The electrocatalytic reduction of dioxygen, thus, was investigated by cyclic voltammetry (CV) and chronocoulometry (CC) at glassy carbon electrodes (GCEs) modified with metal (Co, Fe, Mn) complexes of SALEN encapsulated inside NaY in pH 6.90 aqueous solutions. The results have shown that the M(SALEN)/Y/GCEs (M = Mn, Fe, Co) exhibited efficient electrocatalytic activity towards dioxygen reduction with reduced overpotentials of about 505 mV, 393 mV and 397 mV for Co(SALEN)/Y, Fe(SALEN)/Y and Mn(SALEN)/Y, respectively, lower than bare GC electrode and enhanced peak currents. The electroreduction of O 2 on these modified GCEs is an irreversible and diffusion-controlled process. The transferred number of electrons and the transfer coefficient for dioxygen reduction reaction were determined by CV and CC. These results suggest that zeolite-encapsulated M(Co, Fe, Mn)SALEN complexes can efficiently activate molecular oxygen by decreasing the overpotential and increasing current of oxygen reduction reaction. And dioxygen is reduced to form water in the process. The significance of this work lies in evaluating the catalysis of the hybrid catalysts for oxidation reaction by electrochemical techniques.

Porphyrin−Kaolinite as Efficient Catalyst for Oxidation Reactions

The preparation, characterization, and application in oxidation reactions of new biomimetic catalysts are reported. Brazilian Sao Simao kaolinite clay has been functionalized with [meso-tetrakis(pentafluorophenyl)porphinato]iron(III), Fe(TPFPP). To obtain the functionalized clay, the natural clay was purified by dispersion-sedimentation, expanded by insertion of dimethyl sulfoxide (DMSO), and functionalized with amino groups by substitution of DMSO with ethanolamine. These previous steps allowed clay functionalization with Fe(TPFPP), leading to a layered material with a basal spacing of 10.73 A. Clay functionalization with the porphyrin was confirmed by formation of the secondary amine, as demonstrated by FTIR bands at 3500-3700 cm(-1). UV-vis spectroscopy revealed a red shift in the Soret band of the iron porphyrin in the functionalized material as compared to the parent iron porphyrin catalyst in solution, indicating Fe(III)P --> Fe(II)P reduction. The catalytic performance of the functionalized clay was evaluated in the epoxidation of cyclooctene, with complete selectivity for the epoxide (100% epoxide yield), and ketonization of cyclohexane, cyclohexanone being the major product. The novel catalyst was also evaluated in the Baeyer-Villiger (BV) oxidation of cyclohexanone, with 85% conversion of cyclohexanone in epsilon-caprolactone, with total selectivity to epsilon-caprolactone.

Aluminosilicate obtained by sol–gel process as support for an anionic iron porphyrin: Development of a selective and reusable catalyst for oxidation reactions

An anionic iron(III) porphyrin was immobilized on a synthetic aluminosilicate obtained by the sol–gel process and used as catalyst in the oxidation of organic substrates. Aluminosilicate was prepared by modification of a method previously described in the literature, using an ethanol/water solution of AlCl 3·6H 2O and Si(OC 2H 5) 4 (TEOS). Iron(III) porphyrin immobilization was carried out using magnetic stirring and reflux, and a good immobilization rate (88%) was obtained. Immobilization of a neutral iron(III) porphyrin on the solid was also tested, without success. The obtained materials were characterized by ultraviolet–visible and infrared spectroscopies, X-ray diffraction, TGA analysis, nitrogen absorption, and electron paramagnetic resonance (EPR). The catalytic activity of the immobilized iron(III) porphyrin was evaluated in the oxidation of cyclooctene, cyclohexane, and n-heptane, using iodosylbenzene as the oxygen donor. The results obtained in the present study show that the novel immobilized catalyst is a promising system for efficient and selective oxidation reactions. Besides that, the stable interaction between the iron(III) porphyrin complex and the support enables reuse of the heterogeneous catalyst.

Characterization and Catalytic Properties of Surface La-rich LaFeO3Perovskite

(B = transition metal) oxides are proved to be highly active catalysts for oxidation reactions in connection with air pollution control. Especially, they are considered as potential catalysts in substitution of noble metal catalysts because of their high thermostability. Many investi-gators have suggested that oxygen vacancies in the perovskite oxides play a major role in catalytic oxidations although there is still debate on the origin of their catalytic activity.

Immobilization of anionic iron(III) porphyrins into ordered macroporous layered double hydroxides and investigation of catalytic activity in oxidation reactions

The first generation anionic iron(III) porphyrin [Fe(TSPP)] and the second generation anionic complexes [Fe(TDFSPP)], [Fe(TCFSPP)], and [Fe(TDCSPP)] were immobilized into three-dimensionally macroporous layered double hydroxide (3DM-LDH), using the direct reconstruction of 3DM-LDH from macroporous mixed oxides MOX or the anionic exchange on DDS intercalated 3DM-LDH. The macroporous layered double hydroxides were obtained at the surface of nanometric polystyrene spheres, which were synthesized by an inverse opal method. Polystyrene was removed after calcination in oxidizing atmosphere, nanostructured mixed oxides (3DM-MOX) were obtained, which after reconstruction give origin to macroporous layered double hydroxide (3DM-LDH). Following metalloporphyrin immobilization, the resulting materials were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), UV–vis (glycerin mull) spectroscopy, attenuated total reflectance Fourier transform infrared spectroscopy (ATR/FTIR), and electron paramagnetic resonance (EPR). Results revealed that the complexes are either immobilized at the surface of the macroporous layered double hydroxide or intercalated between the layers, displacing some dodecylsufate anions. The obtained materials were investigated as catalysts for oxidation reactions, to find out whether they function as cytochrome P-450 models.