Dioxygen Affinities and Catalytic Oxidation Performance of Cobalt （Ⅱ）Complexes with N—Aryl Hydroxamic Acid

The oxygenation of cobalt(Ⅱ) hydroxamates(CoL2) and its catalytic performance in oxidation of p-xylene to p-toluic acid (PTA) were examined.The effects of X and Y bonded to hydroxamate group on dioxygen affinities and catalytic oxidation performance were also investigated.     

Synthesis,O_2-binding ability and catalytic oxidation performance of cobalt(Ⅱ) complexes with dihydroxamic acid functionalized N-pivot lariat ethers

Novel Co(Ⅱ) complexes with dihydroxamic acids functionalized N-pivot lariat ether CoL~1-CoL~4 were synthesized and characterized.Their oxygenation constants(ln K_(O2)) and thermodynamic parameters(△H°,△S°) were measured.And their catalytic performance in oxidation of p-xylene to p-toluic acid(PTA) was investigated.The enhancement of O_2-binding and catalytic oxidation activity by the oxa aza crown ether ring of the cobalt complexes were discussed.     

Co,K-supported Hexagonal Mesoporous Silicas for Catalytic Oxidation of 4-t-Butyltoluene

<正>Co,K-Supported hexagonal mesoporous silicas(HMS) have been prepared by incipient wetness impregnation with cobalt acetate tetrahydrate and potassium acetate as metal precursors,and ethylene glycol as impregnation solvent.The products have been characterized via powder X-ray diffraction,N_2 adsorption-desorption isotherms and diffuse reflectance UV-Vis spectroscopy.The divalent cobalt with a tetrahedral oxygen coordination exists mainly in the calcined samples.The catalytic properties have been tested for the oxidation of 4-t-butyltoluene with dioxygen in liquid phase at mild conditions.The products offered good catalytic activities in the oxidation reactions.Co-K-HMS catalyst with loading 4%Co and 2%K(mass fraction) affords a higher yield(22.4%) of 4-t-butylbenzaldehyde at a conversion of 28.3%under the reaction conditions.Adding a proper amount of potassium in Co-HMS results in an improvement catalytic activity and stability.     

Electrocatalytic Behavior of Metalloporphyrins(Ⅶ)——Kinetic Study of Cysteine Oxidation on Heat-Treated Cobalt Tetramethoxyphenyl Porphyrin Adsorbed on Graphite

The metnoas or rotating ring-disc electrode(RRDE) ana cyclic voltammetry were used to study the oxidation of cgsteine on heat-treated cobalt tetramethoxyphenyl porphyrin adsorbed on graphite(Co-TMPP/graphite) in solutions of various pH.Experimental results showed that Co-TMPP/graphite exhibits significant catalytic activity for cysteine oxidation in solutions with various pH.The current efficiency of cysteine oxidation on Co-TMPP/graphite in basic media is more than 90%.It was found that the kinetics of cysteine oxidation on Co-TMPP/graphite is a simple irreversible reaction controlled by rate of charge transfer.The standard rate,constants(k) of cysteine oxidation were calculated and the reaction mechanism of this reaction in solutions of various pH wes discussed.     

Dimerization of Propylene by Nickel （II） and Cobalt （II） Catalysts Based on Bidentate Nitrogen-phosphino Chelating Ligands

The catalytic property of propylene dimerization by several nickel (II), cobalt (II) complexes containing N-P bidentate ligands was studied in combination with organoaluminum co-catalysts. The effects of the type of aluminum co-catalysts and its relative amount, the nature of precursors in terms of ligand backbone and metal center were investigated. The results indicated that precursor I (N,-N-dimethyl-2-(diphenylphosphino)aniline nickel (II) dichloride)exhibited high activity in propylene dimerization in the presence of the strong Lewis acid Et3A12Cl3, whereas low productivity by its cobalt analogues was observed under identical reaction conditions.     

Role of Bismuth Oxide in Bi-MCo2O4（M=Co,Ni,Cu,Zn） Catalysts for Wet Air Oxidation of Acetic Acid

Two series of cobalt (Ⅲ)-containing spinel catalysts were prepared by the decomposition of the corre-sponding nitrates. The catalysts doped with bismuth oxide exhibit a higher activity in the wet air oxidation ofacetic acid than those without dopant bismuth oxide. The catalysts were investigated by XRD, TEM, ESR,UV-DRS and XPS, and the interaction between Co and Bi was studied as well. It has been found that nano-sized bismuth oxide is paved on the surface of cobalt spinel crystal and the structures of cobalt(Ⅲ)-containingspinel are still maintained. The shift of the binding energy of Bi4/7/2 is related to the catalytic activity of thesecatalysts doped with bismuth oxide.     

Effects of oxidation pretreatment temperature on Kovar used as CO_2 reforming catalyst

The effect of oxidation pretreatment temperature(500 ~ 1 000 ℃) on the catalytic activity of Kovar applied on hydrocarbon CO2reforming was examined. Catalytic performance evaluation using tetradecane at 800 ℃ with 70 μmol/s CO2revealed 700 and 1 000 ℃ as the best pre-oxidation temperature in producing CO and H2,respectively. XRD and SEM-EDX analyses showed that a separate metal oxide layer composed of iron oxide(Fe2O3and F3O4),nickel,cobalt,and possibly their respective oxides started to form when oxidation was conducted at 700 ℃ or higher.The presence of iron enhanced the stability of nickel in the structure while the compact structure of Fe3O4resulted into the formation of a thick and rigid metal oxide layer on the surface of the Kovar tube. The strong physical bond between the metal oxide layer and Kovar tube provided the catalyst good mechanical strength and consequently good catalytic activity.     

SYNTHETIC AND CATALYTIC PROPERTY STUDIES ON SILICA SUPPORTED BIS-(ACETYLACETONATO) COBALT(Ⅱ) COMPLEXES**

This paper reports mainly the preparation of silica supported acetylacetone ligands and their cobalt complexes, the characterization of their chemical structure, and the evaluation of their catalytic activity in the reaction for the preparation of ethers directly from alkanols and benzyl chloride. The results indicate that those silica supported β-diketone cobalt complexes (SACO) not only can simplify the reaction procedure of the ether preparation but also show a much higher catalytic activity in comparison with other homogeneous catalysts. In addition, SACO can be recovered and reused although their catalytic activity descend gradually as a result of the decrease in their cobalt content.     

Dioxygen Affinity and Catalytic Performance of Bis-(furaldehyde) Schiff Bases Co(II) Complexes in Cyclohexene Oxidation

As mimetic oxygen carrier or oxidation catalyst, Schiff base cobalt complexes such as Co (II) salen have been widely studied1-4. However their high-price greatly limited their application. The synthesis of cheap furaldehyde Schiff bases and their complexes with Co (II), as well as the dioxygen affinity and biomimetic catalytic oxidation performance of these complexes are worth trying to study. In this paper, the saturated dioxygen uptake of cobalt complexes with different bis-(furaldehyd…     

Studies on PNPP Hydrolysis Catalyzed by Schiff Base Cobalt（Ⅱ） Complexes Containing Benzoaza-15-crown-5

Three novel Schiff base cobalt（Ⅱ） complexes containing benzoaza-15-crown-5, CoL^1, CoL^2 and CoL^3 were synthesized and characterized, and these complexes were used in catalytic hydrolysis of carboxylic ester （PNPP, p-nitrophenyl picolinate） as mimic hydrolytic metalloenzyme. The analysis of specific absorption spectra of the hydrolytic reaction systems indicated that the catalytic hydrolysis involved the key intermediates formed by PNPP with cobalt（Ⅱ） complexes. The CoL^3 bearing the electron withdrawing group shows better catalytic activity due to its stabilization effect on active species MLS^-. The catalytic mechanism of PNPP hydrolysis was also proposed. The kinetic parameter of PNPP catalytic hydrolysis has been calculated and the activation energy for the catalytic hydrolysis is 43.69, 39.76 and 35.44 kJ·mol^-1, respectively.     

Prospects and crucial problems in oligomerization and polymerization with iron and cobalt complex catalysts

<正>The discovery of highly active 2,6-bis(imino)pyridyl iron and cobalt complexes provided a milestone of latetransition metal catalysts for ethylene oligomerization and polymerization with being currently investigated for the scale-up process.The crucial problems are remaining in the catalytic systems:the catalytic systems targeting ethylene polymerization produce more oligomers at elevated reaction temperatures,however,there is a recognizable amount of high-molecular-weight polyethylene remained in the modified catalytic system for the oligomerization process.Beyond the modification of bis(imino)pyridyl metal complexes,several alternative procatalysts' models have been developed in our group.This review highlighted the achievements in exploring new iron and cobalt complexes with tridentate NNN ligands as procatalysts for ethylene oligomerization and polymerization.     

Cobalt catalysts supported on silica nanotubes for Fischer-Tropsch synthesis

Silica nanotubes(SNT) have been synthesized using carbon nanotubes(CNT) as a template.Silica-coated carbon nanotubes(SNT-CNT) and SNT were loaded with a cobalt catalyst for use in Fischer-Tropsch synthesis(FTS).The catalysts were prepared by incipient wetness impregnation and characterized by N2 physisorption,X-ray diffraction(XRD),hydrogen temperature programmed reduction(H2-TPR) and transmission electron microscopy(TEM).FTS performance was evaluated in a fixed-bed reactor at 493 K and 1.0 MPa.Co/CNT and Co/SNT catalysts showed higher activity than Co/SNT-CNT in FTS because of the smaller cobalt particle size,higher dispersion and stronger reducibility.The results also showed that structure of the support affects the product selectivity in FTS.The synergistic effects of cobalt particle size,catalytic activity and diffusion limitations as a consequence of its small average pore size lead to medium selectivity to C5+ hydrocarbons and CH4 over Co/SNT-CNT.On the other hand,the Co/CNT showed higher CH4 selectivity and lower C5+ selectivity than Co/SNT,due to its smaller average pore size and cobalt particle size.     

Oxidation of 2,2＇-Dihydroxy-3,3＇-di-tert-buty-5,5＇-dimethoxyl-biphenyl to 3,3＇-Di-tert-butylbiphenyl-2,5,2＇,5＇-diquinone with Copper（Ⅱ）Chloride as Catalyst：Synthesis,Structure and Spectral Properties of Diquinone

Use of free air as oxidant and copper(II)chloride as catalyst,3,3'-di-tert-butylbi-phenyl-2,5,2',5'-diquinone(BBDQ)was prepared via catalytic oxidation of 2,2'-dihydroxy-3,3'-di-tert-butyl-5,5'-dimethoxy-biphenyl(di-BHA).The yield of reaction attained 95% and the selectivity for BBDQ was 100%.The single-crystal X-ray diffraction analysis reveals that the dihedral angle between two rings(benzene rings for di-BHA and quinone rings for BBDQ)changes from 89.8 to 45.3o,indicating the steric hindrance effects of methyl disappear in the oxidation process.The crystal structures of di-BHA and BBDQ are further confirmed by their spectral characterizations.The probable mechanism for this oxidation process is also discussed.     

Additive effects of alkaline-earth metals and nickel on the performance of Co/γ-Al_2O_3 in methane catalytic partial oxidation

Nano-sized γ-alumina (γ-Al2O3) was first prepared by a precipitation method. Then, active component of cobalt and a series of alkaline- earth metal promoters or nickel (Ni) with different contents were loaded on the γ-Al2O3 support. The catalysts were characterized by N2 adsorption-desorption, X-ray diffraction (XRD) and thermogravimetry analysis (TGA). The activity and selectivity of the catalysts in catalytic partial oxidation (CPO) of methane have been compared with Co/γ-Al2O3, and it is found that the catalytic activity, selectivity, and stability are enhanced by the addition of alkaline-earth metals and nickel. The optimal loadings of strontium (Sr) and Ni were 6 and 4 wt%, respectively. This finding will be helpful in designing the trimetallic Co-Ni-Sr/γ-Al2O3 catalysts with high performance in CPO of methane.     

邻二甲苯选择氧化V-Ti-O复合氧化物超细微粒催化剂

The structure and catalytic properties of V Ti O ultrafine particle catalyst for selective oxidation of o xylene have been studied. TEM and XRD results show that the particle size is in the range of 20～40 nm, and vanadium oxide is highly dispersed in TiO 2 (anatase). The catalytic activity of the V Ti O ultrafine particle catalyst for selective oxidation of o xylene to phthalic anhydride(PA) is higher than that of the larger oxide particles with the same catalyst composition prepared by impregnation and coprecipitation methods, indicating that the ultrafine V Ti O oxide particles are potentially new catalytic materials for the selective oxidation of o xylene to phthalic anhydride.     

Recent Progress in Direct Partial Oxidation of Methane to Methanol

The direct conversion of methane to methanol has attracted a great deal of attention for nearly a century since it was first found possible in 1902, and it is still a challenging task. This review article describes recent advancements in the direct partial oxidation of methane to methanol. The history of direct oxidation of methane and the difficulties encountered in the partial oxidation of methane to methanol are briefly summarized. Recently reported developments in gas-phase homogeneous oxidation, heterogeneous catalytic oxidation and liquid phase homogeneous catalytic oxidation of methane axe reviewed.     

Efficient oxidation of ethylbenzene catalyzed by cobalt zeolitic imidazolate framework ZIF-67 and NHPI

Efficient catalytic oxidation of ethylbenzene to acetophenone was realized using the catalytic system of cobalt zeolitic imidazolate framework ZIF-67/N-hydroxyphthalimide （NHPI） under mild conditions. 95.2% conversion of ethylbenzene with 90.3% selectivity to acetophenone could be obtained at 373 K under 0.3 MPa 02 for 9 h. The results show that there exists synergetic effect between ZIF-67 and NHPI. 1-Phenylethyl hydroperoxide （PEHP） was generated via a radical process involving the hydrogen abstraction from ethylbenzene by phthalimide N-oxyl, and subsequently effectively decomposed to acetophenone by ZIF-67.     

Steroid-bismetalloporphyrin as enzyme model of cytochrome P-450 monooxygenase

The model compounds of androgenic steroid-bismetallopor-phyrins 3a-3d and androgenic monometalloporphyrins 2a-2d have been synthesized. Catalytic study in two-phase condition on epoxidation of styrene under the catalysis of model catalysts shows (hat the catalytic performances of steriod-bismet-alloporphyrin is superior to steroid- metalloporphyrin and the corresponding simple metalloporphyrin. The excellent catalytic property of steriod-bismetallopotphyrin can be rationalized as the hydrophobic action of steroid framework and the cooperative action of two metalloporphyrins in catalysis.     

Kinetic Study of the Electro-Catalytic Oxidation of Hydrazine on Cobalt Hydroxide Modified Glassy Carbon Electrode

Electrocatalytic oxidation of hydrazine was investigated on a cobalt hydroxide modified glassy carbon (CHM-GC) electrode in alkaline solution. The process of oxidation involved and its kinetics were established by using cyclic voltammetry, chronoamperometry techniques as well as steady state polarization measurements. In cyclic voltammetry (CV) studies, in the presence of hydrazine the peak current increase of the oxidation of cobalt hydroxide is followed by a decrease in the corresponding cathodic current. This indicates that hydrazine is oxidized on the redox mediator that is immobilized on the electrode surface via an electrocatalytic mechanism. A mechanism based on the electrochemical generation of Co(IV) active sites and their subsequent consumption by the hydrazine in question was also investigated.     

OXIDATIVE ETHOXYCARBONYLATION OF ANILINE TO ETHYL PHENYLCARBAMATE CATALYZED BY SILICA- SUPPORTED POLY-γ-AMINOPROPYLSILOXANEMETAL COMPLEXES

Several silica-supported poly-γ-aminopropylsiloxane-monometal and bimetal complexes (Si-NH_2-M,M = Cu or Co ; Si-NH_2-Cu-M', M' =Co, Sn, Mn, Ni or Fe) have been prepared. Their catalytic properties for oxidative ethoxycarbonylation of aniline to ethyl phenylcarbamate have been investigated.The catalytic reaction was carried out under relatively mild conditions. The catalyst Si-NH_2-Cu-CO had high activity and selectivity, and the turn-over number (molar of aniline converted/molar of metal in Si-NH_2-Cu-CO added) could amount to 450 under the conditions: 150℃, 4 MPa (CO/O_2 =3) and 40 hours.The results of XPS and IR indicated that the coordination bonds were formed between nitrogen and metals in Si-NH2-Cu, Si-NH_2-Co and Si-NH_2-Cu-Co, and the coordination pattern was not single. In the oxidative ethoxycarbonylation of aniline to ethyl phenylcarbamate, the catalytic property of Si-NH_2-Cu-CO bimetallic complex was better than Si-NH_2-Cu or Si-NH_2-Co monometatlic complex. This indicated that there was synergistic action between different metals in the bimetallic complex.