高分子多糖载体对四苯基金属卟啉催化性能影响

在壳聚糖四苯基金属卟啉中, 氨基或羟基可能对金属卟啉的稳定性和催化活性起重要作用. 为探索这两类基团的作用效果差异, 并调查具有类似壳聚糖结构的纤维素作为载体, 对金属卟啉的保护以及羟基的协助催化作用, 制备了纤维素四苯基铁、钴和锰卟啉. 研究了纤维素四苯基铁、钴和锰卟啉催化空气氧化环己烷的能力, 并与相应的壳聚糖金属卟啉比较. 在418 K和0.8 MPa的空气压力下, 纤维素四苯基铁(钴或锰)卟啉均只能作一次性催化而耗尽; 所获得的醇酮选择性均低于相应的壳聚糖四苯基金属卟啉. 研究结果表明: 纤维素对四苯基铁、钴和锰卟啉没有明显的保护作用, 羟基对其催化环己基过氧化氢的协助分解作用也比较小. 壳聚糖对金属卟啉有很强的保护作用, 氨基有较强的协助金属卟啉催化环己基过氧化氢分解的能力, 使醇酮选择性提高.     

金属卟啉/MgAl水滑石催化醇选择性氧化制备羰基化合物

将MgAl水滑石引入到金属四苯基卟啉(MTPPs,M=Co,Fe,Mn,Ni)催化氧化体系中,实现了醇的选择性氧化。 结果表明,在分子氧/异丁醛体系中,CoTPP在苯甲醇氧化制苯甲醛反应中表现出优异的催化活性,MgAl水滑石添加剂可有效地提高醛的选择性。 在苯甲醇1 mmol、乙腈2 mL、CoTPP 5 mg、MgAl水滑石18 mg、异丁醛5 mmol、反应温度60 ℃、氧气气氛下反应2 h,苯甲醇的转化率和苯甲醛的选择性分别达到94%和92%。 另外,此催化体系在其它醇类化合物的氧化反应中也具有较好催化活性。     

Efficient catalytic cycloalkane oxidation employing a "helmet" phthalocyaninato iron(III) complex

We have examined the catalytic activity of an iron(III) complex bearing the 14,28-[1,3-diiminoisoindolinato]phthalocyaninato (diiPc) ligand in oxidation reactions with three substrates (cyclohexane, cyclooctane, and indan). This modified metallophthalocyaninato complex serves as an efficient and selective catalyst for the oxidation of cyclohexane and cyclooctane, and to a far lesser extent indan. In the oxidations of cyclohexane and cyclooctane, in which hydrogen peroxide is employed as the oxidant under inert atmosphere, we have observed turnover numbers of 100.9 and 122.2 for cyclohexanol and cyclooctanol, respectively. The catalyst shows strong selectivity for alcohol (vs. ketone) formation, with alcohol to ketone (A/K) ratios of 6.7 and 21.0 for the cyclohexane and cyclooctane oxidations, respectively. Overall yields (alcohol + ketone) were 73% for cyclohexane and 92% for cyclooctane, based upon the total hydrogen peroxide added. In the catalytic oxidation of indan under similar conditions, the TON for 1-indanol was 10.1, with a yield of 12% based upon hydrogen peroxide. No 1-indanone was observed in the product mixture.     

Catalytic oxidation of cyclohexane with hydrogen peroxide and a tetracopper(II) complex in an ionic liquid

The catalytic peroxidative oxidation (with H₂O₂) of cyclohexane in an ionic liquid (IL) using the tetracopper(II) complex [(CuL)₂(μ₄-O,O′,O′′,O′′′-CDC)]₂·2H₂O [HL = 2-(2-pyridylmethyleneamino)benzenesulfonic acid, CDC = cyclohexane-1,4-dicarboxylate] as a catalyst is reported. Significant improvements on the catalytic performance, in terms of product yield (up to 36%), TON (up to 529), reaction time, selectivity towards cyclohexanone and easy recycling (negligible loss in activity after three consecutive runs), are observed using 1-butyl-3-methylimidazolium hexafluorophosphate as the chosen IL instead of a molecular organic solvent including the commonly used acetonitrile. The catalytic behaviors in the IL and in different molecular solvents are discussed.     

Increasing the ketone selectivity of the cobalt-catalyzed radical chain oxidation of cyclohexane

A variety of heterogeneous catalysts for the radical chain oxidation of cyclohexane has been prepared by immobilization of the well-defined cobalt acetate oligomers [py(3)Co(3)(mu(3)-O)(OH)(O(2)CCH(3))(5)](PF(6)) (1) and [py(4)Co(2)(OH)(2)(O(2)CCH(3))(3)](PF(6)) (2) on carboxy-modified mesoporous silica supports A-D by carboxylate exchange. The catalytic oxidation of cyclohexane with tert-butyl hydroperoxide (TBHP) in the presence of these homogeneous and immobilized cobalt acetate complexes afforded the corresponding alcohol and ketone in high yield. The immobilization of 1 and 2 results in a significant increase of catalytic activity. TBHP acts as a radical initiator and as source of molecular oxygen, which is also involved in the overall oxidation process. The rate of cyclohexane conversion is limited by the diffusion of molecular oxygen, and steady-state concentrations of cyclohexanone (K, ketone) and cyclohexanol (A, alcohol) are established; these determine the maximum K:A ratio.     

Gold & silver nanoparticles supported on manganese oxide: Synthesis,characterization and catalytic studies for selective oxidation of benzyl alcohol

Nano-gold and silver particles supported on manganese oxide were synthesized by the co-precipitation method. The catalytic properties of these materials were investigated for the oxidation of benzyl alcohol using molecular oxygen as a source of oxygen. The catalyst was calcined at 300, 400 and 500 °C. They were characterized by electron microscopy, powder X-ray diffraction (XRD) and surface area. It was observed that the calcination temperature affects the size of the nanoparticle, which plays a significant role in the catalytic process. The catalyst calcined at 400 °C, gave a 100% conversion and >99% selectivity, whereas catalysts calcined at 300 and 500 °C gave a conversion of 69.51% and 19.90% respectively, although the selectivity remains >99%.     

Mechanism of cyclohexane oxidation by molecular oxygen in the biomimetic iron porphyrin system with proton and electron donors: II. A molecular pathway

The kinetics of the accumulation of cyclohexyl hydroperoxide, alcohol, and ketone during cyclohexane oxidation in an O₂/FeP/AcOH/Zn/CH₃CN biomimetic system is studied by gas-liquid chromatography. The factors determining the selectivity of the nonradical oxidation pathway, which results in the formation of more than 80% of the products, are considered. A scheme of the molecular pathway of alcohol and ketone formation is proposed, which agrees well with the experimental data. The kinetic parameters for cyclohexane oxidation catalyzed by iron porphyrins with various substituents in the phenyl rings in this system with and without an electron carrier (methylviologen) are calculated.     

Mechanistic Insight into the Catalytic Oxidation of Cyclohexane over Carbon Nanotubes: Kinetic and In Situ Spectroscopic Evidence

As some of the most interesting metal‐free catalysts, carbon nanotubes (CNTs) and other carbon‐based nanomaterials show great promise for some important chemical reactions, such as the selective oxidation of cyclohexane (C₆H₁₂). Due to the lack of fundamental understanding of carbon catalysis in liquid‐phase reactions, we have sought to unravel the role of CNTs in the catalytic oxidation of C₆H₁₂ through a combination of kinetic analysis, in situ spectroscopy, and density functional theory. The catalytic effect of CNTs originates from a weak interaction between radicals and their graphene skeletons, which confines the radicals around their surfaces. This, in turn, enhances the electron‐transfer catalysis of peroxides to yield the corresponding alcohol and ketone.     

Investigation of the CO oxidation rate oscillations using electrochemical promotion of catalysis over sputtered-Pt films interfaced with YSZ

The oscillatory behaviour of CO oxidation was studied at 250 °C and atmospheric pressure using an electrochemical catalyst composed of a thin (60 nm) sputtered-Pt film interfaced with an yttria-stabilized zirconia membrane. Oscillations of CO oxidation rate showed a perfect correlation with those of the electrochemical potential values. Electrochemical promotion of catalysis was used to initiate and stop the oscillatory behaviour. Small current application induced a permanent effect on the oscillatory behaviours. An extremely small negative current (? 17 μA) led to a 4-fold increase of the catalytic activity and created oscillations that were stable even after current interruption. This permanent effect in the oscillatory behaviour of CO oxidation rate is observed for the first time using EPOC. This has been interpreted by the higher tendency of the nanometric-Pt particles to form PtO_x in thin sputtered films.     

Electrodeposited fabrication of highly ordered Pd nanowire arrays for alcohol electrooxidation

Highly ordered Pd nanowire arrays (NWAs) are prepared using a porous aluminum oxide template by pulse electrodeposition. The obtained Pd nanowire arrays with the diameter of 50 nm and length of 850 nm have been characterized by scanning electron microscopy, energy dispersive X-ray analysis, and high resolution transmission electron microscope. Meanwhile, the electrocatalytic activity of Pd NWAs electrodes for methanol and isopropanol oxidation in alkaline media is studied. It is found that the obtained nanostructures exhibit excellent catalytic activity for alcohol electrooxidation. The isopropanol oxidation shows the higher activity on Pd NWAs electrode than methanol in alkaline medium.     

Evaluation of the ionic liquids 1-alkyl-3-methylimidazolium hexafluorophosphate as a solvent for the extraction of benzene from cyclohexane: (Liquid + liquid) equilibria

In the catalytic hydrogenation of benzene to cyclohexane, the separation of unreacted benzene from the product stream is inevitable and essential for an economically viable process. In order to evaluate the separation efficiency of ionic liquids (ILs) as a solvent in this extraction processes, the ternary (liquid + liquid) equilibrium of 1-alkyl-3-methylimidazolium hexafluorophosphate, [C_nmim][PF₆] (n = 4, 5, 6), with benzene and cyclohexane was studied at T = 298.15 K and atmospheric pressure. The reliability of the experimentally determined tie-line data was confirmed by applying the Othmer–Tobias equation. The solute distribution coefficient and solvent selectivity for the systems studied were calculated and compared with literature data for other ILs and sulfolane. It turns out that the benzene distribution coefficient increases and solvent selectivity decreases as the length of the cation alkyl chain grows, and the ionic liquids [C_nmim][PF₆] proved to be promising solvents for benzene–cyclohexane extractive separation. Finally, an NRTL model was applied to correlate and fit the experimental LLE data for the ternary systems studied.     

Oxidation of carbon black,propene and toluene on highly reducible Co/SBA-15 catalysts

Different cobalt loadings (3, 6, 12, 24 wt%) were impregnated using the double-solvent technique on SBA-15 calcined at 500 °C presenting a high specific surface area. The impregnated solids were stabilized at 450 °C in the air. The impregnation of cobalt led to the incorporation of cobalt oxide nanoparticles in the mesoporosity of the SBA-15. The cobalt nanoparticles were easily reducible compared to similar solids prepared by different methods. The presence of these nanoparticles enhanced significantly the reactivity of the catalysts in the considered reaction. The addition of more than 12 wt% of cobalt did not enhance the catalytic reactivity due to the deposition of cobalt oxide species on the surface of the support. The cobalt-impregnated solids are efficient in decreasing the oxidation temperature of different probe molecules and are totally selective towards the formation of CO₂ and H₂O.     

Measurement of (liquid + liquid) equilibria for ternary systems of (N-formylmorpholine + benzene + cyclohexane) at temperatures (303.15, 308.15, and 313.15) K

This work demonstrates the ability of N-formylmorpholine (NFM) to act as an extraction solvent for the removal of benzene from its mixture with cyclohexane. The (liquid + liquid) equilibria (LLE) were measured for a ternary system of {N-formylmorpholine (NFM) + benzene + cyclohexane} under atmospheric pressure and at temperatures (303.15, 308.15, and 313.15) K. The experimental distribution coefficients (K) and selectivity factors (S) were obtained to reveal the extractive effectiveness of the solvent for separation of benzene from cyclohexane. The LLE results for the system studied indicate that increasing temperature decreases selectivity of the solvent. The reliability of the experimental results was tested by applying the Othmer–Tobias correlation. In addition, the universal quasichemical activity coefficient (UNIQUAC) and the non-random two liquids equation (NRTL) were used to correlate the LLE data using the interaction parameters determined from the experimental data. The root mean square deviations (RMSDs) obtained comparing calculated and experimental two-phase compositions are 0.0367 for the NRTL model and 0.0539 for the UNIQUAC model.     

Permanent electrochemical promotion of C3H8 oxidation over thin sputtered Pt films

The effect of “permanent electrochemical promotion of catalysis” (P-EPOC) was studied for the first time in the catalytic deep oxidation of C₃H₈ over a thin (～ 150 nm) sputtered Pt film on YSZ, under excess of oxygen at 350 °C. Short positive potential application (+ 1 V) resulted in a 5.6-fold increase of the catalytic rate, where C₃H₈ conversion reached 33%, while the apparent Faradaic efficiency was ～ 330. After positive current interruption the catalytic rate remained in a highly active steady-state, determined by the total charge of the anodic polarization step. Restoration of the catalytic activity to the initial value occurred only by a similar negative potential imposition. This new stable steady-state after current interruption can be interpreted by storage of a non-reactive oxygen species upon anodic polarization at the proximity of the Pt/YSZ interface and subsequent enhanced migration of spillover O^δ? species from the electrolyte support to the Pt/gas interface under open-circuit conditions.     

Electrodeposition of PtCo alloy nanoparticles on inclusion complex film of functionalized cyclodextrin–ionic liquid and their application in glucose sensing

Platinum–cobalt (PtCo) alloy nanoparticles (NPs) are successfully fabricated by ultrasonic-electrodeposition method, using an inclusion complex (IC) film of functionalized cyclodextrin (CD)–ionic liquid (IL) as support. The morphology and composition of the PtCo alloy NPs are characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction, respectively. It is found that they are well-dispersed on the CD–IL surface and exhibit many unique features. The resulting modified glassy carbon electrode shows excellent catalytic activity for glucose oxidation. Under the physiological condition, the oxidation current of glucose is linear to its concentration up to 20 mM with sensitivity of 13.7 μA mM^?1 cm^?2. In addition, the interference from the oxidation of ascorbic acid and uric acid could be effectively avoided. Therefore, it is promising as a nonenzymatic glucose sensor.     

Mercarbide: An unusual organomercury polymer

Mercarbide [CHg₄O₂](OH)₂, is a mercury derivative of ethane in which all of the ethane hydrogen atoms are substituted by mercury atoms. Mercarbide exhibits basic and anion exchange properties in addition to showing unique stability towards mineral acids as well as oxidizing and reducing agents. The selectivity of mercarbide towards organic anions shows selectivity dependence on the size and configuration of the pendant hydrocarbon group. Titration of mercarbide with Hammett indicators shows that mercarbide in its hydroxide form is a solid base with sites allocation 7.2 < H₀ < 26.5. Studies of the catalytic activity of mercarbide towards alcohol oxyethylation and aldol condensation show that it functions as a homogeneous basic catalyst, but with increased activity owing to the higher basicity of its active sites. The present paper reviews the synthesis, structure, physicochemical, and catalytic properties of mercarbide.     

Bismuth as an additive modifying the selectivity of palladium catalysts

The influence of bismuth addition on the activity and selectivity of palladium catalysts supported on SiO₂ in the reaction of glucose oxidation to gluconic acid was studied. The catalysts modified with Bi show much better selectivity and activity than palladium catalysts. The XRD studies proved the presence of intermetallic compounds BiPd and Bi₂Pd, which probably increase activity and selectivity of PdBi/SiO₂ catalysts in the oxidation of glucose. The TPO studies of catalysts containing 5 wt.% Pd/SiO₂, 3 wt.% Bi/SiO₂ and 5 wt.% Pd–5 wt.% Bi/SiO₂ show that palladium oxidation occurs at much higher temperatures than in the case of bismuth. The maximum rate of Pd oxidation occurs at around 580 K while the maximum rate of Bi oxidation takes place at around 430 K. Considering the above facts, a reaction involving bimetallic catalysts in oxidizing atmosphere at 333 K should not lead to surface oxidation of palladium and thus their deactivation.     

Catalytic wet peroxide oxidation of phenol over pillared clays containing iron or copper species

The catalytic wet oxidation of phenol by hydrogen peroxide in the presence of oxygen is catalysed, at room temperature, by copper or iron homogeneous species at pH 5 or 3.5, respectively. In such conditions phenol mild oxidation is mainly observed, the total phenol oxidation to CO₂ (TOC abatement) not exceeding 20 %. In similar experimental conditions, Fe, Al or Cu, Al pillared clays (FAZA or CAZA) are much more active, the phenol or the TOC conversion being directly related to the iron or copper content. Moreover, in the presence of iron containing pillared clay (FAZA), the TOC abatement can reach 80 % at 70 °C, with only a H₂O₂ stoichiometric excess equal to 1.5. The low iron leaching (less than 0.2 % of the total amount of iron in the catalyst) observed after a standard experiment (4 h) shows that the FAZA catalyst is highly stable in water media and could be used several consecutive times. These properties could result in the iron species stabilization in the interlamellar space of the pillared clays both by bonding with the Al pillars (60 % of the iron species) or as oxide clusters dispersed between the clay layers.     

Synthesis and characterization of carbon-supported transition metal oxide nanoparticles — Cobalt porphyrin as catalysts for electroreduction of oxygen in acids

Unpyrolyzed, non noble metal catalysts for Oxygen Reduction Reaction (ORR), denoted MeOx–CoP/C, were obtained using a two-step procedure. The procedure consisted of a synthesis of carbon-supported transition metal (Me═Co, or Ni, or Fe) nanoparticles, followed by adsorption of cobalt porphyrin (CoP). TEM and XPS analyses confirm the formation of nanoparticles and the presence of transition metal oxides. Rotating disk electrode measurements showed that the as-synthesized materials exhibit catalytic ORR activity in acidic medium toward oxygen reduction, which is higher than that of cobalt porphyrin on carbon. This reveals that the metal oxide nanoparticles enhance the activity of the metalloporphyrin without being electroactive themselves. The catalytic activity follows the sequence: CoOx–CoP/C > NiOx–CoP/C > FeOx–CoP/C, showing the influence of nature of the transition metal on the enhancing effect. The presence of a cobalt center incorporated in the macrocycle was found to be essential to the oxygen reduction reaction, appearing thus to be the catalytic active site of the reaction. Our data suggest the ORR occurs at a single active site.     

Efficient dynamic kinetic resolution of secondary alcohols with a novel tetrafluorosuccinato ruthenium complex

Dynamic kinetic resolution (DKR) of a series of secondary alcohols has been conducted with a novel dinuclear ruthenium complex, bearing tetrafluorosuccinate and (rac)-BINAP ligands as the racemization catalyst. Novozym 435 has been used as the enzyme, and isopropyl butyrate as the acyl donor. Five substrates underwent DKR successfully: an aliphatic and an aromatic secondary alcohol, an aromatic alcohol with an electron-withdrawing substituent on the phenyl ring, an aromatic alcohol bearing an electron-donating substituent on the ring and a heteroaromatic secondary alcohol. The catalyst performed optimally at 70 °C. Typically the reaction reached complete conversion within 1 day with 0.1 mol % of racemization catalyst relative to the substrate. The addition of the ketone corresponding to the substrate stabilizes the active Ru complex and, therefore, increases the rate of the reaction.