(R,R)-DPEN-modified Ru/gamma-Al2O3 - An efficient heterogeneous catalyst for enantioselective hydrogenation of acetophenone

An efficient enantioselective catalyst of 5 wt.% Ru/-gamma-Al2O3 modified with R,R-1,2-diphenylethylene-diamine ((R,R)-DPEN) for the hydrogenation of a non-activated aromatic ketone of acetophenone has been investigated, a relatively high enantiomeric excess (ee) of 60.5% was obtained at both the conversion and selectivity larger than 99%, it was about three times higher than the ee values reported up to now for acetophenone hydrogenation with the supported transition metal catalysts modified by chiral reagents. The influences of some reaction parameters such as phosphine ligand, substrate/catalyst/modifier molar ratios, base, solvent, pressure and reaction temperature have been discussed. The chiral modifier of (R,R)-DPEN was very important in controlling the enantioselectivity through adsorption competing with other substrates on the surface of active metal species. The phosphine ligand and base were also important and indispensable in the present reaction.

The real role of carbon in Pt/C catalysts for oxygen reduction reaction

A new electrocatalysis of carbon materials for oxygen reduction reaction (ORR) on Pt/C catalysts was discovered. It was found that there exist two kinds of electroactive sites on these supports of carbon materials, which can effectively electrocatalyze the reduction of peroxide intermediated from oxygen reduction on Pt, as this provides continuous driving force to move the equilibrium toward the production of peroxide from ORR.

The enhancement effect of Eu3+ on electro-oxidation of ethanol at Pt electrode

It is reported for the first time that the slow electrochemical kinetics process for the electro-oxidation of ethanol can be promoted by changing the electrochemical environment. The electro-oxidation of ethanol at a Pt electrode in the presence of Eu3+ cations was studied and an enhancement effect was exhibited. Cyclic voltammetry experiment results showed that the peak current density for the electro-oxidation of ethanol was increased in the presence of EU3+ in the ethanol solution. A preliminary discussion of the mechanism of the enhancement effect is given. This is based on a CO stripping experiment, which shows that either the onset potential or the peak potential of CO oxidation is shifted negatively after adding Eu3+ to the solution.

Atom transfer radical polymerization of butadiene using MoO2Cl2/PPh3 as the catalyst

Atom transfer radical polymerization has been used to successfully synthesize polybutadiene. This was achieved by using MoO2Cl2/triphenyl phosphine as the catalyst and the various organic halide compounds such as methyl-2-chloropropionate, CCl4, 1,4-dichloromethyl benzene, I-phenylethyl chloride, and benzyl chloride as initiators. The monomer conversion increased up to 50% with polymerization time. The polydispersity indices of the polymers were as high as above 1.5. However, the polymerizations were controlled and the polydispersity indices of the polymers were less than 1.5 throughout the polymerization in reverse atom transfer radical polymerization. The chemical structure of the polymer obtained was characterized by (HNMR)-H-1 and FTIR. The valency states of molybdenum in this reactive system were detected by UV-vis spectra.

Synthesis and assembly of Au-Pt bimetallic nanoparticles

Au-Pt bimetallic nanoparticles (NPs) were synthesized by reducing the mixture of HAuCl4 and K2PtCl6 with ethanol in the presence of cinnamic acid (C6H5CHCHCO2H, CA) through a thermal process. It was found that the isolated NPs could gradually self-assemble into chain-like structures, ultimately to 3-dimensional network nanostructures by adjusting the molar ratio of CA to K2PtCl6. Energy-dispersive Spectroscopy, X-ray photoelectron spectroscopy and X-ray diffraction was used to confirm the formation of Au-Pt bimetallic nanostructures. It was worthwhile noting that the bimetallic NPs with the novel structures prepared by our method exhibited an attractive catalytic activity for the hydrogen evolution reaction in an acidic solution.

Study of carbon-supported Au catalyst as the cathodic catalyst in a direct formic acid fuel cell prepared using a polyvinyl alcohol protection method

In this paper, it is reported for the first time that a carbon-supported Au (Au/C) catalyst for the cathodic catalyst in a direct formic acid fuel cell (DFAFC) was prepared using a polyvinyl alcohol (PVA) protection method. The results indicated that for oxygen reduction, the electrocatalytic activity of the Au/C catalyst prepared with the PVA protection method is much better than that of a Au/C catalyst prepared with the pre-precipitation method. This is due to the small average size and low relative crystallinity of the An particles in the Au/C catalyst prepared by the PVA protection method, compared to that of the Au/C catalyst prepared by the pre-precipitation method, illustrating that the average size and the relative crystallinity of the ALL particles has an effect on the electrocatalytic activity of the Au/C catalyst for oxygen reduction. In addition, because An has no electrocatalytic activity for the oxidation of formic acid, the Au/C catalyst possesses a high formic acid tolerance. After the electrocatalytic activity of the Au/C catalyst for the oxygen reduction is improved, it is suitable to be used as the cathodic catalyst in DFAFC.

纳米管结构对碳纳米管载Pt催化剂电催化性能的影响

在制备单、双壁及不同管径的多壁碳纳米管(CNTs)的基础上,用液相还原法把Pt沉积到单、双壁和管径不同的多壁CNTs上.发现制得的CNTs载Pt(Pt/CNTs)催化剂对甲醇氧化的电催化活性随CNTs管径减小而增加.这归结于管径小的CNTs的比表面积较大,含氧基团多,有利于提高Pt粒子分散度,加上管径小的单壁CNTs具有更高的导电性,这些因素都有利于提高Pt/CNTs催化剂对甲醇氧化的电催化活性.

不同载量Pt/C催化剂制备及其对甲醇氧化的电催化活性

用甲醇作溶剂,SnCl2作还原剂,采用改进的有机溶胶方法制备了用于直接甲醇燃料电池(DMFC)中甲醇氧化的炭载Pt(Pt/C)催化剂。制得的Pt/C催化剂中的Pt粒子具有高度的均一性和良好的分散度。通过控制溶剂的蒸发温度,能够获得Pt粒子平均粒径基本相同、Pt载质量分数为10%～60%的Pt/C催化剂,粒径为3.3～4.3nm。将获得的催化剂通过涂膜-热压法制备成DMFC膜电极,研究了Pt载量对甲醇电催化氧化性能的影响。结果表明,质量分数为40%的Pt/C催化剂对甲醇的电催化氧化显示出优异的电催化性能。

Fe对Pt-Fe/C催化剂电催化氧还原反应活性的影响

制备了用作直接甲醇燃料电池的碳载Pt-Fe(Pt-Fe/C)阴极催化剂,X射线能量色散谱(EDX)、X射线衍射谱和电化学测量的结果表明,在Pt-Fe/C催化剂中,Fe以3种形式存在.质量分数大约为20%的Fe进入Pt的晶格,形成Pt-Fe合金,质量分数大约为80%的Fe没有进入Pt的晶格而以Fe和Fe2O3的形式单独存在.该催化剂经酸处理后,非合金化Fe和Fe2O3被溶解,而使Pt-Fe/C催化剂的电化学活性比表面积要比未经酸处理前的增加约30%左右,导致Pt-Fe/C催化剂对氧还原的电催化活性优于未经酸处理前的Pt-Fe/C催化剂.研究结果表明,Pt-Fe/C催化剂的电化学活性比表面积对氧还原的电催化活性起重要的作用,另外,只有与Pt形成合金的Fe能提高Pt对氧还原的电催化活性,而非合金化的Fe对Pt催化剂对氧还原的电催化活性基本没有影响.

碳黑预处理对Pt/C催化剂对甲醇氧化电催化活性的影响

直接甲醇燃料电池(DMFC)由于具有较多的优点而受到广泛的关注.但是碳载Pt(Pt/C)阳极催化剂电催化活性低是限制其应用的一个主要问题.为了提高Pt/C催化剂对甲醇氧化的电催化性能,分别用CO2,空气,H2O2或HNO3对常用作为载体的VulcanXC-72碳黑进行预处理.结果表明,在用CO2,空气,HNO3,H2O2处理的及未处理的碳黑作载体制得的Pt/C催化剂电极上,甲醇氧化峰的峰电流密度顺序为39,33,32,20和18mA?cm-2,表明用CO2处理的碳载体制备的Pt/C催化剂对甲醇氧化有最好的电催化活性和稳定性.其主要原因是用CO2处理能减少碳黑表面的含氧基团和增加石墨化程度,而使碳黑的电阻降低及Pt粒子在碳黑上的分散性变好.

CoTPP-Pt/C作直接甲醇燃料电池阴极催化剂

制备了炭载四苯基钴卟啉(CoTPP)和Pt(CoTPP-Pt/C)复合催化剂,研究了炭载四苯基铁卟啉对氧还原的电催活性。电化学研究发现,CoTPP-Pt/C催化剂对氧还原有很高的电催化活性。CoTPP-Pt/C催化剂对氧还原的极限电流密度比Pt/C催化剂高30%左右,但抗甲醇的能力未改善。

Mesoporous acid solid as a carrier for metallocene catalyst in ethylene polymerization and a catalyst in catalytic degradation of polyethylene

The possibility of mesoporous acid solid as a carrier for metallocene catalyst in ethylene polymerization and catalyst for polyethylene (PE) catalytic degradation was investigated. Here, HMCM- 41 and AIMCM-41, and mesoporous silicoaluminophosphate molecular sieves (SAPO1 and SAPO2) were synthesized and used as acid solid. Much more gases were produced during catalytic degradation in PE/acid solid mixtures via in situ polymerization than those via physical mixing. The particle size distribution results exhibited that the particle size of SAPO1 in the PE/SAPO1 mixture via in situ polymerization was about 1/14 times of that of the original SAPO1 or SAPO1-supported metallocene catalyst. This work shows a novel technology for chemical recycling of polyolefin.

Electronic structures of MCO (M = Nb, Ta, Rh, Ir, Pd, Pt) molecules by density functional theory

Equilibrium geometries, vibrational frequencies, and dissociation energies of the transition metal carbonyls MCO (M = Nb, Ta, Rh, Ir, Pd, Pt) were studied by use of diverse density functional methods B3LYP, BLYP, B3P86, B3PW91, BHLYP, BP86, and PBE1PBE. It was found that the ground electronic state is (6)Sigma(+) for NbCO and TaCO, (2)Sigma(+) for RhCO,(2)Delta for IrCO, and (1)Sigma(+) for PdCO and PtCO, in agreement with previous theoretical studies. The calculated properties are highly dependent on the functionals employed, in particular for the dissociation energy. For most of the molecules, the predicted bond distance is in agreement with experiments and previous theoretical results. BHLYP is the worst method in reproducing the experimental results compared with the other density functional methods for the title molecules.

Synthesis and characterization of polyethylene/clay-silica nanocomposites: A montmorillonite/silica-hybrid-supported catalyst and in situ polymerization

A novel approach to the preparation of polyethylene (PE) nanocomposites, with montmorillonite/silica hybrid (MT-Si) supported catalyst, was developed. MT-Si was prepared by depositing silica nanoparticles between galleries of the MT. A common zirconocene catalyst [bis(cyclopentadienyl)zirconium dichloride/methylaluminoxane] was fixed on the MT-Si surface by a simple method. After ethylene polymerization, two classes of nanofillers (clay layers and silica nanoparticles) were dispersed concurrently in the PE matrix and PE/clay-silica nanocomposites were obtained. Exfoliation of the clay layers and dispersion of the silica nanoparticles were examined with transmission electron microscopy. Physical properties of the nanocomposites were characterized by tensile tests, dynamic mechanical analysis, and DSC. The nanocomposites with a low nanofiller loading (<10 wt %) exhibited good mechanical properties. The nanocomposite powder produced with the supported catalyst had a granular morphology and a high bulk density, typical of a heterogeneous catalyst system.

Zirconocene catalyst well spaced inside modified montmorillonite for ethylene polymerization: role of pretreatment and modification of montmorillonite in tailoring polymer properties

Zirconocene catalyst was heterogenized inside an organosilane-modified montmorillonite (MMT) pretreated by calcination and acidization, for supported catalyst systems with well-spaced alpha-olefin polymerization active centers. The varied pretreatment and modification conditions of montmorillonite are efficient for supported zirconocene catalysts in control of polyethylene microstructures, in particular, molecular weight distribution. In contrast to other supported catalyst systems, Cp2ZrCl2/modified montmorillonite(MMT-7)-supported catalysts with a distinct interlayer structure catalyzed ethylene homopolymerization and copolymerization with I-octene activated by methylaluminoxane (MAO), resulting in polymers with a bimodal molecular weight distribution (MWD).