SC-IrO2NR-carbon hybrid: A catalyst with high electrochemical stability for oxygen reduction

The enhanced electrochemical stability of the synthesized hybrid catalyst has been demonstrated by the introduction of the synergistic effect between carbon powder additive and the prepared catalyst.Single crystal IrO 2 nanorod (SC-IrO 2 NR) catalyst was prepared by a sol-gel method.The structure and performance of the catalyst sample were characterized by X-ray diffraction spectroscopy (XRD),scanning electron microscope (SEM),transmission electron microscope (TEM),rotating disk electrode (RDE) and cyclic voltammetry (CV) measurements.XRD patterns and TEM images indicate that the catalyst sample has a rutile IrO 2 single crystal nanorod structure.The onset potential for oxygen reduction reaction (ORR) of the SC-IrO 2 NR-carbon hybrid catalyst specimen is 0.75 V (vs.RHE) in RDE measurement.CV and RDE test results show that the SC-IrO 2 NR-carbon hybrid catalyst has a better electrochemical stability in comparison with the commercial Pt/C catalyst,with attenuation ratios of 17.67% and 44.60% for the SC-IrO 2 NR-carbon hybrid catalyst and the commercial Pt/C catalyst after 1500 cycles,respectively.Therefore,in terms of stability,the SC-IrO 2 NR-carbon hybrid catalyst has a promising potential in the application of the proton exchange membrane fuel cell.     

沉淀方法对铜基甲醇合成催化剂前驱体及其性能的影响

 分别采用共沉淀法 (CP)、两步沉淀法 (TP) 和分步沉淀法 (FP) 制备了 Cu/ZnO/Al₂O₃ 甲醇合成催化剂. 结果发现, FP 催化剂上甲醇收率比 CP 催化剂上高 46.3%, 比 TP 催化剂上高 9.3%. 采用 X 射线衍射、微分热重分析、红外光谱、N₂ 吸附-脱附、程序升温还原及 N₂O 滴定等方法表征了催化剂. 结果表明, FP 催化剂前驱体中 (Cu,Zn)₂CO₃(OH)₂ 和 (Zn,Cu)₅(CO₃)₂(OH)₆ 两种高活性物相较多, 而 (Cu,Zn)₆Al₂(OH)₁₆CO₃•4H₂O 物相较少, 焙烧后形成了较多的 CuO-ZnO 固溶体, 同时形成了较多的碳酸盐, 因而催化活性更高.     

Polymerization of Olefins by a Ziegler Catalyst Supported on Poly(ethylene-co-Vinyl Alcohol)

The polymerization and catalytic behavior of a Ziegler type catalyst supported on poly(ethylene-co-vinyl alcohol) (EVA) were investigated. The rate of ethylene polymerization by a catalyst prepared from titanium tetrachloride supported on EVA (vinyl alcohol 18 mole %) and triethylaluminum (AlEt₃) is much higher than that of an n-butoxytitanium trichloride (BTT)-AlEt3 catalyst. The polymer-supported catalyst has prolonged high activity during polymerization compared with the BTT-AlEt₃ catalyst. The stabilization of the catalyst seems to depend on its slower reduction by alkylaluminum compounds, due to steric hindrance by bulky polymer ligands. Polypropylene prepared by the polymer supported Ziegler catalyst is essentially atactic, and it differs little from that prepared with a BTT-AlEt₃ catalyst. Vinyl chloride was also polymerized by this catalyst. The catalytic activity was, however, very small.     

Generation of sulfate radicals by supported ruthenium catalyst for phenol oxidation in water

In this study we report the preparation of RuO₂/Fe₃O₄@nSiO₂@mSiO₂ core–shell powder mesoporous catalyst for heterogeneous oxidation of phenol by peroxymonosulfate (PMS) as oxidant. The properties of this supported catalyst were characterized by SEM–EDS (scanning electron microscopy–energy dispersive X-ray spectroscopy), XRD (powder X-ray diffraction), TEM (transmission electron microscopy), and nitrogen adsorption–desorption. It is found that using ruthenium oxide-based catalyst is highly effective in activating PMS for related sulfate radicals. The effects of catalyst loading, phenol concentration, PMS concentration, reaction temperature, and reusability of the as-prepared catalyst on phenol degradation were investigated. In RuO₂/Fe₃O₄@nSiO₂@mSiO₂ mesoporous catalyst, Oxone (PMS) was effectively activated and 100 % phenol degradation occurred in 40 min. The magnetic RuO₂/Fe₃O₄@nSiO₂@mSiO₂ catalyst was facility separated from the solution by an external magnetic field. To regenerate the deactivated catalyst and improve its catalytic properties, three different methods involving annealing in air, washing with water, and applying ultrasonics were used. The catalyst was recovered thoroughly by heat treatment.     

Epoxidation of propylene with hydrogen peroxide catalyzed by heteropolyphosphatotungstate

The epoxidation of propylene with hydrogen peroxide catalyzed by a reaction-controlled phase transfer catalyst (RCPT) composed of quaternary ammonium heteropolyoxotungstates in acetonitrile medium is studied. The influence of several factors on the reaction is studied, such as the reaction temperature, the effect of H₂O amount, the reaction time, the effect of the catalyst amount, solvent effect and the recycle of the catalyst. Under mild conditions, H₂O₂ conversion is 98.6%, and propylene oxide (PO) selectivity based on H₂O₂ is 97.2%. During the epoxidation, the catalyst is dissolved in the solution. However, after H₂O₂ is used up, the catalyst can be recovered as a precipitate and can be recycled. We find that the recycled catalyst has similar catalytic activity as the fresh one.     

Polymerization of styrene with VCl4–aluminum alkyls

Polymerization of styrene has been carried out with VCl₄–AlEt₃ and VCl₄–Al(i-Bu)₃ catalyst systems. These two systems have been found to behave in a similar manner but their behavior is different from those systems where VOCl₃ has been used instead of VCl₄. Reaction is first order with respect to monomer concentration for both the systems and first order with respect to catalyst in the case of VCl₄–AlEt₃. In the case of VCl₄–Al(i-Bu)₃, the rate of polymerization is independent of catalyst concentration but intrinsic viscosities increase with increasing catalyst concentration. The average valence of vanadium in the catalyst complexes has been discussed in relation to nature of catalyst sites. Activation energy and effect of diethyl zinc support the anionic mechanism for the two systems.     

A Noble‐Metal‐Free Nickel(II) Polypyridyl Catalyst for Visible‐Light‐Driven Hydrogen Production from Water

The complex [Ni(bpy)₃]²⁺ (bpy=2,2′‐bipyridine) is an active catalyst for visible‐light‐driven H₂ production from water when employed with [Ir(dfppy)₂(Hdcbpy)] [dfppy=2‐(3,4‐difluorophenyl)pyridine, Hdcbpy=4‐carboxy‐2,2′‐bipyridine‐4′‐carboxylate] as the photosensitizer and triethanolamine as the sacrificial electron donor. The highest turnover number of 520 with respect to the nickel(II) catalyst is obtained in a 8:2 acetonitrile/water solution at pH 9. The H₂‐evolution system is more stable after the addition of an extra free bpy ligand, owing to faster catalyst regeneration. The photocatalytic results demonstrate that the nickel(II) polypyridyl catalyst can act as a more effective catalyst than the commonly utilized [Co(bpy)₃]²⁺. This study may offer a new paradigm for constructing simple and noble‐metal‐free catalysts for photocatalytic hydrogen production.     

Deactivation and regeneration of the B2O3/TiO2-ZrO2 catalyst in the vapor phase Beckmann rearrangement of cyclohexanone oxime

The deactivation and regeneration of B₂O₃/TiO₂-ZrO₂ catalyst for the vapor phase Beckmann rearrangement of cyclohexanone oxime to -caprolactam were studied. The fresh, deactivated and regenerated catalysts were characterized by using adsorption of nitrogen, X-ray diffraction (XRD), thermogravimetry (TG) and NH₃-temperature-programmed desorption (NH₃-TPD) techniques. The crystal structure and pore size distribution of the catalyst were retained after reaction, but the number of acid sites decreased significantly. There was a relationship between the amount of coke deposited on the catalyst and the decline in catalytic activity. These results suggest that the coke deposition on the surface of catalyst is mainly responsible for the catalyst deactivation. The catalytic activity can be recovered completely after calcining the deactivated catalyst in air flow at 600 °C for 8 h.     

Aqueous-Phase Nitrile Hydration Catalyzed by an In Situ Generated Air-Stable Ruthenium Catalyst

RuCl₂(PTA)₄ (PTA=1,3,5-triaza-7-phosphaadamantane) is an active, recyclable, air-stable, aqueous-phase nitrile hydration catalyst. The development of an in situ generated aqueous-phase nitrile hydration catalyst (RuCl₃⋅3 H₂O+6 equivalents PTA) is reported. The activity of the in situ catalyst is comparable to RuCl₂(PTA)₄. The effects of [PTA] on the activity of the reaction were investigated: the catalytic activity, in general, increases as the pH goes up, which shows a positive correlation with [PTA]. The pH effects were further explored for both the in situ and RuCl₂(PTA)₄ catalyzed reaction in phosphate buffer solutions with particular attention given to pH 6.8 buffer. Increased catalytic activity was observed at pH 6.8 versus water for both systems with turnover frequency (TOF) up to 135 h⁻¹ observed for RuCl₂(PTA)₄ and 64 h⁻¹ for the in situ catalyst. Catalyst loading down to 0.001 mol % was examined with turnover numbers as high as 22 000 reported. Similar to the preformed catalyst, RuCl₂(PTA)₄, the in situ catalyst could be recycled more than five times without significant loss of activity from either water or pH 6.8 buffer.     

表面覆盖SiO2用于提高Pt-Pd/CeO2-ZrO2-Al2O3商用柴油机氧化型催化剂的抗硫性

向Pt-Pd/CeO₂-ZrO₂-Al₂O₃ （Pt-Pd/CZA）商用柴油机氧化型催化剂（DOC）中加入多孔SiO₂以提高其抗硫性. 使用多层涂覆法在Pt-Pd/CZA 催化剂表面覆盖一层多孔SiO₂,从而制得SiO₂/Pt-Pd/CeO₂-ZrO₂-Al₂O₃（SiO₂/Pt-Pd/CZA）抗硫DOC. 并使用扫描电子显微镜（SEM）,H₂程序升温还原（H₂-TPR）,氮气吸脱附,X射线能谱（EDX）和热重分析（TGA）等对其进行表征. SEM结果显示,SiO₂层以多孔形式均匀覆盖在催化剂表面. 氮气吸脱附结果表明,所添加的SiO₂的织构性质与Pt-Pd/CZA 催化剂的织构性质相似,因而表面覆盖的SiO₂并未明显改变Pt-Pd/CZA催化剂的比表面积和孔结构. H₂-TPR结果证实表面覆盖的SiO₂不影响Pt-Pd/CZA催化剂的还原性能. EDX和TGA结果说明表面覆盖SiO₂可以抑制硫物种在催化剂表面的形成及累积. 最终,本文所制备的SiO₂/Pt-Pd/CZA催化剂在保持Pt-Pd/CZA商用DOC的高活性及耐久性的同时有效提高了其抗硫性.     

Study of the compositional heterogeneity of ethylene–hexene-1 copolymers by thermal fractionation technique by means of differential scanning calorimetry

The successive self-nucleation/annealing technique (SSA) by differential scanning calorimetry has been applied to study the heterogeneity of ethylene–hexene-1 copolymers produced with supported catalytic systems of different compositions: highly active supported Ziegler–Natta (Z–N) catalysts—a titanium–magnesium catalyst TiCl₄/MgCl₂ (TMC) and a vanadium–magnesium catalyst VCl₄/MgCl₂ (VMC), a supported zirconocene catalyst Me₂Si(Ind)₂ZrCl₂/SiO₂ (MAO), and a chromium-oxide catalyst CrO₃/SiO₂. Comparative data by SSA technique with the same temperature program were obtained for copolymers differed by MWD from narrow to very broad (Mw/Mn = 2.4–54) and short chain branching distribution from narrow (zirconocene catalyst) to very broad (TMC and chromium oxide catalysts). It is demonstrated that copolymers produced with the zirconocene catalyst have the narrowest melting range and do not contain thick lamellae. The widest lamella thickness distribution has been found for a copolymer produced with the chromium-oxide catalyst. Copolymers produced with the supported Z–N catalysts are ranked in the middle with a more narrow lamella thickness distribution for copolymer prepared with VMC as compared with the one produced with TMC. The SSA results are compared with the data on copolymer fractionation by TREF. It is shown that these methods give a good correlation for copolymers with narrow short-chain branching distribution produced with the supported zirconocene catalyst. In the case of copolymers produced with TMC, TREF yields a higher content of the high-branched fractions.     

Catalytic Performance of Amorphous Ti/SiO2 in the Gas-Phase Epoxidation of Propylene with H2O2

The epoxidation of propylene with dilute H₂O₂ aqueous solution over titanium silicalite-1 (TS-1) zeolite catalyst is a green chemical reaction for propylene oxide (PO) production. Carrying out the reaction in gas-phase can get rid of problems caused by using methanol solvent. This paper reports an attempt of using non-zeolite catalyst for the gas-phase epoxidation. Amorphous Ti/SiO₂, obtained by grafting amorphous SiO₂ with TCl₄ in ethanol solvent in a chemical liquid-phase deposition (CLD) process, has been used as the catalyst. Results show that the CLD Ti/SiO₂ with appropriate Si/Ti molar ratio is an active catalyst for gas-phase epoxidation, achieving 9.8 % propylene conversion and 66.9 % PO selectivity with 40.3 % H₂O₂ utilization, which indicates that this amorphous Ti/SiO₂ catalyst deserves extensive studies in the future.     

The roles of oxidation state,Lewis acid cocatalyst and solvent polarity in activating titanium compounds for olefin polymerization

The polymerization activity of the following three catalyst systems towards ethylene has been investigated and compared: 1) methyltitanocene chloride-Me₂AlCl 2) η³-allyltitanocene-Me₂AlCl and 3) titanium dichloride tetrahydrofuranate-Me₂AlCl. The first two catalysts formed homogeneous phases and produced linear polymer; the last catalyst functioned in a heterogeneous medium and formed crosslinked polymer. The titanium(IV) catalyst was about 30 times more active than the titanium(III) system and the titanium(II) catalyst on MgCl₂ could be made 8 times more active than the titanium(IV) system. A novel mechanism is proposed to explain the behavior and activity of the titanium(II) system.     

Depolymerization behavior of nylon 6 anionically obtained with NaAL(Lac)4 at high temperature

Depolymerization and consumption of catalyst in the polymerizing system were investigated in the polymerization of ?-caprolactam by using NaAl(Lac)₄ catalyst at 255°C. In the first stage of depolymerization, marked consumption of catalyst was observed. The relationship between the degree of polymerization of resulting polymer and the catalyst concentration, during the polymerization time from 10 min to 3 hr, was different from that observed for the final polymer in the case of sodium phenylacetate or sodium catalyst, and follows the equation, P_n ∞ 1/[Lac].^0.4 This behavior is ascribed to the peculiar catalytic behavior of Al(Lac)₃, which is a component of this catalyst.     

Ni-based catalyst derived from Ni/Mg/Al hydrotalcite-like compounds and its activity in the methanation of carbon monoxide

The supported Ni-based catalyst is widely used in the methanation process. Nevertheless, the major disadvantages of this catalyst are a poor behavior in the water-gas-shift (WGS) reaction and the deactivation at higher temperatures. A new kind of catalyst, nickel-containing oxides catalyst (NiMgAl), obtained from thermal treatment of hydrotalcite-like compounds (HTlcs) was prepared using the co-precipitation method. The performance of this catalyst was systematically investigated and compared with that of the Ni/Al₂O₃ catalyst. It was found that the NiMgAl catalyst shows an enhanced methanation activity compared to that of the Ni/Al₂O₃ catalyst and the former catalyst shows a better performance for the methanation especially at temperature over 550°C. Three NiMgAl catalysts with different nickel content were prepared and tested in the methanation operated at a GHSV of 15000 h^?1 and n(H₂)/n(CO) of 1.5. The results indicate that with the NiMg8 catalyst a higher activity and stability could be achieved than with the NiMg5 and NiMg6 samples, the effect mainly attributed to a higher extent of Ni dispersion was confirmed by XRD results.     

ZIF‐8‐Nanocrystalline Zirconosilicate Integrated Porous Material for the Activation and Utilization of CO2 in Insertion Reactions

The conversion of CO₂ to useful chemicals, especially to atom economical products, is the best approach to utilize an excess of CO₂ present in the atmosphere. In this study, a metal‐organic framework (ZIF‐8) is integrated with nanocrystalline zirconosilicate zeolite to develop an integrated porous catalyst for CO₂ insertion reactions. The catalyst exhibits excellent activity for the CO₂ insertion reaction of epoxide to produce cyclic carbonate in neat condition without the addition of any co‐catalyst. The catalyst is stable and recyclable during the cyclic carbonate synthesis. Further, the catalyst also exhibits very good activity in another CO₂ insertion reaction to produce quinazoline‐2,4(1H, 3H)‐dione.     

钯配合物催化烯烃氧化合成酮类物质的研究进展

本文系统地评述了钯配合物催化烯烃氧化合成酮类物质的研究进展。综述了改进Wacker 类催化剂催化活性的几种方法。总结了烯烃氧化合成酮类物质反应的几种典型催化体系及其作用机理。着重介绍了Pd (Ⅱ) HPA (杂多酸)、Pd (Ⅱ) FePc (酞菁铁)、Pd (Ⅱ) HQ (氢醌) FePc、Pd (Ⅱ) HQHPA、Pd (Ⅱ) CuSO₄ HPA 等Wacker 类催化体系在烯烃氧化合成酮类物质中的应用; 对Pd (Ⅱ) LCoNO₂、PdCl₂(MeCN)₂ CuCl、Pd (OAc)₂ 吡啶、氟两相等非Wacker 类催化体系在烯烃氧化合成酮类物质中的应用也作了讨论。     

Growth of polystyrene films via gas‐phase polymerization with [Pd(CH3CN)4][BF4]2 thin film catalyst

The heterogeneous catalytic polymerization of styrene vapor with a tetrakis(acetonitrile)palladium(II) tetrafluoroborate, [Pd(CH₃CN)₄][BF₄]₂, thin film has been demonstrated. The catalyst is deposited by nebulization of dilute solutions onto a quartz crystal microbalance (QCM) and then exposed to styrene vapor in controlled environments. The use of QCM allows in situ monitoring of catalyst deposition and polymer growth kinetics. The polymerization process appears to involve the entire catalyst film rather than polymerization only at the catalyst film surface. The styrene vapor polymerization occurs rapidly after a short induction time needed for monomer dissolution and catalyst activation. The narrow molecular weight distribution of the produced polymer suggests that the deposited film acts as a single site catalyst. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1930–1934, 2005     

The polymerization of propadiene by Ni(acac)2, C3H4, RnAlX3−n catalysts

Catalyst formation in the system Ni(acac)₂, C₃H₄, R_nAlX_3?n was studied. Polymerization experiments showed that, by replacing ionic groups such as acac^?, Br^?, Cl^? with alkyl or hydride groups, an active catalyst is obtained. Electrolysis of Ni(acac)₂ in tetrahydrofuran also gives an active catalyst. Lewis acids like (iBu)₃Al and Et₃Al increase the polymerization rate, while Lewis bases like pyridine and triphenylphosphine not only decrease the rate but also change selectivity. The selectivity is not changed if different transition metals (e.g. Co, Pd, Ni) are used. Kinetic measurements show a first order dependence on Ni. The dependence on (iBu)₃Al changes from first to zero order with increasing $\text{Al}\text{Ni}$ ratio. This can be explained by assuming that the very active catalyst is formed via an equilibrium between a nickel complex and (iBu)₃Al. A first order deactivation of the nickel catalyst is observed; it is faster during polymerization than during ageing of the catalyst.     

Crystalline titanium dichloride—an active catalyst in ethylene polymerization. I. Catalyst activation

Crystalline titanium dichloride, in the absence of organometallic cocatalyst, is a very poor catalyst for the polymerization of ethylene. It is transformed into a very active catalyst through mechanical activation (ball-milling). This catalyst is active in the absence not only of organometallic cocatalysts, but also metals and compounds (such as aluminium and AlCl₃) capable of forming organometallic compounds in situ (i.e., with ethylene, before polymerization starts). Ball-milling causes not only the expected increase in surface area but also disproportionation of Ti⁺⁺ to Ti⁺⁺⁺ and metallic titanium, as well as a crystal phase change to a structure not previously identified with those of TiCl₂ or TiCl₃. Catalyst activity (polymerization rate) is shown to be proportional to surface area and a direct function of Ti⁺⁺ content of the catalyst; an empirical equation relates catalyst activity to surface area and to Ti⁺⁺ lost through disproportionation. Titanium trichloride was found to be inactive in the absence of organometallic cocatalyst, even after ball-milling. The difference in structure of the catalytically active species in the conventional Ziegler (organometallic cocatalyst) and in the titanium dichloride catalyst are discussed. The mechanism of polymerization is compared with that of the supported (CrO₃ on SiO₂/Al₂O₃ and MoO₃ on Al₂O₃) catalyst systems.