负载液相催化剂的研究进展

负载液相催化剂是一种新型的“混合型”催化剂,它结合了均相催化高活性、高选择性和多相催化接触面积大、容易分离的优点,有广阔的应用前景。综述了迄今为止关于负载液相催化剂的研究进展,总结了负载液相催化剂的特点及其在许多重要化学反应中的应用。     

均相多相化体系中环境友好催化工艺进展

评述了可形成第三相相间转移（PTC）催化剂，水溶性配合物催化剂，氟溶催化剂，离子液体催化反应和固载催化剂的多相催化的发展过程以及这些催化剂均相/多相化催化过程所表现的良好性能，由于均相催化多相化的实现，不仅催化剂容量从反应产物得以分离循环再用，而且也有利于环保，具有显著的社会和经济效益。     

Characterization and Catalytic Oxidation of Carbon Monoxide Over Supported Cobalt Catalysts

Three types of supported cobalt catalysts (CoO_x/SiO₂, CoO_x/TiO₂ and CoO_x/Al₂O₃) were prepared by incipient wetness impregnation with aqueous Co(NO₃)₂·6H₂O solution. The phase composition and the interactions of cobalt with supports under different calcined temperatures were investigated using thermogravimetry (TG), N₂-adsorption at −196 °C, X-ray diffraction (XRD), temperature-programmed reduction (TPR) and diffuse reflectance spectroscopy (DRS). Their catalytic activities towards the CO oxidation were further studied in a continuous flow micro-reactor. The results showed that the interaction of cobalt oxide with supports was much stronger in the kinds of Al₂O₃ and TiO₂, while no conclusive evidence of any interaction was found for SiO₂. Besides the crystalline Co₃O₄ which was formed in three supported catalysts, both high-temperature phases CoAl₂O₄ and CoTiO₃ spinel were also detected under XRD, DRS and TPR analysis. The degree of interaction between cobalt oxide and the support not only affected the surface area and reduction behavior of the catalysts, the catalytic activity toward the CO oxidation also affected simultaneously. As the CoAl₂O₄ and CoTiO₃ spinel formed, both the surface area and catalytic activity decreased significantly.     

XAFS study of the state of platinum in a sulfated zirconia catalyst

EXAFS and XANES data show that platinum, present in a Pt-SO₄-ZrO₂ catalyst, exists in the metallic state following calcination in air at 725°C for 2 h, and that no detectable change in the valence state of Pt occurs during use of the catalyst for hydrocarbon conversion at 150°C under hydrogen pressure. The metallic Pt is present in reasonably large crystals where the average coordination number of Pt is about 12.     

Supported ionic liquids: versatile reaction and separation media

The latest developments in supported ionic liquid phase (SILP) systems for catalysis and separation technology are surveyed. The SILP concept combines the advantages of homogeneous catalysis with heterogeneous process technology, and a variety of reactions have been studied where supported ionic liquid catalysts proved to be more active and selective than common systems. In separation applications the use of supported ionic liquids can facilitate selective transport of substrates across membranes.     

Ethylene Polymerization using Combined Ni and Ti Catalysts Supported in situ on MAO‐Modified Silica

Summary: Branched polyethylene/linear polyethylene blends (BPE/LPE) were prepared using the combined Ni(α‐diimine)Cl₂ ( 1 ) (α‐diimine = 1,4‐bis(2,6‐diisopropylphenyl)acenaphthenediimine) and {Tp^Ms*}TiCl₃ ( 2 ) (Tp^Ms* = hydridobis(3‐mesitylpyrazol‐1‐yl)(5‐mesitylpyrazol‐1‐yl)) catalysts supported in situ on methylaluminoxane (MAO)‐modified silica (4.0 wt.‐% Al/SiO₂). The polymerization reactions were performed in toluene at two different polymerization temperatures (0 and 30 °C) and several nickel molar fractions (x_Ni), using MAO as external cocatalyst. At all temperatures, the activities show an approximate linear correlation with x_Ni, indicating a non‐synergistic effect between the nickel and the titanium species. Higher activities were found at 0 °C. The melting temperatures for the polyethylene blends produced at 0 °C decrease as x_Ni increases in the medium, indicating good compatibility between the polyethylene phases made by both catalysts. The melting temperature (T_m) of the polyethylene blends was shown to depend on the order in which the catalysts were immobilized on the MAO‐modified silica support. The initial immobilization of 1 on the support ( 2 / 1 /SMAO‐4) affords polymers with a lower T_m than those produced with 1 / 2 /SMAO‐4. In addition, scanning electron microscopy (SEM) studies revealed that the spherical morphology of the supported catalyst is replicated in the polyethylene particles.

Influence of polymerization temperature on the activity of 1 / 2 /SMAO‐4 with varying x_Ni.     

负载金属催化剂的结构性能表征

综述了H2-TPR,TEM,XRD等物化方法在负载型金属催化剂的结构性能（包括金属分散度、表面结构、电子状态）方面的应用,为更好地认识和使用负载型金属催化剂提供了可靠的依据。     

Taking “Nothing” into Consideration: Supported Metal Catalysts by SAXS

The analysis of the X‐ray diffraction patterns scattered at small‐angles (SAXS) by porous materials is a powerful analytical tool providing relevant structural information on supported metals used as heterogeneous catalysts. In particular, the technique offers valuable structural insights on the interphases which govern the chemical behaviour of these materials. Using a series of silica‐supported palladium catalysts we show how SAXS experiments address the crucial importance of porosity (or “nothing”) in affecting the structure of these catalysts.     

Characterization and Catalytic Performance of PtSn Catalysts Supported on Al2O3 and Na-doped Al2O3 in n-butane Dehydrogenation

PtSn/Al₂O₃ and PtSn/Al₂O₃–Na catalysts display important modifications of the metallic phase with respect to Pt/Al₂O₃ one. In this sense, TPR and XPS results show the presence of strong interactions between Pt and Sn, with probable alloy formation, which would be responsible for the decrease of the reaction rate and the increase of the activation energy in cyclohexane dehydrogenation. Besides the experiments of cyclopentane hydrogenolysis show that the alkali metal addition to bimetallic PtSn/Al₂O₃ catalysts completely eliminates the hydrogenolytic ensembles, which could be due to a geometric modification of the metallic phase. These important modifications in the nature of the metallic function due to the simultaneous addition of Na and Sn to Pt/Al₂O₃ are responsible for the excellent catalytic performance in the n-butane dehydrogenation, thus giving high conversions, selectivities to butenes higher than 95%, and lower deactivation capacity than those corresponding to bimetallic PtSn catalysts (with different Sn contents) supported on undoped alumina. The excellent stability of PtSn/Al₂O₃–Na catalysts would be due to a low carbon formation during the reaction, such as it was observed from pulse experiments.     

负载型金催化剂在多相催化中的应用

文章综述了近年负载型金催化剂在环境保护及化学工业方面的应用研究进展,包括CO的常温催化氧化、卤代有机化合物的消除、氮氧化物的还原、丙烯的选择性氧化和氢氧直接氧化法合成双氧水。     

New Polymer‐Supported Catalysts for the Asymmetric Transfer Hydrogenation of Acetophenone in Water – Kinetic and Mechanistic Investigations

Heterogenization is a powerful approach for the generation of easily recyclable catalysts. In this study, a modified tethered rhodium(III)‐ p‐toluenesulfonyl‐1,2‐diphenylethylenediamine (Rh‐TsDPEN) complex immobilized on polymeric supports was applied to kinetic and up‐scaling experiments on the asymmetric transfer hydrogenation of acetophenone in water. Study of the catalyst has helped in understanding some aspects of its operating mode. The results indicate that, in the investigated range, a simple second‐order model describes the enantioselective conversion of acetophenone to phenylethanol. Optimal reaction conditions were determined, and particularly the solution pH was found to play a decisive role for the activity and reusability of the catalyst. The good performance under optimized conditions emphasizes the practical usefulness of this recyclable catalytic system for environmentally benign asymmetric transfer hydrogenation processes.     

Aqueous-Phase Reforming of Ethylene Glycol Over Supported Platinum Catalysts

Aqueous-phase reforming of 10 wt% ethylene glycol solutions was studied at temperatures of 483 and 498 K over Pt-black and Pt supported on TiO₂, Al₂O₃, carbon, SiO₂, SiO₂-Al₂O₃, ZrO₂, CeO₂, and ZnO. High activity for the production of H₂ by aqueous-phase reforming was observed over Pt-black and over Pt supported on TiO₂, carbon, and Al₂O₃ (i.e., turnover frequencies near 8-15 min^-1 at 498 K); moderate catalytic activity for the production of hydrogen is demonstrated by Pt supported on SiO₂-Al₂O₃ and ZrO₂ (turnover frequencies near 5 min^-1); and lower catalytic activity is exhibited by Pt supported on CeO₂, ZnO, and SiO₂ (H₂ turnover frequencies lower than about 2 min^-1). Pt supported on Al₂O₃, and to a lesser extent ZrO₂, exhibits high selectivity for production of H₂ and CO₂ from aqueous-phase reforming of ethylene glycol. In contrast, Pt supported on carbon, TiO₂, SiO₂-Al₂O₃ and Pt-black produce measurable amounts of gaseous alkanes and liquid-phase compounds that would lead to alkanes at higher conversions (e.g., ethanol, acetic acid, acetaldehyde). The total rate of formation of these byproducts is about 1-3 min^-1 at 498 K. An important bifunctional route for the formation of liquid-phase alkane-precursor compounds over less selective catalysts involves dehydration reactions on the catalyst support (or in the aqueous reforming solution) followed by hydrogenation reactions on Pt.     

One‐Pot/Four‐Step/Palladium‐Catalyzed Synthesis of Indole Derivatives: The Combination of Heterogeneous and Homogeneous Systems

One‐pot, four‐step syntheses of indoles using both solid‐supported heterogeneous and homogeneous palladium catalysts and reagents were carried out. Such a combination of these two‐phase catalysts and reagents causes a dramatic increase in yield, and it is a simple process. The presented methodology is effective for four‐step reactions to provide various functionalized indoles.     

活性炭负载[Rh(COD)Cl]2催化剂的制备及其催化性能

以氧化活性炭(OAC)为载体、自制[Rh(COD)Cl]_2为活性组分,制备了负载型催化剂[Rh(COD)Cl]_2/OAC(COD为1,5-环辛二烯),用XPS、N2吸-脱附、FTIR等对其结构进行了表征与分析,以β-蒎烯加氢反应为探针反应,考察了载体种类、氧化剂HNO3浓度、[Rh(COD)Cl]_2与OAC质量比对负载型催化剂[Rh(COD)Cl]_2/OAC性能的影响,在此基础上优化了β-蒎烯加氢工艺条件,并测定了催化剂([Rh(COD)Cl]_2/OAC)的重复使用性。结果表明,催化剂的最佳制备条件为:氧化活性炭为较佳载体,HNO3浓度为7.23mol/L,[Rh(COD)Cl]_2与OAC质量比为1∶8.3,此时β-蒎烯转化率均值为99.94%;顺式蒎烷选择性(以只生成蒎烷计,下同)均值为88.64%;顺式蒎烷收率均值为88.59%;β-蒎烯加氢工艺的最佳条件为:反应温度50℃,反应压力3.5 MPa,催化剂用量为β-蒎烯质量的3.5%,反应时间4.0 h,此条件下β-蒎烯转化率均值为99.88%;顺式蒎烷选择性均值为89.00%;顺式蒎烷收率均值为88.90%,[Rh(COD)Cl]_2/OAC催化剂在β-蒎烯加氢反应中表现出较佳的催化活性。催化剂重复使用4次后,β-蒎烯转化率仍可达89.64%,活性组分Rh的流失是造成催化剂失活的主要原因。     

负载型非晶态合金催化剂的制备、表征及其研究进展

介绍了负载型非晶态合金催化剂的特点,总结了负载型非晶态合金催化剂的制备方法、表征手段及最新的研究进展.负载型非晶态合金催化剂将是一种有着广阔发展前景的催化材料.     

Thiazolium‐Based Catalysts for the Etherification of Benzylic Alcohols under Solvent‐Free Conditions

Thiazolium and imidazolium hybrid materials were prepared by radical reactions between a mercaptopropyl‐modified SBA‐15 mesoporous silica and bis‐vinylthiazolium or bis‐vinylimidazolium dibromide salts. These hybrid materials were characterized by several techniques and were employed in the etherification reaction of 1‐phenylethanol. Solvent‐free conditions at 160 °C under different gas phases (oxygen, air, nitrogen and argon) were used. The thiazolium‐based material displayed excellent performances. Further studies were carried out using unsupported thiazolium salts, with or without a methyl group at the C‐2 position of the thiazolium moiety. These studies allowed us to propose a reaction mechanism. The supported thiazolium‐based material was successfully used in the etherification reaction of two other benzylic alcohols and also in seven consecutive cycles. This work represents the first use of thiazolium‐based compounds as catalysts for the etherification reaction of alcohols.

     

Effect of the Helical Tether of a Resin‐Supported Peptide Catalyst for Friedel–Crafts‐Type Alkylation in Water

A detailed investigation of the helical part of the resin‐supported peptide catalyst possessing a turn motif and helical unit was conducted to clarify the structure‐activity relationship. The peptide catalyst with an α‐ or 3₁₀‐helical tether was effective for an enantioselective Friedel–Crafts‐type alkylation in water. From the spectral analysis of the peptide with an optimum sequence, it was demonstrated that the helical moiety of the peptide catalyst played a role for stabilizing a terminal turn structure.     

Gas/Surface Titration Microcalorimetry. Energetics of Oxygen Adsorption on Supported Iridium Catalysts

Measurements of the heat of adsorption of hydrogen on Ir/Al₂O₃ catalysts of different metal particle size were made by employing adsorption microcalorimetry. The values of this quantity were different for each sample and the results also indicated the heterogeneity of the iridium surface. In contrast to this, the heat of adsorption of oxygen measured on the same samples in the same manner was practically the same for all of them. The heat of oxygen adsorption as presented in the differential calorimetric isotherms was constant up to half the monolayer coverage for all the samples. This result is unexpected and in contradiction to the presence of surface heterogeneity in the iridium crystallites, as revealed by hydrogen adsorption. To clarify these anomalies the energetics of oxygen adsorption was determined using a different method. Titration experiments with hydrogen of preadsorbed oxygen were carried out. The heat of adsorption of oxygen was calculated from these results by means of adopting a thermochemical cycle. The values of heat of adsorption obtained as a function of the amount adsorbed unveiled the heterogeneity of the iridium surface. The differences found between the samples can be correlated to both the different particle size and degree of sintering of the samples.