长碳链烯烃歧化研究进展

目前,虽然直链烯烃歧化研究的重点仍是碳四烯烃歧化制丙烯技术,但是长碳链烯烃歧化研究已开始引起人们的重视。本文介绍了铼基催化剂、钼基催化剂和钨基催化剂催化长碳链烯烃歧化反应的研究进展。重点介绍了钨基催化剂上长碳链歧化研究状况,分别介绍了钨基催化剂上1-己烯自歧化、1-庚烯自歧化、1-辛烯自歧化的最优工艺条件研究以及预处理条件对钨基催化剂歧化性能的影响。同时分别介绍了含氧化合物对歧化催化剂中毒失活的研究以及钨基催化剂上结焦失活的研究状况。     

Al-KIT-6对负载型W基催化剂上丁烯自歧化制丙烯的影响

通过水热法合成具有不同Si/Al比的Al-KIT-6载体,采用浸渍法制备负载型钨基催化剂,并将制备的催化剂应用于丁烯自歧化生产丙烯的反应过程中。采用XRD、BET、Py-IR、H_(2)-TPR和NH_(3)-TPD等测试手段对所制备催化剂进行系统的表征。结果表明,与10%W/KIT-6相比,采用Al掺杂KIT-6载体,可以引入酸性位点,使氧化钨物种在载体表面高度分散,进一步提高反应的异构活性与歧化活性。10%W/10Al-KIT-6具有最高的歧化活性中心,丁烯转化率58.2%,丙烯收率14.4%。     

MgO在WO3/SiO2催化烯烃歧化反应中的作用

综述了负载型钨基催化剂用于烯烃歧化领域的研究情况,简要介绍了烯烃歧化催化剂的研究进展以及歧化反应机理,着重介绍了Mg O助剂在WO3/Si O2催化的丙烯歧化反应中的作用,如生成活性的气相激发物种、促进1-丁烯异构成2-丁烯、调节酸性以减少副反应以及吸附毒物净化原料等,并对Mg O在歧化体系中的作用机理问题进行了部分探讨。此外,还提出了共催化体系的研究趋势,希望能对以后开发高活性的Mg O-WO3/Si O2共催化体系提供有益的指导和参考依据。     

钨基催化剂催化甘油氢解制1,3-丙二醇研究进展

综述了钨基催化剂催化甘油氢解制1,3-丙二醇研究进展。在催化甘油氢解过程中,引入钨酸、含钨杂多酸和氧化钨3种钨基物质可以有效促进甘油向1,3-丙二醇方向反应,有助于形成稳定的中间碳正离子。以固体酸WO_3为活性组分的非均相催化剂,简化了催化反应的后续分离过程,将会成为甘油氢解主流发展方向。     

负载型单中心催化剂用于烯烃聚合的研究进展

综述了近年来在单中心尤其是负载后过渡金属催化剂的最新研究进展,包括单中心催化剂负载的方法、过程和机理以及在烯烃聚合中的应用。通过与均相单中心催化剂性能的比较,进一步说明了负载的目的和必要性?指出了负载型单中心催化剂目前存在的问题和未来研究的方向。     

合成间同立构PS用单中心催化剂的研究进展

综述了茂金属催化剂和非茂钛催化剂合成间同立构聚苯乙烯的研究进展,其中,茂金属催化剂主要包括茂钛催化剂、单茂钛催化剂、茚钛催化剂、双核金属催化剂及负载型催化剂等。今后的研究重点是负载型茂金属催化剂和非茂钛催化剂,单中心催化剂将对合成间同立构聚苯乙烯的工业化发展发挥重要的作用。     

负载型金属催化剂的热稳定机制

负载型金属催化剂是一类重要的催化材料,在石油炼制、环境保护以及材料合成等领域起着重要的作用。然而,由于活性金属在反应环境下容易烧结团聚,以致活性降低乃至失活,因此,如何提高其热稳定性成为负载型金属催化剂研究的一个关键问题。概述了催化剂的金属团聚成因及其稳定机制。简要介绍了Ostwald效应以及颗粒合并长大两种团聚模型,从热力学角度解释了导致催化剂烧结团聚的原因。总结了现阶段几种提高负载型金属催化剂热稳定性能的方法,具体包括以包覆封装隔离为原理的物理方法,以及以形成化学键为基础的化学方法,可为进一步开发高热稳定性的负载型金属催化剂提供借鉴。     

固态紫外光谱法在炼油催化剂表征中的应用

总结了有关固态紫外光谱法在炼油催化剂表征中的应用，包括载体与催化剂的吸附、金属界面、金属中心、孔道结构、负载型过渡金属催化剂及杂多型分子筛等，并对其应用方法和技术进行了评述。     

掺杂型负载金属催化剂在甲烷裂解反应中的研究进展

甲烷催化裂解反应能够同时制取不含碳氧化物的高纯氢和纳米碳材料,引起研究界的广泛关注。Ni、Fe和Co是常用的甲烷裂解反应的催化剂的活性组分,但单活性组分的负载型金属催化剂往往存在转化率低和寿命短等缺点,通过催化剂的设计改进其性能是催化剂研究工作的重要方向之一。除了制备方法的选择和反应条件的优化,利用不同金属组分性质间的差异,在其中引入第二或第三组分,同样能够有效改善催化剂的性能。对掺杂型负载金属催化剂的研究进行了综述。概述了催化剂的失活机理及模型（活性位覆盖模型和孔道口堵塞模型）,以及如何从失活原因出发进行掺杂型负载金属催化剂的设计。根据掺杂元素作用方式不同,分类介绍了当前掺杂型负载金属催化剂的主要研究成果及其未来的发展方向。     

氧化钨空心球制备及其光催化性能

在较低温度下制备出氧化钨空心球,一方面可以提高催化剂对光源的利用率,另一方面能够降低催化剂成本。以氯化钨为钨源,将其在70 ℃下醇解和水解,于磺化聚苯乙烯微球表面形成氧化钨前驱体纳米颗粒,通过煅烧制备了氧化钨空心球。利用场发射扫描电镜（FE-SEM）、X射线衍射（XRD）、傅里叶变换红外光谱（FT-IR）和综合热分析（TG-DTG）对所制备的产物进行表征。通过光催化降解罗丹明B溶液来测试氧化钨空心球的催化性能,结果表明光照60 min后催化剂对罗丹明B溶液的光催化降解率可达86.61%。     

Efficient Heterogeneous Dual Catalyst Systems for Alkane Metathesis

A fully heterogeneous and highly efficient dual catalyst system for alkane metathesis (AM) has been developed. The system is comprised of an alumina‐supported iridium pincer catalyst for alkane dehydrogenation/olefin hydrogenation and a second heterogeneous olefin metathesis catalyst. The iridium catalysts bear basic functional groups on the aromatic backbone of the pincer ligand and are strongly adsorbed on Lewis acid sites on alumina. The heterogeneous systems exhibit higher lifetimes and productivities relative to the corresponding homogeneous systems as catalyst/catalyst interactions and bimolecular decomposition reactions are inhibited. Additionally, using a “two‐pot” device, the supported Ir catalysts and metathesis catalysts can be physically separated and run at different temperatures. This system with isolated catalysts shows very high turnover numbers and is selective for the formation of high molecular weight alkanes.     

Optimizing activity of tungsten oxides for 1-butene metathesis by depositing silica on γ-alumina support

A series of catalysts made of tungsten oxide loaded on SiO₂, γ-Al₂O₃, SiO₂–Al₂O₃ and silica deposited γ-alumina are tested for 1-butene metathesis. Among these catalysts, the catalyst 6W/20SiO₂/Al₂O₃ gives the highest activity for 1-butene metathesis reaction with 1-butene conversion up to 71 mol% and the yield of propene up to 21 mol%. The excellent catalytic activity is related to the moderate dispersion of tungsten oxide and the suitable acidity of the support. The dispersion of WO_x species and the acidity of supports were studied by characterization of XRD, Raman spectra, UV–vis, H₂-TPR and NH₃-TPD in detail. The surface properties of silica modified γ-alumina leads to the moderate aggregation of supported tungsten oxide, which appears to be more effective for 1-butene metathesis at the low temperature of 453 K. Optimized activity was realized by tuning the dispersion of tungsten species on silica deposited alumina.     

Olefin Metathesis on a TLC Plate as a Tool for a High‐Throughput Screening of Catalyst‐Substrate Sets

A methodology for screening either various catalysts for a given metathesis reaction, i.e., ring opening‐ring closing alkene metathesis (RO‐RCM) and cross‐metathesis (CM), or various substrates for a given pre‐catalyst on a thin layer chromatography (TLC) plate has been developed. As the substrates elute with the solvent, this TLC‐based system acts as a heterogeneous catalyst bed (“TLC reactor”). Selected promising catalyst candidates were screened on a TLC plate and their initial catalytic potential as observed in the TLC test was later fully confirmed in a classical heterogeneous reaction set‐up using standard commercially available silica (D11‐10). Reacting polyfunctional, natural product‐like substrates in our TLC reactor allows the simultaneous screening of various substrates and the convenient micro‐scale preparation and isolation of potentially biologically active products.     

Effect of Surface Tungstate W<Superscript>5+</Superscript> Species on the Metathesis Activity of W-Doped Spherical Silica Catalysts

The high surface area W-doped spherical silica (SSP) catalysts were prepared with different sequences of W and Si addition (W–Si_(Alt), Si₁–W_2, and W₁–Si₂) by the sol–gel method with CTAB as a structure directing agent and compared with the impregnated one (W/SSP). All the catalysts exhibited high specific surface area (～?1100 m² g^?1) with a closely perfect spherical shape. The presence of surface/sub-surface tungstate W⁵⁺ species, crystalline bulk WO₃, and tetrahedral tungsten oxide species on the prepared catalysts was investigated by means of X-ray photoelectron spectroscopy depth profile analysis, X-ray diffraction, and Raman spectroscopy. Without in situ reduction by the reactants/products, tungstate W⁵⁺ species was found on the top surface of the as-prepared W–Si_(Alt) whereas for the Si₁–W₂, W/SSP, and W₁–Si₂, the W⁵⁺ appeared only on the sub-surface of the catalysts after 5 and 15 s Ar⁺ etching. The abundance of surface W⁵⁺ species is suggested to facilitate the establishment of the active tungsten carbenes and was correlated well to the catalytic activity in propene metathesis. The surface W⁵⁺-activity relationship of the WO₃-based metathesis catalysts is useful especially when the catalyst activity did not depend solely on the amount of active tetrahedral coordinated tungsten oxides.     

Katalysatorrecycling in der homogenkatalysierten Kreuzmetathese von Ölsäuremethylester und 4‐Octen

The recycling of homogeneous metathesis catalysts is a big challenge in alkene metathesis. Within this contribution the recycling of these catalysts is investigated in the cross metathesis of methyl oleate and 4‐octene as model reaction. Fluid‐fluid separation technique and temperature dependent solvent systems allow the separation of the homogeneously solved catalysts from the metathesis products. The catalyst phase was successfully recycled in multiple recycling runs only with minor loss of yield.     

Ring-Opening Metathesis Polymerization of 5,6-Bis(Chloromethyl)-Norbornene by Tungsten(II) and Molybdenum(II) Complexes

The reaction of endo,endo-5,6-bis(chloromethyl)bicyclo[2.2.1]hept-2-ene in the presence of seven-coordinate tungsten(II) and molybdenum(II) complexes of the type [MCl(M'Cl₃)(CO)₃(NCMe)₂] (M'=W, Mo; M=Sn, Ge) leads to ring-opening metathesis polymerization and to the formation of high-molecular-weight soluble polymers with dispersity index in the range 1.4-2.0 and number average molecular weights in the range 300 000-790 000 g mol^-1. The geometric structure of these polymers was determined by means of ¹H- and ¹³C-NMR spectroscopy. Molybdenum catalysts gave polymers with lower cis vinylene content (20-50%), whereas tungsten catalysts gave polymers with higher cis vinylene content (84-95%).     

Alumina supported tungsten hydrides, new efficient catalysts for alkane metathesis

Silica and alumina supported tantalum and tungsten hydrides were tested in alkane metathesis, for comparison of their catalytic properties. In propane metathesis [W]–H/Al₂O₃ proves to be twice more efficient than the usual [Ta]–H/SiO₂ catalyst which is still better than [Ta]–H/Al₂O₃ and [W]–H/SiO₂. Tungsten based catalysts lead to a narrower distribution in the products selectivity and to a higher amount of linear products than [Ta]–H/SiO₂. [W]–H/Al₂O₃ is also a better catalyst than [Ta]–H/SiO₂ for butane metathesis but is less efficient with ethane. Whereas the results in the case of propane or butane can involve the higher initial activity and a lower deactivation of the tungsten catalyst, in the case of ethane, mechanistic or kinetic aspects can be envisaged in particular concerning the difficulty to dehydrogenate ethane into ethylene.     

Baeyer–Villiger oxidation of cyclohexanone catalyzed by cordierite honeycomb washcoated with Mg–Sn–W composite oxides

In this work, a series of Mg–Sn–W oxide powder catalysts with different tungsten oxide contents(0, 15 wt% and 30 wt%) were prepared and washcoated on cordierite honeycomb monoliths to produce monolithic catalysts,which were tested for the Baeyer–Villiger oxidation of cyclohexanone. The obtained monolithic catalysts,which combined the advantages of both homogeneous and heterogeneous catalysts, showed high catalytic efficiency and overcame the problems of product separation that occurred in the homogeneous catalytic process.SEM and EDX tests showed that the catalytic coating, with a thickness of approximately 20 μm, was compact and homogeneous, and an enlarged BET surface area was indicated by N_2 adsorption–desorption compared with the bare cordierite honeycomb. The chemical properties on the catalytic surface of the powder and monolithic catalysts were characterized by XPS, which indicated the tin and tungsten on the catalysts exhibited their full oxide states and presented mainly as stannate and tungstate, as confirmed by XRD and FTIR characterizations.Moreover, the catalytic activity test indicated that the tungsten content of the catalysts played an important role in catalytic efficiency and that monolithic catalysts were produced without obvious catalytic activity loss compared with the corresponding powders.(M)W30, which exhibited excellent mechanical stability and maintained high activity after recycling three times, was the optimal catalyst, showing a high selectivity that exceeded 86%and a conversion above 64%. Therefore, the structured Mg–Sn–W oxide catalysts have great potential for application in practical production.     

The monometallic initiation of the metathesis polymerization of cyclopentene

A detailed study of the monometallic initiation of the polymerization of cyclopentene by WCI₆ has shown that the kinetics of polymerization are extremely complex. The complexity is associated with the formation of a heterogeneous system. Two species have been postulated to act as metathesis catalysts: (i) a toluene soluble species with low activity and (ii) experimental confirmation of a highly active toluene insoluble species that requires the presence of oxygen for its activity.