碳化钨催化剂上烷烃异构化研究进展

综述了用于长链烷烃异构化的碳化钨催化剂的研究进展。介绍了催化剂的制备方法和异构化反应机理。分析了此类催化剂今后的发展趋向和应用前景。     

烯烃歧化反应中的负载氧化钨催化剂

综述了负载型钨基催化剂用于烯烃歧化领域的研究情况,着重介绍了负载氧化钨催化剂的制备、反应机理和工艺条件的研究,简要介绍了负载有机钨催化剂的研究进展。在此基础上,文章总结了影响负载氧化钨催化剂活性的几个重要因素,如中心金属（钨）的价态、金属中心的构型、催化剂的酸性以及负载金属的分散性等,并提出了负载型钨基歧化催化剂的研究趋势,希望能对以后开发高活性的氧化钨催化剂提供有益的指导和参考依据。     

Solid acid catalysts based on supported tungsten oxides

Supported WO _x clusters are active and stable catalysts for isomerization, dehydration, and cracking reactions. Brønsted acid sites form on WO _x clusters when a lower valent element replaces W^{6 +} or when W^{6 +} centers reduce slightly during catalytic reactions. WO _x clusters of intermediate size provide the balance between reducibility and accessibility required to maximize the number of surface H⁺ species in WO _x –ZrO₂, zirconium tungstate, and oxygen-modified WC catalysts. H₂ is involved in the generation and maintenance of Brønsted acid sites during catalytic reactions on WO _x clusters.     

Synthesis, characterization and hydrotreating performance of supported tungsten phosphide catalysts

Supported tungsten phosphide catalysts were prepared by temperature-programmed reduction of their precursors (supported phospho-tungstate catalysts) in H₂ and characterized by X-ray diffraction (XRD), BET, temperature-programmed desorption of ammonia (NH₃-TPD) and X-ray photoelectron spectroscopy (XPS). The reduction-phosphiding processes of the precursors were investigated by thermogravimetry and differential thermal analysis (TG-DTA) and the suitable phosphiding temperatures were defined. The hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities of the catalysts were tested by using thiophene, pyridine, dibenzothiophene, carbazole and diesel oil as the feedstock. The TiO₂, γ-Al₂O₃ supports and the Ni, Co promoters could remarkably increase and stabilize active W species on the catalyst surface. A suitable amount of Ni (3%–5%), Co (5%–7%) and V (1%–3%) could increase dispersivity of the W species and the BET surface area of the WP/γ-Al₂O₃ catalyst. The WP/γ-Al₂O₃ catalyst possesses much higher thiophene HDS and carbazole HDN activities and the WP/TiO₂ catalyst has much higher dibenzothiophene (DBT) HDS and pyridine HDN activities. The Ni, Co and V can obviously promote the HDS activity and inhibit the HDN activity of the WP/γ-Al₂O₃ catalyst. The G-Ni5 catalyst possesses a much higher diesel oil HDS activity than the sulphided industrial NiW/γ-Al₂O₃ catalyst. In general, a support or promoter in the WP/γ-Al₂O₃ catalyst which can increase the amount and dispersivity of the active W species can promote its HDS and HDN activities.     

碳化钨载铂的制备及其对硝基苯的电催化还原

以偏钨酸铵（AMT）为钨源前驱体,气流式喷雾干燥仪造粒,得到空心球状结构偏钨酸铵,固定床气固反应,以CO/CO₂为还原碳化气氛在800℃下制备了介孔空心球状碳化钨。采用氯铂酸作为铂源,用浸渍、气相还原法制备了Pt/WC粉末催化剂。通过XRD和SEM测试手段对Pt/WC粉末样品进行了表征,表明Pt成功负载在介孔WC材料上。采用循环伏安法、以Pt/WC粉末微电极为工作电极,研究了Pt/WC对在质子惰性介质中硝基苯的硝基还原的催化作用。结果表明,Pt/WC催化剂对硝基还原有着良好的电催化活性和化学稳定性。     

凹凸棒土固载N-杂环卡宾催化安息香缩合反应

本文将五种不同的NHCs催化剂前体接枝到凹凸棒土表面，制备了五种负载型NHCs催化剂。通过FT-IR、元素分析、BET和SEM对五种催化剂进行了表征，表征结果表明NHCs催化剂前体成功地固定在凹凸棒土表面。进一步的实验结果表明，这些负载型NHC可以作为安息香反应的有效催化剂。接着探究了这些负载型催化剂催化安息香反应的优化条件。结果发现，当BTBCl@ATP(催化剂B, 1 mmol%咪唑盐)作为催化剂，0.4当量NaOH作为碱，2ml CH3OH作为溶剂，在110℃油浴中，在Ar气氛中反应8小时，收率最高。在此优化条件下，负载型NHCs催化剂可以催化多种芳香醛的安息香反应，产率为61-86%。催化剂的重复使用实验表明，这些负载型催化剂可以简单地从反应体系中分离出来，重复使用四次后，这些负载型催化剂的催化活性没有明显下降。     

Investigation of the preparation and catalytic activity of supported Mo,W, and Re oxides as heterogeneous catalysts in olefin metathesis

For several decades olefin metathesis reactions over supported Mo, W, and Re oxides catalysts have attracted remarkable interest owning to their growing industrial applications. Therefore, particular attention was devoted to improve the catalytic activity of these catalysts. In the way of exploration of the catalytic performances of these heterogeneous Mo, W, and Re oxides systems, it was found that high dispersion of metal oxide on the support surface and the oxidation state of the metal oxide on the surface of catalyst play crucial factors on the catalysts efficiency. Importantly, these factors have an origin in the preparation methods and the properties of the used supports. In this regard, we have tried to address the various preparation methods of immobilized Mo, W, and Re oxide catalysts as well as properties of supporting material to better understand their impacts on the catalytic performances of these catalysts.     

The activity of molybdenum and molybdenum oxide model catalysts for olefin metathesis

The activity of various molybdenum oxides supported on a molybdenum foil substrate for the catalysis of propylene metathesis is measured using an isolatable, high-pressure reactor incorporated in an ultra-high vacuum (UHV) chamber which allows samples to be transferred directly from vacuum into the catalytic test chamber. MoO _x samples are prepared both by oxidation of metallic molybdenum and reduction of molybdenum trioxide. The results suggest that the presence of an oxygen overlayer on the catalyst inhibits reaction and that the ranking of activity for metathesis at 870 K using 450 Torr of propylene for oxide samples is MoO₂>MoO₃>Mo where MoO₂ is 30 times more active than molybdenum metal under these conditions.     

Oxidation of 5-hydroxymethylfurfural over supported Pt, Pd and Au catalysts

Supported Pt, Pd, and Au catalysts were evaluated in the aqueous-phase oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) at 295 K and high pH in a semibatch reactor. The intermediate reaction product 5-hydroxymethyl-2-furancarboxylic acid (HFCA) was formed in high yield over Au/C and Au/TiO₂ at 690 kPa O₂, 0.15 M HMF and 0.3 M NaOH, but did not continue to react substantially to FDCA at the specified O₂ pressure and base concentration. In contrast, the final reaction product FDCA was formed over Pt/C and Pd/C under identical conditions. The initial turnover frequency of HMF conversion was an order of magnitude greater on Au catalysts compared to either Pt or Pd. Increasing the O₂ pressure and NaOH concentration facilitated the conversion of HFCA to FDCA over the supported Au. The significant influence of base concentration on the product distribution indicates an important role of OH⁻ in the activation, oxidation and degradation of HMF.     

复分解电渗析清洁生产谷氨酸钠新工艺

谷氨酸钠（sodium glutamate,NaGA）是味精（monosodium glutamate,MSG）的主要成分,其传统生产方法为"等电点结晶-酸碱中和"法,传统工艺存在工艺流程长、酸碱消耗大、环境污染严重等问题,而且其谷氨酸钠产品液浓度尚未达到结晶工艺所需的浓度。为此本文提出复分解电渗析离子重组工艺来清洁生产谷氨酸钠,并对该工艺进行了实验验证及过程优化。复分解电渗析可实现原料液的一步转化,直接获得高浓度谷氨酸钠产品液,在优化条件下,最终产品液浓度为1.79mol/L （约30.2%）,转化率为91.2%,能耗为2.98kW·h/kgNaGA,其副产（NH₄）₂SO₄可作为生产铵肥的原料,不存在二次污染。此工艺具有工艺流程短、酸碱零消耗、无二次污染的优点,而且所得谷氨酸钠产品液浓度达到了结晶工艺所需的浓度要求,这对电驱动膜过程在味精产业的应用具有重要意义。并通过对树脂填充床电渗析与普通电渗析、均相离子交换膜与异相离子交换膜的比较实验,验证了选用异相膜树脂填充床电渗析生产谷氨酸钠的合理性。     

W-SBA-15的直接合成及其对2-丁烯与乙烯歧化制丙烯反应的催化性能

以Na₂WO₄为钨源,以正硅酸乙酯为硅源,采用直接水热法合成了W-SBA-15介孔分子筛,并用XRD、N₂吸附、HRTEM、UV-Vis DRS、NH₃-TPD、H₂-TPR等手段对合成的分子筛进行了表征。表征结果表明,当分子筛中硅钨摩尔比为44时,钨物种以高度分散的四面体和八面体形式存在于分子筛的骨架中,随着钨含量的增加,当硅钨比为30时,分子筛中出现了微量的骨架外钨物种,当硅钨摩尔比为20时,骨架外钨含量增多。W-SBA-15分子筛在乙烯与2-丁烯歧化制丙烯反应中表现出优异的催化性能,在反应温度300℃、压力3.0 MPa、质量空速6.4 h^-1的实验条件下,反应24 h后丁烯的转化率和丙烯的选择性分别高于50%和96％,优于传统的负载型WO₃/SiO₂催化剂。硅钨摩尔比为44时的W-SBA-15具有最好的钨物种分散性和最佳的烯烃歧化性能。     

Cathode catalysts for fuel cell development: A theoretical study based on band structure calculations for tungsten nitride and cobalt tungsten nitrides

Band structure calculations were performed for tungsten nitride, cobalt tungsten nitrides, and platinum slabs. The major requirements for the development of a superior cathode catalyst are: (1) that the Fermi level of the cathode catalyst is close to the energy level of the lowest unoccupied molecular orbital of O₂, the lowest unoccupied atomic orbital of an oxygen atom, and the lowest unoccupied atomic orbital of a hydrogen atom so that they can readily interact with one another; and (2) that the cathode catalysts have smaller ΔE value which represent the difference between the Fermi level and the peak position of the density of states of the O_p orbital of O₂ adsorbed on the catalyst. The active site structures of cobalt tungsten nitrides for activation of the oxygen reduction reaction were found to have the surface structure of Co–O–Co, which lowered the unoccupied orbital of the oxygen atom to approximately that of the Fermi level. However, this structure concomitantly lowered the Fermi level, which resulted in an increase in ΔE. Consequently, the optimal cathode catalyst regarding the surface conformation contains a Co–O–Co structure that is dispersed on the surface of the cobalt tungsten nitride. The cobalt tungsten oxynitride exhibited a catalytic activity for the oxygen reduction reaction. A linear dependence is observed between the ΔE and the oxygen reduction reaction offset potentials of the tungsten nitride, cobalt tungsten nitride, cobalt tungsten oxynitride, and platinum.     

非球面玻璃模造用碳化钨模仁磁控溅射铼-铱镀膜工艺优化

通过钽过渡镀层与铼-铱复合镀层相结合的膜层结构,解决了非球面玻璃模造碳化钨模仁热压寿命短、沾黏等问题。通过离子源和镀膜层厚度参数的优化调整,得到了最佳镀膜工艺和参数,改善了模仁的表面品质,延长了模仁的使用寿命。镀钽膜层15min及铼-铱膜层21min后所得镀膜的总厚度约为270nm,模仁热压寿命可超过3000次。     

Alumina supported MoO3: an efficient and recyclable catalyst for selective oxidation of tertiary nitrogen compounds to N-oxides using anhydrous TBHP as oxidant under mild reaction conditions

Alumina-supported MoO₃ was found to be an efficient heterogeneous and recyclable catalyst for the oxidation of tertiary nitrogen compounds to N-oxides in excellent yields using anhydrous t-BuOOH as oxidant under mild reaction conditions.     

Core-shell structured HZSM-5@mesoSiO2 catalysts with tunable shell thickness for efficient n-butane catalytic cracking

A series of core-shell HZSM-5@mesoSiO₂ with tunable shell thickness from 10 to 70 nm was prepared and studied for n-butane catalytic cracking. With introducing of SiO₂ shell, the catalytic performance of HZSM-5@mesoSiO₂ was largely enhanced, and n-butane conversion rate per Al site reached to 2.43 min⁻¹ over HZSM-5@mesoSiO₂(1:4) at 675°C which is nearly twice to that of HZSM-5 (1.34 min⁻¹). The diffusion property of n-butane over as-prepared sample was quantified by measuring the diffusional time constants using zero length column chromatography technique (ZLC). Combining with chemical reaction kinetic analysis, the quantitative relationship between diffusion property and catalytic performance was effectively established for the first time in n-butane catalytic cracking. Positive linear correlation between diffusional time constant (D/R²) and n-butane conversion rate per Al site could be found, which confirms that diffusion enhancement by hierarchical structure is an effective strategy to improve the activity of HZSM-5 in catalytic cracking.     

Relationship between structure and point of zero surface charge for molybdenum and tungsten oxides supported on alumina

Laser Raman spectroscopy was used to characterize alumina-supported molybdenum and tungsten oxides at loadings ranging from 0.5 to 15 wt% Mo and 0.5 to 30 wt% W. The structure of calcined Mo⁶⁺/Al₂O₃ and W⁶⁺/A1₂O₃ was governed by the point of zero surface charge of each system, with the point of zero surface charge being dependent on metal loading. The structures formed by the molybdenum and tungsten overlayers at the sample point of zero surface charge were found to be analogous to the structures formed by molybdenum and tungsten oxyanions in aqueous solution at a solution pH equal to the sample point of zero surface charge.     

RhCl(TPPTS)3 supported on iota-carrageenan as recyclable catalysts for Suzuki cross-coupling

A rhodium complex was immobilized for the first time in iota-carrageenan polysaccharide to render a xerogel catalyst. This new heterogeneous catalyst was successfully used in Suzuki cross-coupling and was easily separated from the reaction mixture and recycled two times without loss of activity. The rhodium heterogeneous catalyst was characterized by FTIR, SEM-EDS, and TEM analyses, which demonstrated that the catalyst complex successfully embedded within the polysaccharide and exhibited an unordered, porous structure. Moreover, it was demonstrated that the novel and simple heterogenization procedure, which has been used previously for palladium complexes, is a general route to immobilize transition metal complexes in polysaccharide matrixes. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48200.     

Alumina supported cobalt–palladium catalysts for the reduction of NO by methane in stationary sources

In order to improve a “Three Function Catalysts Model”, the present paper deals with alumina based catalysts containing cobalt and palladium for the NO reduction by methane.

The deNO_x temperature window was estimated by adsorption and subsequent desorption of NO in lean conditions. Two NO_x desorption peaks were detected for both catalysts. For Pd(0.63)Co(0.58)/Al₂O₃, the two desorption peaks appeared at 205 and 423 °C, whereas for Pd(0.14)Co(0.57)/Al₂O₃, the maxima desorption temperature peaks were at 205 and 487 °C. In addition, NO oxidation was also studied to evaluate the catalyst first function. It was found that, the oxidation begins on Co–Pd/Al₂O₃ around 250 °C. On Pd(0.63)Co(0.58)/Al₂O₃, 8% of deNO_x were found in the range of the second NO_x desorption peak temperature (410 °C). During TPSR, C_xH_yO_z species such as formaldehyde were detected. These oxygenate species are the reactive intermediate for deNO_x by methane.