An atomic X-ray absorption fine structure study of the influence of hydrogen chemisorption and support on the electronic structure of supported Pt particles

The physical principles of atomic XAFS (AXAFS) are presented along with important details on how to isolate the AXAFS contribution from the experimental XAFS data. Intuitive illustrations are given showing how various interactions of the absorber atom with its neighbours influence the AXAFS contribution. Hydrogen chemisorbed on the surface of the supported metal particles is shown to have a strong influence on the amplitude of the Fourier transform AXAFS peak. The effect of the support (with different amounts and types of charge compensating ions (H⁺, K⁺), different Si/Al ratio and extra-framework Al) on the experimental AXAFS spectra of Pt dispersed in zeolites (LTL,Y) and on flat supports (Al₂O₃–SiO₂, MgO–Al₂O₃) are summarised. It is shown that the essence of the metal–support interaction, as revealed in the AXAFS, is a shift in the ionisation potential of the valence d-orbital electrons brought about by the polarisation induced primarily by the changing charge on the support oxygen atoms. This revised version was published online in June 2006 with corrections to the Cover Date.     

The structure of vanadium oxide species on γ-alumina; an in situ X-ray absorption study during catalytic oxidation

The mechanism of catalytic oxidation reactions was studied using in situ X-ray absorption spectroscopy (XAFS) over a 17.5 wt% V₂O⁵/Al₂O₃ catalyst, i.e., at reaction temperatures and in the presence of reactants. It was found that X-ray absorption near-edge structure (XANES) is a powerful tool to study changes in the local environment and the oxidation state of the vanadium centres during catalytic oxidation. At 623 K, the catalyst follows the associative mechanism in CO oxidation. XAFS revealed that the Mars–van Krevelen mechanism is operative at 723 K for CO oxidation. The extended X-ray absorption fine structure (EXAFS) results showed that the structure of the supported V₂O⁵ phase consists of monomeric tetrahedral (Al–O)₃–V=O units after dehydration in air at 623 K. However, the residuals of the EXAFS analysis indicate that an extra contribution has to be accounted for. This contribution probably consists of polymeric vanadate species. The structure remains unchanged during steady-state CO oxidation at 623 and 723 K. Furthermore, when oxygen was removed from the feed at 623 K, no changes in the spectra occurred. However, when oxygen is removed from the feed at 723 K, reduction of the vanadium species was observed, i.e., the vanadyl oxygen atom is removed. The V³⁺ ion subsequently migrates into the γ-Al₂O₃ lattice, where it is positioned at an Al³⁺ octahedral position. This migration process appears to be reversible; so the (Al–O)₃–V=O units are thus restored by re-oxidation. This revised version was published online in June 2006 with corrections to the Cover Date.     

计算机支持的协同设计研究综述

并行工程及敏捷制造将是２１世纪的生产模式,计算机支持的协同设计是并行工程的关键技术。本文对抗同支持的协同设计的研究进行系统分析综述。     

筒承式群仓自振特性的试验研究

通过对４９ 个筒承式群仓试件的试验研究,分析了组合筒数ｎ 、高径比Ｈ／ Ｄ、开洞率ζ、组合方向与开洞方向的关系及装料程度等因素对筒承式群仓自振特性的影响。研究了各种条件下平动振动、纯扭转振动及平扭耦合振动的自振特性及其规律     

南京市某高层商住楼框支剪力墙结构设计

介绍了某高层商住楼框支剪力墙结构的设计,包括结构概念设计、结构三维整体分析,弹性动力时程分析、转换层有限元分析。指出这类结构体系的设计应从概念设计出发,制定合理的方案,通过正确的模型计算,找出结构薄弱部位,予以加强。文中同时指出,框支剪力墙转换梁不一定是偏心受拉构件。     

掉层RC框架结构基于典型失效模式的失效概率评估

结构失效模式决定了结构在强震下的抗震性能。该文采用基于可靠度理论的割集方法，对掉层框架结构地震作用下的典型失效模型的失效概率进行评估，并与规则框架结构进行对比，分析了掉层框架结构失效模式的特点。结果表明:掉层框架结构的柱极限剪切失效模式年平均发生概率高于规则结构，且掉层框架结构存在剪切破坏先于弯曲破坏的风险，应采取适当加强措施以满足"强剪弱弯"的设计原则；对掉层结构进行基于年平均概率的柱剪力增大系数分析，建议对掉层结构上接地柱进行抗剪承载力设计时，采用抗震等级提高一级所对应的剪力增大系数，且上接地柱全柱段箍筋应加密布置。     

负载贵金属催化剂在挥发性有机物氧化反应中的应用

挥发性有机物(VOCs)是大气污染的主要来源,危害人体健康。催化氧化法是消除挥发性有机物的有效手段,其核心是高效催化剂,新型、高活性、高稳定性催化剂的研发具有重要意义。简要综述近年来负载Au、Pd和Pt贵金属催化剂对VOCs氧化消除的催化性能,分析VOCs氧化在典型催化剂表面形成的活性物种及其对催化活性的影响,并展望VOCs催化氧化的未来发展趋势。     

负载型离子液体在氧化脱硫中的应用进展

离子液体是一类新兴的绿色溶剂和催化剂，负载型离子液体可同时表现出离子液体和载体材料的优点，如较高的催化活性和较大的比表面积，因此成为研究热点。将离子液体负载到载体上可大大降低离子液体的用量并提高利用率，将其应用于燃油脱硫过程中可提高离子液体的氧化活性。笔者综述了负载型离子液体的制备方法，并介绍了负载型Lewis酸离子液体、负载型Br?nsted酸离子液体、负载型多金属氧酸盐离子液体作为催化剂进行燃油催化氧化脱硫性能的研究进展。部分负载型离子液体需加入中性离子液体或有机溶剂作萃取剂才能发挥催化作用，或吸附硫化物并将其催化氧化为砜类物质，达到深度脱硫的目的。     

The meat industry: Do we think and behave globally or locally?

For generations, those that produce livestock and meat generally felt that their country or geographical region (i.e., provenance) reflected a basis for product differentiation. This occurs to the extent that geography of production often is considered a “brand.” For example, there exists “U.S. Grain-Fed Beef” or “Kobe Black Wagyu” or “Uruguayan Grass-Fed Lamb” or “Danish Pork.” However, for most meat trade, industry has evolved beyond this. With the exception perhaps of farms onto which livestock are born, meat company's profits are not generally tied to geographical considerations. Most major companies (e.g., JBS, Marfrig, Tyson, Cargill, Danish Crown, Nippon Meat Packers, etc.) operate in multiple countries and represent to consumers the production of a number of locations. However, there also now exist entrepreneurial options for meat production and “local” sales, albeit at lesser volumes. This discussion explores “global” and “local” meat marketing options.     

MgCl2‐supported catalyst containing mixed internal donors for propylene polymerization

A MgCl₂‐supported catalyst containing diisobutyl phthalate (DIBP) and 2,4‐pentadiol dibenzoate (PDDB) as internal donors was prepared. Propylene polymerizations were carried out using the catalyst in the absence or presence of an external donor. The resulting polymers were characterized by ¹³C‐NMR, crystallization analysis fraction (CRYSTAF) and gel permeation chromatography (GPC). The performance of the catalyst was compared with that of other catalysts containing donor‐free, DIBP and PDDB as internal donors respectively. The results demonstrated that the catalyst containing mixed internal donors not only had high activity and stereospecificity but also produced the polymer with relatively broad molecular weight distribution and the highest [mmmm] value. ¹³C‐NMR analysis results indicated that strongly coordinating donors gave more stereoregular polymers, which was further confirmed by CRYSTAF data. The effects of mixed internal donors on the catalyst properties were discussed systematically. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011