IT-SOFC阳极表面催化反应机理与传递过程的数值模拟与分析

固体氧化物燃料电池(SOFC)具有效率高、污染低、对燃料适应性好、功率大等特点。其性能与工作状态受发生在多孔阳极的化学反应与多种传递过程耦合的影响。基于流体力学方程组和多步基元化学反应模型,建立了描述上述耦合特性的三维数学模型,并自编程序求解分析。结果显示:重整反应主要发生在靠近通道进口的多孔阳极,表面成分Ni_s的覆盖率占70%～80%,其他主要表面成分为CO_s占20%～25%,H_s占6%,O_s占1.5%; Ni_s随工作温度升高而增加;加强吸附基元反应会提高燃料利用率和工作温度;渗透率增加会提高反应气体在多孔介质内的传递效果,但催化反应会因接触不充分而减弱。通过考虑基元反应机理研究表明,在微观层面,催化剂Ni利用率不高,催化反应受温度、化学反应速率常数、孔隙率等参数影响较大。     

有机锆络合物在高选择性催化反应中的应用

有机锆络合物可以高选择性地催化环辛二烯加氢、烯烃与２－甲基吡啶偶合反应、环酮与醛、醇交叉缩合反应、ＭＰＶ型酮还原和ＯＰＰ型醇氧化反应及多羟基化合物酰基化等反应．这些反应在有机合成中具有应用价值。     

Solid-state NMR as a probe of porous catalysts and catalytic processes

The power of solid-state NMR for the interrogation of porous catalytic materials is illustrated using three examples. First, for the investigation of catalytic processes occurring within the confines of a microporous catalyst NMR is shown to reveal both the details of shape-selectivity and the nature of internal surface species. Second, NMR is shown to be a powerful short-range tool to reveal precise structural information on highly disordered microporous titanosilicates. Despite long-range disorder the short-range order is maintained and can be easily studied. Finally, the same utility of probing short-range chemical phenomena is shown to be crucial for the investigation of novel-ordered-amorphous-mesoporous materials known generically as M41S. This class of material is currently one of the most important with potential catalytic application.     

离子液体在非均相催化反应中的应用研究进展

综述了离子液体和固定化离子液体在液-液和液/气-固等非均相催化反应中的应用研究进展,重点对浸渍法、键合法、溶胶-凝胶法等离子液体的固定化方法进行了评述,并指出了该研究领域目前存在的问题及发展趋势。     

不对称催化加氢技术的研究及其发展趋势

总结了不对称催化加氢技术中手性催化剂的制备、催化机理以及催化工艺的研究，对未来不对称催化加氢技术的发展趋势提出了一些看法。多样化催化剂库的建立、非均相催化技术及其工程应用研究将是推动加氢技术快速发展的研究重点。     

Nuclear magnetic resonance imaging of an operating gas–liquid–solid catalytic fixed bed reactor

This work reports our pioneering application of the nuclear magnetic resonance imaging (MRI) technique to the dynamic in situ studies of gas–liquid–solid reactions carried out in a catalytic trickle bed reactor at elevated temperature. The major advance of these studies is that MRI experiments are performed under reactive conditions. We have applied MRI to map the distribution of liquid phase inside a catalyst pellet as well as in a catalyst bed in an operating trickle-bed reactor. In particular, our studies have revealed the existence of the oscillating regimes of the heterogeneous catalytic hydrogenation reaction caused by the oscillations of the catalyst temperature and directly demonstrated the existence of the coupling of mass and heat transport and phase transitions with chemical reaction. The existence of the partially wetted pellets in a catalyst bed which are potentially responsible for the appearance of hot spots in the reactor has been also visualized. The combination of NMR spectroscopy with MRI has been used to visualize the spatial distribution of the reactant-to-product conversion within an operating reactor.     

二氧化碳的活化及其催化加氢制二甲醚的研究进展

CO₂是一种稳定的物质,其化学惰性限制了CO₂转化技术的发展。本文介绍了化学催化、生物活化、光电活化及等离子体活化等CO₂活化方式,从CO₂催化加氢合成二甲醚的工艺研究、催化剂开发、催化加氢机理和本征动力学研究等方面综述了CO₂催化加氢合成二甲醚的研究进展,认为化学催化法是目前应用最广泛的一种CO₂活化方式。对于一步法催化CO₂加氢合成二甲醚的工艺,其难点是制备高效CO₂活化催化剂。开发高效的CO₂活化及转化催化剂及对CO₂合成二甲醚的反应过程进行机理探究,是推广CO₂转化技术的关键。     

纳米镍粉的固相合成及其催化活性研究

介绍了以NiSO₄·6H₂O和NaOH为原料，固相法合成镍纳米粉。通过XRD、TEM、SEM和XPS等测试手段对产物表面结构进行表征。结果表明，产物为球形分布均匀的纳米镍粉，平均粒径为(30±5) nm。同时考察了不同还原温度和时间下得到的产物的催化活性以及反应中温度、压力和含量等对硝基苯加氢还原催化活性的影响，并在相同的条件下，和Raney Ni进行比较。还原实验表明，400 ℃还原4 h的产物质量分数为4.13%时,硝基苯转化率高达26.26%,催化加氢活性高于Raney Ni,是相同条件下Raney Ni的9倍左右。压力为0.8 kPa时，硝基苯转化率高达76.42％。     

连续微反应加氢技术在有机合成中的研究进展

加氢反应是有机合成中很常见的一种反应类型,采用常规的间歇加氢釜具有反应效率低、操作烦琐和安全性差等问题。而连续加氢微反应器进行非均相催化加氢反应能提供更高的传质性能,催化剂的回收利用与产物的纯化也更为方便,能极大地提高生产效率,减少贵金属催化剂的损失。因为这些优点,连续微反应加氢技术得到了越来越多的关注。本文阐述了连续微反应加氢技术中常用的微反应器与固体金属催化剂类型,以及不同官能团非均相高效催化加氢的研究进展,在此基础,对该技术在精细化工领域的应用进行了展望。连续微反应加氢技术使得加氢过程可以在更安全、更高效、更环保的条件下完成,具有很高的工业应用价值,是未来化学化工领域重点发展的方向之一。     

钯、铂催化剂在硝基苯催化加氢合成对氨基苯酚反应中的比较

制备了一系列不同金属粒径的活性炭负载钯、铂催化剂,用于硝基苯液相催化加氢合成对氨基苯酚反应.采用N2-物理吸附、联碱滴定和TEM等表征手段对活性炭载体及其负载钯、铂催化剂进行表征.结果表明,对氨基苯酚选择性与钯、铂活性组分的金属粒径存在紧密的内在联系,说明活性炭负载钯、铂催化剂对于硝基苯液相催化加氢合成对氨基苯酚的反应...     

NMR imaging and differential scanning calorimetry study on drying of pine,birch, and reed pulps and their mixtures

Drying, water fractions, and water distribution were investigated for pine, birch, and reed pulps and pine–birch, pine–reed, and pine–birch–reed pulp mixtures. Gravimetrically determined drying times showed that the drying rates of the pulps decreased at two to four inflection points. Characterizations of the dried pulps by differential scanning calorimetry (DSC) showed a faster removal of free water than freezing and nonfreezing bound waters; all decreased simultaneously, however. DSC also revealed the critical water contents at which the free water and freezing bound water disappeared. The gravimetrically determined inflection points of the drying curves corresponded with the critical points determined by DSC. NMR line widths and images produced by ¹H‐NMR imaging revealed the nature and regions of the pulp drying. The constant growth rate of the NMR line widths with decreasing water content appeared to change at two inflection points, which fell approximately in the same water content regions as the inflection points of the drying curves. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 937–945, 2006     

Shear‐rate‐dependent rheology effects on mass transport and surface reactions in biomicrofluidic devices

Consideration is given to shear‐rate‐dependent rheology effects on mass transport in a heterogeneous microreactor of rectangular cross section, utilizing both numerical and analytical approaches. The carrier liquid obeys the power‐law viscosity model and is actuated primarily by an electrokinetic pumping mechanism. It is discovered that, considering the shear‐thinning biofluids to be Newtonian fluids gives rise to an overestimation of the saturation time. The degree of overestimation is higher in the presence of large Damkohler numbers and electric double layer thicknesses. It is also increased by the application of a favorable pressure gradient, whereas the opposite is true when an opposed pressure gradient is applied. In addition, a channel of square cross section corresponds to the maximum fluid rheology effects. Finally, the numerical results indicate the existence of a concentration wave when using long channels. This is confirmed by analytical solutions, providing a closed form solution for wave propagation speed. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1912–1924, 2015     

Application of ultramicroelectrodes in studies of homogeneous catalytic reactions—part II. A theory of quasi-first and second-order homogeneous catalytic reactions

The analytical expressions of quasi-first and second order homogeneous catalytic reactions with different diffusion coefficients at ultramicrodisk electrodes under steady state conditions are obtained by using the reaction layer concept. The method of treatment is simple and its physical meaning is clear. The relationship between the diffusion layer, reaction layer, the electrode dimension and the kinetic rate constant at an ultramicroelectrode is discussed and the factor effect on the reaction order is described. The order of a catalytic reaction at an ultramicroelectrode under steady state conditions is related not only to C^*_z/C^*_o but also to the kinetic rate constant and the dimension of the ultramicroelectrode; thus the order of reaction can be controlled by the dimension of the ultramicroelectrode. The steady state voltammetry of the ultramicroelectrode is one of the most simple methods available to study the kinetics of fast catalytic reactions.     

中孔材料在碱催化与氧化催化反应中的应用

中孔材料表面存在大量硅羟基,可稳定地与有机物或有机金属复合物基团相结合,可作为高度分散金属或氧化物载体,也可作为碱催化或氧化催化反应的催化剂。近年来,中孔材料在碱催化或氧化催化反应过程中的应用潜在价值备受关注,对中孔材料的研究成果进行分析,指出中孔材料在新催化体系中制备及应用的发展方向。     

In situ MAS NMR investigations of molecular sieves and zeolite-catalyzed reactions

Solid-state MAS NMR is a powerful technique to study heterogeneous catalysts and the way by which they operate. In situ MAS NMR has been demonstrated to be a powerful method to understand reaction mechanisms, to study the nature, dynamics and reactivity of surface intermediates and active sites, and to characterize structural modifications in the catalyst itself, in particular when using ¹³C strategically labelled substrates. In this paper, three examples selected from our own work are used to illustrate the potential of in situ MAS NMR. They are the formation of cumene and its isomerization to n-propylbenzene on zeolite H-ZSM-11, the activation of propane at low temperature and the alkylation of benzene with propane on zeolite H-ZSM-5, and the characterization of the aluminophosphate molecular sieve VPI-5 structure with temperature. Studies of the alkylation of benzene with propene confirmed that cumene was the primary reaction product. The undesired n-propylbenzene by-product results from the intermolecular reaction between cumene and benzene, enhanced by molecular shape-selective effects in medium pore size zeolites (e.g., H-ZSM-11). It explains why large pore zeolites, e.g., zeolite Beta, are used commercially today for this process. Propane can be activated at low temperature (ca. 573 K) on bifunctional medium pore size zeolites possessing intimately related acidic Brønsted sites and a dehydrogenation function provided by Ga or Zn species. In Ga/H-ZSM-5 catalysts, at 573 K, the activation of propane was shown to occur via a protonated pseudocyclopropane (PPCP) intermediate (or transition state). The latter evolves in a manner that can be formally described by the formation of CH ₃ ⁺ , C₂H ₂ ⁺ , and C₃H ₇ ⁺ carbenium ion intermediates. These species can react with olefins, alkanes, or other electron-rich molecules such as benzene. The primary reaction products of the reaction of propane with benzene are n-propylbenzene (in small amount), ethylbenzene and toluene. Their subsequent reactions lead eventually to toluene and xylenes as the final products. In the structural characterization of VPI-5, ²⁷Al, ³¹P, and ²⁷Al nutation MAS NMR spectra show that, at 294 K, fully hydrated VPI-5 contains three equally populated Al and P crystallographic sites and that one-third of Al is 6-coordinate. The VPI-5 structure then belongs to the P6₃ space group. Above 353 K, VPI-5, fully or partially hydrated, undergoes a structural transformation to a higher framework symmetry, i.e., the P6₃cm space group. The transformation occurs at nearly the same temperature in both cases, indicating that the breakdown of the hydrogen-bonded helical water structure inside the VPI-5 pores is not a factor in the process.     

Crystallinity and amorphous segmental properties in random propylene–ethylene copolymers: NMR correlation

We present a characterization of the state of semi-crystallization of random propylene–ethylene copolymers, observing the transverse relaxation of protons attached to the chains. The degree of crystallinity was determined step by step, from NMR, during the progressive annealing of the copolymers, quenched at room temperature from the melt. The ethylene content varied over the range 0–4.7 (w/w). It is shown that the empirical temperature dependence of the degree of crystallinity, as detected by NMR, obeys a single curve; this curve is translated along the temperature axis in accordance with the melting point depression when the ethylene content varies. The degree of crystallinity is primarily a function of the undercooling, whatever the ethylene content. Considering any state of semi-crystallization, a strong correlation between the degree of crystallinity and the relaxation rate of the protons attached to amorphous segments is established; the NMR sensitivity to crystallinity is considerably enhanced when detected by amorphous properties. © 1999 Society of Chemical Industry     

On the link between intrinsic catalytic reactions kinetics and the development of catalytic processes: Catalytic dehydrogenation of ethylbenzene to styrene

A procedure linking kinetic modeling of catalytic reactions to reactor modeling for different configurations is developed and applied to the catalytic dehydrogenation of ethylbenzene to styrene. The procedure is applied to four configurations, namely fixed bed with/without hydrogen selective membranes and bubbling fluidized beds with/without selective membranes. The kinetic data for the industrial catalyst are extracted from industrial fixed bed data using a rigorous heterogeneous model. The kinetic data for the three in-house prepared catalysts are obtained from the laboratory scale experiments using pseudo-homogeneous models.