Development of a Mixing Device for Gas-Solid Systems and Its Application to MT Reactors

A new arrangement to achieve adequate mixing between gas and solid is described. Residence time distribution studies ensured that the behavior of this device actually approaches that of a completely mixed system. The applicability of this device in MT reactors was verified by studying the vapor phase catalytic oxidation of anthracene over vanadium pentoxide.

Characterization of Ni-Pd alloy as anode for methanol oxidative fuel cell

Electrochemical deposition of Ni-Pd alloy films of various compositions from bath solution containing ethylenediamine (EDA) was carried out to use as anode material for methanol oxidative fuel cell in H2SO4 medium. Electronic absorption spectrum of bath solution containing Ni2+ Pd2+ ions and EDA indicated the formation of a four coordinate square planar metal-ligand complex of both the metal ions. X-ray diffraction (XRD) patterns of the deposited alloy films show an increase in Pd-Ni alloy lattice parameter with increase in Pd content, and indicate the substitution of Pd in the lattice. A nano/ultrafine kind of crystal growth was observed in the alloy film deposited at low current density (2.5 mA cm(-2)). X-ray photoelectron spectroscopic (XPS) studies on the successively sputtered films showed the presence of Ni and Pd in pure metallic states and the surface concentration ratio of Ni to Pd is less than bulk indicating the segregation of Pd on the surface. Electro-catalytic oxidation of methanol in H2SO4 medium is found to be promoted on Ni-Pd electrodeposits. The anodic peak current characteristics to oxidation reaction on Ni-Pd was found typically high when compared to pure nickel and the relative increase in surface area by alloying the Ni by Pd was found to be as much as 300 times. (C) 2003 Elsevier Science B.V. All rights reserved.

Synthesis and electrocatalytic properties of manganese dioxide for non-enzymatic hydrogen peroxide sensing

Manganese dioxide nanoparticles were synthesized by chemical reduction route at different growth temperatures of 40 degrees C, 80 degrees C, 100 degrees C and were characterized using X-ray Diffraction (XRD), Field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), Cyclic Voltammetry (CV) and chronoamperometry (CA) analysis. FESEM results show that on increasing growth temperature the morphology changes from clusters into mixture of rods and flakes. XPS analysis reveals the formation of MnO2. Then these particles were immobilized on Pt electrode. A platinum (Pt) electrode modified with low dimensional MnO2 was investigated as a chronoamperometric (CA) sensor for hydrogen peroxide sensing (H2O2). The sample prepared at 100 degrees C shows good electrocatalytic ability for H2O2 sensing when compared with the samples prepared at 40 degrees C and 80 degrees C. At an operating potential of 0.3 V vs. Ag/AgCl catalytic oxidation of the analyte is measured for chronoamperometric (CA) monitoring. The CA signals are linearly proportional to the concentration of H2O2. It is also found that the morphology of the nanostructure plays a vital role in the detection of H2O2. (C) 2014 Elsevier Ltd. All rights reserved.

Estimation of catalyst activity profiles and deactivation parameters from reactor operating data with applications to naphtha reforming

Techniques are developed for estimating activity profiles in fixed bed reactors and catalyst deactivation parameters from operating reactor data. These techniques are applicable, in general, to most industrial catalytic processes. The catalytic reforming of naphthas is taken as a broad example to illustrate the estimation schemes and to signify the physical meaning of the kinetic parameters of the estimation equations. The work is described in two parts. Part I deals with the modeling of kinetic rate expressions and the derivation of the working equations for estimation. Part II concentrates on developing various estimation techniques.

Part I: The reactions used to describe naphtha reforming are dehydrogenation and dehydroisomerization of cycloparaffins; isomerization, dehydrocyclization and hydrocracking of paraffins; and the catalyst deactivation reactions, namely coking on alumina sites and sintering of platinum crystallites. The rate expressions for the above reactions are formulated, and the effects of transport limitations on the overall reaction rates are discussed in the appendices. Moreover, various types of interaction between the metallic and acidic active centers of reforming catalysts are discussed as characterizing the different types of reforming reactions.

Part II: In catalytic reactor operation, the activity distribution along the reactor determines the kinetics of the main reaction and is needed for predicting the effect of changes in the feed state and the operating conditions on the reactor output. In the case of a monofunctional catalyst and of bifunctional catalysts in limiting conditions, the cumulative activity is sufficient for predicting steady reactor output. The estimation of this cumulative activity can be carried out easily from measurements at the reactor exit. For a general bifunctional catalytic system, the detailed activity distribution is needed for describing the reactor operation, and some approximation must be made to obtain practicable estimation schemes. This is accomplished by parametrization techniques using measurements at a few points along the reactor. Such parametrization techniques are illustrated numerically with a simplified model of naphtha reforming.

To determine long term catalyst utilization and regeneration policies, it is necessary to estimate catalyst deactivation parameters from the the current operating data. For a first order deactivation model with a monofunctional catalyst or with a bifunctional catalyst in special limiting circumstances, analytical techniques are presented to transform the partial differential equations to ordinary differential equations which admit more feasible estimation schemes. Numerical examples include the catalytic oxidation of butene to butadiene and a simplified model of naphtha reforming. For a general bifunctional system or in the case of a monofunctional catalyst subject to general power law deactivation, the estimation can only be accomplished approximately. The basic feature of an appropriate estimation scheme involves approximating the activity profile by certain polynomials and then estimating the deactivation parameters from the integrated form of the deactivation equation by regression techniques. Different bifunctional systems must be treated by different estimation algorithms, which are illustrated by several cases of naphtha reforming with different feed or catalyst composition.

银基催化剂催化氧化反应的研究

银催化剂是工业上较为重要的催化剂，它不仅大量地使用在乙烯环氧化，甲醇脱氢反应中，还在异丙醇氧化脱氢制丙酮，乙醇脱氢制乙醛，乙二醇氧化制乙二醛，烷基胺氧化制睛类化合物等工业过程中广为应用。由于银催化剂具有如此重要的工业应用价值，所以银催化剂一百多年来一直是催化领域的研究重点。银催化剂的特异催化行为得益于银元素较为特殊的电子结构以及氧物种在银催化上的独特催化行为。银催化剂表面既存在导致非选择氧化反应的氧物种（a氧），也存在导致选择氧化反应的氧物种（Y氧），这两种氧物种在催化剂上的状态与反应气氛及催化剂结构密切相关。一氧化碳氧化反应在环境保护、能源利用（燃料电池）、安全防护（火场、煤矿）有较为重要的用途；甲酸甲醋是近年新兴的较为重要的碳一化学中间体，它可以广泛应用于有机合成反应中，也可以作为安全的合成气载体；醇类选择氧化制备相应的醛酮化合物也是有机合成工业的重要反应之一；甲苯气相氧化制备苯甲醛是研究烃类选择氧化较为重要的模型反应，在工业上存在潜在的应用价值。本论文以上述的四个反应为探针反应研究了银基催化剂的催化行为，得到以下的结果：1．以烷基胺为模板剂制备了过渡金属离子掺杂的介孔分子筛，通过模板剂－离子交换技术制备了含银基复合氧化物的介孔分子筛催化剂。该系列催化剂对一氧化碳氧化反应有较好的活性。同时研究了金属盐的种类及掺杂量对介孔分子筛结构的影响，发现金属离子的掺杂会破坏介孔分子筛的结构的有序性，随着掺杂量的增大，介孔分子筛的结构的有序性变差；金属盐的阴离子对介孔分子筛的结构的有序性亦有影响。2．较为系统研究了银基催化剂上由甲醇制备甲酸甲酷的催化行为，发现银基催化剂是一个选择性较高的催化体系。分立测试了不同的氧物种对甲醇反应的影响，提出了a氧与Y氧协同作用的机理，为解决甲醇脱氢反应机理争端提供了有价值的信息。3．系统研究了低级醇在金属银催化剂的脱氢反应，分立测试了不同的氧物种对甲醇、乙醇反应的影响，发现低于550K时不同的氧物种对乙醇的反应性能有显著的差异，认为低温（＜550K）条件下，醇类在金属银催化剂上发生的是氧化脱氢历程。通过借鉴均相醇类氧化脱氢反应研究所取得的成果，试图从本质上解释银是醇类气相氧化脱氢最好的催化剂的原因，即在过渡金属中，金属银上的氧物种的碱性是最强的，氧的再生能力也是很强的。4．在甲苯的选择氧化研究中发现在高温（600℃）、纯氧、甲醇参与的条件下，Pt一Ag催化剂对苯甲醛的收率最好（-6％），提出了分子氧参与生成含氧自由基中间产物、醇类淬灭自由基态中间产物的反应历程，与传统甲苯氧化所经历的Mars-Krevelen机理有差别，为烃类的选择氧化提供了新的信息。

Multilayer assemblies consisting of tri-vanadium-substituted heteropolyanions and its electrocatalytic properties

We describe the controlled fabrication of ultrathin multilayer films consisting of tri-vanadium- substituted heteropolytungstate anions (denoted as P2W15V3) and a cationic polymer of quaternized poly (4-vinylpyridine) partially complexed with osmium bis(2,2'-bipyridine) (denoted as QPVP-Os) on the 4-aminobenzoic acid (4-ABA) modified glassy carbon electrode (GCE) surface based on layer-by-layer assembly. Cyclic voltammetry and UV-vis absorption spectrometry have been used to easily monitor the thickness and uniformity of thus-formed multilayer films. The V-centered redox reaction of P2W15V3 in the multilayer films can effectively catalyze the reduction of BrO3- and NO2-. The resulting P2W15V3/QPVP-Os multilayer film modified electrode behaves as a much promising electrochemical sensor because of the low overpotential for the catalytic reduction of BrO3- and NO2-, and the catalytic oxidation of ascorbic acid.

Identification of o-phenylenediamine polymerization product catalyzed by cytochrome c

The hydrogen peroxide (H2O2) and cytochrome c-dependent oxidation of o-phenylenediamine (o-PD) was investigated by spectrophotometry and electrochemistry. The results indicated that o-PD underwent facile catalytic oxidation in the presence of cytochrome c, and that the degradation of cytochrome c by hydrogen peroxide can also be partly prevented in the presence of o-PD. The hydroxyl radical scavengers (mannitol and sodium benzoate) and oxo-heme species scavenger (uric acid) do not inhibit the oxidation, which implies that the hydroxylation of o-PD may not be involved in its oxidation. Combining with the results of the mass spectrum, elemental analysis, nuclear magnetic resonance and Fourier transform infrared spectrum of the isolated product, a conceivable structure of the product was suggested. (C) 1998 Elsevier Science B.V.

Kinetics of electrocatalytic ascorbic acid at ultramicroelectrode modified by Eastman-AQ polymer containing tris(2,2-'-bipyridine) osmium(III/II) complexes as electron-transfer centers

The theoretical model[17] of an ultramicroelectrode modified with a redox species film is used as the diagnostic tool to characterize the catalytic oxidation of ascorbic acid at carbon fiber ultramicrodisk electrodes coated with an Eastman-AQ-Os(bpy)(3)(2+) film. The electrocatalytic behavior of ascorbic acid at the ultramicroelectrode modified by an Eastman-AQ polymer containing tris(2,2'-bipyridine) osmium(III/II) as mediators is described. In order to determine the five characteristic currents quantitatively, the radius of the ultramicroelectrode and the concentration of ascorbic acid are varied systematically. The kinetic zone diagram has been used to study the electrocatalytic system. This system with 0.5-2.75 mM ascorbic acid belongs to SR + E case, and the concentration profiles of the catalyst in the film are given in detail. Finally, optimizing the design of catalytic system is discussed.

Kinetic study of the accelerating effect of coal-burning additives on the combustion of graphite

The catalytic and accelerating effects of three coal-burning additives (CBA) on the burning of graphite were studied with the help of thermogravimetric (TG) analysis. The kinetic study on the catalytic oxidation of the graphite doped with CBA was carried out and the results were presented. The results show that the CBA can change the carbon oxidation/combustion course by catalytic action and change the activation energy, thus improving the combustion efficiency.

Epoxidation of styrene on Si/Ti/SiO2 catalysts prepared by chemical grafting

Titania-silica (Ti/SiO2) and silica-titania-silica (Si/Ti/SiO2) catalysts were:prepared by chemical grafting using TiCl4 and tetraethyl orthosilicate (TEOS) as precursors and SiO2 as support. The prepared catalysts were characterized by UV Raman and visible Raman spectroscopies, XRD and the epoxidation of styrene; Ti/SiO2: catalyst grafted with only titanium species is not very active for epoxidation using H2O2 (30%), but is active and-selective when one uses tert-butyl hydroperoxide (TBHP). The catalyst grafted at high temperatures shows better epoxide selectivity. Si/Ti/SiO2 catalyst, the titanium-silica grafted further with TEOS, is active and selective for the epoxidation of styrene using either dilute H2O2 or TBHP, possibly due to the fact that the grafting of Ti/SiO2 with TEOS modifies the coordination structure of titanium and makes the titanium sites of Si-O-Ti-O-Si species less hydrophilic. A characteristic band at 1085cm(-1) due to Ti-O-Si species is detected for the grafted catalysts by UV resonance Raman spectroscopy. Reaction between TiCl4 and SiO2 at high temperatures favors the formation of Ti-O-Si species. Better activity and selectivity to epoxide,is found for the catalysts with more Ti-O-Si species. It is assumed that the active sites are the highly isolated Ti-O-Si species. For Si/Ti/SiO2 catalyst, the gas phase O-2 can participate in the catalytic oxidation of styrene when H2O2 is present ana:ii causes the formation of benzaldehyde. (C) 2000 Elsevier Science B.V. All rights reserved.