Unique properties of Ir/ZSM-5 catalyst for NO reduction with CO in the presence of excess oxygen

The reduction of NO with CO in the presence of excess oxygen was investigated over different noble metal catalysts for probing the relationship between catalytic properties and adsorption behaviors. Among the four precious metal catalysts investigated, Ir/ZSM-5 was found to be the only active one for NO reduction with CO under lean conditions. With the decreasing of the Ir content, higher NO conversion and CO selectivity was obtained. Temperature-programmed reaction (TPR) studies of NO/H-2/O-2 and NO/CO/O-2 showed that the Pt/ZSM-5 was active when H-2 was used as the reductant, whereas, the Ir/ZSM-5 was active when CO was the reducing agent. This difference is due to the different mechanisms of the two reactions. Temperature-programmed desorption (TPD) of NO, CO and O-2 showed that NO could dissociate more easily over the Ir/ZSM-5 than on the Pt/ZSM-5, while the oxidation of CO by O-2 proceeded more rapidly on the Pt/ZSM-5 than on the Ir/ZSM-5. The presence of excess O-2 inhibited drastically the dissociation of NO, which is considered as the key step for the NO-CO reaction. The high dissociation rate of NO over the Ir/ZSM-5 is visualized as the key factor for its superior high activity in NO reduction with CO under lean conditions. (C) 2002 Elsevier Science B.V. All rights reserved.

Enolic Schiff base aluminum complexes and their catalytic stereoselective polymerization of racemic lactide

A series of enolic Schiff base aluminum(III) complexes LAIR (where L = NNOO-tetradentate enolic Schiff base ligand) containing ligands that differ in their steric and electronic properties were synthesized. Their single crystals showed that these complexes are five -coordinated around the aluminum center. Their coordination geometries are between square pyramidal and trigonal bipyramidal. Their catalytic properties in the solution polymerization of racemic lactide (rac-LA) were examined. The modifications in the auxiliary ligand exhibited a dramatic influence on the catalytic performance.

Preparation, physico-chemical behavior and catalytic property for ammonia oxidation of perovskite like mixed oxides La2-xSrxCuO4-lambda

A series of Sr2+ doped perovskite like oxides La2-xSrxCuO4-lambda (x = 0 similar to 1) were prepared, the structure, lattice parameters, content of Cu3+, oxygen vacancies created by Sr2+ substitution and composition of these complex oxides were studied by XRD and iodic titration method. The redox ability,active oxygen species and surface image were evaluated and analyzed with TPD, TG, XPS and SEM measurements. The catalytic activity for ammonia oxidation over these oxides was tested, and the relationship among the catalytic properties, structure, nonstoichiometric oxygen,redox ability and surface behavior were correlated and some information on the mechanism of ammonia oxidation was obtained.

Facile route to fabricate large-scale silver microtubes

Large-scale uniform Ag microtubes with high length diameter ratios have been first successfully synthesized by a facile approach, using low-cost super fine glass fibers as templates. The samples were characterized by SEM and XRD. The investigations showed that calcining or adding of PEG-1000 and alcohol could greatly improve the mechanical strength of the sample. Especially the products exhibited favorable catalytic properties during the degradation of Rhodamine B by NaBH4. (c) 2007 Elsevier B.V. All rights reserved.

新型固体酸催化剂的设计制备及其性能研究

酸催化剂可以用来催化烃类裂解、重整、异构、烯烃水和、烷基化和酯化等重要化学反应，在石油炼制和石油化工领域有极其广泛的应用。与传统液体酸相比，新型固体酸催化剂具有容易与反应物和产物分离、易再生、不腐蚀反应器、环境污染少等优点，因此研究开发环境友好的新型固体酸催化剂成为国际上催化领域研究的热点。本论文研究新型固体酸催化剂的酸强度和延长催化剂使用寿命的方法，具有很高的工业实用价值和理论意义。 研究了固体酸催化剂在正己烷异构化和异丁醇脱水这两个反应的催化活性，结果显示：1）复合超强酸催化剂，2）Hβ及其负载催化剂，3）负载杂多酸，4）ZrO2·Bi2O3、ZrO2·CaO四类催化剂酸强度较高且强度大小为:1＞2≈3＞4。氢溢流的引入提高了Pt-SO42-/ ZrO2催化剂在反应中的催化活性,一定程度上弥补了酸强度的不足，也使一些原本没活性的催化剂有了一定的活性，如MOO3催化剂。 研究了异丁烷在12wt%V2O5/γ-Al2O3催化剂上脱氢制异丁烯的反应和异丁烯在50wt%HSiW/SiO2、Amberlyst-15和Amberlyst-35树脂催化剂上的迭代反应，均获得了较好的催化活性。 首次将催化剂表面的疏油性应用在酸催化领域，在硅胶负载的钨硅酸中掺杂不同含量聚四氟乙烯制备出具有一定疏油性的催化剂，用异丁烯迭代反应作为探针反应着重研究了催化剂表面的适当疏油性对催化剂的寿命和产物选择性的影响。结果显示催化剂表面的疏油性不仅提高了C8 =的选择性并且有效延长催化剂寿命。这主要是由于催化剂表面具有适当的疏油性，反应的中间产物C8=易于从具有疏油性的表面脱附，减少了C8=继续在催化剂表面进行连续反应生成C12=和C16=的机会，因此提高了C8=的选择性。这可能促进了更高的产物选择性，低的积炭量和较长的催化剂使用寿命。 研究了催化剂表面的疏水疏油性在醋酸与正丁醇的酯化反应中的应用。结果显示，当酯化反应产物为液相时，催化剂表面的疏水疏油性非常有利于产物从催化剂表面脱附，能有效提高正丁醇的转化率。 关键词：酸强度，钨硅酸，聚四氟乙烯，疏油性，寿命

Difference of ZSM-5 zeolites synthesized with various templates

ZSM-5 zeolites with similar SUM ratio were synthesized successfully using various templates (n-butylamine (BTA), ethylamine (ETA), isopropylamine (IPA), ethylenediamine (EDA), ethanol (ETL), ethanol-ammonium (ETL-AM) and no template (NT)) under hydrothermal conditions. The samples were characterized by XRD, SEM, XRF, NH3-TPD and BET surface area measurements in order to understand the template effects and the differences of the ZSM-5 samples. The synthesis of ZSM-5 with organic templates was relatively easier than those with inorganic templates and without template. SEM results revealed that ZSM-5 synthesized with different templates had different morphology and particle size. The Si/Al ratio and BET specific surface area of the sample with ethanol as template was the lowest. NH3-TPD results showed that the sample synthesized without template had fewer strong acid sites than others. n-Hexane cracking reaction was carried out over the samples to evaluate the catalytic properties. All ZSM-5 zeolites were effective in n-hexane cracking reaction, especially for the sample synthesized without template. (C) 2004 Elsevier B.V. All rights reserved.

Structural probing of D-fructose derived ligands for asymmetric addition of diethylzinc to aldehydes

A series of new chiral ligands derived from D-fructose have been synthesized and applied in the enantioselective addition of diethylzinc to aldehydes. Comparison of the enantioselectivities obtained with these ligands demonstrated that the catalytic properties are highly dependent upon the structure of ligands, a rational explanation of the structural effects on the catalytic properties is provided. (C) 2003 Elsevier Science Ltd. All rights reserved.

The mechanism studies of ethanol oxidation on PdO catalysts by TPSR techniques

The paper studies the direct oxidation of ethanol and CO on PdO/Ce0.75Zr0.25O2 and Ce(0.75)Zr(0.2)5O(2) catalysts. Characterization of catalysts is carried out by temperature-programmed desorption (TPD), temperature-programmed surface reaction (TPSR) techniques to correlate with catalytic properties and the effect of supports on PdO. The simple Ce0.75Zr0.25O2 is in less active for ethanol and CO oxidation. After loaded with PdO, the catalytic activity enhances effectively. Combined the ethanol and CO oxidation activity with CO-TPD and ethanol-TPSR profiles, we can find the more intensive of CO2 desorption peaks, the higher it is for the oxidation of CO and ethanol. Conversion versus yield plot shows the acetaldehyde is the primary product, the secondary products are acetic acid, ethyl acetate and ethylene, and the final product is CO2. A simplified reaction scheme (not surface mechanism) is suggested that ethanol is first oxidized to form intermediate of acetaldehyde, then acetic acid, ethyl acetate and ethylene formed going with the formation of acetaldehyde, acetic acid, ethyl acetate; finally these byproducts are further oxidized to produce CO2. PdO/Ce0.75Zr0.25O2 catalyst has much higher catalytic activity not only for the oxidation of ethanol but also for CO oxidation. Thus the CO poison effect on PdO/Ce0.75Zr0.25O2 catalysts can be decreased and they have the feasibility for application in direct alcohol fuel cell (DAFC) with high efficiency.

Crystallization and Si incorporation mechanisms of SAPO-34

In this study of the synthesis of SAPO-34 molecular sieves, XRD, SEM, XRF, IR and NMR techniques were applied to monitor the crystalloid, structure and composition changes of the samples in the whole crystallization process in order to get evidence for the crystallization as well as Si incorporation mechanism of SATO-34. XRD results revealed that the crystallization contained two stages. In the first 2.5 h (the earlier stage), high up to similar to80% of relative crystallinity could be achieved and the crystal size of SAPO-34 was almost the same as that of any longer time, indicating a fast crystallization feature of the synthesis. In this stage, IR revealed that the formation of SAPO-34 framework structure was accompanied by the diminution of hydroxyls, suggesting that crystal nuclei of SAPO-34 may arise from the structure rearrangement of the initial gel and the condensation of the hydroxyls. NMR results reveal that the template and the ageing period are crucial for the later crystallization of SAPO-34. Preliminary structure units similar to the framework of SAPO-34 have already formed before the crystallization began (0 h and low temperature). Evidence from IR, NMR, and XRF shows that the formation of the SAPO-34 may be a type of gel conversion mechanism, the solution support and the appropriate solution circumstance are two important parameters of the crystallization of SAPO-34. Meanwhile, NMR measurements demonstrated that about 80% of total Si atoms directly take part in the formation of the crystal nuclei as well as in the growth of the crystal grains in the earlier stage (<2.5 h). Evidence tends to support that Si incorporation is by direct participation mechanism rather than by the Si substitution mechanism for P in this stage (<2.5 h). In the later stage (>2.5 h), the relative content of Si increased slightly with a little decrease of Al and P. The increase of Si(4Al) and the appearance of the Si(3Al), Si(2Al), Si(1Al) and Si(OAl) in this stage suggest that substitution of the Si atoms for the phosphorus and for the phosphorus and aluminum pair takes place in the crystallization. The relationship among structure, acidity and crystallization process is established, which suggests a possibility to improve the acidity and catalytic properties by choosing a optimum crystallization time, thus controlling the number and distribution of Si in the framework of SAPO-34. (C) 2002 Elsevier Science Inc. All rights reserved.

Research progress on noble metal composite nanoparticles

Noble metal composite nanoparticles, as attractive building blocks of advanced functional materials, have received enormous attentions due to their specific optical, electronic and catalytic properties that are distant from those of the corresponding monometal nanoparticles. Such materials have important applications in such areas as sensors, optical materials, catalysis and biology, and developed into an increasingly important research area in nanomaterials science. This article reviews the recent progress in the synthesis, properties, and applications of noble metal composite nanoparticles with core-shell, heterostructure, and alloy structure.