Cyclohexane transformations over metal oxide catalysts. 2. Selective cyclohexane ring opening to form n-hexane over mono- and bimetallic rhodium catalysts

The activity of monometallic Rh and Pt catalysts and bimetallic Pt—Rh catalysts on oxide supports in cyclohexane ring opening to form n-hexane was studied. The Rh-containing catalysts are highly active and selective in this reaction. Cyclohexane dehydrogenation predominates in the case of the Pt catalysts. The use of the bimetallic alumina-supported Pt—Rh catalysts allows one to minimize the contribution of cyclohexane cracking and to enhance the selectivity for n-hexane with the yield of the latter slightly depending on the metal ratio in the bimetallic system under the experimental conditions.     

ZnO负载Ni—Cu双金属催化剂的程序升温还原与X—射线光电子能谱研究

用ＴＰＲ和ＸＰＳ和ＺｎＯ负载Ｎｉ－Ｃｕ双金属催化剂中Ｎｉ与Ｃｕ的相互作用进行了研究。ＴＰＲ结果表明，Ｎｉ－Ｃｕ双金属催化剂中，Ｃｕ在低温下还，而Ｎｉ在高温下还原，还原的Ｃｕ能促进Ｎｉ的还原。     

Synthesis and Crystal Structure of a Cyano- bridged Bimetallic Complex[La(DMSO)_3(H_2O)_3- Cr(CN)_6]·H_2O (DMSO = Dimethylsulfoxide) with One-dimensional Chain Molecular Structure

1 INTRODUCTION Over the last decade, there has been continuous interest in cyanide-bridged lanthanide-transition me- tal complexes due to their extensive applications in preparing rare earth orthoferrites[1], chemical sensor materials[2], fluorescent ma…     

Magnetic interactions and Preisach distributions of nanostructured barium hexaferrite

Barium hexaferrite (phase M) samples with different nanostructures were studied. Sample M1 is composed of nanocrystals of BaFe₁₂O₁₉ produced after milling the elemental oxides (Fe₂O₃ and BaCO₃) and heating in air atmosphere. Two more samples were produced by milling the same oxides and a 20% excess of -Fe. The resulting powder (composed of phase M and a 20% hematite) was heat-treated in different conditions, resulting in samples MF1 (with a partially sintered structure) and MF8 (with almost completely sintered structure).

In order to have an insight into the interactions in each sample, Preisach distributions were obtained using first-order reversion curves (FORCs) measurements. The Preisach distribution corresponding to M1 is a Gaussian-shaped one, with a maximum around 4.1 kOe. The distribution of MF1 has a narrow and high peak at 5.3 kOe, a number of overlapping small peaks down to 2.6 kOe and a distinct and low-intensity peak at 2 kOe. MF8 has a Preisach distribution with a succession of equally spaced distinct peaks from 4.2 to 1.5 kOe.

The found Preisach distributions suggest that the interactions occur among nanocrystals inside conglomerates with different number of particles.     

凝胶燃烧法制备超细YBa2Cu3O7-x超导粉末

纳米级细度的YBa2Cu3O7-x超导粉末有可能在第二代超导带材的研制中得到应用．超细YBa2Cu3O7-x超导粉朱已经通过凝胶燃烧法制备成功．使用的起始物质是钇、钡、铜的硝酸盐以及作为燃烧剂的柠檬酸．产物颗粒的尺寸大小及其超导性能依赖于自燃过程的情况，而自燃过程又与凝胶中柠檬酸盐-硝酸盐的YBa2Cu3O7-x超导粉末．在本实验中我们发现最好的燃烧剂一氧化剂摩尔比为0．5．     

多核Nd—Al双金属配合物对共轭双烯烃的聚合：Ⅲ.溶剂等因素的影响

报道了多核Ｎｄ－Ａｌ双金属配合物活性体对共轭双烯烃的溶液聚合。结果表明，适宜的振荡时间有利于提高活性体的催化活性；通过外加Ａ１Ｅｔ３，验证了聚合体系的纯度和活性体的稳定性。溶剂类型对活性和聚合物分子量影响较大，活性次序为甲苯≥环己烷＞正己烷；对产物［η》的影响则相反：甲苯＜＜环己烷＜正己烷。不同单体的定向聚合性能有差别，聚丁二烯的顺１，４含量较低，且易受反应条件的影响。     

Addition of Alkynes to High Nuclearity Platinum–Ruthenium Carbonyl Cluster Complexes

The reactions of the mixed metal cluster complexes PtRu₅(CO)₁₆(μ₆-C)[Pt(PBu )], 5 and PtRu₅(CO)₁₆(μ₆-C)[Pt(PBu ]₂, 6 with selected alkynes have been investigated. Compound 5 adds one and two equivalents of PhC₂H to yield the new compounds PtRu₅(CO)₁₅(μ₆-C)(μ₃-PhC₂H)[Pt(PBu )], 8 and PtRu₅(CO) -C)( -PhC₂H)₂[Pt(PBu )], 9 at 40 and 68°C, respectively. Compound 6 was found to react with PhC₂H at 40°C to yield the new compound PtRu₅(CO) -C)( -PhC₂H)[Pt(PBu )]₂, 10. The reaction of 6 with PhC₂Ph at 97°C yielded the new compound PtRu₅(CO) -C)( -PhC₂Ph)₂[Pt(PBu )]₂, 11. All products were characterized crystallographically by single crystal X-ray diffraction techniques. The structure of 8 consists of a pseudo-octahedral PtRu₅ cluster with a second platinum atom bridging a basal edge of the Ru₅ square pyramid. A triply bridging PhC₂H ligand is bonded to the two platinum atoms and one of the ruthenium atoms. The structure of 9 consists of a nido-dodecahedral Pt₂Ru₅ cluster with a carbido ligand in the interior that is not bonded to all seven of the metal atoms. It also contains two triply bridging PhC₂H ligands. The structure of 10 consists of a central octahedral cluster of five ruthenium atoms and one platinum atom. Two additional platinum atoms are bonded to the platinum atom in this cluster but these atoms are not bonded to any other metal atoms of the PtRu₅ cluster. A triply bridging PhC₂H ligand is coordinated to the group of three platinum atoms. The structure of 11 consists of an octahedral PtRu₅ cluster with two additional platinum atoms capping two PtRu₂ triangular faces. There are two PhC₂Ph ligands bridging two Ru₃ triangular faces of the central octahedron. This report is dedicated to Professor Ilya Moiseev on the occasion of his 75th birthday for his many pioneering contributions to the chemistry of metal clusters.     

Structure, room-temperature magnetic and optical properties of Mn-doped TiO2 nano powders prepared by the sol-gel process

TiO 2 nano powders with Mn concentration of 0 at%-12 at% were synthesized by the sol-gel process,and were annealed at 500 C and 800 C in air for 2 hrs.X-ray diffraction (XRD) measurements indicate that the Mn-TiO 2 nano powders with Mn concentration of 1 at% and 2 at% annealed at 500 and 800 C are of pure anatase and rutile,respectively.The scanning electron microscope (SEM) observations reveal that the crystal grain size increases with the annealing temperature,and the high resolution transmission electron microscopy (HRTEM) investigations further indicate that the samples are well crystallized,confirming that Mn has doped into the TiO 2 crystal lattice effectively.The room temperature ferromagnetism,which could be explained within the scope of the bound magnetic polaron (BMP) theory,is detected in the Mn-TiO 2 samples with Mn concentration of 2 at%,and the magnetization of the powders annealed at 500 C is stronger than that of the sample treated at 800 C.The UV-VIS diffuse reflectance spectra results demonstrate that the absorption of the TiO 2 powders could be enlarged by the enhanced trapped electron absorption caused by Mn doping.     

Ultrathin silver‐coated gold nanoparticles as suitable substrate for surface‐enhanced Raman scattering

Surface‐enhanced Raman scattering (SERS) is an extremely powerful tool for the analysis of the composition of bimetallic nanoparticle (BNP) surfaces because of the different adsorption schemes adopted by several molecules on different metals, such as Au and Ag. The preparation of BNPs normally implies a change in the plasmonic properties of the core metal. However, for technological applications it could be interesting to synthesize core–shell structures preserving these original plasmonic properties. In this work, we present a facile method for coating colloidal gold nanoparticles (NPs) in solution with a very thin shell of silver. The resulting bimetallic Au@Ag system maintains the optical properties of gold but shows the chemical surface affinity of silver. The effectiveness of the coating method, as well as the progressive silver enrichment of the outermost part of the Au NPs, has been monitored through the SERS spectra of several species (chloride, luteolin, thiophenol and lucigenin), which show different behaviors on gold and silver surfaces. A growth mechanism of the Ag shell is proposed on the basis of the spectroscopic and microscopic data consisting in the formation and deposit of Ag clusters on the Au NP surface. Copyright © 2009 John Wiley & Sons, Ltd.     

Hydrophobic Bimetallic Catalysts for H/D Exchange Reaction between Hydrogen and Water

Hydrophobic bimetallic catalysts of Pt-M on styrenedivinylbenzene were prepared, where M represents successively: Ir, Rh, Pd, Cu and Ag. The total metal loading was 0.5 wt% and the weight fractions of the metal M were: 0.0,0.05,0.1,0.25,0.5,0.75 and 1.0. For each sample, the catalytic activity for H/D exchange between hydrogen and water vapor was measured. In case of monometallic catalysts, no activity was detected for M = Cu and M = Ag, and the order of the activity values for the other metals was: Pt < Ir < Rh < Pd. For each bimetallic catalyst, the activity measurements indicated a clear interaction between the platinum and the second metal, thus the activity was significantly increased for M = Ir, increased for M = Rh, decreased for M = Pd, drastically decreased for M = Cu and M = Ag.