具有强酸位的六方和立方介孔硅铝分子筛合成及催化活性比较

六方 MCM- 41和立方 MCM- 48介孔分子筛是长程有序的介孔材料 ,由于其孔壁是无定形结构 ,具有较弱的酸性 ,限制了其应用范围 .若能提高它们的酸强度则可提高其在石油炼制和精细化工中的应用价值 .现已采用多种改进方法来提高其酸强度 [1～ 6 ] ,但所合成的介孔材料均为六方结构 ,而具有立方结构的材料未见文献报道 .本文采用两步晶化合成法 ,用低浓度的表面活性剂合成出具有强酸位的立方介孔分子筛 ( MB48) ,还通过调节溶液的酸碱性合成出六方介孔分子筛 ( MB41 ) ,对样品的结构、酸性和催化性能进行了表征和比较 .1　实验部分1 .1　 β…     

密堆积六方结构Ni纳米颗粒的制备与表征

采用溶胶-凝胶方法制备前驱体, 将前驱体进行热处理制得密堆积六方结构(hcp)的Ni纳米粉末. 利用TG-DTA, XRD和TEM等测试手段对材料的合成条件、结构、形貌以及结构演变过程进行了分析. 结果表明, 于300 ℃进行热处理所合成的样品为球形的具有密堆六方结构的Ni纳米颗粒, 晶胞参数a=0.2652 nm, c=0.4334 nm, 平均晶粒尺寸约为12 nm. 随着热处理温度的升高, 样品结构发生由密堆六方结构向面心立方结构的转变.     

多树枝结构和立方结构PbS的水热合成及形成机理

在无模板条件下,用Pb(NO₃)₂做铅源,(CH₄N₂S)做硫源,用水热法在160 ℃反应24 h制备了结晶度好的多树枝结构PbS。利用XRD、SEM、EDX、TEM对产物进行了表征,结果表明所得产物为面心立方多树枝状结构,单个树枝的长度为1.0～3.0 μm。此外,在碱性条件下丙三醇/水体系中制备了具有不同凹面的立方结构PbS,边长为2.0～5.0 μm。对2种不同形态PbS的影响因素进行了讨论,并提出了形成机理。同时对其荧光及紫外性质进行了研究,结果表明立方结构的PbS在309和373.5 nm处出现了2个荧光峰,在211和232 nm处出现了2个紫外吸收峰。     

模板法合成六方介孔SiO2

模板法合成六方介孔SiO2;六方结构;低聚表面活性剂     

六钨酸盐为模板的三维网状超分子化合物[La2(DNBA)4(DMF)8][W6O19]的合成和晶体结构

0 Introduction polyoxometalates (POMs), in addition to their im- portance in catalysis, biochemical separation and medicinal chemistry, play an important role for the design of new materials with novel electronic, magnet- ic and topological properties[1￣…     

含环烷巯基配体的Fe_4S_4类立方烷簇合物的合成和结构表征

报道了 2个含烷巯基配体的Fe4S4类立方烷簇合物 ,它们在氯化亚铁 ,四硫代金属酸盐及环烷硫醇组成的反应体系中生成 ,化合物的结构参数分别为 :[PhCH2 NMe3 ]2 [Fe4S4(SC5 H9) 4](Ⅰ ) ,属单斜晶系 ,空间群P2 1/c,a =1 .6 32 7( 4)nm ,b=1 .1 2 2 9( 3)nm ,c=2 .80 2 5 ( 1 0 )nm ,β =94.6 3( 2 )°,Z =4,R =0 .0 74;(Et4N) 2 [Fe4S4(SC6H11) 4](Ⅱ ) ,,属四方晶系 ,空间群I42m ,a=1 .1 6 70 5 ( 9)nm ,b=1 .1 6 70 6 ( 2 )nm ,c=2 .0 6 32 6 ( 5 )nm ,Z =2 ,Dcalc=1 .2 7g/cm3 ,R =0 .0 78.环烷巯基配体的引入没有引起Fe4S4核心结构的明显变化 ,同时讨论了阳离子对Fe4S4簇阴离子结构对称性的影响     

含MoFe3Se4类立方烷核芯簇合物的合成与结构表征

室温下［Ｅｔ_４Ｎ］_２ＭｏＳｅ_４, ＦｅＣｌ_２和 Ｒ_２ＮＣＳ_２Ｎａ在 ＤＭＦ和 ＣＨ_３ＣＮ混合溶剂中反应,得到含ＭｏＦｅ_３Ｓｅ_４核芯的Ｍｏ－Ｆｅ－Ｓｅ簇合物ＭｏＦｅ_３Ｓｅ_４（μ－Ｒ_２ＮＣＳ_２）_２（Ｒ_２ＮＣＳ_２）_４（Ｒ２＝Ｍｅ_２（１）,Ｅｔ_２（２）,Ｃ_４Ｈ_８（３））．化合物２的单晶Ｘ射线衍射分析表明,其分子结构为２个桥式和４个螫合Ｅｔ_２ＮＣＳ_２~－配体包围的一个扭曲类立方烷Ｍ_４Ｓｅ_４簇核对３个化合物的ＣＶ进行了表征,它们在ＤＭＳＯ溶液中的电化学行为表现出了多电子可逆的传递过程．     

有关立方金刚石的思维训练

以立方金刚石为研究对象,从基本结构单元的剖析、几何体的嵌入与辅助、相似结构的类推与变形、空间结构的扩大延伸与局部选取、图形平移与旋转、不同视角的投影等方面进行提炼,提升思维品质,力争在有关晶体思维的“准确度、清晰度、深度、广度、速度”等方面的训练有更大的飞跃。     

六钨酸盐为模板的三维网状超分子化合物[La2(DNBA)4(DMF)8][W6O19]的合成和晶体结构

A new three-dimensional (3D) lanthanide-aromatic monocarboxylate dimer supramolecular network [La₂(DNBA)₄(DMF)₈][W₆O₁₉] (DNBA=3,5-dinitrobenzoate, DMF=dimethylfomamide) was synthesized using hexatungstate anion (W₆O₁₉^2-) as template. The crystal structure of the title compound has been determined by single-crystal X-ray diffraction. It crystallizes in triclinic, space group P1 with a=1.334 54(18) nm, b=1.387 52(19) nm, c=1.426 06(19) nm, α=102.189(2)°, β=101.023(2)°, γ=116.349(2)°, V=2.187 2(5) nm³, D_c=2.364 g·cm^-3, Z=1, F(000)=1 453.40. The single crystal structure reveals that two La(Ⅲ) ions are bridged by four 3,5-dinitrobenzoate anions as asymmetrically bridging ligands, leading to dimeric cores, [La₂(DNBA)₄(DMF)₈]²⁺; [La₂(DNBA)₄(DMF)₈]²⁺ groups are joined together by π-π stacking interaction between the aromatic groups to form a two-dimensional grid-like network; the 2D supramolecular layers are further extended into 3D supramolecular network with a 1D box-like channels by hydrogen bonding interactions, in which hexatungstate polyanions reside. CCDC: 284694.     

硼砂与尿素合成六方氮化硼的机理

研究了N_2气氛下硼砂与尿素反应生成六方氮化硼以及主要副产物产生和变化的过程,采用热重-差示扫描量热法(TG-DSC)、X射线衍射(XRD)、扫描电子显微镜(SEM)等检测手段对反应产物和氮化硼样品进行了分析.研究结果表明,氮化硼在700℃左右完全生成,随焙烧温度的提高其结晶度不断提高.反应副产物偏硼酸钠的生成是导致氮化硼产率较低的主要原因,在高温焙烧过程中偏硼酸钠的存在有利于六方氮化硼的结晶过程.研究结果可为硼砂-尿素法六方氮化硼制备工艺的优化和改进提供理论基础.     

石墨变金刚石:蓝丝黛尔石与钻石的动力学竞争

<正>六方金刚石(hexagonal diamond,HD),又称蓝丝黛尔石(Lonsdaleite)是自然界中神秘的物质。六方金刚石在自然界非常稀少,科学界普遍认为自然界中的六方金刚石是流星上的石墨坠入地球时形成的。流星撞击地球会产生了巨大的热量与压强,从而导致石墨发生相变形成金刚石。第一次发现六方金刚石是在美国亚利桑那州的巴林杰     

Dynamic Elasticity of Cubic Diamond

Previously, the structure of the carbon allotrope glitter has been disclosed, and a theory accompanying the structural report as to its bulk modulus at pressure predicted it would be among the hardest materials possible. The dynamic elasticity theory developed in that paper, involving the forces generated in elastic chemical bond deformations resulting from applied mechanical forces, is here applied to the cubic diamond lattice. Stresses, both lateral and axial, contribute to the bulk modulus of cubic diamond at pressure. The ultimate strength of the cubic diamond lattice, in the approximations of the dynamic elasticity theory presented in this paper, is estimated to be in excess of 1 TPa, at modest bond length deformations of about 0.1 ?, and when including the zero pressure bulk modulus B ₀ in the computation. In particular, the dynamic elasticity model predicts the hardest direction of cubic diamond will be for an isotropic mechanical force applied along 〈111〉 directions of the structural unit cell.     

Preparation and Characterization of Structurally Stable Hexagonal and Cubic Mesoporous Silica Thin Films

Single-layered In₂O₃-SnO₂ coatings, with a Sn/(Sn + In) ratio of 25–50 at.%, were fabricated by a spin-coating method using coating solutions prepared from tin and indium 2-isopropoxyethoxides. The electrical conductivity of the air- and H₂-annealed samples were analyzed. The maximum conductivity for the air-annealed samples, 24 S/cm, were obtained with the smallest Sn content. H₂ annealing induces a remarkable permanent increase in the conductivity of the films with a specific Sn content of 30–40 at.%. The highest relative conductivity increase was 7600% (1 S/cm 76 S/cm). The effect of the H₂ annealing on the chemical composition and the crystal structure of the fabricated films having a Sn/(Sn + In) ratio of 35.5 at.% was followed using XPS and XRD, respectively.     

Electrode Reactions on Synthetic Diamond and Cubic Boron Nitride in Ionic Melts

The behavior and corrosion resistance of synthetic diamond and cubic boron nitride in chloride, chloride-oxide, and oxide salt melts at 750-900°C were studied by potentiometric and voltammetric methods.     

The Role of Water for the Phase‐Selective Preparation of Hexagonal and Cubic Cobalt Oxide Nanoparticles

A selective preparation and the formation mechanism of hexagonal and cubic CoO nanoparticles from the reaction of [Co(acac)₂] (acac=acetylacetonate) and amine have been investigated. CoO nanoparticles with a hexagonal pyramidal shape were yielded under decomposition conditions with amine. Importantly, the addition of water altered the final phase to cubic and comprehensively changed the reaction mechanism. The average sizes of the hexagonal and cubic CoO nanoparticles could be controlled either by changing the amine concentration or by using different reaction temperatures. Detailed formation mechanisms are proposed on the basis of gas chromatography–mass spectrometry data and color changes of the reaction mixture. The hexagonal CoO phase is obtained through two distinct pathways: solvolysis with C C bond cleavage and direct condensation by amine. On the other hand, the cubic CoO nanoparticles were synthesized by strong nucleophilic attack of hydroxide ions from water and subsequent C C bond breaking. The resulting caboxylate ligand can stabilize a cobalt hydroxide intermediate, leading to the generation of a thermodynamically stable CoO phase.     

Rapid Transformation of Hexagonal to Cubic Silicon Carbide (SiC) by Electric Discharge Assisted Mechanical Milling

Silicon carbide powder was successfully transformed from hexagonal SiC into cubic SiC using the electric discharge assisted mechanical milling (EDAMM) method. The milling process was conducted in nitrogen plasma at atmospheric pressure. The effects of pulsed alternating current (AC) and direct current (DC) discharge on product formation were investigated. Products were characterized by X-ray diffractometry, scanning electron microscopy, transmission electron microscopy and nanohardness. It was found that hexagonal SiC can be transformed into cubic SiC under EDAMM processing, near complete transformation occurring within 5 min when applying AC mode electrical pulses, and within 10 min when applying DC mode discharges.     

Influence of Hexagonal Boron Nitride on Electronic Structure of Graphene

By performing first-principles calculations, we studied hexagonal-boron-nitride (hBN)-supported graphene, in which moiré structures are formed due to lattice mismatch or interlayer rotation. A series of graphene/hBN systems has been studied to reveal the evolution of properties with respect to different twisting angles (21.78°, 13.1°, 9.43°, 7.34°, 5.1°, and 3.48°). Although AA- and AB-stacked graphene/hBN are gapped at the Dirac point by about 50 meV, the energy gap of the moiré graphene/hBN, which is much more asymmetric, is only about several meV. Although the Dirac cone of graphene residing in the wide gap of hBN is not much affected, the calculated Fermi velocity is found to decrease with the increase in the moiré super lattice constant due to charge transfer. The periodic potential imposed by hBN modulated charge distributions in graphene, leading to the shift of graphene bands. In agreement with experiments, there are dips in the calculated density of states, which get closer and closer to the Fermi energy as the moiré lattice grows larger.     

Understanding the Central Location of a Hexagonal Hole in a B36 Cluster

The most stable form of a B₃₆ cluster has a central hexagonal hole. Such an interesting finding has led to the possible synthesis of a 2D boron sheet by employing the B₃₆ cluster as the building unit. Herein, a DFT study to investigate the reason for the central location of the hexagonal hole in the B₃₆ cluster is presented. The results show that the B₃₆ cluster with a central hexagonal hole is highly thermodynamically and kinetically stable. More importantly, such high stability is further understood through chemical bonding analysis.