以水热法合成的水合氧化锆为载体的Pt／WO3-ZrO2上的正己烷异构化

通过水热法合成了一系列水合氧化锆,以之为载体采用浸渍法制备了Pt/WO3-ZrO2催化剂,考察了氢氧化锆的水热温度对Pt/WO3-ZrO2异构化活性的影响.通过X射线衍射、NH3程序升温脱附及H2程序升温还原表征了样品的晶相结构、酸性及还原性能.结果表明,水合氧化锆及以此为载体的催化剂的晶相结构均随着氢氧化锆水热温度的变化而变化,水热温度升高,四方相氧化锆比例下降.具有一定晶相结构的水合氧化锆为载体的催化剂具有较无定形氢氧化锆为载体的催化剂更多的强酸中心和更高的异构化催化活性.高的异构化活性可能与催化剂上更多的强酸中心有关。     

一种制备用于正庚烷异构化的Pt-WO3/ZrO2催化剂的新方法

 采用不同的ZrO(OH)2前驱体制备了WO3-ZrO2和Pt/WO3-ZrO2催化剂. 结果表明,与常规的ZrO(OH)2水凝胶为前驱体制备的WO3-ZrO2-CP催化剂相比,以常压流动氮气中干燥处理的ZrO(OH)2乙醇凝胶为前驱体制备的WO3-ZrO2-AN催化剂对正庚烷临氢异构化反应具有更高的催化活性. 当在 WO3-ZrO2-AN中添加少量Pt时,其催化活性和稳定性均得到显著提高. 表明以ZrO(OH)2醇凝胶为前驱体可以制备出高效稳定的Pt/WO3-ZrO2-AN催化剂.     

固体强酸催化剂Pd/WO3-ZrO2的制备及其对正庚烷异构化反应的催化性能

 采用共沉淀方法制备了固体酸载体WO3-ZrO2,考察了W含量和焙烧温度等对WO3-ZrO2酸性和物相结构的影响,并且考察了Pd/WO3-ZrO2催化剂对正庚烷异构化反应的催化性能. 结果表明,Pd/WO3-ZrO2催化剂的催化性能与固体强酸的W含量及晶相结构密切相关. 在w(W)=13.2%～15.8%时,经700～800 ℃焙烧,WO3在ZrO2表面达到单层分散,且大部分ZrO2以四方晶相存在,所制备的0.5%Pd/WO3-ZrO2对正庚烷异构化反应的催化活性可达到70.4%,选择性可达到81.0%.     

ZrO2前体的制备方法对WOX-/ZrO2

考察了ZrO2前体的制备方法对WOX-/ZrO2的性质及其正庚烷临氢异构化反应性能的影响,同时采用BET、XRD、Py-IR等手段对其进行了表征.结果表明,ZrO2前体的制备方法会明显影响ZrO2前体的比表面积及WOX-/ZrO2催化剂中四方ZrO2和单斜ZrO2晶型的比例,同时WO3的分散程度也有差异.单斜ZrO2太多及WO3晶型的出现会降低正庚烷临氢异构化反应活性;而ZrO2全部为四方晶型时,虽然有利于提高低温反应活性,但缺点是裂解选择性太高;而当单斜ZrO2和四方ZrO2共存,但以四方ZrO2为主,且没有WO3晶型出现时,既可保持较高的反应活性,同时又具有极高的异构化选择性.     

载体的晶化对Ni/WO3-ZrO2催化剂结构及催化正庚烷异构化活性的影响

采用XRD、BET、IR、SEM、NH3-TPD方法对以无定形Zr(OH)4和已晶化的ZrO2为载体制备的Ni-WO3/ZrO2催化剂进行了表征,考察了载体晶化对催化剂结构、酸性及催化性能的影响。结果表明,载体晶化减弱了W与Zr间的相互作用,抑制了四方相ZrO2的生成,减少了催化剂上强酸中心的数目,从而降低了Pt-WO3/ZrO2催化剂上正庚烷异构化反应活性.     

Effect of Crystallization of Zirconium Hydroxide on the Structure and Isomerization Performance for n-Heptane Hydroisomerization of Ni-WO3/ZrO2

采用XRD、BET、IR、SEM、NH3-TPD方法对以无定形Zr（OH）4和已晶化的ZrO2为载体制备的Ni-WO3/ZrO2催化剂进行了表征,考察了载体晶化对催化剂结构、酸性及催化性能的影响。结果表明,载体晶化减弱了W与Zr间的相互作用,抑制了四方相ZrO2的生成,减少了催化剂上强酸中心的数目,从而降低了Pt-WO3/ZrO2催化剂上正庚烷异构化反应活性.     

Pt/Al2O3/WO3/ZrO2催化剂对正己烷异构化反应的催化性能

 通过浸渍法制备了系列Pt/Al2O3/WO3/ZrO2催化剂样品,采用X射线衍射、傅里叶变换红外光谱和程序升温还原等方法表征了催化剂的结构、表面酸性和氧化还原性能,考察了不同反应条件下催化剂对正己烷异构化反应的催化性能. 结果表明, Pt的加入显著改变了WO3/ZrO2载体的氧化还原性,并使催化剂由单一的酸中心催化变成由酸中心与金属中心共同催化; Al2O3的加入增强了WO3与ZrO2之间的相互作用,增加了催化剂的Lewis酸位. 在n(H2)/n(n-C6H14)=1.5, WHSV=0.7 h-1, m(cat)=2.0 g, p=1.0 MPa, θ=220 ℃和t=3 h的反应条件下, Pt/Al2O3/WO3/ZrO2催化剂上正己烷的转化率和2,2-二甲基丁烷的选择性分别达到84.9%和22.9%,裂解反应产物的收率低于1.5%. 经 1000 h的寿命试验,催化剂没有出现失活.     

WO3/ZrO2固体强酸催化剂上异丁烷/丁烯的烷基化反应Ⅱ.过渡金属的助催化作用

制备了一系列用过渡金属M (M =Pt,Co ,Ni,Mn ,Fe,Cu)活化的WO3 /ZrO2 固体强酸催化剂 ,用XRD ,DTA TG ,H2 TPR ,NH3 TPD等测定了其晶型结构、表面状态和酸量 .结果表明 ,各样品中的ZrO2 主要以T晶相存在 ,但T晶相ZrO2 所占的比例因过渡金属不同而异 ,比表面积比WO3 /ZrO2 稍有下降 ;金属Pt的引入使呈单层分散的WO3 的表面状态发生了改变 .研究了异丁烷 /丁烯烷基化反应 ,其反应活性与酸量的测定结果有对应关系 ;与WO3 /ZrO2 相比 ,M WO3 /ZrO2 上的丁烯转化率均稍有下降 ,但具有更高的i C08选择性 .从反应机理分析了添加过渡金属无显著效果的原因 .     

Ga_2O_3对Pt/WO_3/ZrO_2催化剂上正庚烷异构化反应的促进作用

考察了Ga2O3掺杂的Pt/WO3/ZrO2(Pt/WGZ)催化剂在200℃时正庚烷临氢异构化反应性能.结果表明,少量Ga2O3的加入能显著提高Pt/WGZ的催化活性,异构化选择性也有所增加,这是由于B酸位增加和B酸/L酸比的改变而引起的.Pt/WGZ催化剂连续反应80 h,正庚烷转化率和异构化选择性分别稳定在76%和94%.     

苯对Pt/Ga2O3/WO3/ZrO2和Pd/Al2O3/WO2/ZrO2催化剂上正己烷异构化反应的影响

研究了苯对Pt/Ga2O3/WO3/ZrO2(PtGWZ)和Pd/Al2O3/WO3/ZrO2(PdAWZ)催化剂上正己烷异构化反应的影响.结果表明,苯可影响PtGWZ和PdAWZ上正己烷异构化反应性能,苯含量越高影响越显著.与PdAWZ相比较,苯对PtGWZ上正己烷异构化反应的影响相对较小;苯对PtGWZ上正己烷异构化反应活性的影响是可逆的,撤除苯后PtGWZ对正己烷异构化的催化性能可完全恢复;苯对PtGWZ上正己烷异构化反应的稳定性没有影响.苯对PdAWZ上正己烷异构化反应活性的影响足不可逆的,PdAWZ用于含苯正己烷异构化反应催化剂会逐渐失活.热失重法积炭分析结果表明,相同条件下,含苯正己烷异构化反应后,PtGWZ上的积炭量较PdAWZ上的积炭量少.分析讨论了苯对PtGWZ和PdAWZ上正己烷异构化反应影响差异性的原因.     

Early Stages of Crystallization in Gel Derived ZrO2 Precursors

Three different precursor materials giving rise to contrasted nanostructures, xerogels, aerogels and precipitates, are prepared by a sol gel route in the Zrn -propoxide—acetylacetone—water—n-propanol system. Clear homogeneous gels are made by using a proper amount of acetylacetone and water. The gels are dried either by conventional processing (xerogels) or by supercritical evacuation of alcoholic solvent (aerogels). The complexation ratio (R = [acetylacetone]/[Zr(OR)₄]) is the main parameter controlling the size of ZrO₂ primary particles. WhenR = 0 , precipitates are obtained.Xerogels, aerogels and precipitates are characterized and their textures are compared through small angle X-ray scattering measurements. The fractal structure of gels is destroyed by conventional drying and is preserved in aerogels. On the other hand precipitates are described as homogeneous agglomerates of very small primary units.The first crystallization steps are studied by transmission electron microscopy and X-ray diffraction experiments. The contribution of crystallite size and microstrain effects are investigated by Rietveld whole pattern fitting. The crystallization of precipitate powders starts at the agglomerate scale with large crystal like distorted lattices.     

Preparation and Self-assembly of Zirconia Nanoparticles via Hydrothermal Method

Zirconia nanoparticles were synthesized via hydrothermal method without any additives. This work focuses on the effect of preparation conditions1 such as the precursor preparation condition and crystallization time of nanocrystallite in autoclave on the properties of as-prepared products. The results indicated that the amount of tetragonal zirconia varied with the preparation conditions. It increased with the increase of the concentration of KOH solution in precursor producing process and reduced with the prolongation of crystallization time. At the same time, the particle size and morphology were also affected by the preparation conditions. In addition, the self-assembled spindle- like aggregates were observed in present works.     

Texture of zirconia obtained by forced hydrolysis of ZrOCl2 solutions

The structure and surface properties of ZrO₂ strongly depend on its preparation. In the present work the impact of prolonged aging at basic conditions (pH = 9, T = 100°C, t = 48 h), on the phase composition and textural properties, obtained by calcination of the precipitate, was investigated using several techniques conjointly (DTA/TG, DSC, XRD, porosimetry). The thermal effects accompanying the ZrO₂·xH₂O gel formation, the coalescence of the particles and crystallization were evaluated and discussed in terms of the structural differences between the aged and non-aged samples. This revised version was published online in July 2006 with corrections to the Cover Date.     

C掺杂ZrO_2四方纯相粉体的甲醇溶剂热制备及热稳定性研究

在ZrO(NO_3)_2·2H_2O-CO(NH_2)_2-CH_3OH溶剂热过程中,水的缺乏使得甲醇通过其甲氧基与Zr~(4+)发生亲核取代或以分子配位,直接参与锆盐的水解-缩聚反应,形成具有[ZrO_z(OH)_p(OCH_3)_q·rCH_3OH]_n结构的无机聚合物;同时,甲醇对聚合物低的溶解能力强烈抑制了Ostwald熟化过程,阻碍了溶剂热产物的晶化与热力学支持的结构重排。尿素通过其水解作用与锆盐竞争体系中的水及锆物种骨架上的羟基,这不仅导致无机聚合物中Zr-O-Zr键合相对Zr-OH键合的比例增加,使得溶剂热产物发生结构重排的几率进一步下降;而且也一定程度上增加了溶剂热产物中甲氧基的含量。含有大量甲氧基团的溶剂热产物经400℃焙烧后,形成C掺杂ZrO_2。C掺杂与溶剂效应共同稳定了ZrO_2的四方相。在500-600℃中等温度、空气气氛焙烧过程中,C掺杂ZrO_2四方相结构显示了良好的热稳定性;提高焙烧温度至700℃,游离于颗粒表面的C被完全氧化去除,固溶于晶格中的C也部分脱溶,导致了部分四方相失稳转变成单斜相。     

Dehydration and crystallization process in sol-gel zirconia

Sol-gel zirconia was characterized using high-resolution thermogravimetry (Hi-Res TG) and differential scanning calorimetry (DSC) and compared with X-ray diffraction, Raman scattering, and UV-Vis spectroscopy. ZrO_2-x(OH)_2x·yH₂O annealed below 400°C show typical behavior of amorphous material. As the annealing temperature is increased, the tetragonal and monoclinic phases crystallize. Typical Hi-Res TG curve shows that the samples are continuously dehydrated in a long temperature range, between room temperature and 600°C. The total mass loss relative to the initial mass is of about 29%. The DSC analysis coupled with TG and structural information, indicate that the exothermic processes about 355 and 447°C can be related to the nucleation process of the formation of tetragonal zirconia, with bulk crystallization at 447°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Two-dimensional crystallization of hard sphere particles at a liquid–liquid interface

A method for studying crystallization of hard sphere like particles in two dimensions is presented. The method involves trapping the particles at the interface between two immiscible liquids. Particles at the interface undergo 2D Brownian motion, and at sufficiently high densities crystallization is observed. The pseudo hard sphere nature of the particle interactions under these conditions is maintained, as demonstrated by the area density at which crystallization occurs. In contrast to established techniques for studying crystallization in pseudo 2D hard spheres, the particles trapped at the interface undergo no vertical motion, so the system is in principle closer to a true 2D system. The method is therefore amenable to the study of the effects of polydispersity on crystallization behaviour. The advantages and disadvantages of the method are discussed.     

Supramolecular crystal growth in concentrated suspensions of charged monodisperse spherical silica particles

Concentrated suspensions of charged monodisperse spherical silica particles (MSSP) stabilized by alkalis or ammonia are able to crystallize at a certain destabilization. Crystal structures with the particles fixed at certain distances from each other show an isotropic normal mechanism of continuous growth with a rough phase boundary. The crystallization is determined by three parameters,víz. the concentration of particles, temperature, the thickness of the ion atmosphere around the particles and the concentration of counterions. The crystallization of MSSP suspensions is considered as a model of the supramolecular crystallization in the field of synthesis of mesoporous structures.     

Synthesis and Characterization of Monodisperse Spherical Zirconia Particles

Monodisperse zirconia spherical particles are prepared by hydrolysis of zirconium propoxide in 2-methoxyethanol in presence of decanoic acid as a shape stabilizer. The powder is analyzed by computer image analysis on TEM micrographs, TG-DSC, FTIR, X-ray diffraction and nitrogen adsorption isotherms. A competition phenomenon between aggregation and individual growth of the particles during precipitation is deduced from the observations.     

Effect of Oxygen Environment on the Decomposition and Crystallization of an Aqueous Sol-Gel Derived Zirconium Acetate Gel

A precursor gel was prepared by desiccation of an aqueous solution of zirconium acetate and pyrolyzed to form crystalline powders in selected gas environments. Thermal analysis, X-ray powder diffraction, mass spectrometry and Fourier transform infrared spectroscopy were used to investigate the decomposition of the gel and the transformations occurring during pyrolysis to 800°C in nitrogen, air and oxygen. Three transition temperatures were detected: the amorphous-to-cubic crystal transformation, cubic-to-tetragonal transformation, and the initiation of tetragonal-to-monoclinic transition. The presence of molecular oxygen decreased the crystallization temperature, increased the grain size of the tetragonal crystals formed and decreased the temperature at which the tetragonal-to-monoclinic transformation was initiated. The decrease in the crystallization temperature in the presence of oxygen occurred despite an increase in the temperature corresponding to the loss of the major portion of the organic component of the gel.