紫外拉曼光谱研究焙烧气氛对氧化锆相变的影响

 以紫外拉曼光谱技术研究了在不同焙烧气氛中氧化锆样品的表面晶相结构及其转变过程．结果表明，在有氧气氛中焙烧的氧化锆样品易转变为单斜相，而在惰性气氛中焙烧可以有效地稳定样品体相和表面的四方相结构．在缺氧气氛中焙烧的样品暴露于空气中后，表面极易转变为单斜相，而其体相仍为四方相结构，这表明四方相氧化锆在样品表面是极不稳定的．     

Preliminary Synthesis and Characterization of Mesoporous Nanocrystalline Zirconia

A novel method to prepare mesoporous nano-zirconia was developed. The synthesis was carried out in the presence of PEO surfactants via a solid-state reaction. The materials exhibit a strong diffraction peak at low 28 angle and their nitrogen adsorption/desorption isotherms are typical of type IV with H1 hysteresis loops. The pore structure imaged by TEM can be described as wormhole domains. The tetragonal zirconia nanocrystals are uniform in size (around 1.5 nm) and their mesopores focus on around 4.6 nm. The zirconia nanocrystal growth is tentatively postulated to be the result of an aggregation mechanism. This study also reveals that the PEO surfactants can interact with the Zr-O-Zr framework to reinforce the thermal stability of zirconia. The ratio of NaOH to ZrOC12, crystallization and calcination temperature play an important role in the synthesis of mesoporous nano-zirconia.     

层状和MSU结构的介孔纳米二氧化锆

在不添加任何结构稳定剂的条件下, 首次用固态反应结构导向法成功地合成了具有层状结构和MSU结构的介孔纳米二氧化锆. 研究发现, 通过有效地控制晶化条件, 二氧化锆的晶相、比表面和孔结构可以方便地得以调变. 晶相的转变由粒度大小控制, 并且构成无机骨架的相态不同, 合成样品的热稳定性存在差异. 结果显示, 介孔纳米二氧化锆的形成仍遵循超分子液晶模板机制, 且由碱锆摩尔比的大小控制介观相的转化, 低碱锆摩尔比条件下形成层状相, 而高碱锆摩尔比条件下为维持整个体系的低能稳定状态, 在电荷作用下形成反棒状胶束结构.     

纳米二氧化锆在甲醇合成催化剂Cu/Ga2O3/ZrO2中的作用

The introduction of mesoporous nanosize zirconia to the catalyst for methanol synthesis dedicates the nanosized catalyst and mesoporous duplicated properties. The catalyst bears the larger surface area, larger mesoporous volume and more uniform diameter, more surface metal atoms and oxygen vacancies than the catalyst prepared with the conventional coprecipitation method. The modification of microstructure and electronic effect could result in the change of the reduced chemical state and decrease of reducuction temperature of copper, donating the higher activity and methanol selectivity to the catalyst. The results of methanol synthesis demonstrate that the Cu^＋ is the optimum active site. Also, the interaction between the copper and zirconia shows the synergistic effect to fulfil the methanol synthesis.     

酸性化合物在十二胺-N,N-二亚甲基膦酸改性氧化锆固定相上的分离

酸性化合物在十二胺-N; N-二亚甲基膦酸改性氧化锆固定相上的分离;氧化锆;色谱固定相;十二胺-N; N-二亚甲基膦酸     

Reactions of Metal Salts and Alkali Metal Nitrates. Role of the Metal Precursors and Alkali Metal Ions in the Resulting Phase of Zirconia

Zirconia powders are prepared by reaction of a zirconium precursor with an alkali metal nitrate. The major part of the reactions takes place before the melting points and then the reactions go slowly to completion at 450°C in the molten salts. The roles of the precursor and the alkali metal ion are discussed considering the reaction between two precursors, octahydrated zirconium oxychloride and zirconium tetrachloride, and two nitrates, LiNO₃ and NaNO₃, and some resulting physico-chemical differences. The obtained zirconia powders contain very small amounts of alkali metal ions which act as stabilizing agent. Their effect on the balance tetragonal-monoclinic ZrO₂ depends upon the homogeneity of their distribution which is related to their ability to diffuse inside the bulk of particles and their polarizing power when located mainly on the surface.     

Phase Transition and Phase Transformation in Block Copolymer Nanoparticles

Block copolymer nanopaticles were prepared from the mixture solutions containing good/poor solvents by a simple evaporation process. The block copolymers formed disorder, unidirectionally stacked lamellar, and onion‐like structures in nanoparticles depending on preparation temperatures. Thermal annealing induced the disorder‐order phase transition and order‐order phase transformation in the block copolymer nanoparticles, even though the annealing temperature is lower than the of one polymer segment. The unusual thermal behaviors suggest that the glass transition temperature of the block copolymer is decreased by the effect of nanoparticle, whose surface areas are larger than their volumes.

     

Room Temperature Solid State Reaction Involving Structural Transformation of Covalent Oxide Network

An interesting structural transformation from a two dimensional (2d) covalent oxide network with a layered structure to a three-dimensional (3d) network with a tunnel structure was found at room temperature in the mixture of hydrated alkali-metal molybdenum bronze and amorphous alkali-metal molybdate. From various experimental results it was concluded that the transformation was due to a room temperature solid state reaction.     

纳米 ZrO2 作分散剂的 Ru-Zn 催化剂上苯选择加氢制环己烯

 采用水热法合成了比表面积分别为 34 和 87 m2/g 的 ZrO2 样品 (分别记为 ZrO2-34 和 ZrO2-87), 并考察了它们作分散剂时 Ru-Zn 催化剂上苯选择加氢制环己烯反应的性能. 结果表明, 两个 ZrO2 样品具有相近的纯度和物相, 晶粒粒径分别为 21.6 和 11.4 nm. 其中 ZrO2-34 具有较小的比表面积、较大的孔径、较小的粒径、集中的粒度分布和较大的堆密度, 因而更适合用作苯选择加氢制环己烯 Ru-Zn 催化剂的分散剂, 且循环使用多次催化剂仍表现出较高的选择性和稳定性.     

新型固定床Raney Ni制备过程中晶相结构的转化

以拟薄水铝石制备粘结剂，加入镍铝合金粉和田菁粉捏合、成型，在空气中高温焙烧，然后用苛性碱溶液充分浸取，制备出可应用于固定床加氢的活性Raney Ni催化剂。采用XRD和TG-DTA分析了催化剂制备过程中晶相结构的转化，结果表明，成型合金焙烧过程中，富铝合金相（如Al₃Ni-Al和Al₃Ni）逐渐转变为贫铝合金相（如Al₃Ni₂和AlNi），释放出的金属铝依次发生氧化，同时抑制金属镍的氧化；在高于1 123～1 133K焙烧时金属铝氧化生成α-Al₂O₃，使催化剂获得较高的颗粒强度。苯加氢活性评价结果表明，该新型固定床Raney Ni催化剂活性高于负载型镍催化剂，也高于参照专利方法制备的有机聚合物粘结的同类型催化剂，并且具有较好的低温加氢活性。     

Preparation of MMA－BA－DMAEMA Nanosized Latex

The terpolymer latex of methyl methacrylate (MMA)/butyl acrylate (BA)/ dimethyl aminoethyl methacrylate (DMAEMA) with diameter of less than 100 nm was prepared by seeding semi-continuous emulsion copolymerization using APS (ammonium pcrsulfate) / TMEDA (N,N,N,N-tetramethylethylenediamine) as the redox initiators and SDS (sodium dodecylsulfate) and OP (P-octylpolyethylene glycol phenylether) as co-emulsifiers. The factors that influenced the process stability of the copolymerization and the particle size of the latex were investigated. The addition of aqueous ammonia as coagulation inhibitor provided better process stability of the copoly- merization. The addition of acetic acid as the acidification agent caused a remarkable reduction of the latex particle size.     

高岭土相转变的非等温动力学

<正>高岭土为三斜晶系,一般为无色至白色的细小鳞片,单晶呈假六方板状或书册状,平行连生的集合体往往呈蠕虫状或手风琴状,是造纸、陶瓷、化工、涂料、医药和国防等几十个行业中必须的矿物     

苄基膦酸改性氧化锆固定相的制备和性能评价

通过室温浸泡和回流改性的方式,制备了苄基膦酸改性氧化锆色谱固定相.元素分析表明,室温浸泡和加热回流都能够得到较大膦酸吸附量.红外光谱、差热分析证实苄基瞵酸是以Lewis酸碱作用吸附在氧化锆表面的.色谱分析该固定相具有很好的疏水性能和离子交换性能,对某些碱性物质的分离有一定的应用前景.     

纳米锐钛矿相变的原位XRD研究

钛氧化物具有3种物相：锐钛矿、板钛矿和金红石，其中，锐钛矿和板钛矿为室温稳定相．在温度较高的条件下会向热力学更稳定的金红石相转变。锐钛矿向金红石的相变是热力学亚稳定相向稳定相的转变，由于这种相变过程不存在平衡温度．分析研究其相变过程无论从理论方面还是从实际应用方面均具有重要的意义。     

纤维素-三(3,5-二甲基苯基氨基甲酸酯)涂敷氧化锆手性固定相的制备和色谱评价

制备并表征了涂敷纤维素-三(3，5-二甲基苯基氨基甲酸醋)-ZrO2手性固定相。以正己烷／异丙醇为流动相，研究了正相色谱条件下手性固定相对几类光学异构体的手性拆分能力。实验结果表明：氧化锆载体表面的碱性性质对光学对映体的手性拆分有很大影响；在常用流动相条件下，酸性对映体被完全滞留；纤维素-三(3，5-二甲基苯基氨基甲酸醋)-ZrO2手性固定相对于中性及碱性对映异构体的分离呈现出较好的手性拆分能力。     

纳米尺寸氧化钇团簇阴离子与正丁烷反应的研究

在单一原子量分辨水平上研究纳米尺寸过渡金属氧化物团簇(M_xO_y^q)与小分子的反应不仅能够获得氧化物纳米颗粒的反应性随原子组成和尺寸连续变化的演变规律, 而且对认识其结构特征以及表面活性氧物种(如O^-•自由基)的产生机制等具有重要意义. 本工作分别采用耦合快速流动反应管和耦合四极质量过滤器-线形离子阱的两套反射式飞行时间质谱研究了不同“氧缺陷指数”(Δ)的氧化钇团簇Y_xO_y^- (x≤50,y≤76; Δ≡2y–1–3x, Δ=0~5)和掺杂氟(F)原子团簇Y _xO_yF^- [x≤49,y≤74; Δ≡(2y+1)–1–3x, Δ=1]与 n-C₄H₁₀分子的反应. 实验观测到Δ=1系列团簇(Y₂O₃)_NO^- (N=1~25)、(Y₂O₃)_NYO₂F^- (N=1~24)及Δ=4系列团簇(Y₂O₃)_NYO₄^- (N=1, 3~24)具有氢抽取反应活性, N≥2时其它Δ系列团簇(Δ=0, 2, 3, 5)在相同实验条件下没有表现出明显的反应性. 密度泛函理论研究Δ=1或4系列小尺寸团簇(Y₂O₃)_NY_xO_yF_0,1^- (N≤4;x=0, 1)的结构揭示O^-•自由基是氢抽取反应的活性位点, 结合实验可推测Δ=1或4系列纳米尺寸团簇(Y₂O₃)_NY_xO_yF_0,1^- (x=0, 1)结构中也含有O^-•自由基. 这些结果表明Δ=0系列惰性纳米尺寸团簇(Y₂O₃)_NYO₂^-可以通过吸附一个O₂分子发生电子转移生成O^-•自由基(O^2-+O₂→O^-•+O₂^-•), 也可以通过掺入F原子的方式生成O^-•自由基(O^2-+F^•→O^-•+F^-).     

Sol-Gel Synthesis and Phase Evolution Behavior of Sterically Stabilized Nanocrystalline Zirconia

Nanocrystalline as well as submicron sized, non-agglomerated, spherical ZrO₂ particles have been successfully synthesized using the sol-gel technique utilizing hydroxypropyl cellulose (HPC) as a polymeric steric stabilizer. The effect of various parameters such as the ratio of molar concentration of water and alkoxide (R), the molar concentration [HPC] and the molecular weight (MW_HPC) of HPC polymer as well as the calcination temperature on ZrO₂ nanocrystallites size and their phase evolution behavior is systematically studied. The phase evolution behavior of nanocrystalline ZrO₂ is explained and correlated with the adsorption behavior of HPC polymer on ZrO₂ nanoparticles surface, which is observed to be a function of R, [HPC], MW_HPC and the calcination temperature. Optimum synthesis parameters for obtaining 100% tetragonal phase in nanocrystalline ZrO₂ are identified for the present sol-gel method of synthesizing nanoparticles.     

Phase Transformation Strategies for the Construction of Heterojunction TiO2 Photocatalysts

Heterojunction TiO₂ has attracted great attention in photocatalytic applications due to its high efficiency in the separation of photogenerated electron-hole pairs and strong ability of light absorption. This work concisely summarizes the distinct crystal phases of TiO₂ and elucidates the prevalent methods employed in the synthesis of TiO₂ heterojunctions. Furthermore, the review highlights novel strategies for the realization of TiO₂ phase transformation, thereby contributing to a deeper understanding and advancement in the application of mixed-phase TiO₂ photocatalysts.     

Cu-Fe基催化剂上CO加氢反应过程中物相的转化行为

研究了Cu-Fe基催化剂上CO加氢反应过程中各组分尤其是铁的体相和表面微观结构的转化行为.通过XRD、Mssbauer谱、XPS和Raman光谱等表征手段全程跟踪铁形态的变化.结果表明,还原后体相的铁发生了明显的碳化,物相以Fe3O4和χ-Fe5C2为主,随着反应温度的升高,χ-Fe5C2的含量出现最大值.而还原后催化剂表面没有检测到明显的铁的碳化.这种表面性质与体相的差异来源于铁独特的还原方式,这种还原方式造成锌和锰等组分在催化剂表面富集.而在反应过程中,系统中还原/氧化气氛的变化导致铁组分在催化剂表面富集.还原后自由碳原子在催化剂表面沉积,并随着反应的进行,碳原子的形态发生变化,显著抑制了Cu和Fe之间的协同作用,削弱了Cu-Fe基催化剂的链增长能力.