Characterization of Y zeolites dealuminated by solid-state reaction with ammonium hexafluorosilicate

In the present work the solid-state dealumination of Y zeolite with ammonium hexafluorosilicate for various reaction times was studied. A detailed characterization of the porosity of the samples, and their hydrophobic-hydrophilic properties, was made. The characterization techniques used, besides the low temperature nitrogen adsorption and the room temperature water adsorption, include also the FTIR, the powder XRD and the ²⁷Al and ²⁹Si MAS NMR. These techniques showed evidence for the complex mechanism of dealumination that for sufficiently long times of reaction allows the partial reconstitution of the structure. Due to this mechanism the evolution of the Si/Al ratio, as well as the porosity and the hydrophobic-hydrophilic properties, do not run monotonically with the time.     

Reaction bonded aluminum oxide composites containing cubic boron nitride

The properties of alumina can be improved by incorporating second phases like zirconia or carbides. It has also been reported that reaction bonded aluminum oxide (RBAO) process can be used as a host matrix for large scale second phase reinforcement particles without causing harmful residual stresses normally encountered with shrinking matrix materials. The potential of using cubic boron nitride in reinforcing alumina has not yet been reported. This work reports some improvements in mechanical properties of alumina achieved by incorporating cubic boron nitride particles in a reaction bonded aluminum matrix. Attrition milled aluminum, alumina and cubic boron nitride powders were heat treated to 800 °C in air followed by sintering to 1300 °C in argon. Sintered samples were found to have better density, hardness and fracture toughness compared to conventionally sintered samples of same composition.     

Characterization and property of magnetic ferrite ceramics with interesting multilayer structure prepared by solid-state reaction

Polyhedral MnFe₂O₄ with multilayer structure was successfully synthesized, and the possible originating mechanism of multilayer structure was firstly determined in current study. The phase formation, morphology evolution and interface reaction of the solid-state reaction of MnO₂ and Fe₂O₃ mixture under air and reduction atmospheres were comparatively investigated, and the microwave absorption property of polyhedral MnFe₂O₄ with multilayer structure were discussed via the XRD, SEM, XPS, TEM, AFM and vector network analyzer measurements. Experiment results showed that multilayer MnFe₂O₄ can be synthesized both in the air at 1200–1300 °C and in 4 vol%CO at 1000–1100 °C. The reduction atmosphere was favorable to the formation of multilayer structure of MnFe₂O₄ due to the occurrence of multilayer MnO as the intermedium. In addition, morphology evolution demonstrated that the particle size of MnO₂ after reduction was decreased remarkably which was also beneficial to the formation of MnFe₂O₄. However, air atmosphere is unfavorable to the generation of MnFe₂O₄ due to the recrystallization growth of Fe₂O₃ to lump impeding the element diffusion. Resultantly, the required temperature for the synthesis of MnFe₂O₄ in air was much higher than that in 4 vol% CO. One possible mechanism for the polyhedral MnFe₂O₄ with multilayer structure was based on the combination of the greater growth speed of (111) plane in the cubic MnFe₂O₄ crystal and terrace-ledge-kink (TLK) growth model. Moreover, multilayer MnFe₂O₄ prepared by the solid-state reaction presented good microwave absorbing property compared with that of the ferrites synthesized via the representative wet chemistry and combined methods.     

Preparation of bifunctional catalysts by solid-state ion exchange in zeolites

Bifunctional catalysts containing an acidic as well as a hydrogenation/dehydrogenation function were prepared by solid-state ion exchange. Preparation and properties of Pd-loaded H-ZSM-5 are described in detail. The catalytic behavior of the reduced catalysts was investigated using hydrogenation and hydroisomerisation of ethylbenzene as a test reaction. The catalytic performance of the catalysts could be significantly improved by concomitant incorporation of Ca²⁺. This was advantageously achieved in a two-step procedure, where first a solid-state ion exchange with CaCl₂ and subsequently a second solid-state ion exchange with PdCl₂ was carried out. A Ca, H-ZSM-5 with 1.5 wt-% Pd obtained via this two-step procedure and subsequent reduction in H₂ exhibited high activity, long life-time and good selectivity with respect to hydrogenation and hydroisomerisation of ethylbenzene to ethylcyclohexane and dimethylcyclohexanes, respectively. Electron micrographs of the reduced catalyst showed finely dispersed palladium with maximum size of about 2.0 nm.On leave from Central Research Institute of Chemistry of the Hungarian Academy of Sciences.     

Catalytic conversion of trichloroethylene on nickel containing beta zeolites into value added products

Nickel containing BEA zeolites, NiSiBEA and NiHAlBEA, with 2 wt% of Ni were prepared by a two-step postsynthesis method and conventional wet impregnation. The calcination of NiSiBEA and NiHAlBEA at 773 K for 3 h in air led to the formation of C-NiSiBEA and C-NiHAlBEA. After reduction at 873 K for 3 h in flowing 10% H₂/Ar, red-C-NiSiBEA and red-C-NiHAlBEA were obtained and investigated as the catalysts in hydrodechlorination of trichloroethylene at 503 K. Comparative study performed on red-C-NiSiBEA and red-C-NiHAlBEA showed very high stability of the catalyst prepared by a two-step postsynthesis method and strong deactivation of the catalyst prepared by conventional wet impregnation during ~ 17 h of reaction. Application of both catalysts resulted in high selectivity to unsaturated hydrocarbons that are the most desired products in HDC processes. TPH of the catalysts after kinetic run have shown that the main cause of deactivation of NiHAlBEA is the formation of carbonaceous species during hydrodechlorination of trichloroethylene.     

Zeolite ZnY catalysts prepared by solid-state ion exchange

Zeolites ZnY with various overall zinc contents were prepared from mixtures of zeolite NH₄Y and crystalline zinc chloride by solid-state ion exchange. The obtained materials were investigated with carbon monoxide, xenon, and nitrogen adsorption as well as with ¹²⁹Xe NMR and XRF spectroscopy. From the results of these measurements, the zinc cation distributions between the different types of cages of the faujasite framework as well as between the crystallographic positions SIII and SII within the large voids (supercages) were quantitatively determined. The concentrations of zinc cations in the supercages of the presently prepared zeolites are considerably higher than in materials obtained from NaY by conventional wet ion exchange using aqueous zinc salt solutions. Experimental evidence is provided for salt inclusion under certain conditions of preparation. This revised version was published online in August 2006 with corrections to the Cover Date.     

含硼聚硅酸锌镁絮凝剂预处理皂素废水

以硅酸钠、硫酸锌、硫酸镁和硼砂为原料制备了含硼聚硅酸锌镁絮凝剂(PSZMB),并用于处理皂素废水,考察了各因素对PSZMB絮凝性能的影响.结果表明,各因素的最佳值为:n(B):n(Si)0.20,n(Mg):n(Zn)=2.0,n(Mg+Zn):n(Si)=2.0,絮凝剂投加量为8 mL/L,pH=8.PSZMB的絮凝...     

铌酸钾粉体的固相法制备研究

以甲酸钾为钾源,草酸铌及氢氧化铌为铌源,少量水为溶剂,充分研磨干燥后得到前驱体。利用红外光谱(FTIR)、热重分析(TG)技术对前驱体及产品进行分析。在氢氧化铌为铌源时,600℃焙烧后可获得较纯净的KNbO3粉体。在草酸铌为铌源时的反应效果较好,能够在较低温度(475℃)下制备出较纯净的KNbO3粉体。     

Evaluation of boron removal by electrocoagulation using iron and aluminum electrodes

Boron compounds are used in the variety of products manufacturing and are introduced to the environment in the form of waste. Here the feasibility of the boron removal from wastewater by electrocoagulation (EC) is studied. Aluminum and iron were simultaneously used in the reactor as materials for cathode and anode. The results show that the EC process for boron removal strongly depends on the current density, initial concentrations, and time. The process is examined under varying indices in order to determine optimal operating conditions. It is important to note the EC application needs no chemical reagents and makes the boron-containing wastewater treatment easy for regulation and automation.     

Few-atomic-layered boron carbonitride nanosheets prepared by chemical vapor deposition

Few-atomic-layered boron carbonitride (BCN) nanosheets have been grown on Si substrate by microwave plasma chemical vapor deposition from a gas mixture of CH(4)-N(2)-H(2)-BF(3). The grown BCN nanosheets are oriented with their base planes perpendicular to the substrate surface. Ultrathin BCN nanosheets with thickness from 2 to a few atomic layers account for a considerable portion of the products, although many of them have more than 10 layers. Photoluminescence is measured for the BCN nanosheets and intense emission at 3.27 eV with very weak defect-related emission is observed for the nanosheets with the composition of B(0.38)C(0.27)N(0.35). The present BCN nanosheets are promising for applications in nanoelectronics, catalyst supports, gas adsorption, etc.     

原位生成甲基丙烯酸铝对POE的补强

用氢氧化铝和甲基丙烯酸（MAA）经原位反应生成了甲基丙烯酸铝[Al（MAA）3],并将其作为补强剂用于补强聚烯烃热塑性弹性体（POE）,研究了过氧化二异丙苯（DCP）用量、Al（OH）3和MAA的物质的量比和Al（MAA）3理论生成量对POE硫化胶力学性能的影响。结果表明,当DCP用量为3份、Al（OH）3/MAA的物质的量比为1∶3时,原位生成Al（MAA）3能够显著地提高POE硫化胶的力学性能。随着Al（MAA）3理论生成量的增加,硫化胶的拉伸强度先增加后减少,当Al（MAA）3理论生成量为30份时,拉伸强度达到最大值为24.31 MPa,而扯断伸长率保持在500%以上。另外,Al（MAA）3补强的POE硫化胶还具有较好的耐热氧老化性能和较高的邵A硬度。     

Phase and structural evolution of zirconolite ceramics prepared by solid-state reaction sintering

The evolution of phase assemblage and microstructure of stoichiometric zirconolite (CaZrTi₂O₇) ceramics, prepared by a solid-state reaction sintering route, was systematically investigated as a function of sintering temperature. Using powder XRD and quantitative phase analysis data, it was determined that the formation of zirconolite was a one-step reaction, without formation of intermediate phases. The accompanying fractions of secondary CaTiO₃ and ZrO₂ phases were reduced to approximately 2 wt % each after sintering at 1200 °C, with zirconolite formed as the major phase (> 99 wt%) after reaction at 1300 °C. Notable product densification only occurred at T ≥ 1400 °C, at which it was possible to achieve a relative density of 96.97% which is highly desirable for applications as a nuclear wasteform. The zirconolite-2M polytype structure (space group: C2/c) was formed in all products as expected, confirmed by combined high resolution TEM-ED analyses.     

Crystal-oriented mechanism of dynamic recrystallization nucleation in cubic boron nitride

Structural transformations occurring at 8 GPa and 2400 °C in twinned cubic boron nitride (cBN) with a triplex texture [112] have been explored by electron microscopy using the thin foil procedure. The following reconstructions have been established: destruction of the texture that occurs by rotation about the [220] axis, fragmentation of twinned grains, detwinning of large fragments by rotation about the [110] axis and formation of nuclei of a primary recrystallization from fragments with no twins.     

微波固相法制备铁酸锌脱硫剂的硫化动力学

通过微波与常规固相法制备了铁酸锌高温煤气脱硫剂,使用X射线衍射（XRD）、氮吸附、扫描电子显微镜（SEM）以及X射线光电子能谱（XPS）对两种不同焙烧方式制备的脱硫剂的物相组成、织构形貌和表面元素进行了表征。数据显示微波焙烧制备的脱硫剂具有孔隙结构丰富、表面金属元素含量高、结合能低等优点。使用热天平对铁酸锌脱硫剂硫化行为进行了研究,根据等效粒子模型计算了两种脱硫剂与硫化氢气体反应的动力学参数,得到了硫化反应动力学方程,并在固定床上对其煤气脱硫性能进行了考察。结果表明硫化过程分为化学反应控制区和颗粒内扩散控制区。微波焙烧制备脱硫剂的化学反应活化能和颗粒内扩散活化能较低,说明其在硫化氢气体脱除上具有更高的活性。在模拟煤气气氛下,相比常规焙烧方法制备的脱硫剂,微波制备的脱硫剂的脱硫性能显著提高,具有更高的硫容和更长的精脱硫时间。     

High-quality boron carbide nanowires prepared by catalyst-free template growth method

In this study, high-quality boron carbide nanowires (B₄C-nanowires) were prepared via catalyst-free template growth (TG) method at low temperatures. SEM, XRD and TEM tests were carried out to explore the most suitable preparation parameters. Then, a ball milling process of 8 h and a growth temperature of 1050 °C were selected as the most suitable parameters to be applied to the boron substrate and carbon nanotubes (CNTs) template. The obtained B₄C-nanowires possess a good crystallinity with an average diameter of 60 nm and lengths of 1–5 μm. In addition, the growth mechanism was studied as the diffusion and crystal reconstruction between the boron powders and the CNTs, while the ball-milling process improved the growth by dispersing CNTs and introducing more defects to the CNTs template. Finally, 5 vol% B₄C-nanowires/Al composites were fabricated with the B₄C-nanowires exhibited a high strengthening effect up to 215%. This work offered a new research idea for one-dimension ceramic materials and their application in composites.     

固相反应法制备纳米氧化铜及其光催化性能研究

以硫酸铜为原料,采用固相反应法制备纳米级氧化铜,讨论了反应物配比、分散时间及表面活性剂对产物粒径大小的影响,在太阳光照射下,研究纳米CuO对有机染料的降解。结果表明,最佳反应条件为:n(CuSO_4)∶n(NaOH)为1∶3.5,超声波分散时间为8 min,表面活性剂聚二乙醇600的用量为0.5%。产物为纤维状纳米CuO,具有较好的光催化活性,对50 mL浓度10 mg/L有机染料甲基紫,加入0.025 g纳米CuO,在太阳光照射下5 h,甲基紫降解率70%。     

Acid sites topology in aluminas and zeolites from high-resolution solid-state NMR

High-resolution solid-state nuclear magnetic resonance (NMR) spectroscopy is recognized as one of the most powerful tools in characterization of acid catalysts. Hundreds of research papers and tens of reviews and monographs appear each year. It is evidently an impossible task not only to discuss all recent contributions but even to mention each of them. Therefore, we restricted ourselves to a rather narrow (but fast developing) field, namely, the characterization of surface topology of real catalysts by heteronuclear dipolar interaction between magnetic nuclei. The common desire of all spectroscopists to obtain spectra with the best possible resolution competes with the general trend to obtain the greatest amount of information on systems. In this review we outline experimental approaches to this problem and describe several editing techniques which introduce new dimension into conventional NMR. The discussion is furnished with examples from current literature, however the emphasis is given to our recent publications in which the introduction of new experimental ideas resulted in deeper insight into the nature of surface acidity. In particular, two problems are discussed in detail, namely, how to observe selectively surface species (cross-polarization experiments) and how to retrieve dipolar contribution from the overall lineshape (double-resonance spin-echo experiments). The results obtained from these experiments allowed us to reach important conclusions concerning the nature of Lewis acidity in aluminas and the role of isolated Al atoms in formation of Brønsted sites in zeolites.     

前驱体转化法制备碳化硼粉体的研究进展

碳化硼材料具有优良的物理和化学性能,被广泛应用于各个领域。目前,传统的碳热还原方法生产碳化硼粉体存在温度高、产率低、环境污染重等问题。相比之下,前驱体转化法具有能耗低、工艺简便、原料易得、产品尺寸小等特点,在制备碳化硼粉体方面有明显的优势。详细介绍了前驱体转化法合成碳化硼粉体的制备过程,综述了使用不同碳源经前驱体转化法合成碳化硼粉体的最新研究进展,并展望了前驱体转化法合成碳化硼的研究方向。     

低温固相法制备纳米氧化锌及其在脱硫中的应用

以乙酸锌和草酸为原料,采用低温固相法制备了纳米氧化锌,考察了表面活性剂和焙烧温度对氧化锌晶粒的影响,采用XRD、TG-DTA、IR和TEM等技术进行表征。以不同晶粒的氧化锌为锌源,采用等体积浸渍法制备一系列NiO/ZnO吸附荆;以噻吩/正庚烷为模型化合物,在固定床微反装置考察氧化锌晶粒对吸附剂脱硫性能的影响。结果表明,表面活性剂以十二烷基硫酸钠效果最好,合适的焙烧温度为400℃;制备的氧化锌呈球形,为六方晶系纤锌矿结构,具有较好的分散性,平均粒径约15 nm。活性评价表明,NiO/ZnO吸附剂对噻吩类硫化物具有较高的活性。可以实现超深度脱硫;氧化锌晶粒越小,相应NiO/ZnO吸附剂的脱硫活性越高;脱硫前后吸附剂的XRD谱图对比表明,脱硫过程中S以ZnS的形式固定在吸附剂上。