Effect of Mechanochemical Activation on the Catalytic Properties of Ferrites with the Spinel Structure

It was found experimentally that stacking defects formed in the mechanochemical activation of zinc ferrite enhanced the specific catalytic activity in the reaction of CO oxidation. The specific rate of CO oxidation was a linear function of defect concentration, which was determined using Mössbauer spectroscopy and X-ray diffraction. A conclusion was drawn that the same centers are responsible for an increase in the catalytic activity, the sorption capacity for hydrogen sulfide, and the reactivity of zinc ferrite in the interaction with hydrochloric acid. It was assumed that analogous factors caused an increase in the catalytic activity and reactivity of magnesium ferrite.     

Effect of Zinc Oxide on Morphology and Mechanical Properties of Polyoxymethylene/Zinc Oxide Composites

This paper studies the effects of zinc oxide (ZnO) on morphology and mechanical properties of pure polyoxymethylene (POM) and POM/ZnO composites. POM/ZnO composites with varying concentration of ZnO were prepared by melt mixing technique in a twin screw extruder. The dispersion of ZnO particles on POM composites was studied by scanning electron microscope (SEM). It is observed that the dispersion of ZnO particles is relatively good. The mechanical properties of the composites such as tensile strength, stress at break, Young's modulus and impact strength were measured. Increasing content of ZnO up to 4.0 wt% increases the impact strength of POM. Addition of ZnO beyond 4.0 wt% decreases the impact strength. The composites containing ZnO content greater than 2.0 wt% show increased Young's Modulus. The tensile strength and stress at break decrease with increasing ZnO content. This may be due to the compatibility between ZnO and POM.     

烟酸与氧化锌或碱式碳酸锌的机械化学反应

用行星式球磨机或振荡式球磨机作为机械能发生装置,水(50 μL)或DMF(50 μL)或甲醇(150 μL)作为球磨过程中滴加的辅助溶剂,分别研究了烟酸（HNA）和氧化锌、烟酸和碱式碳酸锌的机械化学反应。 结果表明,当上述的2个化学反应在行星式球磨机(45 Hz)或在振荡式球磨机(20 Hz)中球磨30 min,少量水或者DMF均可以促使生成零维的四水合二烟酸锌（Ⅱ）：[Zn(NA)2(H2O)4]。 在行星式球磨机中球磨烟酸、氧化锌和少量水的混合物,在15 Hz条件下球磨30 min,只产生少量目标产物,当球磨时间延长为60 min可生成大量目标产物,而且达到反应平衡。     

Mechanochemical Activation of Zinc and Application to Negishi Cross‐Coupling

A form independent activation of zinc, concomitant generation of organozinc species and engagement in a Negishi cross‐coupling reaction via mechanochemical methods is reported. The reported method exhibits a broad substrate scope for both C(sp³)–C(sp²) and C(sp²)–C(sp²) couplings and is tolerant to many important functional groups. The method may offer broad reaching opportunities for the in situ generation organometallic compounds from base metals and their concomitant engagement in synthetic reactions via mechanochemical methods.     

NO选择性催化还原Ce-Mn-Ti-O催化剂铈组分助催化作用

用NH3程序升温脱附(NH3-TPD)、X射线衍射(XRD)、X射线光电子能谱(XPS)、H2程序升温还原(H2-TPR)和BET表面积测试结合NO选择性催化还原(SCR)微型反应评价等方法,研究了溶胶-凝胶法制备的Ce-Mn-Ti-O复合氧化物催化剂中铈组分的助催化作用.结果表明随铈含量增加,NO转化率大幅度增加,在Ce/Mn摩尔比约0.08时达极大值,其后随铈含量进一步增加,NO转化率又逐渐下降.适量铈组分的加入对Mn-Ti-O催化剂表面酸性影响不大,但增加了催化剂活性组分Mn物种的表面浓度,提高了Mn4+物种的相对含量和Mn物种的可还原性,从而提高催化剂低温SCR活性.当Ce/Mn摩尔比超过0.08,催化剂表面的Mn组分与Ce组分可能形成无定型结构的多层聚集的Ce-O-Mn物种,导致催化剂Mn/Ti摩尔比下降和Mn物种可还原性下降,从而导致催化剂SCR活性的下降.     

氧化锌空心微球的制备及其催化性能

以乙二醇为溶剂,聚乙二醇-10000为表面活性剂,硝酸锌和醋酸钠为原料,利用溶剂热法,合成了氧化锌空心微球。 并用X射线衍射、扫描电子显微镜、热重、比表面和孔径分布等对其进行了表征。 考察了硝酸锌用量、聚乙二醇-10000用量、反应时间和反应温度等对氧化锌空心微球形貌和大小的影响。 考察了氧化锌空心微球催化分解高氯酸铵的性能,结果表明,由于氧化锌空心微球的加入,高氯酸铵的分解温度由442 ℃降低至280 ℃左右。     

Controlling the Catalytic Properties of Copper-Containing Oxide Catalysts

The results of a systematic study of the formation of Cu–Zn, Cu–Zn–Al, Cu–Zn–Cr, Cu–Zn–Si, Cu–Cr, and Cu–Si oxide catalysts with a widely varied ratio between their components are generalized within the chemical approach developed by G.K. Boreskov to establish the quantitative relation between their chemical composition and catalytic activity. Simultaneously, their catalytic properties, such as selectivity and activity, are measured under the same conditions in the methanol synthesis and dehydrogenation and water gas shift reactions, whose common feature is a reductive reaction medium. The activity of Cu–Zn–Al–Cr— Si-oxide catalysts in all the studied reactions is governed by the Cu⁰ nanoparticles formed on their surface in the process of reductive activation. Nanoparticles of different catalysts have similar sizes (3–8 nm). However, the ratios between the catalytic activities per unit of the copper surface area for catalysts with various structures of their oxide support (spinel, wurtzite, zincsilite, or silica type) are appreciably different in each reaction. The relation between the chemical composition of a catalyst and its catalytic activity in a certain reaction is established by the chemical composition of its precursor representing a hydroxo compound, i.e., the nature of the selected cations and the quantitative ratio between them. The decomposition of hydroxo compounds to oxides (and the further activation of oxides) should be performed at medium temperatures, providing the incomplete elimination of ОН^– and CO₃^2- anions, i.e., the formation of anion-modified oxides. The structure of the latter and the type of interaction between Cu⁰ nanoparticles and an oxide support are governed by the structure of the hydroxo precursor compound.     

Mechanochemical Synthesis of Catalytic Materials

The mechanochemical synthesis of nanomaterials for catalytic applications is a growing research field due to its simplicity, scalability, and eco-friendliness. Besides, it provides materials with distinct features, such as nanocrystallinity, high defect concentration, and close interaction of the components in a system, which are, in most cases, unattainable by conventional routes. Consequently, this research field has recently become highly popular, particularly for the preparation of catalytic materials for various applications, ranging from chemical production over energy conversion catalysis to environmental protection. In this Review, recent studies on mechanochemistry for the synthesis of catalytic materials are discussed. Emphasis is placed on the straightforwardness of the mechanochemical route—in contrast to more conventional synthesis—in fabricating the materials, which otherwise often require harsh conditions. Distinct material properties achieved by mechanochemistry are related to their improved catalytic performance.     

Effect of the Sulfate Sulfur Content and the Preparation Procedure on the Catalytic Properties of Sulfated Zirconium Oxide

The effects of the composition and the procedure of preparing sulfated zirconium oxides on their catalytic properties in the reactions of 1-butene isomerization to 2-butenes and isobutanol dehydration were studied. The activity was found to depend on the nature of parent zirconium oxide, the sulfate sulfur content, and the temperature of calcination. Catalysts prepared from a crystalline oxide exhibited the highest activity. Their activity depends on the sulfate sulfur content. The calcination of catalysts at temperatures higher than 400°C resulted in a detectable loss of sulfate. The activity of sulfated oxides prepared from an amorphous oxide was noticeably lower; it depended only slightly on the temperature of calcination and sulfate sulfur content. The catalytic behavior of the sulfated oxide in both of the reactions is indicative of the absence of superstrong proton sites. Based on the results, assumptions on the nature of formed surface compounds were made.     

铁酸锌纳米晶的机械化学合成

以αFe₂O₃和ZnO粉体为原料,在高能球磨的作用下,室温(约25℃)合成了铁酸锌(ZnFe₂O₄)纳米晶.用XRD、TEM、M?sbauer谱及IR光谱等方法对纳米晶进行了表征.结果表明:所得纳米晶具有非正型分布的尖晶石结构,为超顺磁性;纳米晶内存在着较多的缺陷.     

Properties of Zinc Oxide Adsorbent for Adsorbing Hydrogen Sulfide

Russian Journal of Applied Chemistry - The paper defines the conditions for the synthesis of hydrogen sulfide adsorbent based on zinc oxide from basic zinc carbonate in order to produce strong,...     

Mechanochemical Synthesis and Catalytic Properties of the Calcium Ferrite Ca2Fe2O5

The formation of the real structure of calcium ferrite prepared by the calcination of a mechanochemically activated hydroxide mixture at 600–1100°C was studied by X-ray diffraction analysis, electron microscopy, thermal analysis, Moessbauer spectroscopy, IR spectroscopy, small-angle X-ray scattering, and secondary-ion mass spectrometry. It was found that low-temperature calcium ferrite is an anion-modified oxide, in which the ordering of oxygen vacancies was incomplete. Regions with a disordered structure were detected on the surface of crystallites. As the calcination temperature was increased, the brownmillerite crystal structure was improved and the intercrystalline boundaries were formed and then annealed. At the surface, these processes were accompanied by a change in the predominant form of adsorbed NO from nitrosyl to dinitrosyl species. An increase in the specific catalytic activity of samples with calcination temperature can be associated with the perfection of the brownmillerite structure and with a change in the state of adsorption centers.     

Controllable Synthesis and Optical Properties of Connected Zinc Oxide Nanoparticles

Connected zinc oxide (ZnO) nanoparticles are successfully synthesized by a simple solution‐based chemical route that uses evaporation and concentration technology. The influences of processing parameters, especially the evaporation and concentration time on the size and morphology of the nanoparticles, have been investigated by transmission electron microscopy (TEM) and high‐resolution TEM (HRTEM). The structure and optical properties are systematically characterized by X‐ray diffraction (XRD), UV/Vis spectrophotometery, and fluorescence spectroscopy (FL). It is found that the average diameter and morphology are strongly affected by the evaporation and concentration time. Additionally, the formation mechanism of the nanoparticles is also discussed. The studies revealed that the evaporation and concentration are important aggregation or nucleation processes for ZnO growth, which leads to the macro‐differences in morphology. These results provide some insight into the growth mechanism of ZnO nanostructures. The synthetic strategy developed in this study may also be extended to the preparation of other nanomaterials and promising applications in various fields of nanotechnology.     

Catalytic Activation of a Solid Oxide in Electronic Contact With Gold Nanoparticles

Although inert in its bulk form, nanostructured gold supported on oxides has been found to be catalytically active. In many cases, the oxide promotes the activity of Au. It is now shown that in turn, nanoscale Au particles can chemically activate the solid oxide. Specifically, it was discovered that 4 nm Au nanoparticles deposited on zinc oxide catalyze the transformation of the oxide into the sulfide in the presence of an organosulfur species. Contact of the oxide with Au nanoparticles lowers the activation barrier for the solid‐state reaction by approximately 20 kJ mol^?1, allowing the reaction to be achieved closer to ambient temperatures. Electron transfer from oxygen vacancies to Au nanoparticles is proposed to generate acidic sites on the surface of the zinc oxide, resulting in the enhanced reactivity of the oxide. Knowledge of such electronic interactions between the noble metal and oxide can be exploited for engineering reactive heterostructures for low‐temperature pollutant sorption and hydrocarbon processing.     

Mechanochemical Synthesis of Nanosize Metastable Zirconium Oxide

The formation of oxide phases in the course of mechanical activation of amorphous zirconium hydroxide was studied.