Effect of Pr doping on magnetic and dielectric properties of Ni-Zn ferrites by “one-step synthesis”

Pr³⁺-doped Ni-Zn ferrites with a nominal composition of Ni_0.5Zn_0.5Pr_xFe_2−xO₄ (where x=0-0.08) were prepared by a one-step synthesis. The magnetic and dielectric properties of the as-prepared Ni-Zn ferrites were investigated. X-ray diffraction data indicated that, after doping, all samples consisted of the main spinel phase in combination of a small amount of a foreign PrFeO₃ phase. The lattice constants of the ferrites initially increased after Pr³⁺ doping, but then became smaller with additional Pr³⁺ doping. The addition of Pr³⁺ resulted in a reduction of grain size and an increase of density and densification of the as-prepared samples. Magnetic measurement revealed that the saturation magnetization of the as-prepared ferrites, M_s, decreased, while the coercivity, H_c, increased with increasing substitution level, x, and the Curie temperature, T_c, kept a rather high value, fluctuating between 308 and 320 °C. Both the real and imaginary parts of permeability of the ferrites decreased slightly after Pr³⁺ doping. However, the natural resonance frequency shifted towards higher frequency from 13.07 to 36.17 MHz after the addition of Pr³⁺, driving the magnetic permeability to much higher frequency, reaching the highest value (36.17 MHz) when x=0.04. Introduction of Pr³⁺ ions into the Ni-Zn ferrite reduced the values of the dielectric loss tangent, especially in the frequency range of 1-400 MHz. However, the magnitude of dielectric loss of the samples doped with different amounts of Pr³⁺ raised little.     

Influence of impregnation conditions on the activity of CrOx/Al2O3 catalysts in dehydrogenation of isobutane in fixed bed reactor

The development of catalysts for dehydrogenation of light paraffin hydrocarbons in a fixed bed reactor is of great importance for the world petrochemical industry. The preparation of granules (~3 mm in diameter) of CrO_x/Al₂O₃ catalysts is hindered by such problems as homogeneous distribution of active component and modifiers, high strength of granules, etc. In this paper, the alumina support dissolution in the impregnating solution containing chromic acid and the opportunity to apply vacuum impregnation to minimize this effect in the preparation of CrO_x/Al₂O₃ catalysts are discussed. A series of catalysts is synthesized at different impregnation pressures (1, 0.85, and 0.7 atm), characterized by a complex of physical–chemical methods (low-temperature N₂ adsorption, SEM, XRD, TPR-H₂), and tested in isobutane dehydrogenation. The use of vacuum impregnation is shown to lead to the reduction of the specific surface area of the catalysts from to 91 to 56 m²/g and the growth of content of CrO_x phases that decreases the catalytic activity in dehydrogenation. The isobutylene yield at 610 °C decreases from 68% to 54% for the catalyst prepared at P = 0.7 atm as compared with the one prepared at atmospheric pressure. The high activity and stability are connected with the hierarchical structure of the alumina support and homogeneous chromia distribution on its surface.     

改性纳米HZSM-5沸石催化剂上C5～C8混合烷烃的芳构化反应

在小型固定床反应器上研究了水蒸气钝化及过渡金属(Ni,Co,Cu,Zn)改性对调变纳米HZSM-5沸石催化剂上C5~C8混合烷烃芳构化反应的作用.采用NH3-TPD和Py-FT-IR方法表征了改性催化剂的表面酸性质,并与其催化芳构化性能进行了关联.结果表明,在450℃下进行水蒸气钝化能显著提高催化剂的芳构化选择性,减少甲烷和乙烷等低碳烷烃的生成;催化剂进一步用锌盐或铜盐溶液浸渍改性,可以显著提高催化剂的抗积炭失活能力.这是由于水蒸气钝化能适当减少沸石表面的酸量,降低酸强度,而铜、锌改性可进一步减少B酸中心,增加L酸中心,并与B酸中心协同作用形成具有脱氢活性的催化中心,从而影响混合烷烃的活化方式与芳构化路径.     

纳米Au粒子作为直接硼氢化钠-过氧化氢燃料电池阴极催化剂

采用浸渍还原法制备了纳米Au/C, 并将其用作直接硼氢化钠-过氧化氢燃料电池阴极催化剂. 通过X-射线衍射(XRD)和透射电镜(TEM)对催化剂进行结构和形貌分析, 结果表明10～20 nm的纳米Au粒子均匀地分散在Vulcan XC-72R碳黑表面上. 循环伏安测试表明, 在0.5 mol•L－1 H2SO4和2 mol•L－1 H2O2混合溶液中, 纳米Au/C在0.85 V处表现较强的不可逆还原电流. 以纳米Au/C为阴极催化剂, AB5储氢合金为阳极催化剂制成直接硼氢化钠-过氧化氢燃料电池. 电池在30 ℃下的最大功率密度可达到78.6 mW•cm－2. 当电池工作温度升高至50 ℃时, 电池的最大功率密度超过120 mW•cm－2. 此外, 研究了阴极溶液中H2SO4和H2O2浓度对电池性能的影响. 当阴极溶液中H2SO4浓度小于0.5 mol•L－1时, 酸浓度对电池性能影响较大; H2O2浓度对电池性能影响较小. 确定了阴极溶液中H2SO4和H2O2的最佳浓度分别为0.5和2 mol•L－1.     

介孔气体吸附剂

介孔二氧化硅经过表面修饰,赋予介孔材料不同的特性,具有很多的潜在用途,是无机材料研究的热点之一。本文综述了近年来以介孔二氧化硅（M41S 和 SBA）为载体设计的气体吸附剂的研究进展。详细讨论了二氧化碳和可挥发性有机物(VOCs)在介孔吸附剂上的吸附过程;介绍了二氧化碳介孔吸附剂的不同制备方法和影响二氧化碳在介孔吸附剂上吸附的因素,以及介孔吸附剂的结构对可挥发性有机物吸附过程的影响。最后,对介孔气体吸附剂的发展进行了展望。     

椰壳活性炭氧化后负载硅基复合氧化物低温脱硝催化剂的研究

椰壳活性炭经硝酸氧化处理后做载体,采用浸渍法负载含SiO_2的复合氧化物,用做低温脱硝催化剂.在锰氧化物中添加Ti O2,可以提高催化剂的抗硫性能,但低温脱硝活性降低.然而在锰氧化物中添加SiO_2,不仅提高了催化剂的抗硫性能,而且也提高了脱硝活性.TEM结果表明加入SiO_2可以有效的减小复合氧化物晶粒尺寸,更提高了其在载体上的分散度.NH_3-TPD结果显示加入SiO_2后催化剂表面酸性显著增强.XPS分析发现加入SiO_2还增大了催化剂表面Mn~(4+)的相对含量.此外,经硝酸氧化处理过的椰壳活性炭,表面含氧基团增加,从而也大大提高了对NH_3及NO的吸附容量.在相同脱硝条件下,与原料活性炭负载的催化剂比较,硝酸氧化处理后的活性炭负载的催化剂具有更高的脱硝效率.     

Anti-idiotypic nanobody-alkaline phosphatase fusion proteins: Development of a one-step competitive enzyme immunoassay for fumonisin B1 detection in cereal

A rapid and sensitive one-step competitive enzyme immunoassay for the detection of FB₁ was developed. The anti-idiotypic nanobody–alkaline phosphatase (Ab2β−Nb−AP) was validated by the AP enzyme activity and the properties of bounding to anti-FB1-mAb (3F11) through colorimetric and chemiluminescence analyses. The 50% inhibitory concentration and the detection limit (LOD) of colorimetric enzyme-linked immunosorbent assay (ELISA) for FB₁ were 2.69 and 0.35 ng mL⁻¹, respectively, with a linear range of 0.93–7.73 ng mL⁻¹. The LOD of the chemiluminescence ELISA (CLIA) was 0.12 ng mL⁻¹, and the IC₅₀ was 0.89 ± 0.09 ng mL⁻¹ with a linear range of 0.29–2.68 ng mL⁻¹. Compared with LC-MS/MS, the results of this assay indicated the reliability of the Ab2β−Nb−AP fusion protein based one-step competitive immunoassay for monitoring FB₁ contamination in cereals. The Ab2β−Nb−AP fusion proteins have the potential to replace chemically-coupled probes in competitive enzyme immunoassay systems.     

MIL-88B(Fex,Co1?x)催化剂制备及甲醇液相H2O2氧化一步合成甲酸甲酯

甲醇选择氧化合成甲酸甲酯是获得高附加值甲醇下游化学品的最具吸引力的催化反应工艺之一.目前,甲醇选择氧化的研究大多为气相催化反应,存在反应温度较高和产物选择性较低的难题.甲醇液相选择氧化过程的反应温度较低,反应条件易于控制,产物选择性相对较高.然而,以氧气作为氧化剂的甲醇液相选择氧化反应,有时难以脱离反应体系的爆炸极限.以H2O2为氧化剂的甲醇液相选择氧化反应,可以在温和反应条件下实现甲醇催化选择氧化.含Fe活性组分的催化剂对醇类液相选择氧化具有很好的催化性能,金属有机框架材料(MOFs)在三维空间中具有均匀分布的酸位等催化活性位,因此,含Fe的MOFs催化剂是兼具有氧化还原活性和酸性的双功能催化剂,并且引入另外一些催化活性组分时可以改善催化剂的反应性能.本文以Fe3+和Co2+为金属离子,通过简单的一锅水热法合成了一系列不同Fe/Co摩尔比的MIL-88B(Fex,Co1–x)双功能催化剂,采用X射线粉末衍射、扫描电镜(SEM)、高分辨透射电镜(HRTEM)、傅里叶变换红外光谱、X射线光电子能谱、氮气吸附-脱附和电感耦合等离子体质谱等手段表征了催化剂的结构,研究了Fe和Co催化活性组分在甲醇液相选择氧化一步合成甲酸甲酯反应中的协同作用,提出了甲醇液相H2O2氧化一步合成甲酸甲酯的可能催化反应机理.SEM和HRTEM测试结果表明,MIL-88B(Fex,Co1–x)催化剂为平均长度400–600 nm,宽度100–150 nm的针状形态,Fe和Co元素的分布比较均匀,Co掺杂没有改变MIL-88B(Fex,Co1–x)的拓扑结构.X射线光电子能谱分析结果表明从Co到Fe的供电子效应,Co的引入可以调节Fe中心的电子环境,Fe和Co具有协同催化作用.通过甲醇液相氧化性能测试发现,MIL-88B(Fe0.7,Co0.3)表现出最优的催化性能,使用0.5当量的H2O2为氧化剂,在80℃下反应60 min后,甲醇转化率为34.8％,甲酸甲酯选择性由50.7％(单金属Fe)提高至67.6％.且经过四次催化循环后,MIL-88B(Fe0.7,Co0.3)的催化活性没有明显降低.催化反应机理研究表明,Fe是吸附活化H2O2进而选择氧化甲醇的主要活性中心,H2O2首先在Fe3+上吸附和活化,甲醇通过氢键作用吸附在MOF的骨架O原子上,被逐步氧化为甲酸,然后甲酸与剩余甲醇在Lewis酸性位点Fe3+和Co2+上反应生成甲酸甲酯;Co的掺杂加速了Fe(Ⅲ)/Fe(Ⅱ)的电子转移,提供了更多的配位不饱和金属位点,增强了对中间产物甲酸的吸附,促进了甲酸向甲酸甲酯转化,从而提高产物选择性.     

一步法高效制备纳米Si/C复合材料及其在高性能锂离子电池中的应用

开发了一种一步高效合成纳米硅/碳复合材料的新方法, 该方法通过球磨SiCl₄、 Mg₂Si和商业碳片, 使SiCl₄自下而上还原, 原位形成的纳米硅均匀生长在碳片上, 高效制备了纳米硅与碳片均匀复合物(Nano-Si/C). 该Nano-Si/C用作锂离子电池负极材料展现出高的可逆储锂容量(2450 mA·h/g)、 良好的倍率性能及优异的长循环稳定性, 在2 A/g电流密度下, 经过600次循环后, 容量仍然稳定在1400 mA·h/g. 其突出的电化学性能主要归因于小尺寸纳米硅与碳片均匀复合的纳米结构, 在循环嵌锂/脱锂过程中仍能保持结构和电化学性质的稳定性.