共查询到20条相似文献,搜索用时 31 毫秒
1.
The effects of fluorine, phosphate and chelating agents on hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) are reviewed. All three additives enhance the activity of NiMo/Al 2O 3 catalysts in HDN but have only a slightly positive or even a negative effect on the HDS activity of CoMo/Al 2O 3 and NiMo/Al 2O 3 catalysts. The positive effect on HDN is due to the enhancement of the hydrogenation of aromatic rings. On the other hand, these three additives diminish the rates of C–N bond breaking and alkene hydrogenation reactions. All three additives are hard basic ligands that may interact strongly with hard acids such as coordinatively unsaturated Al3+ cations on the alumina surface. A strong interaction with the alumina support has several effects. First, molybdate and tungstate anions are no longer strongly bonded to the support and are predominantly present as polyanions, which can be easily sulfided to MoS2 and WS2 crystallites. The weaker interaction with the smaller support surface also leads to larger MoS2 and WS2 crystallites with a lower dispersion. Second, the Ni2+ and Co2+ cations will also interact more weakly with the alumina, and this makes the formation of Ni and Co promoter atoms in the catalytically active Ni–Mo–S and Co–Mo–S phases more efficient. Third, the weaker interaction of Mo and W with the support leads to a higher stacking of the MoS2 and WS2 crystallites and, thus, to the more active type II Ni–Mo–S and Co–Mo–S phases. The increased stacking is beneficial for geometrically demanding reactions such as the hydrogenation of aromatics. For less demanding reactions, such as alkene hydrogenation, aliphatic C–N bond breaking and thiophene HDS, the loss in dispersion is important. 相似文献
2.
二维材料具有独特的层状结构、稳定的物理化学性质等特点。近年来,由二维材料层层堆叠构成的二维膜在膜分离领域展示了非同凡响的应用潜力。本文采用成膜中共混方法将La 3+插入到MoS 2膜层间,利用原子力显微镜(AFM)和X射线光电子能谱仪(XPS)技术表征了MoS 2片层结构和成分;利用扫描电镜(SEM)和X射线衍射仪(XRD)技术表征了膜结构与层间距;通过加压过滤装置和渗透装置考察了La 3+-MoS 2膜的渗透截留性能。实验结果表明,La 3+插层改性后的MoS 2膜由于层间距增加而显著地提高了纯水通量,La 3+-MoS 2膜的纯水通量相较于MoS 2膜提高了约18.5倍。La 3+-MoS 2膜对分子量300~800g/mol染料表现出了基于空间位阻理论的截留作用,对金属离子(Na +、K +、Mg 相似文献
3.
SiO 2- and Al 2O 3-supported MoS 2 and WS 2 catalysts were prepared to exploit the evaluation technique of the edge dispersion of MoS 2 and WS 2 particles. A chemical vapor deposition (CVD) technique using Co(CO) 3NO as a probe molecule was used for the evaluation. Results were compared with those from conventional techniques such as NO adsorption and TEM. A proportional correlation was obtained between the amount of NO adsorption and the amount of Co atoms accommodated by the CVD technique on WS 2/SiO 2 and WS 2/Al 2O 3 catalysts, demonstrating a selective location of the Co atoms on the edges of WS 2 particles, as previously established for MoS 2 catalysts. A comparison of the amounts of NO adsorption and Co accommodation on MoS 2 and WS 2 catalysts suggested a 70% higher density of sulfur vacancy on MoS 2 particles than on WS 2 particles regardless of the support. The Co atoms on the edges of MoS 2 and WS 2 particles showed the identical NO adsorption property. We propose that Co(CO) 3NO can be used as a probe molecule to evaluate and directly compare the edge dispersions of MoS 2 and WS 2 catalysts. The dispersion of MoS 2 particles was about two times higher than that of WS 2 particles with the SiO 2-supported catalysts. With the Al 2O 3-supported catalysts, MoS 2 and WS 2 particles were dispersed to a similar extent but much more highly dispersed than the counterparts in the SiO 2-supported catalysts. The evaluation of the edge dispersion of MoS 2 and WS 2 particles by means of TEM may pose problems when SiO 2- and Al 2O 3-supported catalysts are compared. The edges of unpromoted MoS 2 particles exhibited a significantly higher intrinsic activity for the HDS of thiophene than those of WS 2 particles. 相似文献
4.
尽管最近兴起的二维膜材料相较于传统的聚合物基膜材料呈现出明显提升的分离性能。但是二维膜中分子传质需要经过层层堆积的二维通道,传输路径较长,限制了二维膜渗透通量的进一步提升。提出用一维金属有机框架纳米线来调控二维膜实现通量提升,同时不降低分离能力。该策略的实现是通过Zn-BTC纳米线插层MoS 2层级膜,制备了Zn-BTC/MoS 2复合膜。该复合膜的有机溶剂通量比MoS 2二维膜提高了2~6倍,丙酮渗透通量高达3562 L·m -2·h -1·bar -1。同时该复合膜保持了与MoS 2膜同等优异的筛分能力,对于尺寸大于0.42 nm的染料分子,可以实现100%截留。 相似文献
5.
基于可再生生物质在二维层状晶体表面的自组装及其与四硫代钼酸铵的化学配位作用,发展了一种镶嵌单层MoS 2纳米片的超薄硼氮共掺杂碳纳米片的制备策略。此结构中,二维纳米碳结构利于提供更大的电化学活性表面积、连续的电子传导通路并大幅缩短电子传输路径,同时实现单层MoS 2纳米结构的均匀分散;均匀镶嵌其内的单层MoS 2纳米结构则显著提升了钠离子存储容量,并加速其在充放电过程中氧化还原反应动力学速率。应用于钠离子负极材料时,此类二维复合结构表现出了优异的储钠比容量、倍率性能和循环稳定性。 相似文献
6.
利用二硫化钼和葡萄糖为原料,采用一锅乙醇/水复合溶剂热-后热处理法制备了绣球花状结构MoS 2/C复合材料。考查了乙醇/水复合溶剂的合理组成和MoS 2/C复合材料中碳的合理含量,分别采用SEM和TEM表征了MoS 2/C材料的形貌结构,通过TGA测试和计算了材料中的碳含量。采用循环伏安、恒流充放电和交流阻抗等测试了MoS 2/C复合电极的电化学性能。结果表明,MoS 2/C复合材料拥有多级花球状结构,缓解了MoS 2的团聚,使电极材料的利用率和电化学稳定性显著提高。当V(乙醇):V(水)为1:2,碳含量为50%时,MoS 2/C复合电极在200 mA·g -1的电流密度下,充放电循环100次后,可逆容量达到762 mA·h·g -1。 相似文献
7.
在溶剂热法制备ZnO纳米粒子的基础上,利用物理剥离和纳米粒子互剪切作用成功制备了MoS 2/ZnO异质结构纳米复合物。以扫描电子显微镜、透射电子显微镜、X射线能量色散光谱、粉末X射线衍射、拉曼光谱仪、紫外-可见漫反射光谱、光致发光谱等对样品进行了结构形貌和性能表征。结果表明,利用物理剥离和互剪切作用能有效地获得MoS 2/ZnO复合物,复合作用使得MoS 2位于378cm -1( E12g)和400cm -1( A1g)处的两个特征拉曼峰显著增强。复合物中MoS 2含量越少,两个特征拉曼峰强度反而越高,且两峰波数间隔相应减小。可归因于MoS 2含量较低时,ZnO纳米粒子对MoS 2的物理剥离效果越显著,同时,MoS 2体现出良好的分散性和较小的厚度。MoS 2含量对MoS 2/ZnO的发光具有明显的调制作用,显著增强了复合物在可见光区域的吸收。随着MoS 2含量增加,其可见光发光强度迅速减小,紫外峰出现明显的蓝移。纯ZnO对苯酚的降解率最高达90%,而MoS 2/ZnO复合物对苯酚的降解率达100%,复合物对苯酚的最终降解率明显高于纯氧化锌。 相似文献
8.
采用水热法合成了一系列不同比例的MoS 2/Y分子筛复合物,并将其制成碳基复合电解池阴极。线性扫描伏安法(LSV)测试表明,当MoS 2和Y分子筛质量比为5∶2、碳纸负载量为1.5mg/cm 2时,阴极催化析氢性能最佳。通过SEM、TEM、XRD、XPS和BET对复合材料进行表征,SEM测试表明MoS 2/Y分子筛为片状和八面体相互交织叠加的云状形貌。BET测试表明其具有排列规整的微孔-介孔多级孔道结构,利于加速H +还原和H 2扩散。本文还考察了以MoS 2/Y分子筛作为微生物电解池(MEC)阴极的析氢性能。在MEC运行5个周期的产氢实验中,MoS 2/Y分子筛所产生的平均最大电流密度、氢气产率和产氢量等都高于Pt电极,且具有长期稳定性。因此,MoS 2/Y分子筛是一种适于实际应用的析氢催化剂。 相似文献
9.
针对市场对于高性能储锂、储钠负极材料的巨大需求和解决金属硫化物存在的关键制约问题,设计并开发了一系列纳米棒、纳米块和微米球等不同形貌和纳米结构的硫化钨,研究了形貌和石墨烯表面修饰对硫化钨储能性能的影响。研究结果表明:相比于WS 2纳米块和WS 2微米球,WS 2纳米棒比表面积更大、结晶性更好,展现了更好的储能性能。进一步通过冷冻干燥法,在WS 2纳米棒表面包裹上一层石墨烯,有效地提升了所制硫化钨的循环稳定性和倍率性能。在500 mA·g -1下循环500圈,其储钠放电容量仍保持在65.9 mAh·g -1,在1 000 mA·g -1下循环500圈,其储锂放电容量可保持在288.3 mAh·g -1。 相似文献
10.
Two-dimensional (2D) MoS 2 nanomaterials have been extensively studied due to their special structure and high theoretical capacity, but it is still a huge challenge to improve its cycle stability and achieve superior fast charge and discharge performance. Herein, a facile one-step hydrothermal method is proposed to synthetize an ordered and self-assembled MoS 2 nanoflower (MoS 2/C NF) with expanded interlayer spacing via embedding a carbon layer into the interlayer. The carbon layer in the MoS 2 interlayer can speed the transfer of electrons, while the nanoflower structure promotes the ions transport and improves the structural stability during the charging/discharging process. Therefore, MoS 2/C NF electrode exhibits exceptional rate performance (318.2 and 302.3 mA·h·g -1 at 5.0 and 10.0 A·g -1, respectively) and extraordinary cycle durability (98.8% retention after 300 cycles at a current density of 1.0 A·g -1). This work provides a simple and feasible method for constructing high-performance anode composites for sodium ion batteries with excellent cycle durability and fast charge/discharge ability. 相似文献
11.
Single layer transition metal sulfides (SLTMS) such as MoS 2, WS 2, and ReS 2, play an important role in catalytic processes such as the hydrofining of petroleum streams, and are involved in at least two of the slurry-catalyst hydroconversion processes that have been proposed for upgrading heavy petroleum feed and other sources of hydrocarbon fuels such as coal and shale oils. Additional promising catalytic applications of the SLTMS are on the horizon. The physical, chemical, and catalytic properties of these materials are reviewed in this report. Also discussed are areas for future research that promise to lead to advanced applications of the SLTMS. 相似文献
12.
Nd 3+-ion-doped ZnCl 2-based glasses were prepared via the melt-quenching method. The Nd 3+-ion upconversion excitation mechanism and the ability to disperse Nd 3+ ions into ZnCl 2-based glasses were investigated using absorption and upconversion fluorescence spectra of Nd 3+ ions. The ZnCl 2-based glass that had an average cationic radius equal to the ionic radius of Nd 3+ (98 pm) had the greatest ability to disperse Nd 3+ ions. The 20KCl·25BaCl 2·55ZnCl 2glass, which had the average cationic radius nearest to 98 pm, dispersed Nd 3+ ions the most, and it had the strongest upconversion fluorescence. 相似文献
13.
制备了Pt和Pd纳米颗粒修饰的单层MoS 2纳米片(Pt-Pd/MoS 2),通过扫描电镜(SEM)、透射电镜(TEM)和X射线光电子能谱(XPS)对Pt-Pd/MoS 2外部形貌、内部结构和组成进行表征分析,并基于Pt-Pd/MoS 2修饰玻碳电极,并于表面固定乙酰胆碱酯酶(AChE),制备AChE生物传感器。对比了Pt和Pd双金属纳米颗粒、商品化Pt/C及Pt-Pd/MoS 2的电化学性能,结果发现,Pt-Pd/MoS 2的电化学性能明显优于其他两种。测定电极表面酶催化反应的动力学参数 Km为883μmol/L;以马拉硫磷和甲基对硫磷为代表,考察制备电极的检测性能以及制备电极对有机磷农药的检测性能,马拉硫磷的检测范围是1×10 -14~1×10 -5mol/L,检测限为4.69×10 -14mol/L;甲基对硫磷的检测范围是1×10 -15~1×10 -5mol/L,检测限为5.23×10 -15mol/L(S/N=3);并应用于真实样品检测OPs的回收率为91.4%~103%,显示出良好的回收率和准确性,可应用于实际样品的分析。Pt-Pd/MoS 2为二维纳米材料构建高效生物传感器提供了新思路。 相似文献
14.
Chloride glasses of the ZnCl 2 and 20KCl-20BaCl 2-60ZnCl 2-0.5ErCl 3 systems were prepared using NH 4Cl as a dehydrating and chlorinating agent, under the melt-quenching method. Water- and ammonium-chloride-related residues in ZnCl 2 glasses were investigated by infrared and near-infrared absorption spectra. Water, Zn—OH, ClO, ClO 2−, Zn 2+-coordinated water, free NH 3, NH 4+, and Zn 2+-coordinated NH 3 were identified in ZnCl 2 glasses. 20KCl-20BaCl 2-60ZnCl 2-0.5ErCl 3 glasses prepared by melting at 500°C for 20 min, under reduced pressure, contained the smallest amounts of water, Zn—OH, and Zn 2+-coordinated NH 3 and showed strong Er 3+ upconversion fluorescence. 相似文献
15.
在浸没式循环撞击流反应器中,以氨水为沉淀剂,用七水合硫酸亚铁和六水合三氯化铁为原料,采用共沉淀法制备了纳米四氧化三铁粒子。考察了搅拌转速、亚铁与三价铁物质的量比、反应温度和溶液pH对所得纳米四氧化三铁的分散性和粒径的影响。采用傅里叶红外光谱仪、透射电镜、X射线衍射仪等对制得的纳米粒子的结构和性能进行了表征。结果表明:用撞击流反应器制备纳米四氧化三铁粒子的最佳工艺条件:亚铁与三价铁物质的量比为1 ∶1,反应温度为40 ℃,搅拌转速为1 600 r/min,以氨水作沉淀剂,最佳pH控制在11.0左右。在上述条件下,可以制备出分散性好、纯度高、平均粒径为10 nm的四氧化三铁粒子。 相似文献
16.
Catalytic effects of Mo and W compounds in various chemical reactions have been known for decades. Supported catalysts containing Mo or W components as essential active ingredients are the most widely used catalysts in refinery practice. In spite of this, the forms of active Mo or W species and their intimate roles in catalytic reactions are not well understood, Although the presence of sulfides such as MoS 2 and WS 2 is frequently reported in these materials, their participation in catalytic reactions is a matter of speculation. In recent years, significant progress has been made in this respect as the result of applying modern techniques, particularly spectroscopy. 相似文献
17.
以冬瓜和钛酸四丁酯为原料,采用水热法和冷冻干燥法成功制备出含TiO 2炭气凝胶(WTCA),研究了其对罗丹明B废水的光催化降解性能,并考察了水中常见无机盐离子对其光催化效果的影响。利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、拉曼光谱仪(Raman)和荧光光谱仪(FL)等对样品结构和性能进行了表征。XRD、Raman和EDS分析表明复合气凝胶中含有锐钛矿TiO 2和碳元素;SEM和TEM分析表明TiO 2纳米颗粒均匀地负载在具有多级孔洞结构的炭气凝胶的骨架表面;含TiO 2炭气凝胶的光催化活性明显高于纯TiO 2,当负载量达30%时,其对罗丹明B的光催化降解效率最高(降解率达96.11%)。此外,无机盐阴离子对复合气凝胶的光催化效果有一定的抑制作用(CO 32- > SO 42- > Cl - > NO 3-),而无机盐阳离子Na +、K +、Ca 2+和Mg 2+的抑制作用不明显。 相似文献
18.
The emergence of MoS 2 nanopores has provided a new avenue for high performance DNA sequencing, which is critical for modern chemical/biological research and applications. Herein, molecular dynamics simulations were performed to design a conceptual device to sequence DNA with MoS 2 nanopores of different structures (e.g., pore rim contained Mo atoms only, S atoms only, or both Mo and S atoms), where various unfolded single-stranded DNAs (ssDNAs) translocated through the nanopores driven by transmembrane bias; the sequence content was identified by the associating ionic current. All ssDNAs adsorbed onto the MoS 2 surface and translocated through the nanopores by transmembrane electric field in a stepwise manner, where the pause between two permeation events was long enough for the DNA fragments in the nanopore to produce well-defined ionic blockage current to deduce the DNA’s base sequence. The transmembrane bias and DNA-MoS 2 interaction could regulate the speed of the translocation process. Furthermore, the structure (atom constitution of the nanopore rim) of the nanopore considerably regulated both the translocate process and the ionic current. Thus, MoS 2 nanopores could be employed to sequence DNA with the flexibility to regulate the translocation process and ionic current to yield the optimal sequencing performance. 相似文献
19.
Upconversion fluorescences of the green 4S 3/2→ 4I 15/2 and red 4F 9/2→ 4I 15/2 transitions of the Er 3+ ion are studied for Yb 3+- and Er 3+-codoped sodium germanate, potassium tantalum gallate, and barium tellurite glasses by InGaAs laser-diode pumping. The phonon energies of the host glasses are determined by infrared-reflection measurements. Compositional effects on the Judd—;Ofelt parameters for the Er 3+ ion, the spontaneous emission probability (SPE) of the 2F 5/2→ 2F 7/2 transition for the Yb 3+ ion, and the phonon energy of the glass network are discussed in terms of glass structure. The factors that affect the upconversion fluorescence intensities of the Er 3+ ion are discussed, using the phonon energy of the host glass and the SPE for the Yb 3+ ion in the germanate, gallate, and tellurite glasses. 相似文献
20.
Y 1.9Er 0.1O 3 and Y 1.7Yb 0.2Er 0.1O 3 nanocrystalline powders were prepared via a reverse-strike coprecipitation method using nitrates and ammonia as raw materials. The obtained powders were of cubic-phase structure of Y 2O 3 and the particle size was in the range of ∼60–80 nm. Strong red ( 4F 9/2– 4I 15/2) and green ( 2H 11/2/ 4S 3/2– 4I 15/2) upconversion luminescence were observed in all the samples when excited with a 980-nm continuous wave diode laser. The possible upconversion mechanisms in Y 1.9Er 0.1O 3 and Y 1.7Yb 0.2Er 0.1O 3 were discussed. Power studies indicated that two-photon processes are responsible for the green and red upconversion luminescence in these systems. The codoping of Yb 3+ greatly enhanced the red ( 4F 9/2– 4I 15/2) upconversion emission. 相似文献
|