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排序方式: 共有369条查询结果,搜索用时 15 毫秒
1.
Qianqian Hao Xiuquan Jia Dr. Jiping Ma Mingxia Gao Xiaomeng Fan Jin Gao Prof. Jie Xu 《化学:亚洲杂志》2021,16(11):1388-1391
Organic modifiers have shown promising potential for regulating the activity and selectivity of heterogeneous catalysts via tuning their surface properties. Despite the increasing application of organic modification technique in regulating the redox-acid catalysis of metal oxides, control of the acidity of metal oxide catalysts for enhanced reaction selectivity without sacrificing their redox activity remains a substantial challenge. Herein, we show the successful control of redox-acid catalysis of metal oxides with aprotic tertiary amine modifiers. Robust modification of manganese dioxide catalysts with N,N-dialkylcyclohexylamine selectively blocks the Lewis acid sites, with their redox activity mostly unaffected. This enables efficient synthesis of imines in high to excellent selectivity via aerobic oxidation of structurally diverse aryl amines. 相似文献
2.
Polypropylene-block-poly(vinylpyrrolidone) copolymer was synthesized through the esterification of dicarboxyl-terminated polypropylene with monohydroxyl-terminated poly(vinylpyrrolidone) and used as a macromolecular surface modifier to improve the surface hydrophilicity of PP. The results of ATR-FTIR and contact angles measurements indicated that PP-b-PVP could diffuse preferably onto the surface by the inducement of high energy interface and lower the water contact angle of polypropylene. Lower loading and lower molecular weight of PP and PVP segment would result in higher surface selective enrichment. 相似文献
3.
This review highlights the basis of gradient reversed-phase high-performance liquid chromatography (RP-HPLC) of ionogenic analytes.We describe pH-gradient RP-HPLC in strict theoretical terms, with examples of experiments to provide improvements in analyte separations and peak shapes, and an original method of pKa determination.Finally, we present the concept of the combined pH/organic-modifier gradient mode of RP-HPLC and illustrate it with applications. It allows optimization of separation of ionogenic analytes, along with a method for determining their biorelevant physico-chemical parameters [e.g., hydrophobicity (log kw) and acidity (pKa)]. The method is applicable to drugs and other xenobiotic mixtures, including individual analytes of interest assayed in biological fluids. 相似文献
4.
《Journal of Energy Chemistry》2014,23(5):633-638
MgO-modified Ni/Al2O3 catalysts with different Ni loadings were prepared and employed in dry reforming of methane (DRM). The effect of Ni loadings on the activity and coke formation of Ni/MgO-Al2O3 catalysts were investigated. The synthesized catalysts were characterized by XRD, N2 adsorption-desorption, SEM, TPO and TPR techniques. The obtained results showed that increasing nickel loading decreased the BET surface area and increased the catalytic activity and amount of deposited carbon. In addition, the effect of gas hourly space velocity (GHSV) and feed ratio were studied. 相似文献
5.
Barium hexaferrite BaFe12O19 powders have been synthesized using the modified co-precipitation method. Modification was performed via the ultrasonication of the precipitated precursors at room temperature for 1 h and the additions of the 2% KNO3, surface active agents and oxalic acid. The results revealed that single phase magnetic barium hexaferrite was formed at a low annealing temperature of 800 °C for 2 h with the Fe3+/Ba2+ molar ratio 8. The microstructure of the powders appeared as a homogeneous hexagonal platelet-like structure using 2% KNO3 as the crystal modifier. A saturation magnetization (60.4 emu/g) was achieved for the BaFe12O19 phase formed at 1000 °C for 2 h with Fe3+/Ba2+ molar ratio 8 using 5 M NaOH solution at pH 10 in the presence of 2% KNO3. Moreover, the saturation magnetization was 52.2 emu/g for the precipitated precursor at Fe3+/Ba2+ molar ratio 12 in was achieved for the precipitated precursor ultrasonicated for 1 h and then annealed at 1200 °C for 2 h. Coercivities from 956.9 to 4558 Oe were obtained at different synthesis conditions. 相似文献
6.
Electrothermal atomization of beryllium from graphite and tungsten surfaces was compared with and without the use of various chemical modifiers. Tungsten proved to be the best substrate, giving the more sensitive integrated atomic absorption signals of beryllium. Tungsten platform atomization with zirconium as a chemical modifier was used for the determination of beryllium in several NIST SRM certified reference samples, with good agreement obtained between the results found and the certified values. The precision of the measurements (at 10 μg L−1), the limit of detection (3σ), and the characteristic mass of beryllium were 2.50%, 0.009 μg L−1 and 0.42 pg, respectively. 相似文献
7.
反相液相色谱中离子抑制剂的有机调节剂作用 总被引:1,自引:0,他引:1
系统地研究了在反相液相色谱(RPLC)流动相中作为离子抑制剂的酸、碱及缓冲溶液对中性化合物保留行为的影响,着重探讨了有机酸、有机碱离子抑制剂的有机调节剂作用,定量地考察了甲醇和乙腈、甲醇和乙酸、甲醇和三乙胺、乙腈和乙酸、乙腈和三乙胺在十八烷基硅烷键合相上洗脱强度之间的关系,为RPLC中有机调节剂的洗脱强度排序提供一种评判方法.另外,讨论了乙酸和三乙胺作为有机调节剂时不同的作用机理.本实验结果对于RPLC分离方法的快速建立和准确优化都具有一定的借鉴意义. 相似文献
8.
《Journal of mass spectrometry : JMS》2017,52(12):823-829
Ion mobility spectrometry (IMS) is an analytical technique that separates gas‐phase ions drifting under an electric field according to their size to charge ratio. We used electrospray ionization‐drift tube IMS coupled to quadrupole mass spectrometry to measure the mobilities of glucosamine (GH+) and caffeine (CH+) ions in pure nitrogen or when the shift reagent (SR) 2‐butanol was introduced in the drift gas at 6.9 mmol m−3. Binding energies of 2‐butanol‐ion adducts were calculated using Gaussian 09 at the CAMB3LYP/6‐311++G(d,p) level of theory. The mobility shifts with the introduction of 2‐butanol in the drift gas were −2.4% (GH+) and −1.7% (CH+) and were due to clustering of GH+ and CH+ with 2‐butanol. The formation of GBH+ was favored over that of CBH+ because GBH+ formed more stable hydrogen bonds (83.3 kJ/mol) than CBH+ (81.7 kJ/mol) for the reason that the positive charge on CH+ is less sterically available than on GH+ and the charge is stabilized by resonance in CH+. These results are a confirmation of the arguments used to explain the drift behavior of these ions when ethyl lactate SR was used (Bull Kor Chem Soc 2014, 1023–1028). This study is a step forward to predict IMS separations of overlapping peaks in IMS spectra, simplifying a procedure that is trial and error by now. 相似文献
9.
共沉淀法制备了Ru-Zn催化剂,考察了反应修饰剂ZnSO4和预处理对苯选择加氢制环己烯Ru-Zn催化剂性能的影响。结果表明,反应修饰剂ZnSO4可以与Ru-Zn催化剂中助剂ZnO反应生成(Zn(OH)2)3(ZnSO4)(H2O)盐。随反应修饰剂ZnSO4浓度增加,(Zn(OH)2)3(ZnSO4)(H2O)盐量的逐渐增加,Ru-Zn催化剂活性逐渐降低,环己烯选择性逐渐升高。因为(Zn(OH)2)3(ZnSO4)(H2O)盐中的Zn2+可以使Ru变为有利环己烯生成的缺电子的Ruδ+物种,而且还可以占据不适宜环己烯生成的强Ru活性位。但当反应修饰剂ZnSO4浓度高于0.41 mol·L-1后,继续增加ZnSO4浓度,由于Zn2+水解浆液酸性太强,可以溶解部分(Zn(OH)2)3(ZnSO4)(H2O)盐,Ru-Zn催化剂活性升高,环己烯选择性降低。但环己烯选择性却略微降低,这是由于ZnSO4溶液中大量的Zn2+可以与生成的环己烯形成配合物,稳定生成的环己烯,抑制生成的环己烯再吸附到催化剂表面并加氢生成环己烷。在ZnSO4最佳浓度0.61 mol·L-1下对Ru-Zn催化剂预处理15 h,Ru-Zn催化剂中助剂ZnO可以与ZnSO4完全反应生成(Zn(OH)2)3(ZnSO4)(H2O)盐,在该催化剂上25 min苯转化68.2%时环己烯选择性和收率分别为80.2%和54.7%。而且该催化剂具有良好的稳定性和重复使用性能。 相似文献
10.
利用沉淀法制备了纳米Ru催化剂,在ZnSO4存在下考察了Na2SiO3·9H2O和二乙醇胺作反应修饰剂对Ru催化剂催化苯选择加氢制环己烯性能的影响,并用X-射线衍射(XRD)、X-射线荧光光谱(XRF)和透射电镜-能量散射谱(TEM-EDS)等物理化学手段对加氢前后Ru催化剂进行了表征。结果表明,在水溶液中Na2SiO3与ZnSO4可以反应生成Zn4Si2O7(OH)2H2O盐、H2SO4和Na2SO4,化学吸附在Ru催化剂表面上的Zn4Si2O7(OH)2H2O盐起着提高Ru催化剂环己烯选择性的关键作用。Na2SiO3·9H2O量的增加,生成的Zn4Si2O7(OH)2H2O盐逐渐增加,Ru催化剂的活性降低,环己烯选择性逐渐升高。向反应体系中加入二乙醇胺,它可以中和Na2SiO3与ZnSO4反应生成的硫酸,使化学平衡向生成更多的Zn4Si2O7(OH)2H2O盐的方向移动,导致Ru催化剂环己烯选择性增加。当Ru催化剂与ZnSO4·7H2O、Na2SiO3·9H2O和二乙醇胺、分散剂ZrO2的质量比为1.0:24.6:0.4:0.2:5.0时,2 g Ru催化剂上苯转化73%时环己烯选择性和收率分别为75%和55%,而且该催化剂体系具有良好的重复使用性和稳定性。 相似文献