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61.
62.
The vanadium trapping effect of Mg and La containing additives in cracking catalyst contaminated with 2300 ppm Ni and 4700 ppm V has been analyzed by microactivity test (MAT) and imaging secondary ion mass spectrometry (SIMS). The results of SIMS imaging are consistent with cracking activity data and show that the La/spinel is a superior vanadium trap for the fluid catalytic cracking of hydrocarbons (FCC) operation. La/spinel serves as a dual function additive for both vanadium trap and SOx removal. The optimum amount of La/spinel added to the cracking catalyst is about 15% by weight. This results in an increased catalytic activity, an increase in gasoline yield, and a decrease in coke and gas factors. The MgAl2O4 phase of Mg/Al2O3 additive is found capable of trapping vanadium while its MgO of Mg/Al2O3 phase can migrate to zeolite particles (the active component of the FCC catalyst) that, in turn, causes a decline in the activity of that catalyst. 相似文献
63.
J. Ravichandran C. M. Lakshmanan B. Sivasankar 《Reaction Kinetics and Catalysis Letters》1996,59(2):301-308
Treatment of montmorillonite and vermiculite with hydrochloric acid results in an overall increase in acidity and acidic sites. IR and DSC studies of base adsorbed catalysts have revealed the heterogeneity of surface acidity on the activated catalysts. Clay catalysts have been found to dehydrate 1-butanol to 1-butene, which directly isomerizes tocis- andtrans-2-butenes, confirming the presence of Lewis and Brönsted acid sites. Cumene cracking studies using the clay catalyst also confirm the presence of Brönsted acid sites. The temperature and concentration of acid have been found to have a significant influence on the catalytic activity. 相似文献
64.
《Arabian Journal of Chemistry》2022,15(11):104302
Traditional Chinese medicine (TCM) is the key to unlock treasures of Chinese civilization. TCM and its compound play a beneficial role in medical activities to cure diseases, especially in major public health events such as novel coronavirus epidemics across the globe. The chemical composition in Chinese medicine formula is complex and diverse, but their effective substances resemble “mystery boxes”. Revealing their active ingredients and their mechanisms of action has become focal point and difficulty of research for herbalists. Although the existing research methods are numerous and constantly updated iteratively, there is remain a lack of prospective reviews. Hence, this paper provides a comprehensive account of existing new approaches and technologies based on previous studies with an in vitro to in vivo perspective. In addition, the bottlenecks of studies on Chinese medicine formula effective substances are also revealed. Especially, we look ahead to new perspectives, technologies and applications for its future development. This work reviews based on new perspectives to open horizons for the future research. Consequently, herbal compounding pharmaceutical substances study should carry on the essence of TCM while pursuing innovations in the field. 相似文献
65.
ICP-AES中内标法的应用研究 Ⅲ.用内标法校正基体干扰 总被引:1,自引:0,他引:1
通过观测基体对分析元素发射强度的干扰情况,分析干扰机制,从而确定用来校正基体干扰的内标元素与分析元素的匹配条件。实验结果表明,只要选择合适的内标元素,可以校正基体干扰。 相似文献
66.
J. L. Martínez Vidal A. Garrido Frenich T. López López I. Martínez Salvador L. Hajjaj el Hassani M. Hassan Benajiba 《Chromatographia》2005,61(3-4):127-131
An analytical method for determining residues of twenty pesticides by liquid chromatography (LC) coupled to electrospray ionisation (ESI) tandem mass spectrometry (MS-MS) in eight commodities, cucumber, tomato, pepper, green bean, eggplant, zucchini, melon and watermelon, has been developed and validated. On one hand, calibration curves prepared in solvent were compared with calibration curves prepared in a blank matrix extract of each target matrix. On the other hand, calibration curves and recoveries for each commodity were compared. Cucumber was selected as potential reference matrix for the target vegetables. 相似文献
67.
肿瘤的生长依赖于血管的生成,新生血管不仅为肿瘤生长提供必需的营养物质,而且为肿瘤细胞扩散提供了重要的途径。1997年哈佛大学的O'Reilly等发现了一种内源性新血管生成抑制因子内皮抑素(Endoscatin),显示出特异抑制激活的血管内皮细胞增殖和肿瘤新血管生成的生物学活性,其抗肿瘤作用具有高效、低毒、无耐药性的优点。目前,内皮抑素的研究引起了国内外广泛的兴趣,在美国已进行以安全性为目的的I期临床实验,国内也有多家公司对内皮抑素进行了抗肿瘤研究并申报一类新药。内皮抑素有望成为医治肿瘤而又没有化疗和放疗的毒副作用的一种新的治疗方法,但是否能作为药物应用于临床,尚需对内皮抑素的结构特点及抑制肿瘤和内皮细胞的作用机制等方面进行许多深入的研究。 相似文献
68.
Matrix isolation infrared studies of complexes formed between substituted phenols and trimethylamine
Infrared spectroscopy and matrix isolation technique have been used to study the 1 : 1 complexes formed between 2,4,5-trichlorophenol (TCP), pentachlorophenol (PCP) or 2-chloro-4,6-dinitrophenol (CNP) and trimethylamine (TMA) isolated in solid argon. The results were analyzed in relation to the type of complex formed. Depending on the proton-donor ability of the phenol three different types of hydrogen bonded complexes have been identified in argon matrices. The weakest phenol in the series, TCP (pKa = 6.72), forms a strong molecular hydrogen bonded complex with TMA as indicated by the broad ν(OHN) absorption with a maximum at 2490 cm−1 and a band at 811 cm−1 due to the νs(C3N) mode of the perturbed amine. The strongest phenol, CNP (pKa = 2.01), interacts with TMA in an argon matrix to form ionic complex with the proton transferred to the base molecule. This is evidenced by the presence of the ν(NH+---O−) absorption between 3000−1800 cm−1, by the νas(C3N+) and νs(C3N+) absorptions due to the protonated amine and by numerous product bands due to the relatively strongly perturbed modes of the phenol ring. The interaction between TMA and a phenol of intermediate strength, PCP (pKa = 4.74), in solid argon probably leads to the formation of two types of hydrogen bonded complexes: an ionic complex with the proton transferred to the amine molecule and a pseudosymmetric one with the proton more or less equally shared between the phenol and amine molecules. In this case the protonic absorption consists of two broad features situated in the 3000–1600 cm−1 and 950–400 cm−1 regions due to the ν(NH+O−) and ν(OHN) modes, respectively. 相似文献
69.
70.
The use of a so-called trihedral and a T-shaped cross-flow pneumatic nebulizer with dual solution loading for inductively coupled plasma optical emission spectrometry has been studied. By these devices analyte clouds from two solutions can be mixed during the aerosol generation step. For both nebulizers the correction of matrix effects using internal standardization and standard addition calibration in an on-line way was investigated and compared to elemental determinations using a conventional cross-flow nebulizer and calibration with synthetic standard solutions without matrix matching. A significant improvement of accuracy, both for calibration with internal standardization and standard addition, was obtained in the case of four synthetic solutions containing each 40 mmol L− 1 Na, K, Rb and Ba as matrix elements and 300 μg L− 1 Cd, Co, Cr, Cu, Fe, Mn, Ni and Pb as analytes. Calibration by standard addition in the case of dual solution loading has been shown to be very useful in the determination of elements at minor and trace levels in steel and alumina reference materials. The results of analysis for minor concentrations of Cr, Cu and Ni in steel as well as for Ca, Fe, Ga, Li, Mg, Mn, Na, Si and Zn in alumina powder certified reference materials subsequent to sample dissolution were found to be in good agreement with the certificates. Limits of detection were found to be only slightly above those for a conventional cross-flow nebulizer and a precision better than 3% was realized with both novel nebulizers. 相似文献