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排序方式: 共有157条查询结果,搜索用时 31 毫秒
121.
Alexandre de Lambert de Boisjan Christophe Allemann Luca Fadini 《Helvetica chimica acta》2021,104(6):e2100035
The aim of this work was to understand if solvent contaminants can interfere in Suzuki’s cross-coupling reactions and if it can explain the lack of robustness in industrial processes. For this purpose, several parameters were tested on the industrial model reaction between 2-bromonaphthalene and phenylboronic acid catalyzed by Pd/C. Best results were obtained using THF as solvent. Traces of the precursors of the used solvents, such as 2,3-dihydrofurane or maleic anhydride (100–300 ppm related to the solvent) strongly poisoned the reaction, decreasing the conversion significantly. This means that to ensure robust production, solvent quality must be analyzed at the ppm level. Fortunately, addition of triphenylphosphine can circumvent the catalyst poisoning. 相似文献
122.
竹/塑复合材料力学性能评定及其应用 总被引:5,自引:0,他引:5
<正> 复合材料从利用天然材料到利用人工材料,从原始经验到高技术的发展,标志了材料发展史上,从第一代利用天然材料的复合材料到第四代先进复合材料的进程。先进复合材料性能优越,但高性能的碳纤维、芳纶纤维等造价高,影响了广泛应用。利用天然纤维采用新的复合工艺,制成性能良好而又价廉的复合材料,将是广泛应用于生产、生活的材料新品种。 相似文献
123.
Yixin Zhang Guofeng Qiu Rumeng Wang Yang Guo Fanhui Guo Jianjun Wu 《Molecules (Basel, Switzerland)》2021,26(19)
Using bamboo powder biochar as raw material, high-quality meso/microporous controlled hierarchical porous carbon was prepared—through the catalysis of Fe3+ ions loading, in addition to a chemical activation method—and then used to adsorb copper ions in an aqueous solution. The preparation process mainly included two steps: load-alkali leaching and chemical activation. The porosity characteristics (specific surface area and mesopore ratio) were controlled by changing the K2CO3 impregnation ratio, activation temperature, and Fe3+ ions loading during the activation process. Additionally, three FBPC samples with different pore structures and characteristics were studied for copper adsorption. The results indicate that the adsorption performance of the bamboo powder biochar FBPC material was greatly affected by the meso/micropore ratio. FBPC 2.5-900-2%, impregnated at a K2CO3: biochar ratio of 2.5 and a Fe3+: biochar mass ratio of 2%, and activated at 900 °C for 2 h in N2 atmosphere, has a very high specific surface area of 1996 m2 g−1 with a 58.1% mesoporous ratio. Moreover, it exhibits an excellent adsorption capacity of 256 mg g−1 and rapid adsorption kinetics for copper ions. The experimental results show that it is feasible to control the hierarchical pore structure of bamboo biochar-derived carbons as a high-performance adsorbent to remove copper ions from water. 相似文献
124.
125.
竹炭模板合成高度有序二氧化硅微米线组 总被引:6,自引:0,他引:6
通过扫描电子显微镜(SEM)系统地研究了竹炭的微观结构,并以竹炭孔道为模板,以正硅酸乙酯为硅源,采用溶胶-凝胶法合成出高度有序的二氧化硅微米线组,其形貌和组成分别通过SEM,EDX和XRD进行表征.结果表明,所得微米线为较纯的方石英晶型,直径约1~2μm,长达200μm以上,呈束状高度有序排列,其形貌高度复制了竹炭微孔孔道的结构,说明微孔在限域反应中起模板作用. 相似文献
126.
Pd/C: An efficient and reusable catalyst for the synthesis of flavones via carbonylation of aryl halides
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This work describes an efficient and mild approach for the synthesis of flavones via catalytic carbonylation of aryl halides with 2‐hydroxyacetophenone using the commercial Pd/C as an efficient, heterogeneous and recyclable catalyst. Under balloon pressure of CO, 0.6 mol% Pd/C is sufficient for moderate yields of flavones for the carbonylation of aryl iodides under phosphine‐free conditions and aryl bromides in the presence of phosphine ligand. The catalyst is easily separable and shows significant recyclability. Moreover, the reaction mechanism was discussed, and a possible mechanism that contains two different cyclisation pathways was proposed. 相似文献
127.
竹材非等温热解动力学 总被引:1,自引:0,他引:1
利用热重分析技术对竹材在高纯N2条件下,从室温至1273K进行了非等温热解分析,研究了升温速率(5、10、20和40K/min)对热解过程的影响,探讨了其热解机理。研究表明,竹材非等温热解过程主要分为失水干燥、快速热解和缓慢分解三个阶段组成,其中第二阶段是整个过程的主要阶段,析出大量挥发分造成明显失重。升温速率对热解过程有显著影响,随着升温速率的增加,最大热解速度增大,对应的峰值温度升高,热滞后现象加重,热解各阶段向高温侧移动。热解机理满足一维扩散Parabolic法则,反应机理函数为g(α)=α2。不同升温速率下活化能为75.32-82.99kJ.mol-1,指前因子为1.17×105-1.12×106min-1。 相似文献
128.
Fu‐Chu Yang Kuo‐Hui Wu Wen‐Po Lin Ming‐Kuan Hu Tsung‐Sheng Sheu Deng‐Nan Horng 《中国化学会会志》2009,56(2):327-334
Bamboo charcoal supporting silver (BC/Ag) was prepared by activation and chemical reduction. The BC/Ag composites were characterized by silver particle size and distribution, silver ion (Ag+) release and antibacterial properties. Scanning and transmission electron microscopy (SEM and TEM) showed that the Ag particles were distributed uniformly on the BC matrix. The Ag particle size was found to be less than 150 nm based on TEM. The Ag+ release increased initially which was followed by a marginal increase between the 8th and 24th hour. Composites contained higher amounts of silver exhibited a further rise in Ag+ release from the 24‐hours of storage in water. The antibacterial effects of the BC/Ag composite powders against Pseudomonas aeruginosa and Staphylococcus aureus were assessed from the minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) method, and an excellent antibacterial performance was discovered. 相似文献
129.
This paper investigates the synthetic mechanism of trifluoroiodomethane (CF3I) in the reaction of trifluoromethane and iodine via vapor-phase catalytic reaction. It is suggested that CF2 carbene is the key intermediate and is formed in the pyrolysis process of CHF3 at high temperature. However, in pyrolysis of CHF3 under activated charcoal (AC) existing conditions, no C2F4 was detected. H2 and 2-methyl-2-butene could not trap the CF2 carbene. When treating the remained compounds on the used AC with H2, CH4 is formed on the process. It is proposed that CF2 carbene combines with AC strongly and transfers into CF3 radical on heat. In addition, it is found that the AC is not only the catalyst supporter to form CF3I, but also a co-catalyst to promote the formation of CF2 carbene and CF3 radical. 相似文献
130.
Ru-Song Zhao Yan-Long Liu Xiang-Feng Chen Jin-Peng Yuan Ai-Ying Bai Jia-Bin Zhou 《Analytica chimica acta》2013
In this paper, bamboo charcoals were modified using Fe3O4 nanosheets for the first time. The composites, as a novel solid-phase microextraction (SPME) fiber coating, were used for the extraction of seven polybrominated diphenyl ethers (PBDEs) in environmental water samples. The extraction factors (stirring rate, extraction time, and ionic strength) and desorption factors (desorption time and desorption temperature) of the fibers were systematically investigated and optimized. Under optimum conditions, the linear range was 1–1000 ng L−1. Based on the ratio of chromatographic signal to base line noise (S N−1 = 3), the limits of detection (LODs) can reach 0.25–0.62 ng L−1. The novel method was successful in the analysis of PBDEs in real environmental water samples. The results indicate that bamboo charcoal/Fe3O4 as an SPME coating material coupled with gas chromatography–negative chemical ionization-mass spectrometry is an excellent method for the routine analysis of PBDEs at trace levels in environmental water samples. 相似文献