共查询到20条相似文献,搜索用时 46 毫秒
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采用XPS和EXAFS方法,研究了以sol-gel法制得的超累粉体SiO2为载体,用化学还原沉积法制备的负载型非晶态Cu/SiO2催化剂在甲酸甲酯氢解反应前后的表面结构和局域结构。结果表明,非晶态样品中的铜原子以零价铜的形式存在,但配位数却大幅度地低于铜樯档,意味着铜原子在高比表面超细SiO2载体上处于高分散的非晶状态,表面悬空键显著增多,表面能增大,导致配位键收缩。 相似文献
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超细Pd—B/SiO2非晶态合金加氢反应的催化活性 总被引:8,自引:1,他引:7
采用浸渍法并通过KBH4还原制备超细Pd-B/SiO2非晶态合金催化剂,以硝基苯加氢生成苯胺为目标反应,考察了上述催化剂的活性和选择性及热稳定性,并与晶态Pd-B/SiO2和Pd/SiO2催化剂及非负载型Pd-B非晶态合金催化剂进行了比较。 相似文献
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助剂对超细CuO—ZnO—SiO2催化剂性质和CO2加氢反应性能的影响 总被引:3,自引:1,他引:3
研究了9种助剂对用于CO2加氢反应的超细CuO-ZnO-SiO2催化剂性能的影响,并进行了XRD和TPR表征,结果表明,助剂影响超细催化剂的性质和催化性能,TiO2、CeO2、MgO和La2O3是CO2加氢合成的超细CuO2-ZnO-SiO2催化剂体系的优良助剂,在含有不同助剂的CuO-ZnO-SiO2催化剂体系内存在CuO和ZnO2晶相,但除CeO2以外,其它的助剂都可能以微晶或无定型的形式存在 相似文献
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研究了9种助剂对用于CO2加氢反应的超细CuO-ZnO-SiO2催化剂性能的影响,并进行了XRD和TPR表征.结果表明,助剂影响超细催化剂的性质和催化性能,TiO2、CeO2、MgO和La2O3是CO2加氢合成甲醇的超细CuO-ZnO-SiO2催化剂体系的优良助剂.在含有不同助剂的CuO-ZnO-SiO2催化剂体系内存在CuO和ZnO晶相,但除CeO2以外,其它的助剂都可能以微晶或无定型的形式存在.TPR研究表明,添加的助剂除CeO2以外,都使超细CuO-ZnO-SiO2催化剂的还原温度提高,而且助剂对CuO-ZnO-SiO2催化剂活性的影响,按照助剂对CuO-ZnO-SiO2催化剂还原温度的影响进行了探讨 相似文献
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CO_2加H_2合成甲醇Cu-Zn-O催化剂表面化学态研究 总被引:1,自引:0,他引:1
应用XRD、ESR、URDS、XPS及XAES等手段研究了CO_2加H_2合成甲醇Cu-Zn-O催化剂在还原后和反应状态下的表面化学状态,结果表明,在还原及反应状态下,催化剂表面仅能检测到Cu~0,而未发现稳定的Cu~(2+)和Cu~+存在;ZnO被部分还原产生低价锌Zn~(2-δ)(0<δ<2)。关联活性测试结果认为,Cu~0/Zn~((2-δ)+)O构成CO_2加H_2合成甲醇反应的活性中心。 相似文献
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An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions. 相似文献
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An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction. 相似文献
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The Diels-Alder reactivity of 1,2-heteroborines (H4C4B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed. 相似文献
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Xi-Liu YunWen-Ying Bi Jian-Hui HuangYu Liu Daisy Zhang-NegrerieYun-Fei Du Kang Zhao 《Tetrahedron letters》2012,53(38):5076-5080
A variety of N-aryl and N-alkyl carbazolones were conveniently achieved in good to high yields via Pd2(dba)3-mediated intramolecular coupling of N-substituted α-iodo enaminones under microwave irradiation. The Pd(0)-catalyzed cyclization was found to proceed favorably with the more electron-deficient phenyl ring during the reactions involving unsymmetrical N,N-diaryl α-iodo enaminones. This unique property enables the construction of carbazolone skeleton containing nitro substituted benzenoid ring. 相似文献
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Both substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles have been synthesized by the 3+2 intramolecular dipolar cycloaddition of nitrilimines to alkynes. This cyclization has been extended to more versatile 3-bromo derivatives by the use of alkynylbromides as dipolarophiles. 相似文献
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An efficient and benign method for the preparation of aminomethyl-substituted fullerenes has been developed. The process, involving catalyst free, visible-light irradiation of 10% EtOH-toluene solutions containing fullerene C60 and N-trimethylsilylmethyl-substituted amines by using a 20 W compact fluorescent lamp, leads to formation of aminomethyl-substituted fullerene adducts in a highly efficient manner. The photoaddition reaction takes place via a pathway initiated by visible light absorption by C60, followed by SET from the amine to the triplet excited state of C60. Ethanol-promoted desilylation of the resulting a minimum radical then generates the corresponding α-amino radical which couples with the C60 radical anion to form the anion precursor of the fullerene adducts. The new approach using visible-light takes place under mild conditions and it does not require the use of photocatalysts. Thus, the method developed in this effort could broadens the range of functionalized fullerene derivatives that can be readily prepared. 相似文献
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Viktor A. Dmitriev Mariia M. Efremova Alexander S. Novikov Vladimir V. Zarubaev Alexander V. Slita Anastasia V. Galochkina Galina L. Starova Andrey V. Ivanov Alexander P. Molchanov 《Tetrahedron letters》2018,59(24):2327-2331
The reactions of various nitrones with indolyl- and pyrrolylacrylates proceeds regioselectively with high diastereoselectivity in the case of aldonitrones, and represents an effective method for obtaining new indolyl- and pyrrolyl-substituted isoxazolidine carboxylates stabilized by weak (CH?O) and moderate (NH?N) strength intramolecular hydrogen bonding. The resulting cycloadducts exhibit promising in vitro anti-influenza activities. 相似文献
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A transition metal-free method for the direct amination of benzoxazoles using formamides as nitrogen sources is reported, which was mediated by an inexpensive and environmentally friendly tetrabutylammonium iodide/tert-butyl hydroperoxide system and gave the 2-aminobenzoxazole derivatives with moderate to good yields. 相似文献
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Multifunctionalized 1,2,3,4-tetrahydropyridines are concisely synthesized in good yields via l-proline-catalyzed or l-proline/FeCl3-cocatalyzed one-pot multicomponent reactions (MCRs). The MCRs involve a domino hydroamination/prins reaction/Mannich-type reaction/intramolecular dehydration-cyclization process. The molecular structure of 5baa, one of multifunctionalized 1,2,3,4-tetrahydropyridines, was confirmed by single-crystal X-ray diffraction. 相似文献
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M. Saeed Abaee Atefeh Hadizadeh Mohammad M. Mojtahedi Mohammad R. Halvagar 《Tetrahedron letters》2017,58(14):1408-1412
An efficient four-component reaction was developed to take advantage of the reactivity of the 2-aminothiophene-3-carbonitrile functionality, which is obtained during the classical three-component Gewald reaction. Various α-methylene bearing ketones were reacted with malononitrile, elemental sulfur, and aryl/heteroarylnitrile derivatives in t-BuOH/NaOH to afford 2-arylthieno[2,3-d]pyrimidin-4-amines in high yields. Preliminary studies revealed the photophysical properties of the products and their potential for use as metal sensors. 相似文献