共查询到19条相似文献,搜索用时 174 毫秒
1.
用浸渍-原位还原法制备了Ru-Sn/H-CMK-3催化剂. 以肉桂醛选择性加氢制备肉桂醇为探针反应. 详细研究了催化剂的制备及反应条件对肉桂醛选择性加氢性能的影响. 采用X 射线粉末衍射(XRD)、比表面积(BET)、X光电子能谱(XPS)、透射电镜(TEM)等手段对催化剂结构和性质进行了表征. 结果表明, 介孔CMK-3碳材料能够更好地分散活性物种. 添加适量的Sn(IV)有利于Ru处于电子富集状态. 催化剂的主要活性物种是纳米Ru粒子, Ru和Sn之间的相互作用更加有利于C=O的活化. 同时, 反应温度和反应压力等条件的变化对肉桂醛选择性加氢制备肉桂醇反应也具有较大的影响. 相似文献
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用化学还原法制备了La修饰的Co-B非晶态合金催化剂(Co-La-B),并考察了其在乳酸乙酯液相加氢制1,2-丙二醇(1,2-PDO)反应中的催化性能.通过X射线粉末衍射(XRD)、透射电子显微镜(TEM)、比表面积测定(BET)、差示扫描量热(DSC)、电感耦合等离子发射光谱(ICP-OES)、X射线光电子能谱(XPS)、氢气化学吸附、氢气程序升温脱附(H2-TPD)等手段对催化剂进行表征,研究了稀土助剂La对Co-B催化剂催化性能的影响.结果表明,活性组分Co以元素态和氧化态两种形式存在于Co-La-B非晶态合金催化剂中,催化剂中存在B向Co的电子转移,富电子的Co用于活化氢,氧化态形式存在的La3+促进了B向Co的电子转移;适量的La能提高催化剂的热稳定性,显著减小催化剂粒径,使催化剂形成更加单一的Co吸附活性位,有利于吸附活化的氢促进加氢反应进行.在氢气压力6 MPa,反应温度433 K,反应时间9 h的条件下,0.5%Co-La-B催化剂表现出最优的催化加氢性能,乳酸乙酯的转化率达到99.7%,1,2-丙二醇的选择性达到98.5%. 相似文献
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采用CO碳化SiO2和Al3O4负载的Co(NO3)2的方法制备了SiO2和Al3O4负载的Co2C催化剂,采用N2物理吸附、X射线衍射和H2-程序升温还原技术对催化剂进行了表征,并用于催化费托合成反应中.结果显示,需要较长碳化时间才可合成负载的Co2C催化剂;所制催化剂表现出CO加氢生成高碳醇的催化性能,其原因可能在于催化剂表面存在的金属Co物种使CO解离,表面Co物种有利于CO插入,从而导致醇的生成,但体相Co2C则不具有催化活性. 相似文献
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以脱硫选择性不同的2组催化裂化汽油加氢脱硫催化剂为研究对象, 采用CO吸附原位红外光谱表征了2组催化剂的活性相特征, 并通过分子模拟计算方法比较了助剂Co加入前后噻吩和1-己烯在催化剂表面的电荷分布、吸附能及其加氢反应的活化能等, 探讨了助剂Co的加入对选择性加氢脱硫催化剂脱硫选择性的作用机理. 结果表明, 加氢脱硫催化剂CoMoS活性相的增加有利于提高催化剂的加氢脱硫/加氢降烯烃(HDS/HYD)选择性. 与1-己烯加氢位相比, Co的加入显著提高了噻吩分子加氢位的缺电子性, 噻吩在催化剂表面的吸附度增强, 显著降低噻吩加氢反应的能垒, 从而使噻吩加氢反应更易进行. 这也表明CoMoS为高HDS活性、高HDS/HYD选择性的活性相. 相似文献
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聚合物固载Co-Pd 催化剂的结构与活性 总被引:3,自引:0,他引:3
采用溶剂化金属原子浸渍(SMAI)法制备了几种不同金属含量的Co Pd催化剂,用X射线衍射、X射线光电子能谱和磁测定对催化剂进行表征,并与普通浸渍法(CI)制得的相同金属含量的催化剂进行比较.结果表明SMAI法制备的催化剂金属粒度小于CI法制备的催化剂,且前者零价金属含量高于后者.SMAI法制备的催化剂Co在表面上富集,而CI法制备的催化剂Co在表面和体相的金属含量基本相同.在二丙酮醇加氢及电催化反应中, SMAI法催化剂比相同组成的CI法催化剂具有更高的催化活性. 相似文献
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用共沉淀法制备了一组不同组成的MnxCo3-xO4尖晶石型复合氧化物,表面负载碱金属助剂制备改性催化剂,用于催化分解N2O.用X射线衍射(XRD)、N2物理吸附(BET)、红外光谱(FTIR)、扫描电镜(SEM)、H2程序升温还原(H2-TPR)、X射线光电子能谱(XPS)等技术表征催化剂结构.考察了复合氧化物组成、碱金属助剂类型、钾前驱物等制备参数对催化剂结构和催化活性的影响.结果表明:添加助剂K、Cs降低了催化剂表面Co、Mn元素的电子结合能,弱化了Co—O和Mn—O键,有利于氧物种的脱除,提高了催化剂活性.优化出了活性较高的催化剂K/Mn0.4Co2.6O4(K2CO3),有氧无水、有氧有水气氛400℃连续反应50 h,N2O转化率分别保持100%和74.2%,催化剂稳定性较高. 相似文献
8.
通过水解,聚乙烯吡咯烷酮(PVP)保护,NaOH刻蚀等方法制备了多孔及富含表面羟基的SiO2·xH2O负载的RuB催化剂RuB/SiO2·xH2O,并用X射线衍射(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)、傅里叶变换红外(FT-IR)光谱和BET(Brunauer-Emmett-Teller)等手段对该催化剂进行了表征.结果表明该催化剂具有良好的抗中毒能力,在3.0MPa的H2压力和80℃的温和反应条件下,喹啉的转化率高于95%,生成1,2,3,4-四氢喹啉的选择性高于97%.并系统研究了表面羟基和溶剂对催化剂性能的影响,发现以水为溶剂时,RuB/SiO2·xH2O对喹啉加氢反应展示出较高的活性和对1,2,3,4-四氢喹啉较高的选择性,催化剂能够多次循环使用.这一体系的优异催化性能归属于载体表面羟基和水的协同作用. 相似文献
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《高等学校化学学报》2015,(9)
分别以锐钛矿相Ti O2和金红石相Ti O2为载体,采用等体积浸渍法制备了Ni/Ti O2催化剂,考察了其催化顺酐液相加氢性能.采用氮气吸附-脱附、氢气程序升温还原(H2-TPR)、X射线衍射(XRD)、氢气程序升温脱附(H2-TPD)及X射线光电子能谱(XPS)等技术对催化剂进行了表征.催化剂评价结果表明,以锐钛矿型Ti O2为载体催化剂的C O加氢活性明显高于以金红石型Ti O2为载体的催化剂.这主要是由于在还原过程中锐钛矿型Ti O2较易被还原,产生了较高浓度的氧缺陷位,该氧缺陷位可通过接受C O中O的孤对电子来活化C O,促使其与H2发生加氢反应,进而使催化剂表现出较高的C O加氢活性. 相似文献
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Pan-Feng Yuan Zhao Yang Shan-Shan Zhang Can-Ming Zhu Prof. Dr. Xiu-Long Yang Prof. Dr. Qing-Yuan Meng 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2024,136(5):e202313030
Carboxylation with carbon dioxide (CO2) represents one notable methodology to produce carboxylic acids. In contrast to carbon–heteroatom bonds, carbon–carbon bond cleavage for carboxylation with CO2 is far more challenging due to their inherent and less favorable orbital directionality for interacting with transition metals. Here we report a photocatalytic protocol for the deconstructive carboxylation of alkenes with CO2 to generate carboxylic acids in the absence of transition metals. It is emphasized that our protocol provides carboxylic acids with obviously unchanged carbon numbers when terminal alkenes were used. To show the power of this strategy, a variety of pharmaceutically relevant applications including the modular synthesis of propionate nonsteroidal anti-inflammatory drugs and the late-stage carboxylation of bioactive molecule derivatives are demonstrated. 相似文献
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Yuxuan Liu Wang Miao Prof. Weijun Tang Prof. Dong Xue Prof. Jianliang Xiao Prof. Chao Wang Prof. Changzhi Li 《化学:亚洲杂志》2021,16(13):1725-1729
A rhodium terpyridine complex catalyzed transfer hydrogenation of nitroarenes to anilines with i-PrOH as hydrogen source and water as solvent has been developed. The catalytic system can work at a substrate/catalyst (S/C) ratio of 2000, with a turnover frequency (TOF) up to 3360 h−1, which represents one of the most active catalytic transfer hydrogenation systems for nitroarene reduction. The catalytic system is operationally simple and the protocol could be scaled up to 20 gram scale. The water-soluble catalyst bearing a carboxyl group could be recycled 15 times without significant loss of activity. 相似文献
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Syngas Conversion over Co4 Cluster Grafted on HZSM-5 Zeolite: Mechanistic Insights from DFT Modeling
Dr. Sai V. C. Vummaleti Dr. Jia Zhang Dr. Luwei Chen Dr. Michael B. Sullivan Dr. Armando Borgna 《ChemCatChem》2024,16(2):e202300942
We present a detailed DFT-based mechanistic investigation of syngas conversion mechanism over Co4 cluster grafted onto HZSM-5 zeolite, [Co4H], employing a QM/MM embedded cluster approach. Starting from the [Co4H] complex, our results show that a favorable coordination of CO over H2, followed by CO hydrogenation leads to a stable −CH2O complex, [Co4(CH2O)(H)]. Coordination of a second CO molecule to [Co4(CH2O)(H)] complex, followed by CH2−O bond activation, and subsequent removal of CO as CO2 results in the formation of crucial methylene complex [Co4(CH2)(H)], serving as a branching point for the pathways leading to methane, ethene, and ethane. On the pathway to ethene formation, coordination of a third CO molecule to [Co4(CH2)(H)] complex yields the active [Co4(CH2)(CO)(H)] complex, which is 16.0 kcal mol−1 more stable than the methyl complex [Co4(CH3)] on the pathway to methane. From the active species [Co4(CH2)(CO)(H)], we demonstrate that the pathways to both methane and ethene are competing in nature, with the −CH3 hydrogenation barrier, 35.1 kcal mol−1, is lower by only 1.3 kcal mol−1 than the competing C−O bond activation barrier on the pathway to ethene, 36.4 kcal mol−1. However, the significant stability of the active species [Co4(CH2)(CO)(H)] effectively compensates for this minor difference in barriers, ultimately favoring the formation of ethene over methane. Finally, the ethene desorption barrier is 4.1 kcal mol−1 lower than the ethene hydrogenation barrier on the pathway to ethane, indicating the ease of ethene removal from the system. Overall, our DFT study describes that the syngas conversion mechanism catalyzed by [Co4H] system produces ethene selectively via 4CO+2H2→C2H4+2CO2. 相似文献
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Joaquin Guilleme Ernesto Diez Lluis Garrigos Angel L. Esteban 《Magnetic resonance in chemistry : MRC》1984,22(3):140-145
Methyl carbon chemical shifts have been assigned for methylbenzoic acids dissolved in CDCl3, and for methylbenzoate anions obtained by dissolving these acids in aqueous NaOH solution. Chemical shifts have been interpreted by means of additive substituent parameters which reflect conformational features existing between adjacent substituents. Barriers to rotation of a methyl group adjacent to a carboxyl or carboxylate group have been estimated to differ by less than 2 kJ mol?1 from the barrier of a methyl group in o-xylene. 相似文献
15.
Zhiheng Gong Xuepeng Xiang Wenye Zhong Chenghao Jia Peiyan Chen Prof. Nian Zhang Prof. Shijun Zhao Prof. Weizhen Liu Prof. Yan Chen Prof. Zhang Lin 《Angewandte Chemie (International ed. in English)》2023,62(38):e202308775
The complexes of metal center and nitrogen ligands are the most representative systems for catalyzing hydrogenation reactions in small molecule conversion. Developing heterogeneous catalysts with similar active metal-nitrogen functional centers, nevertheless, still remains challenging. In this work, we demonstrate that the metal-nitrogen coupling in anti-perovskite Co4N can be effective modulated by Cu doping to form Co3CuN, leading to strongly promoted hydrogenation process during electrochemical reduction of nitrate (NO3−RR) to ammonia. The combination of advanced spectroscopic techniques and density functional theory calculations reveal that Cu dopants strengthen the Co−N bond and upshifted the metal d-band towards the Fermi level, promoting the adsorption of NO3− and *H and facilitating the transition from *NO2/*NO to *NO2H/*NOH. Consequently, the Co3CuN delivers noticeably better NO3−RR activity than the pristine Co4N, with optimal Faradaic efficiency of 97 % and ammonia yield of 455.3 mmol h−1 cm−2 at −0.3 V vs. RHE. This work provides an effective strategy for developing high-performance heterogeneous catalyst for electrochemical synthesis. 相似文献
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Dewey H. Barich Mark T. Zell Douglas R. Powell Eric J. Munson 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(4):o261-o262
The title compounds (both C9H10O4) have nearly planar structures, and the methyl and/or carboxylic acid groups lie out of the molecular plane, as dictated by steric interactions. 2,5‐Dimethoxybenzoic acid (2,5‐DMBA) forms an unusual intramolecular hydrogen bond between the carboxylic acid group and the O atom of the methoxy group in the 2‐position [O⋯O = 2.547 (2) Å and O—H⋯O = 154 (3)°]. 2,4‐DMBA forms a typical hydrogen‐bond dimer with a neighboring molecule. 相似文献
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Alessandro Toti Antonella Salvini Luca Rosi Carlo Giolli 《Journal of organometallic chemistry》2005,690(16):3641-3651
The ruthenium(II) complexes RuH2(CO)2(PnBu3)2, RuH2(CO)2(PPh3)2, and RuH2(PPh3)4 are catalytically active in the hydrogenation of organic substrates containing a NN, N(O)N or NO2 group. The reduction of the first two groups leads to hydrazine as intermediate and amine as the final product, while reducing a NO2 group the corresponding amine is selectively formed. A complete conversion was reached, depending on temperature, catalyst and substrate concentration. The catalysts are also active in the hydrogenolysis of an N-N group giving the corresponding amine with a 97.3% conversion using RuH2(PPh3)4 as catalyst. A first-order reaction rate with respect to substrate, catalyst or hydrogen pressure was detected in all cases. Finally, the activation parameters and the kinetic constants of these reactions were calculated. In the hydrogenation of azobenzene, the rate determining step involves an associative or a dissociative step depending on the catalyst employed while in the hydrogenation of all other substrates an associative rate determining step is always involved. A catalytic cycle is suggested for the hydrogenation of azobenzene, taking into account the intermediate complexes identified in the reaction medium. 相似文献
18.
Liang Zhang Zhenghua Li Masanori Takimoto Zhaomin Hou 《Chemical record (New York, N.Y.)》2020,20(6):494-512
The development of versatile catalyst systems and new transformations for the utilization of carbon dioxide (CO2) is of great interest and significance. This Personal Account reviews our studies on the exploration of the reactions of CO2 with various substrates by the use of N‐heterocyclic carbene (NHC)‐copper catalysts. The carboxylation of organoboron compounds gave access to a wide range of carboxylic acids with excellent functional group tolerance. The C?H bond carboxylation with CO2 emerged as a straightforward protocol for the preparation of a series of aromatic carboxylic esters and butenoates from simple substrates. The hydrosilylation of CO2 with hydrosilanes provided an efficient method for the synthesis of silyl formate on gram scale. The hydrogenative or alkylative carboxylation of alkynes, ynamides and allenamides yielded useful α,β‐unsaturated carboxylic acids and α,β‐dehydro amino acid esters. The boracarboxylation of alkynes or aldehydes afforded the novel lithium cyclic boralactone or boracarbonate products, respectively. The NHC‐copper catalysts generally featured excellent functional group compatibility, broad substrate scope, high efficiency, and high regio‐ and stereoselectivity. The unique electronic and steric properties of the NHC‐copper units also enabled the isolation and structural characterization of some key intermediates for better understanding of the catalytic reaction mechanisms. 相似文献
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Aerobic and anaerobic photolysis of methyl(pyridine)cobaloxime, benzyl(pyridine)cobaloxime and analogous compounds in CHCl3 results only in an electron transfer reaction from an equatorial ligand producing photo-reduction of CoIII to CoII, the complex retaining its axial ligands.If after the anaerobic photolysis of benzyl(pyridine)cobaloxime the oxygen is introduced without any further photolysis we obtain an ESR spectrum of nitroxide, arising from the attack of a benzyl radical on the dimethylglyoxime equatorial ligand.For the other complexes, homolytic cleavage of the CoC bond occurs and in the presence of oxygen gives rise to the superoxide cobalt complex adduct Py(CoIIIO2?.During photolysis of methyl(pyridine)cobaloxime in isopropanol homolytic cleavage of the CoC bond occurs in preference to electron transfer reaction from the equatorial ligands.The anaerobic photolysis of benzyl(pyridine)cobaloxime in isopropanol or in water at 113–133 K results in an electron transfer reaction. However, at 170 K we observe the formation of the CoII complex arising from CoC bond cleavage.A mechanism for photo-induced insertion of oxygen in the CoC bond is proposed. 相似文献