Mn-N-C催化剂的制备及其在碱性介质中对氧还原反应的电催化性能

选用壳聚糖(CS)为原料制备了壳聚糖水杨醛席夫碱锰配合物(Mn-CS-sal)。将Mn-CS-sal配合物负载于石墨碳上得到碳载配合物(Mn-CS-sal/C),后经高温热处理得到Mn-N-C目标催化剂(Mn-N-C-t,t=200、400、600、800、1 000℃)。采用FT-IR、XRD、XPS和电化学等方法对催化剂的组成和结构进行了表征,对其在氧还原反应中的电催化性能进行了研究。结果表明,所得到的Mn-N-C催化剂对氧还原反应(ORR)具有很好的催化作用,但以600℃热处理制备的催化剂其活性最好。催化剂中Mn-N-C结构是催化ORR的活性位。采用循环伏安法获得了Mn-N-C-t催化ORR的动力学参数,即总的转移电子数n和电子传递系数αnα;具有最佳活性的Mn-N-C-600催化剂的总转移电子数为3.63,说明在此条件下,Mn-N-C-600催化ORR主要以4e转移途径为主,由此提出了可能的氧还原反应的机理。     

氮/硫双杂化非贵金属碱性阴离子膜燃料电池阴极非铂催化剂

以吡咯和对甲苯磺酸(TsOH)作为碳载过渡金属催化剂的掺杂剂,经溶剂分散及600℃热处理制备了一种高效催化氧还原反应(ORR)的碳载双杂化过渡金属催化剂(Fe-N/C-TsOH-600).利用X射线衍射(XRD)和X射线光电子能谱(XPS)对催化剂的结构进行表征.运用旋转圆盘电极(RDE)技术研究了该催化剂在碱性介质中催化氧还原的电化学催化活性和稳定性,探讨了不同浓度甲醇溶液对Fe-N/C-TsOH-600催化剂催化氧还原活性的影响.结果表明,以Fe-N/C-TsOH-600制备的气体扩散电极在0.1 mol/L KOH电解质溶液中对氧具有很高的选择催化还原活性和稳定性.当电极经过4800圈循环伏安(CV)扫描测试后,催化剂催化氧还原的性能基本保持稳定,并以4电子途径将氧气催化还原.此外,研究还发现,Fe-N/C-TsOH-600在混有甲醇的碱性电解质溶液中对氧的催化还原选择性比商业Pt/C催化剂高.XPS结果表明,吡咯氮是催化剂高效催化氧还原的主要活性中心,提供氧还原的活性位,而TsOH作为供硫掺杂剂对提高催化剂的活性具有重要作用,其加入后形成的C—S—C有利于催化剂催化氧还原活性的提高,从而使该催化剂对氧还原表现出很好的电催化性能和选择性.     

高分散钴氮共掺杂碳纳米纤维氧还原催化剂

过渡金属氮掺杂碳基催化剂已成为替代铂基氧还原反应(ORR)电催化剂的理想选择。本文通过静电纺丝技术制备了高比表面、高度分散的钴原子配位氮掺杂的碳纳米纤维催化剂(Co-N/C)。X射线衍射(XRD)和高分辨率透射电镜(HRTEM)结果证实Co元素高度分散于制备的Co-N/C催化剂中。X射线光电子能谱结果表明N元素主要以吡啶N和石墨N形式存在。该Co-N/C催化剂对ORR反应呈现出较高的电催化活性,其氧还原起始和半波电位分别为0.92 V和0.80 V(相对于标准氢电极),接近于商业化Pt/C催化剂的性能。以制备的Co-N/C催化剂作为阴极,25℃下锌空气燃料电池的开路电位1.54 V、最大功率密度达到了190 m V·cm~(-2)表明该催化剂具有良好的应用前景。     

氮掺杂石墨烯的制备及氧还原电催化性能

采用两步热解法, 用尿素掺杂氧化石墨烯(GO)得到N掺杂的还原氧化石墨烯(N-RGO), 通过控制反应温度, 制备了具有不同电催化活性的N掺杂的还原氧化石墨烯. 透射电子显微镜(TEM)和扫描电子显微镜(SEM)结果显示, 制得的氮掺杂石墨烯(nG)表面褶皱和重叠增加. X射线光电子能谱(XPS)证明, 氮元素以吡啶N、 吡咯N和石墨化的N 3种形式掺杂在石墨烯中, 最高摩尔分数为6.6%. 通过循环伏安(CV)和旋转圆盘电极(RDE)测试了nG的电化学性能, 结果表明, 在酸性电解质中对氧还原(ORR)有较高的催化活性, 起始电位在0.1 V左右, 电催化还原氧气时主要为四电子反应, 且相对商用的Pt/C催化剂有更好的电化学稳定性, 其中第一步热解温度为200℃制得的nG催化性能最好.     

非贵金属钴、氮共掺杂碳纳米管负载纸衍生多孔碳电催化剂的制备及其氧还原性能研究（英文）

燃料电池可以直接将化学能转化为电能,是一种极具前景的能量转换设备.目前,铂碳是燃料电池阴极氧还原反应(ORR)常用催化剂,但是铂储量低、价格昂贵、稳定性差且容易受CO毒化,极大地限制了其在燃料电池商业化中的应用.因此,探索价格低廉、性能优越的非贵金属氧还原催化剂显得尤为重要.大量研究发现,碳基材料具有优越的氧还原性能和良好的电化学稳定性.同时,自然界的生物质种类丰富,是很好的碳基材料来源.本文选取日常生活中最常见的富碳生物质废纸作为碳源,二氰二胺和乙酰丙酮钴分别作为氮源和钴源,经过特定气氛下的梯度升温制得非贵金属钴、氮共掺杂碳纳米管负载多孔碳氧还原催化剂(Co/N/CNT@PC-800).考察了杂原子N掺杂、过渡金属Co掺杂对材料形貌和性能的影响,采用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射(XRD)、拉曼(Raman)光谱、氮气吸附-脱附和X射线光电子能谱(XPS)等表征方法探究了Co/N/CNT@PC-800材料的组成与结构,通过循环伏安法(CV)以及线性扫描伏安法(LSV)等电化学测试探究了其氧还原反应性能.SEM和TEM结果表明,Co/N/CNT@PC-800材料为表面生长着大量碳纳米管的多孔碳结构.这是因为二氰二胺和钴引入后,钴催化二氰二胺转化成碳纳米管.金属纳米粒子被封装在碳层之间和碳纳米管中而得到有效的保护,使之不易被酸腐蚀.同时,Co和N元素可以形成更多的活性位点(Co–Nx),增强材料ORR活性.SEM和氮气吸附-脱附结果显示,掺杂Co后,材料的介孔结构会进一步增加,形成微孔/介孔结构.多孔结构可以增强ORR相关物质(O2,H+,OH.,H2O)的传质速率,提升反应速率,达到增强ORR活性的效果.除此之外,多孔的结构也可以促进活性位点的暴露,进而提升材料的ORR性能.XPS结果显示,Co/N/CNT@PC-800材料中N主要以吡啶氮和石墨氮两种形式存在,而这两种类型的氮有利于促进ORR的进行.Raman光谱结果显示,在引入N和Co元素后,材料的缺陷结构有所增加,因而有利于电催化氧还原反应性能的提升.另外,LSV测试结果表明,在引入Co或者N后,材料催化ORR的起始电位、半波电位、极限电流密度均有小幅改善;同时引入Co和N后,Co/N/CNT@PC-800材料催化ORR的起始电位(0.005 V vs.Ag/AgCl)、半波电位(.0.173 V vs.Ag/AgCl)、极限电流密度(.4.117 mA cm.2)均有较大幅度的改善.通过Koutecky-Levich(K-L)方程计算以及旋转环盘电极测得的氧还原极化曲线结果均表明,Co/N/CNT@PC-800材料的氧还原反应是通过准四电子反应转移路径进行.此外,循环(3000圈CV)稳定性测试结果证明,Co/N/CNT@PC-800材料比商业化的Pt/C具有更好的稳定性.总之,本文采用简单的梯度升温法制备出非贵金属钴、氮共掺杂的碳基氧还原催化剂(Co/N/CNT@PC-800),为探索利用生物质制备电催化剂用于燃料电池提供了一种可供选择的途径.     

热处理碳载Fe-三聚氰胺及Fe-g-C3N4催化剂的氧还原催化性能

分别以三聚氰胺和三聚氰胺的聚合物为配体, 采用浸渍法合成了两种氧还原反应(ORR)催化剂Fe-N/C(1)和Fe-N/C(2). 通过X射线衍射光谱(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)和电化学测试对催化剂的成分、形貌和电催化性能进行了表征. 结果表明, 以三聚氰胺聚合物为配体制备的Fe-N/C具有更高的ORR催化活性. 在高温热处理过程中, 催化剂表面能形成更多的石墨N活性点, 是其ORR性能提高的重要原因.     

钴卟啉修饰电极对分子氧电催化还原的扫描隧道显微镜研究

利用扫描隧道显微镜(STM)研究了高定向热解石墨(HOPG)和玻璃碳电极(GC)表面的性质, 并对修饰钴卟啉后的表面形貌变化进行了探讨。结合修饰钴卟啉前后的循环伏安结果和STM形貌图, 讨论了电极表面的结构对分子氧的电催化还原反应的影响。从微观角度阐述了GC电极对氧的电催化还原活性明显高于HPOG电极的内在因素,为修饰电极的表面性能研究提供了经验。     

Fe-N/C-TsOH催化剂应用碱性介质催化氧还原的电催化活性(英文)

通过溶剂分散热处理方法制备了一种吡咯和对甲苯磺酸(TsOH)共同修饰的碳载非贵金属复合催化剂(Fe-N/C-TsOH),并采用扫描电子显微镜(SEM)、X射线衍射(XRD)和X射线光电子能谱(XPS)对催化剂的形貌和组成成分进行表征.借助循环伏安法(CV)和旋转圆盘技术研究了TsOH对催化剂在0.1 mol·L-1KOH介质中催化氧还原性能的影响.结果表明:TsOH的存在对催化剂催化氧还原反应(ORR)的活性影响很大.以其制备的气体扩散电极在碱性电解质溶液中催化氧还原过程时转移的电子数为3.899,远比不含TsOH修饰的催化剂催化氧还原的电子数(3.098)高.此外,研究发现600°C热处理过的Fe-N/C-TsOH催化剂表现出最佳的氧还原催化性能.相比未经热处理过的Fe-N/C-TsOH催化剂,起峰电位和-1.5 mA·cm-2电流密度对应的电压分别向正方向移动30和170 mV.XPS研究结果表明吡咯氮是催化剂主要活性中心,提供氧还原活性位,而TsOH加入形成的C―Sn―C和―SOn―有利于催化剂催化氧还原活性的提高,从而使该催化剂对氧还原表现出很好的电催化性能和选择性.     

Fe-N/C-TsOH催化剂应用碱性介质催化氧还原的电催化活性

通过溶剂分散热处理方法制备了一种吡咯和对甲苯磺酸(TsOH)共同修饰的碳载非贵金属复合催化剂(Fe-N/C-TsOH),并采用扫描电子显微镜(SEM)、X射线衍射(XRD)和X射线光电子能谱(XPS)对催化剂的形貌和组成成分进行表征. 借助循环伏安法(CV)和旋转圆盘技术研究了TsOH对催化剂在0.1 mol·L^-1 KOH介质中催化氧还原性能的影响. 结果表明：TsOH的存在对催化剂催化氧还原反应(ORR)的活性影响很大. 以其制备的气体扩散电极在碱性电解质溶液中催化氧还原过程时转移的电子数为3.899,远比不含TsOH修饰的催化剂催化氧还原的电子数(3.098)高. 此外,研究发现600 ℃热处理过的Fe-N/C-TsOH催化剂表现出最佳的氧还原催化性能. 相比未经热处理过的Fe-N/C-TsOH催化剂,起峰电位和-1.5 mA·cm^-2电流密度对应的电压分别向正方向移动30 和170 mV. XPS研究结果表明吡咯氮是催化剂主要活性中心,提供氧还原活性位,而TsOH加入形成的C―S_n―C和―SO_n―有利于催化剂催化氧还原活性的提高,从而使该催化剂对氧还原表现出很好的电催化性能和选择性.     

氢钼青铜对铂催化氧还原反应的促进作用

采用循环伏安法在玻碳电极上和硫酸溶液中电沉积制备出铂催化剂(Pt)及铂-氢钼青铜复合催化剂(Pt-HxMoO3), 用旋转圆盘电极研究并比较了它们对硫酸溶液中氧还原反应的催化活性. 研究结果表明, HxMoO3能明显地提高Pt对氧还原反应的电催化活性. 通过对静态电极上氧还原的峰电流与扫描速度的关系以及旋转圆盘电极上氧还原电流与旋转速度的关系的分析发现, HxMoO3提高了铂电极氧还原反应电荷传递步骤的传递系数, 因此加快了氧还原的动力学过程.     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

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.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

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.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

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.     

Synthesis of N-substituted carbazolones from α-iodo enaminones via Pd(0)-catalyzed intramolecular coupling under microwave irradiation

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.     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.     

Synthesis of substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles by intramolecular nitrilimine cycloaddition

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.