KVPO_(4)F/carbon nanocomposite with highly accessible active sites and robust chemical bonds for advanced potassium-ion batteries

KVPO_(4)F(KVPF)has been extensively investigated as the potential cathode material for potassium-ion batteries(PIBs)owing to its high theoretical capacity,superior operating voltage,and three-dimensional Kt conduction pathway.Nevertheless,the electrochemical behavior of KVPF is limited by the inherent poor electronic conductivity of the phosphate framework and unstable electrode/electrolyte interface.To address the above issues,this work proposes an infiltration-calcination method to confine the in-situ grown KVPF into the mesoporous carbon CMK-3(denoted KVPF@CMK-3).The assembled KVPF@CMK-3 nanocomposite features three-dimensional interconnected carbon channels,which not only offer abundant active sites and significantly accelerate K t/electron transport,but also prevent the growth of KVPF nanoparticle agglomerates,hence stabilizing the structure of the material.Additionally,V–F–C bonds are created at the interface of KVPF and CMK-3,which reduce the loss of F and stabilize the electrode interface.Thus,when tested as a cathode material for PIBs,the KVPF@CMK-3 nanocomposite delivers superior reversible capacitiy(103.2 mAh g^(-1) at 0.2 C),outstanding rate performance(90.1 mAh g^(-1) at 20 C),and steady cycling performance(92.2 mAh g^(-1) at 10 C and with the retention of 88.2%after 500 cycles).Moreover,its potassium storage mechanism is further examined by ex-situ XRD and ex-situ XPS techniques.The above synthetic strategy demonstrates the potential of KVPF@CMK-3 to be applied as the cathode for PIBs.

Density Functional Studies of the Reaction of Ytterbium Monocation with Fluoromethane:C-F Bond Activation and Electron-Transfer Reactivity

The potential energy surface and reaction mechanism corresponding to the reaction of ytterbium monocation with fluoromethane, which represents a prototype of the activation of C-F bond in fluorohydrocarbons by bare lanthanide cations, have been investigated for the first time by using density functional theory. A direct fluorine abstraction mechanism was revealed, and the related thermochemistry data were determined. The electron-transfer reactivity of the reaction was analyzed using the two-state model, and a strongly avoided crossing behavior on the transition state region was shown. The present results support the reaction mechanism inferred from early experimental data and the related thermochemistry data can provide a guide for further experimental researches.

Interface defect induced upgrade of K-storage properties in KFeSO4Fcathode: From lowered Fe-3d orbital energy level to advancedpotassium-ion batteries

KFeSO_(4)F(KFSF)is considered a potential cathode due to the large capacity and low cost.However,the inferior electronic conductivity leads to poor electrochemical performance.Defect engineering can facilitate the electron/ion transfer by tuning electronic structure,thus providing favorable electrochemical performance.Herein,through the regulation of surface defect engineering in reduced graphene oxide(rGO),the Fe–C bonds were formed between KFSF and rGO.The Fe–C bonds formed work in regulating the Fe-3d orbital as well as promoting the migration ability of K ions and increasing the electronic conductivity of KFSF.Thus,the KFSF@rGO delivers a high capacity of 119.6 mAh g^(-1).When matched with a graphite@pitch-derived S-doped carbon anode,the full cell delivers an energy density of 250.5 Wh kg^(-1) and a capacity retention of 81.5%after 400 cycles.This work offers a simple and valid method to develop high-performance cathodes by tuning defect sites.

STUDIES OF QUANTUM CHEMISTRY CALCULATION ON VALENCE-BOND STRUCTURE AND HYDRATION ACTIVTY OF C_(12)A_7

The structure, chemical bonds and hydra-tion activity of C12A were studied by SCC-DV-Xa method of computational quantum chemistry. The calculated results show that Ca-O bond will be first broken off when C12A hydrates, the reactivity of Al(2)O4 tetrahedron is superior to that of Al(1)O4 tet, thedron and the rupture of the Al-O-Al chain composed of two types of AlO4 tetrahedra under the action of water lies in the very weak Al(2)-O(2) bonds. the Al-O bond strength of C12A7 is between C3A and C11A7·CaF2.

Competition between C-C and C-H Activation in Reactions of Neutral Nickel Atom with Cycloalkanes （n = 3-7）

A theoretical investigation of the reaction mechanisms for C-H and C-C bond activation processes in the reaction of Ni with cycloalkanes C,,H2. （n = 3-7） is carried out. For the Ni ＋ CnH2, （n = 3, 4） reactions, the major and minor reaction channels involve C-C and C-H bond activations, respectively, whereas Ni atom prefers the attacking of C-H bond over the C-C bond in CnH2n （n = 5=7）. The results are in good agreement with the experimental study. In all cases, intermediates and transition states along the reaction paths of interest are characterized, It is found that both the C-H and C-C bond activation processes are proposed to proceed in a one-step manner via one transition state. The overall C-H and C-C bond activation processes are exothermic and involve low energy barriers, thus transition metal atom Ni is a good mediator for the activity of cycloalkanes CnH2n （n = 3 -7）.

分子筛限域单位点钴体系催化芳香族化合物C-H键自调节高效氧化

通过芳香族化合物的碳-氢键活化与选择氧化,可以将廉价芳香烃类原料转化为高附加值含氧产品,因此,该反应在基础研究和工业生产中均受到广泛关注.传统的苯乙酮生产工艺存在毒性底物使用、催化剂回收困难、反应条件苛刻以及产物收率低等问题.通过大量的研究探索,科研人员进一步改进其生产工艺,利用环烷酸钴作为均相催化剂,实现了无溶剂条件下分子氧直接选择氧化乙苯生成苯乙酮.相比均相催化,多相催化在催化剂回收和产物分离方面具有优势,更适合工业化生产.因此,开发用于乙苯选择氧化制苯乙酮的高效稳定多相催化体系非常重要,但具有较大挑战.本文采用原位配体保护的水热合成法将钴配合物(钴-二乙烯三胺)封装在Y型分子筛中,并经进一步焙烧去除配体成功制得Co@Y分子筛催化剂.在无溶剂、无添加剂的条件下,单位点Co作为Co@Y分子筛催化剂的活性位点可催化乙苯选择氧化生成苯乙酮.X射线粉末衍射、透射电镜、紫外可见光吸收光谱和固体核磁共振谱等结果表明,该单位点Co(Co^(2+))通过与骨架氧原子作用稳定限域在Y型分子筛中.为明确Co@Y分子筛催化剂中单位点Co在乙苯氧化反应中所起的重要作用,本文还对比了不同后合成方法所制备的Y分子筛(Co/Y,Co-Y)催化剂及工业环烷酸钴催化剂的催化性能.结果表明,在相同反应条件下,Co@Y分子筛催化剂表现出最高的催化性能,也说明在乙苯氧化反应过程中Co@Y分子筛催化剂的单位点Co有别于上述其他催化剂的活性位点.此外,在Co@Y催化剂热过滤实验中未检测出Co物种浸出,表明Co@Y分子筛催化乙苯氧化反应为多相催化过程,并且在多次循环测试后,Co@Y催化剂结构和反应活性均未发生明显变化.这两项实验均表明Co@Y催化剂具有高稳定性.值得注意的是,在乙苯氧化反应过程中观察到自加速现象,为此进行了对比实验(添加苯甲醛或1-苯乙醇的对比实验)和反应动力学分析.结果表明,痕量苯甲醛或1-苯乙醇的加入会显著改变Co@Y催化剂在乙苯氧化反应中的催化行为,痕量苯甲醛的加入可将反应表观活化能从69.7降至53.7 kJ/mol.本文也通过第一性原理密度泛函理论(DFT)计算系统研究了Co@Y分子筛催化剂单位点Co处乙苯选择氧化反应机理及反应过程中自加速现象产生的原因.DFT计算结果结合上述对比实验和反应动力学分析结果表明,加入痕量苯甲醛或者1-苯乙醇后部分乙苯会直接氧化生成苯乙酮,而非通过乙苯→1-苯乙醇→苯乙酮的途径生成苯乙酮.DFT计算结果也阐明反应过程中自加速现象的产生源于单位点Co处活性氧物种(O^(*))的生成.该活性氧物种在乙苯、苯甲醛和1-苯乙醇的氧化途径中均能自发生成,并且该物种类似“引发剂”促使后续更多链式反应的发生,在乙苯氧化反应过程中具有非常重要的作用.综上所述,本文为理解芳香族化合物碳-氢键选择氧化实验现象与催化作用机制提供了有益见解,可为理性设计开发更高效的催化剂提供新思路.

Efficient Photolytic Halogenation and Oxidation of Unactivated Alkyl sp^(3) C—H Bonds with Iodine(III)

A metal-free,green,and sustainable functionalization of unactivated alkyl sp^(3) C—H bonds is reported using iodine(III)as a feasible dehydrogenation agent under visible light or KBr,and alkyl chlorides,bromides,alcohols,and ketones could be constructed by addition of different coupling reagents.Cheap and safe iodobenzene diacetate was used to form a radical to activate the alkyl sp^(3) C—H bond in a highly efficient manner,which can construct different alkylation products by adding corresponding coupling reagents.

Ni–Al Bimetal-Catalyzed Tertiary C(sp^(3))–H Activation for Dual C–H Annulation of Formamides with Alkynes

3d-Metal-catalyzed tertiary C(sp^(3))–H bond activation has been a formidable challenge.Herein,a tertiary C(sp^(3))–H bond is smoothly activated by Ni–Al bimetallic catalysts for dual C–H annulation of formamides with alkynes,delivering a series of δ-lactams with a quaternary carbon up to 98%yield.Various tertiary C(sp^(3))–H bonds such as noncyclic,monocyclic and bridged-ring tertiary C(sp^(3))–H bonds are all compatible with the reaction.

Molecular Dynamics Simulation Study of CIF in Water： Halogen Bonding Interaction in Liquid

Does the halogen bonding interaction co-exist in liquid when it competes with the hydrogen bonding interaction？ The classical molecular dynamics simulations for the solvation properties of CLF molecule in water are performed with the Lennard-Jones plus Coulomb electrostatic potential parameters that are optimized with ab initio interaction energy calculations for the pre-reactive H2O-CLF complex. We find that the halogen bonding interactions occur between O and CL atoms and have the comparable strength and population with respect to the hydrogen bonding interactions of C1...H.

Catalytic transformation of cellulose and its derived carbohydrates into chemicals involving C–C bond cleavage

The catalytic transformation of cellulose, the major component of abundant and renewable lignocellulosic biomass, into building-block chemicals is a key to establishing sustainable chemical processes. Cellulose is a polymer of glucose and a lot research effort has been devoted to the conversion of cellulose to six-carbon platform compounds such as glucose and glucose derivatives through C-O bond activation. There also ex- ist considerable studies on the catalytic cleavage of C-C bonds in biomass for the production of high-value chemicals, in particular polyols and organic acids such as ethylene glycol and lactic acid. This review article highlights recent advances in the development of new catalytic systems and new strategies for the selective cleavage of C-C bonds in cellulose and its derived carbohydrates under inert, reductive and oxidative atmospheres to produce Q -Cs polyols and organic acids. The key factors that influence the catalytic performance will be clarified to provide insights for the design of more efficient catalysts for the transformation of cellulose with precise cleavage of C-C bonds to high-value chemicals. The reaction mechanisms will also be discussed to understand deeply how the selective cleavage of C-C bonds can be achieved in biomass.

C-F键核自旋偶合常数的理论研究

利用密度泛函中B3LYP方法 ,选择 6 31G 基组 ,研究了四组分别为 1 0、2 0、30、40个分子的C F键的核自旋偶合常数 ,由此拟合出 4个计算核自旋偶合常数的公式 ,并用 4种化合物分别进行检验 ,理论计算值较好地与文献值相符合 .

ECR-CVD沉积a-C∶F薄膜

采用电子回旋共振等离子体化学气相沉积 (ECR CVD)技术 ,用苯和三氟甲烷混合气体 ,制备了氟化非晶碳膜 (a C∶F)。用红外吸收光谱 (FTIR)和X射线光电子能谱 (XPS)分析了a C∶F薄膜的结构。FTIR结果表明 ,氟主要以C—F、CF2 的形式成键形成a C∶F薄膜 ;XPS结果进一步证明a C∶F膜中存在C—F、CF2 键 。

氢键活化的苯环上C-F键的亲核取代反应研究

以2,4,5-三氟苯乙酮在氢化钠作用下与碳酸二乙酯反应制得3,4-二氟-6-乙氧基苯甲酰乙酸乙酯(2);2经对甲基苯磺酸催化水解脱羧,合成3,4-二氟-6-乙氧基苯乙酮(3)路线为模型,研究了苯环上C-F键的亲核取代反应。实验结果证明,在形成分子内氢键的活化作用下,苯环上的C-F键能够被烷氧负离子亲核取代。2和3的结构经1HNMR,19FNMR和MS表征。

Ag(I)-Catalyzed Addition of Cyclopropenones and Alcohols via C—C Bond Cleavage

An efficient method for the synthesis of α-phenylcinnamates via silver catalyzed C—C bond activation reaction of cyclopropenone and alcohol was developed.This protocol features a simple reaction system,specific regioselectivity,good functional group compatibility and good yields.It is of great significance for the later modification of natural products.

Mn-corrolazine-based 2D-nanocatalytic material with single Mn atoms for catalytic oxidation of alkane to alcohol

Heterogenization of organic-macrocyclic metal catalysts is one of the simplest and most efficient methods for effective separation of products and cyclic application of a catalyst.By using an environmentally friendly Mn-corrolazine catalyst as the building unit,which can directly oxidize organic substrates under oxygen atmosphere and mild conditions,we theoretically constructed a novel two-dimensional(2D)Mn-corrolazine nanocatalytic material with high catalytic activity.In this material,each Mn atom maintains its electronic configuration in the monomer and can directly activate O2 as the single-atom catalyst(SAC)center to form a radical-like[Mn]-O-O under mild visible-light irradiation conditions.The newly generated[Mn]–O–O can efficiently and selectively oxidize C–H bonds to form alcohol species through H-abstraction and the rebound reaction.Moreover,the catalytic reaction is easily regulated by an external electric field along its intrinsic Mn–O–O reaction axis.The current study provides a theoretical foundation for further experimental studies and practical applications of the Mn-corrolazine-based SAC.

The mechanism of hydrogen abstraction by high valence transition metal oxo compounds

We present here a systematic theoretical study to explore the underlying mechanisms of the H abstraction reaction from methane. Various abstracting agents have been modeled, using oxygen radicals and a set of high valence metal oxo compounds. Our calculations demonstrate that although H abstraction from CH3-H by metal oxoes can be satisfactorily fitted into the Polanyi correlation on the basis of oxygen radicals, the mechanisms behind are significantly different. The frontier orbital analyses show that there are three electrons and three active orbitals (3e, 3o) involved in H abstraction by oxygen radicals; whereas an additional orbital of pi(M-O)* is involved in H abstraction by M = O, resulting in a (4e, 4o) interaction. In terms of valence bond state correlation diagram, we find that H abstraction by a metal oxo may benefit from the contribution of ionic resonance structures, which could compensate the penalty of opening the M-O pbond. We believe that these findings can help to design more effective catalysts for the activation of light alkanes. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B. V. and Science Press. All rights reserved.

单原子合金对烷基C-H键活化调控的理论研究

单原子合金是指活性金属原子分散在Cu、Ag或Au载体上所构成的催化剂,近年来已成为单原子催化研究中的一颗“新星”.单原子合金上孤立活性位点与载体金属的电子结构不同,具有奇异的电子结构,故通常表现出独特的催化行为。目前尚缺乏一种可靠的单原子合金催化特性描述符.本文系统地考察了甲烷、丙烷和乙苯在15种Rh、Ir、Ni、Pd和Pt掺杂Cu(111)、Ag(111)和Au(111)单原子合金上初始C-H键活化.密度泛函计算表明,烷基C-H键的活化能垒与d带中心和H原子吸附相关较差,而与反应能之间相关性较好.理论分析表明,C原子在顶位的吸附与C-H活化过渡态之间存在着轨道相互作用的相似性,不仅涉及到对d,2轨道给予,也涉及day/dy≥轨道的元反馈.据此,C原子吸附能与甲烷、丙烷和乙苯C-H键活化能也具有很强的相关性(R2>0.9).

不对称C―H/C―H交叉脱氢偶联反应研究进展

近年来交叉脱氢偶联(CDC)反应在有机合成化学领域受到广泛关注,该策略在构建碳-碳键的反应中避免了底物的预官能团化,具有很高的原子经济性,符合绿色化学的发展要求。通过不对称CDC反应可以实现立体选择性构建碳-碳键,是目前有机合成中的热点研究领域。本文综述了不对称CDC反应研究进展,并对该领域未来的发展方向进行了展望。

Syntheses,Characterization and Crystal Structures of Dithiocarbamate-based Mononuclear Palladium(Ⅱ) Complexes

By employing the dithiocarbamate salt （K（PPDC）, where PPDC = 4？-pyridyl-1-pipe-razine-4-dithiocarbamate） as the functional ligand and di-palladium complexes [（N^N）2Pd2（NO3ˉ）2]（NO3ˉ）2 （N^N = 2,2＇-bipyridine, bpy; 4,4＇-dimethylbipyridine, dmbpy） as corner, two novel single metal complexes with Pd（II） centers have been obtained. These organic-metal complexes were characterized by NMR, ESI-MS, elemental analysis, Uv-vis spectra and single-crystal X-ray diffraction analysis. Compound 1？（PF6）2 （[（bpy）Pd（PPDC）]·（PF6）2） crystallizes in triclinic, space group P , a = 8.3968（5）, b = 11.5565（7）, c = 18.2234（11）, α = 97.505（1）, β = 91.424（1）, γ = 106.146（1）o, C22H24N6S2P2F12Pd, Mr = 832.93, V = 1680.58（18） ？3, Z = 2, Dc = 1.646 Mg/m3, μ（MoKα） = 0.863 mm-1, F（000） = 828, the final R = 0.0455 and wR = 0.1390 for 6981 observed reflections with I 〉 2σ（I）. Similarly, compound 2？（PF6）2 （[（dmbpy）Pd（PPDC）]·（PF6）2） also crystallizes in triclinic, space group P , a = 13.9467（3）, b = 14.8390（2）, c = 17.0632（3） ？, α = 81.8680（10）, β = 87.051（2）, γ = 83.4590（10）o, C22H25N5S2P2F12Pd, Mr = 819.93, V = 3470.81（11） ？3, Z = 4, Dc = 1.569 Mg/m3, μ（CuKα） = 7.115 mm-1, F（000） = 1632, the final R = 0.0606 and wR = 0.1637 for 12835 observed reflections with I 〉 2σ（I）. Crystallography reveals that each metal center coordinates with two N atoms from bpy and two S atoms from PPDC in the square coordination mode. In the crystal structure of complex 1, a weak Pd……Pd interaction can be observed. Interestingly, it was also found that the mononuclear moieties of complex 2 could be packed into a 3-D porous framework via multiple intermolecular C–F……H hydrogen-boding interactions which extended in the a, b, and c axes with PF6ˉ anions frozen inside.

Rh催化C-C键选择性活化反应的密度泛函理论研究进展

过渡金属催化C—C键活化反应能快速构建复杂有机分子,是当今有机合成领域的研究热点。特别是过渡金属Rh催化C—C键选择性活化反应具有巨大的应用潜力。对近些年铑催化四元环上、直链上的C—C键选择性活化反应的密度泛函理论研究成果进行了总结,尤其对反应机理和C—C键区域选择性活化的来源做出解释。强调计算结论与实验结论的一致性,旨在为判断C—C键活化反应的选择性提供有益参考。