双功能MoNi4电极实现水参与的氮杂环化合物转移氢化与脱氢

氮杂环的催化氢化在有机合成、药物研发、石油化工等领域有着重要应用.尽管发展了一系列均相和非均相催化加氢体系,但由于通常使用易燃易爆的氢气或价格昂贵且毒性较高的试剂(如:水合肼和硼氢化钠)为氢源,给安全生产及生态环境带来了严重的问题.此外,由于动力学同位素效应,氘代药物具有重要应用.氮杂环结构作为生物医药的构筑单元与关键中间体,现有的策略由于没有合适的氘源难以用于氘代氮杂环化合物的合成.因此,急需开发一种基于非贵金属催化剂和安全易得氢(氘)源的氮杂环催化氢(氘)化策略.水相中的电化学氢化可利用水电解原位产生的活性氢替代传统的氢气裂解实现有机氢化产物的合成,已成为一种理想氢化策略,被广泛应用于二氧化碳还原、硝酸根还原和生物质氢解等.本课题组前期研究已经实现了以氘水为氘源的氘代分子的高效电化学合成(Angew.Chem.Int.Ed.,2020,59,18527–18531;Angew.Chem.Int.Ed.,2020,59,21170–21175;CCS Chem.,2021,3,507–515).然而,要开发一种电化学的杂环氢化方法,一方面要克服氮杂环化合物对催化剂的毒化,另一方面要在电极表面产生大量的活性氢.因此,开发具有较好的水离解性能的非贵金属电极材料是实现氮杂芳烃电化学氢化和氘代的关键.基于上述要求,MoNi4(目前用于碱性电催化水分解制氢的活性较高的非贵金属材料)成为理想的电极材料.本文以喹喔啉(1,2,3,4-四氢喹喔啉骨架作为重要的结构单元存在于许多生物活性化合物中)作为模板底物,设计并制备了三维自支撑的MoNi4多孔纳米片为双功能电极,以水和氘水为氢源和氘源,实现了喹喔啉及其他氮杂环分子的氢化与氢化,同时实现了四氢喹喔啉的电化学氧化脱氢.制备了MoNi4纳米片阵列,利用扫描电子显微镜、透射电子显微镜、X射线衍射和X光电子能谱等手段进行表征,评估了其在碱性电解液中用于喹喔啉电化学转移氢化的性能.结果表明,MoNi4电极加速了动力学缓慢的Volmer步骤,在仅50 mV的过电势下以80％的法拉第效率实现了喹喔啉的电化学氢化.电子顺磁共振等证实水电解生成了H*,并与喹喔啉自由基阴离子偶联实现喹喔啉的氢化.同时,该电化学转移氢化方法可很好地应用于一系列喹喔啉衍生物和其他氮杂芳烃化合物.克级合成体现了该电化学转移氢化方法的潜在应用性.原位拉曼实验结果表明,在MoNi4表面形成的NiOOH是实现1,2,3,4-四氢喹喔啉氧化脱氢的重要物种.此外,以D2O代替H2O,可以较好的收率和高达99％的氘化率实现氘代氮杂环的合成.与传统的氮杂环氢化方法相比,本文的电化学转移氢化策略具有绿色、温和、高效的特点,同时拓宽了电化学氢化在合成化学中的应用.     

重水中固氮酶催化还原乙炔产物的^1H NMR研究

用^1HNMR研究了固氮酶在重水中催化还原乙炔的反应产物氘代乙烯.种用群对称性对^1HNMR谱图进行了归属,计算了几种可能的C`2H~2D~2结构以及C~2H~3D结构的NMR谱线频和强度,得出了理论谱.通过理论谱与实验谱的比较,表明固氮酶在重水中催化还原乙炔的产物主要以顺式结构C~2H~2D~2为主,并含有较多的单氘代烯.单氘代乙烯相对乙烯的化学位移往高场移动约4.0Hz,而双氘代乙烯向高场的位移大约是单氘代乙烯的2倍左右。     

用核磁共振技术研究[C4mim][BF4]在重水和氘代氯仿中的聚集行为

运用核磁共振技术,研究了室温离子液体1-丁基-3-甲基咪唑四氟硼酸盐([C4mim[BF4])在重水和氘代氯仿中的聚集行为.实验结果表明,随着混合体系中离子液体摩尔分数的增加,在重水中,离子液体阳离子上各氢原子的化学位移向低场移动,且呈现了先急剧变化,后趋于平缓的变化趋势;在氘代氯仿中,离子液体阳离子上H2的化学位移向高场移动,H4和H5以及与氮原子直接相连的甲基和亚甲基上的氢原子的化学位移都向低场移动,且各氢原子的核磁共振信号发生了变化.根据质量作用定律及1H NMR化学位移随浓度的变化关系计算了[C4mim][BF4]在重水中的临界聚集浓度和聚集数,并在离子液体阴、阳离子缔合以及离子液体与溶剂相互作用的基础上对实验结果进行了讨论.     

用核磁共振技术研究[C4mim][BF4]在重水和氘代氯仿中的聚集行为

运用核磁共振技术, 研究了室温离子液体1-丁基-3-甲基咪唑四氟硼酸盐([C4mim][BF4])在重水和氘代氯仿中的聚集行为. 实验结果表明, 随着混合体系中离子液体摩尔分数的增加, 在重水中, 离子液体阳离子上各氢原子的化学位移向低场移动, 且呈现了先急剧变化, 后趋于平缓的变化趋势; 在氘代氯仿中, 离子液体阳离子上H2的化学位移向高场移动, H4和H5以及与氮原子直接相连的甲基和亚甲基上的氢原子的化学位移都向低场移动, 且各氢原子的核磁共振信号发生了变化. 根据质量作用定律及1H NMR化学位移随浓度的变化关系计算了[C4mim][BF4]在重水中的临界聚集浓度和聚集数, 并在离子液体阴、阳离子缔合以及离子液体与溶剂相互作用的基础上对实验结果进行了讨论.     

用电化学测氢法研究稀土对变形铝及Al-Zn-Mg合金氢含量的影响

铝及铝合金有强烈的吸氢特性,这一直是铝合金冶金中的一大难题。近年来不少冶金工作者证实,在熔融状态下的工业纯铝、Al-Si、Al-Cu合金中添加稀土对氢含量有影响。但至今未见有关室温下稀土对变形铝合金中氢含量影响的报道。本文采用电化学测氢法,准确测定了室温下金属中氢含量和氢行为的特点,研究了室温下工业纯铝和     

一种新的测定微粒的电化学技术

设计了一种由2个石墨电极短路相连组成工作电极的新的电化学池装置.操作时首先通过外力按压使极少量固体微粒粘附在其中一个石墨电极表面上,然后在溶液存在下将微粒夹紧并固定在2个石墨电极表面之间进行电化学测定.电化学转化过程中生成的可溶性物质被封闭在2个石墨电极表面之间而得到测定.用该技术对钯沉积在氧化铝上而组成的催化剂的电化学行为以及黄铁矿的电化学行为进行了研究.结果表明,其兼具可电解粘合剂碳糊电极和固体微粒伏安法(voltammetry of microparticles)技术的优点而避免了各自的缺点:即不使用粘合剂,从而消除了粘合剂中杂质产生的氧化或还原电流的影响;可测定电化学转化过程中生成的可溶性物质;分辨率好、易于操作.     

测氢扩散系数的电化学交流法研究

应用电化学交流法测定氢在纯铁中的扩散系数 .证明对电解氢在试样中的非稳态扩散 ,按菲克第二定律所设定的边界条件符合实际扩散行为 ,并论证了该方法的可行性     

磷酸二氘钾晶体中氘含量常温气相色谱测定

磷酸二氘钾(KD_2PO_4)是一种优良的电光调制晶体。这种晶体是在重水中培养出来的,晶体中含氘量与晶体性能密切相关。因此,测定晶体中的含氘量对判断和提高晶体的性能、摸索晶体培养的最佳工艺条件,以及研究晶体的结构和性能的关系都有着重要的意义。但是,目前利用气相色谱法测定晶体材料中含氘量的有关报道甚少。我们利用重水和磷酸二氘钾晶体的化学特性建立了本     

无机质子导体的研究进展

无机质子导体是一类重要的功能材料,具有许多潜在的电化学应用,包括燃料电池、氢传感器、氢的电解制备和分离提纯、氢泵、水蒸气泵、氮氧化物消除、有机物的催化氢化和脱氢,核聚变反应堆废气中的氢同位素气体的回收利用,以及常压合成氨等.本文综述了无机质子导体的研究进展,尤其是近年来的最新研究进展,主要包括典型的无机质子导体,无机质...     

PdH_2和YH_2分子热力学稳定性的理论研究

由于纯钯的渗氢速率较低,关于钯合金渗氢材料[1-3]的研究引起广泛关注,如钯钇合金.已有研究报道[3,4]PdH2和YH2分子可能的电子结构、势能函数与光谱性质,并提供了可靠的研究方法.     

Coulometric titrations of bases in propylene carbonate using hydrogenpalladium and deuteriumpalladium generator electrodes

The application of hydrogen and deuterium ions obtained by anodic oxidation of hydrogen and deuterium dissolved in palladium, for the coulometric determination of bases (both individual and in mixtures) in propylene carbonate, is described. The current-potential curves at a palladium anode for supporting electrolyte indicator, titrated bases, hydrogen dissolved in palladium and deuterium dissolved in palladium showed that hydrogen and deuterium are oxidized at much less positive potentials than the oxidation potentials of other substances present in the solution. The generated H⁺ and D⁺ ions were used for the titration of bases (pyridine, quinoline, triethylamine, n-butylaniline, 2,2′-dipiridyl and aminopyrine) with visual and potentiometric detection. The oxidation of hydrogen and deuterium proceeded with 100% current efficiency. Two-component mixtures of bases (aliphatic + aromatic amine) were titrated successfully by using two indicators, Eosin and Crystal Violet. The relative error of the determination with respect to each individual base determination, was less than 2.5% for quantities of bases ranging from 1 to 3 mg.     

The role of tunnelling in light atom diffusion in metals: A comparison of resonant and non-resonant theoretical approaches

We are concerned here with the question of the applicability of resonant (energy splitting) and nonresonant (transmission coefficient) tunnelling theories to the problem of symmetric double well transfer. We apply a recently developed method of the former type, the Generalized Method of Beats (GMOB), to the calculation of interstitial hydrogen and deuterium diffusion in the metals niobium, vanadium and palladium and compare our results to both experiment and earlier calculations using a nonresonant theory. Both theories can be parametrised so as to fit approximately the experimental temperature dependence of the diffusion coefficients, but the parameters differ markedly. For fixed barrier height, the mean jump distance needed to fit a given rate using the resonant theory is jump distance in the resonant approach is 2.0 Å, which is close to an experimental value; in a nonresonant approach by Weiner a very much smaller distance, 1.166 Å, was required. It is noted, however, that the appropriateness of the underlying model assumptions to the interpretation of hydrogen/deuterium migration dynamics in metal requires further investigation.     

The application of deuterium-palladium electrodes in the coulometric-potentiometric determination of bases in ketone media

The application of deuterium-palladium electrodes as generator, indicator and reference electrodes for the determination of organic bases in acetone and methyl ethyl ketone has been investigated. Deuterium dissolved in palladium is oxidized at a potential that is close to the oxidation potential of hydrogen in palladium and more negative than the oxidation potentials of the bases titrated, indicator, and the solvents used. The anodic oxidation of deuterium dissolved in palladium proceeds with 100% current efficiency in the solvents investigated. The relative errors for the determination of 5 x 10(-4)M solutions of bases are less than 1%.     

电解制备二氧化锰强酸性电解液中气体扩散电极的稳定性与失效行为

采用气体扩散电极(GDE)代替传统析氢阴极电解制备二氧化锰(EMD),重点研究了气体扩散电极在强酸性MnSO4-H2SO4电解液中的稳定性、寿命及失效行为.结果表明:气体扩散电极在MnSO4-H2SO4电解液中重现性好、具有一定的稳定性,寿命可达400 h;平行实验表明,阳极沉积一定厚度的EMD是槽电压第一次升高的主要原因;电流密度为100 A m-2时,气体扩散电极失效前阴极过程的速度由氧的离子化反应和氧的扩散混合控制,失效后阴极过程由氧去极化和氢去极化共同组成,主要发生析氢反应;催化层聚四氟乙烯(PTFE)网络结构的破坏和镍网层的溶解是电极失效的原因之一;Pt的团聚降低了电极的电催化活性,是电极失效的主要原因;阴极失效是槽电压再次升高的主要原因.     

Hydrogen generation by plasma-assisted electrochemical pumping

We demonstrated that the reaction between water vapor and sulfur dioxide (SO₂) can be catalyzed plasma-chemically and hydrogen species, products of the reaction, can be pumped out electrochemically as hydrogen molecules (H₂) with the help of palladium (Pd) bipolar electrode. The plasma-energizing effect on the reaction between water vapor and SO₂ is solely played by non-thermal electrons generated by atmospheric pressure electrical microdischarge. Of the reaction products the hydrogen atoms are dissolved in the Pd membrane, transferred to the interface contacting a proton conducting medium through diffusion and eventually anodized at the interface. This type of electrolysis does not require platinum catalyst and opens a possibility of increasing the energy efficiency for hydrogen generation.     

Isotope heat effect in reactions involving hydrogen evolution on palladium catalyst particles

The heat effect in the reduction of copper(II) by formaldehyde on palladium catalyst particles accompanied by hydrogen evolution depends on the presence of deuterium in the system. In the case of 80% substitution of hydrogen in the system by deuterium the heat effect increases 1·5 times. This fact can not be attributed only to the difference in the energies of the bonds of hydrogen and deuterium in compounds participating in the reaction.     

Coulometric generation of H(+) and D(+) ions in aqueous media by anodic oxidation of hydrogen and deuterium dissolved in palladium

Coulometric generation of H(+) and D(+) ions in aqueous media by the oxidation of hydrogen and deuterium dissolved in palladium, is described. Hydrogen and deuterium dissolved in palladium were found to be oxidized at more negative potentials than the oxidation potentials of water and other components present. The H(+) and D(+) ions generated were used for the titration of tris(hydroxymethyl) aminomethane, piperidine, triethylamine and sodium tetraborate, the end-point being determined potentiometrically with a glass electrode and an SCE. In titrations of 0.001-0.1M solutions of the bases, the current efficiency was 100%.     

Preparation and characterization of 4-dimethylaminopyridine-stabilized palladium nanoparticles

4-Dimethylaminopyridine (DMAP)-stabilized palladium nanoparticles with a mean diameter of 3.4 +/- 0.5 nm are prepared from the aqueous phase reduction of Na2PdCl4 using NaBH4 in the presence of DMAP. TEM and UV-vis spectroscopy characterization of the nanoparticle dispersion shows no obvious change in the nanoparticles several months after preparation. 1H NMR spectroscopy of the nanoparticles shows that the nanoparticle dispersion also contains a boron/DMAP complex and two palladium/DMAP complexes. One of the palladium complexes crystallizes out of the dispersion and is identified as Pd(DMAP)4(OH)2 by X-ray crystallography. Following extensive analysis, it is believed that the palladium/DMAP complexes are formed following the oxidation of the palladium nanoparticles. The prepared nanoparticle dispersion promotes selective hydrogen/deuterium (H/D) exchange on the carbon atoms alpha to the endocyclic nitrogen atom on the DMAP-stabilizing ligands through reaction with D2O. This activity is attributed to the presence of the nanoparticles rather than to the presence of the oxidized palladium/DMAP complexes.     

Hydrogen-deuterium exchange in bulk LiBH4

Because of its apparent simplicity, diffusion of hydrogen in solids can be regarded as a general model system for diffusion. However, only rudimentary knowledge exists for the dynamics of hydrogen in complex hydrides. Insight into the specific diffusion process is given by hydrogen-deuterium exchange experiments. Thermogravimetry and Raman spectroscopy are used to measure the hydrogen-deuterium exchange during the decomposition of LiBH4. At a temperature of 523 K the self-diffusion constant of deuterium in LiBH4 is estimated to be D approximately 7 x 10(-14) m(2) s(-1). A careful analysis of the Raman spectra shows that hydrogen is statistically exchanged by deuterium in LiBH4; i.e., the diffusing species is assumed to be the single hydrogen atom.