常温常压电催化合成氨的研究进展

氨不仅是重要的化肥化工原料,还是理想的清洁能源载体.目前人工氨合成主要基于Haber-Bosch过程,但该方法存在能耗大、转化率低、大量排放温室气体等问题.相比而言,利用太阳能催化转化N2和H2O等制NH3是一条实现太阳能至化学能转化的绿色制氢储氢一体化路线,受到世界各国科学家的高度关注.但当前该技术路线的氮还原(NR...     

不同氮源用于电催化合成氨的研究进展

氨是化肥生产和化学工业的重要原料,也是良好的无碳储能燃料.相比于工业应用上能耗大、转化率低的哈勃博施(Haber-Bosch)法,电催化合成氨的方法能够在温和条件下绿色高效地合成氨.本文综合评述了以氮气、硝酸根和一氧化氮作为不同氮源时电催化合成氨的反应机理,并结合不同氮源的特点分析了各自的研究进展与优势,分别讨论了氮气难以溶解在水中被吸附和活化、硝酸盐还原元素价态跨度大难以控制中间体和反应路径及一氧化氮体系复杂、水溶液中析氢副反应难以控制等问题,总结了运用不同策略开发高活性、高稳定性催化剂以提高反应效率和选择性、优化反应装置以减小传质影响、选用不同电解质体系改善反应过程等解决思路.最后,对不同氮源电催化合成氨的未来发展趋势和应用前景进行了展望.     

氧官能团MXenes用于电催化合成氨的理论筛选（英文）

电催化合成氨技术以绿色可再生的电能为驱动力,通过在室温条件下改变外加电压来克服速控步能垒,被认为是一种取代哈伯工艺的潜在选择.然而,该技术存在法拉第效率较低、氨气产率不高等问题.因此,设计高效的电合成氨催化剂是目前亟待解决的关键问题.氧官能团的二维过渡金属碳化物和氮化物(MXenes)由于具有独特的几何结构、高导电性和表面易调变等特点,在全水解、碳转化、氧还原或固氮等电催化过程中应用十分广泛.其中,表面氧官能团不饱和覆盖的MXenes材料的电催化合成氨性能较好,这是因为适量的氧空位能够调节活性中心的电荷分布,从而优化关键中间体的结合强度;同时,氧空位的存在为反应提供了足够的活性位点.然而,氧官能团MXenes家族庞大,种类众多,如何从中筛选出合适的合成氨电催化剂尚且缺乏理论指导.本文设计了一系列氧官能团的二维过渡金属碳化物和氮化物(MXenes)作为合成氨电催化剂,并通过密度泛函理论从稳定性、选择性和活性角度出发提出了一套较完善的筛选流程.以纯MXenes表面覆盖17/18氧官能团所需的极限电位来判断氧官能团MXenes的稳定性.通过对催化剂上氮气分子和氢原子的吸附行为进行比较来证明其...     

单原子负载型MXene用于电催化合成氨过程的理论计算

合成氨在地球氮循环中扮演着重要角色.工业上传统的合成氨方法采用高温高压的反应条件,对反应设备要求高,并且导致了巨大的能耗.因此,以电力为驱动的电催化合成过程作为一种新型的合成氨方法引起了广泛关注.选择和设计合适的催化剂以降低所需的过电势是该过程的一个重要研究课题.常用的电催化剂包括金属基、金属氧化物、聚合物及其他复合性催化剂.其中,单原子催化剂因其极高的原子利用率而广受关注,但必须选择合适的基底使其成为兼具高催化活性和高稳定性的催化剂.二维过渡金属碳/氮化物(MXene)作为一种新型二维材料,拥有和石墨烯类似的电导性质,并与金属有良好的相互作用,是一种富有希望的载体.本文采用密度泛函理论研究了氮气在一系列MXene负载的过渡金属单原子催化剂上的吸附和活化,通过吉布斯自由能计算研究了电催化合成氨的反应路径,给出了相应的过电势.同时,通过研究可能的决速步骤的吉布斯自由能,分析了吉布斯自由能和过电势之间的关系.计算结果表明,在所有的MXene负载的过渡金属单原子上,氮气更倾向于一端吸附.根据吉布斯自由能的定义,负值显示这些催化剂具有良好的氮气活化性能,特别是铁基催化剂(–0.75 eV),这就不难理解工业上广泛应用铁基催化剂.而负载不同的过渡金属对电催化合成氨的过电势具有一定影响.通过吉布斯自由能计算发现,该系列金属的过电势在0.68–2.33 eV, Mo/Ti3C2O2需要的外加电压最少.这对实验上催化剂的选择具有一定的指导意义.同时,我们发现电催化合成氨过程有两个可能的决速步骤:氮气加氢生成NNH和NH2生成氨气.通过比较这两个步骤的吉布斯自由能可快速得到催化剂的过电势.因此,我们可以得出结论,该系列MXene负载的过渡金属单原子催化剂能够有效地改变反应路径,免出现传统反应中氮氮键断裂的巨大能垒,从而有效降低了反应的过电势.这为实验上选择合适的催化剂提供了理论依据.并且,这种通过直接比较决速步骤的吉布斯自由能得到过电势的方法对电催化合成氨以及其他类似反应的催化剂筛选和理性设计具有指导意义.     

车用燃料电池现状与电催化

本文综述了近年来车用燃料电池电催化的发展状况,分析了车用燃料电池电催化的发展趋势,重点介绍了大连化学物理研究所在燃料电池电催化方面的研究进展．指出车用燃料电池电催化的发展方向是提高现有铂基催化剂的活性,在保证车用燃料电池在变载等动态工况下的可靠性与寿命的前提下,应降低膜电极的贵金属铂用量,发展低铂／非铂电催化剂．针对车用燃料电池的使用条件,应发展抗燃料气与空气中杂质的电催化方法与抗腐蚀催化剂载体．从长远考虑,重点发展碱性聚合物膜燃料电池,拓展利于活化顺磁性氧的催化方法,有望摆脱车用燃料电池对铂催化剂的依赖．     

磷掺杂碳负载ZnxPyOz常温常压下高效电催化合成氨

合成氨(NH₃)的发展是现代工业进程和人类生存的基石。受氮气(N₂)化学惰性的限制,当前的合成氨工业能源消耗高并且排放大量的二氧化碳。电化学氮气还原反应(NRR),是有望取代高能耗的Haber-Bosch (HB)合成法的一种绿色可持续的合成氨工艺。然而,因氮气以及析氢竞争富反应(HER)导致电催化氮气还原极低的NH₃产率和能量转换效率一直是目前人工固氮领域面临的挑战。在本文中,我们报道了一种具有丰富孔结构的磷掺杂碳(PC)负载Zn₃(PO₄)₂/Zn₂P₂O₇纳米复合材料(h-PC/Zn₃(PO₄)₂/Zn₂P₂O₇),在酸性和中性介质中将N₂高效催化转化为NH₃。其独特的分级多孔结构提高了表面粗糙度并加快了氮气在催...     

合成氨的微型实验

以气体实验微型装置中的双球管为主,设计了合成氨的微型实验,完成了合成氨原料气的制备、净化,氨的合成与分离及剩余尾气的收集等操作,实验前不用单独制备氢气和氮气,简单易做,可以适用于学生独立实验操作,方便了实验教学。     

Extending Ring-Chain Coupling Empirical Law to Lithium-Mediated Electrochemical Ammonia Synthesis

With its efficient nitrogen fixation kinetics, electrochemical lithium-mediated nitrogen reduction reaction (LMNRR) holds promise for replacing Haber–Bosch process and realizing sustainable and green ammonia production. However, the general interface problem in lithium electrochemistry seriously impedes the further enhancement of LMNRR performance. Inspired by the development history of lithium battery electrolytes, here, we extend the ring-chain solvents coupling law to LMNRR system to rationally optimize the interface during the reaction process, achieving nearly a two-fold Faradaic efficiency up to 54.78±1.60 %. Systematic theoretical simulations and experimental analysis jointly decipher that the anion-rich Li⁺ solvation structure derived from ring tetrahydrofuran coupling with chain ether successfully suppresses the excessive passivation of electrolyte decomposition at the reaction interface, thus promoting the mass transfer of active species and enhancing the nitrogen fixation kinetics. This work offers a progressive insight into the electrolyte design of LMNRR system.     

The Synthesis of Aminoalcohols from Epoxides and Ammonia

In connection with another problem we had need for some simple aminoalcohols which were not commercially available. While textbooks make the reaction of ammonia and amines with epoxides appear inviting for the preparation of aminoalcohols, an examination of the literature yielded surprisingly few clearly written examples of the reactions of ammonia with epoxides and many of the good examples had undesirable features. For instance, one of the aminoalcohols desired was threo-3-amino-2-butanol. Lucas et al^2. reported an improved synthesis of this compound in 76% yield by reacting the meso-epoxide with an excess of concentrated aqueous ammonia. The drawbacks to their synthesis were the long recommended reaction time (10 days) and the large volume of water to be removed by distillation (about 2 liters per mole of product obtained). While the yield is reasonably good, all other examples of the reaction that we have found report lower yields (18–70%). Malinovski³ has reviewed the general reaction and treats the side reaction products obtained. Our procedure does not totally avoid side reactions, but the time involved and the good yields make this method more attractive than former procedures for the derivatives that we have prepared.     

Electrochemical Synthesis of Carbazoles by Dehydrogenative Coupling Reaction

A constant current protocol, employing undivided cells, a remarkably low supporting electrolyte concentration, inexpensive electrode materials, and a straightforward precursor synthesis enabling a novel access to N-protected carbazoles by anodic N,C bond formation using directly generated amidyl radicals is reported. Scalability of the reaction is demonstrated and an easy deblocking of the benzoyl protecting group is presented.     

The Feasibility of Electrochemical Ammonia Synthesis in Molten LiCl–KCl Eutectics

Molten LiCl and related eutectic electrolytes are known to permit direct electrochemical reduction of N₂ to N^3? with high efficiency. It had been proposed that this could be coupled with H₂ oxidation in an electrolytic cell to produce NH₃ at ambient pressure. Here, this proposal is tested in a LiCl–KCl–Li₃N cell and is found not to be the case, as the previous assumption of the direct electrochemical oxidation of N^3? to NH₃ is grossly over‐simplified. We find that Li₃N added to the molten electrolyte promotes the spontaneous and simultaneous chemical disproportionation of H₂ (H oxidation state 0) into H^? (H oxidation state ?1) and H⁺ in the form of NH^2?/NH₂^?/NH₃ (H oxidation state +1) in the absence of applied current, resulting in non‐Faradaic release of NH₃. It is further observed that NH^2? and NH₂^? possess their own redox chemistry. However, these spontaneous reactions allow us to propose an alternative, truly catalytic cycle. By adding LiH, rather than Li₃N, N₂ can be reduced to N^3? while stoichiometric amounts of H^? are oxidised to H₂. The H₂ can then react spontaneously with N^3? to form NH₃, regenerating H^? and closing the catalytic cycle. Initial tests show a peak NH₃ synthesis rate of 2.4×10^?8 mol cm^?2 s^?1 at a maximum current efficiency of 4.2 %. Isotopic labelling with ¹⁵N₂ confirms the resulting NH₃ is from catalytic N₂ reduction.     

由肉桂酸生物合成L-苯丙氨酸

本文评述了L一苯丙氨酸的各种合成路线、国内外的研究现状及工业化情况，重点讨论了由肉桂酸和氨生物合成L一苯丙氨酸约路线，提出了在国内进一步工作的建议。     

由肉桂酸生物合成L-苯丙氨酸

本文评述了Ｌ－苯丙氮酸的各种合成路线、国内外的研究现状及工业化情况，重点讨论了由肉桂酸和氨生物合成Ｌ－苯丙氨酸的路线，提出了在国内进一步工作的建议。     

Streamlined Synthesis of Diaminopyridines by Pd-Catalyzed Ammonia Coupling with Deactivated Amino-Chloropyridines

An efficient and cost-effective two-step synthesis of diaminopyridines, fundamental building blocks of biologically active compounds, is reported. The advantages over previously reported routes include cost and wider availability of the bromo-chloropyridine starting materials and the straightforward accessibility to an extended array of diaminopyridine regioisomers. The key enabler of this synthetic strategy is the development of an unprecedented palladium-catalyzed coupling reaction of ammonia with chloropyridines deactivated by the presence of an alkylamino substituent. The coupling reaction was accomplished with very low catalyst loadings under remarkably mild reaction conditions, making the system particularly suitable for both academic and industrial applications. The utility of this methodology is exemplified by the application to the synthesis of highly relevant scaffolds, including the synthetic intermediates of the marketed drugs Ribociclib and Palbociclib.     

单原子催化剂在电化学合成氨中的理论研究进展

传统Haber-Bosch工艺合成氨需要大量的能源消耗和复杂的工厂基础设备。在可再生能源的推动下,将氮气电化学还原为氨被认为是替代Haber-Bosch工艺最有效的方法,这在科学界引起了极大的关注。然而,这个过程受到氨产量和法拉第效率低的影响,因此开发更有效的电催化剂对其实际应用至关重要。在之前报告的催化剂中,单原子催化剂（SACs）在高效利用原子和不饱和配位方面表现出显著优势,这为优化催化剂性能提供了巨大的空间。文章综述了单原子催化剂在电化学合成氨中的理论研究,详细分析了贵金属催化剂、非贵金属催化剂和非金属催化剂这3类单原子催化剂的性能表现,旨在为电化学合成氨技术的发展提供理论参考。