热催化合成氨催化剂研究进展

氨不仅是一种重要的化工原料,还是一种潜在的储氢能源载体.传统的Haber-Bosch合成氨工艺通常需要较高的温度和压力来解离强的N≡N键(945 kJ·mol~(-1)).因此,开发在温和条件下使用的高效合成氨催化剂引起了广泛关注.本文综述了负载型钌基催化剂、金属间化合物、金属氮化物和金属氢化物在温和条件下合成氨的研究进展,希望通过相应构效关系的关联,能给读者以启迪,更好地理解合成氨催化剂在氨合成过程中的作用,为新型合成氨催化剂的设计提供一定的理论指导.     

低温等离子体合成氨研究进展

氨是人们生产生活最重要的化工原料之一,但传统的合成氨过程需要在高温高压条件下进行,其年均能耗约占到世界能源总消耗的1%～2%。同时,由于其能量来自于化石燃料燃烧,此过程会不可避免地加重温室气体的排放。因此,寻找合适的绿色替代方案,在温和条件下实现高效、低能耗、低排放合成氨,成为该领域的研究热点。低温等离子体合成氨技术可以改善传统合成氨苛刻的反应条件,使反应在更温和的条件下进行,且具有原料廉价易得、不排放温室气体等优点,采用此技术合成氨越来越受到重视。本文综述了国内外低温等离子体合成氨技术近期取得的研究成果,包括等离子体源的选择、催化剂开发、反应器结构设计、放电参数优化、反应机理探索等。此外,基于该领域的研究现状,对低温等离子体合成氨发展方向进行了展望。     

SmCo_(0.8)Fe_(0.2-x)Ni_xO_3(x=0,0.1,0.2)粉体在低温常压电化学合成氨中的阴极催化性能

用溶胶.凝胶法制备了Ce_(0.8)Sm_(0.2)O_(2-δ)(SDC)、SmCoO_3(SCO)和SmCo_(0.8)Fe_(0.2-x)Ni_xO_3(x=0,0.1,0.2)(SCFN)系列纳米粉体,用XRD、TEM等方法对所制的SCO和SCFN粉体进行了表征;以碳纸为支撑,Ni-SDC粉体为阳极材料,分别以SCO和SCFN系列粉体为阴极、Nafion膜为质子交换膜组成电化学合成氨电池,以湿氢气和湿氮气为原料进行电化学合成氨试验,在低温常压条件下,研究了SCO和SCFN系列粉体在电化学合成氨中的阴极电催化性能.结果表明,在低温常压电化学合成氨中,SCO和SCFN系列粉体均有阴极电催化性能,其中SmCo_(0.8)Fe_(0.1)Ni_(0.1)O_3的阴极电催化性能最好,在353K和0.5V条件下,电化学合成氨的速率达到8.01 ×10~(-9)mol/(s·cm~2).     

电化学合成氨研究进展

氨是化学工业中最高产量的化学品之一,在全球经济中占重要地位.传统的合成氨工艺是Haber-Bosch法,该方法具有工作压力高、能耗高、转化率低以及CO_2排放量大等缺点.氮气电化学还原合成氨可以在常压条件下进行,并可由可再生电力提供动力,被认为是最有希望的Haber-Bosch工艺替代方法之一.本文概述了高温(t500℃)、中温(100℃t500℃)和低温(t100℃)下电化学合成氨的研究工作进展,并对电化学合成氨的发展趋势进行了预测.     

基于氢源和氮源的电化学合成氨研究进展

电化学合成氨是未来绿色合成氨工业的可选途径,可在室温常压下进行,近年来成为热门研究领域。从氢源和氮源角度看电化学合成氨,综述了电化学合成氨的研究发展概况。简要地介绍了电化学氮还原合成氨的机理,回顾了不同氢源、不同氮源、不同催化剂以及不同电解质体系下的电化学合成氨的性能,展望了该领域未来的研究发展。     

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.     

环境条件下电催化氮还原的现状、挑战与展望

氨是一种重要的化肥生产原料和清洁能源载体,在工业上主要通过哈伯法合成,但该工艺反应条件苛刻,需要高温高压并消耗大量的化石能源。因此,开发能耗低、反应温和的合成氨方法,对于缓解能源和环境的双重压力具有重要的现实意义。近年来,在温和条件下通过电催化氮还原反应(NRR)合成氨有望替代哈伯法,但该技术的重点在于设计合理的电催化反应体系并开发高效的催化剂以提升缓慢的NRR动力学过程。为此,本文从电催化合成氨的反应机理出发,介绍了电催化氮还原体系的构建,综述了近年来电催化氮还原催化剂的发展现状,重点总结了提升NRR催化剂活性的设计策略,并对这一新兴领域面临的挑战和潜在的应用前景进行了合理的展望。     

打破合成氨反应中线性标度关系的碗型活性位点设计:来自LaRuSi及其同构电子化物的启示（英文）

合成氨反应是现代工业和农业中提供所需氮源的关键基础化学过程,但在温和条件下实现低能耗、高效率合成氨反应的多相催化剂设计依然是一个挑战.其中,一个普适的限制起源于线性标度关系,即合成氨反应中的一系列含氮物种在催化剂表面的吸附能构成正相关的线性关系,这使得同时提高催化剂活化N2与释放NH3的能力形成矛盾,最终导致最优的催化剂设计需要采用折衷办法,即:最优催化剂对含氮物种的吸附既不能太强也不能太弱,这正是Sabatier原则.因此,线性标度关系导致了催化剂设计中的火山型曲线,其顶点限制了最优催化剂的性能.如果想进一步优化催化剂性能,超越该限制,需要设计能打破合成氨反应中线性标度关系的多相催化剂活性位点.基于电子化物LaRuSi催化合成氨反应机理的理论研究,本文揭示了一种能打破合成氨反应中线性标度关系的碗型活性中心设计.采用第一性原理计算,首先确认了LaRuSi催化剂最稳定的(001)-La表面可高效催化合成氨反应,其最优反应路径为解离机理.通过理论分析发现,(001)-La表面上的碗型活性位点在高效催化中起到了关键作用.该碗型活性位点由四个带正电的表面La离子和一个在催化过程中可变正负电荷的...     

基于BiOCl-Fe2O3@TiO2介孔复合材料的光电化学合成氨性能研究

传统合成氨工艺存在能耗高、污染严重的问题. 因此, 高效、低能耗绿色合成氨工艺的开发迫在眉睫. 光电化学以H₂O和N₂为原料, 可以在太阳光驱动下, 在常温常压条件下实现氨的合成, 因而受到广泛重视. 但总的来说, 效率和产率都达不到实际要求. 新型高效催化剂及工艺的开发是提高合成氨产率及效率的关键. 非贵金属催化剂具备成本低、来源广泛、可操作性强的优势, 有利于光电化学合成氨的产业化. 本实验采用溶胶凝胶结合原位热裂解的方法制备了分散性好、结构均匀的BiOCl-Fe₂O₃@TiO₂复合材料, 对其物相、微观结构、表面状态、光学性能、电学性能等方面进行了系统表征, 并探究了该材料在常温常压下光电化学合成氨的催化活性. 结果表明, 同纯介孔TiO₂相比_, BiOCl-Fe₂O₃@TiO₂的吸收带隙变窄, 可见光吸收能力增强, 光生载流子的利用率增加, 光电合成氨的产率提升了7倍, 且BiOCl-Fe₂O₃@TiO₂显示了优异的化学稳定性. 本研究工作为绿色合成氨催化材料及工艺设计提供了新思路.     

尿素法合成氨基甲酸酯类化合物反应的研究进展

综述了有机胺、尿素和醇一步合成氨基甲酸酯类化合物反应的研究进展,重点讨论了合成反应中所涉及的催化剂、反应条件和反应机理,并对该合成方法的应用前景进行了展望。     

Electrical conductivity of the ammonia-water system

The electrical conductivity (EC) of the ammonia-water system was studied in the concentration range 0.1–10 mol/L ammonia and the temperature range 15–60°C. The maximal EC of aqueous ammonia at a given temperature is proposed as the parameter for generalizing experimental results. The normalized EC was calculated as the ratio of the EC of aqueous ammonia of a given concentration to the maximal EC at a given temperature. Over the ranges of the concentrations and temperatures studied, all normalized ECs fall on one curve. The EC activation energy was analyzed as a function of ammonia concentration and temperature.     

Modification of active carbon and zeolite as ammonia separation materials for a new de-NO<Subscript>x</Subscript> process with ammonia on-site synthesis

Ammonia adsorption and desorption behavior of surface treated active carbon (AC) and ion-exchanged Y zeolite, as ammonia separation and storage materials for a new de-NO_x process with ammonia on-site synthesis, were studied. Surface oxidized AC adsorbed more ammonia than non-treated AC due to ammonium ion formation. These materials were found to increase weak adsorption of ammonia and to be useful for pressure swing adsorption. Transition metal ion exchanged Y-zeolite adsorbed more ammonia (both weak and strong form) than Na Y-zeolite due to ammine complex formation. These materials adsorb and desorb more ammonia than treated AC when used for temperature swing adsorption.     

Ammonia and carbon dioxide permeability through perfluorosulfonic membranes

Transmembrane transport of ammonia and carbon dioxide through perfluorosulfonic membranes in ionic forms of transition metals was studied in a wide temperature interval. The different patterns of the temperature plots of the permeability coefficient of ammonia were found for different ionic forms of the membrane. An increase in the ammonia permeability with an increase in the moisture contents of the membrane also depends on its ionic form. The effects observed are explained by the different structures of water—ammonia complexes formed with metal ions. The mechanism of transmembrane transport of ammonia through perfluorosulfonic membranes in various ionic forms is discussed.     

Atmospheric Pressure Ammonia Synthesis Using Non-thermal Plasma Assisted Catalysis

This paper described a novel and green approach on catalytic ammonia synthesis using non-thermal plasma (NTP). The process studied in this paper involves the synthesis and absorption of ammonia under atmospheric pressure and low temperature. The effects of operational parameters including applied voltage, frequency, gas component and flow rate on ammonia synthesis under NTP conditions are studied in this paper. In addition, different selected catalysts and absorbents were investigated under different conditions of NTP treatment and the ammonia efficiency was reported and analyzed. Ru catalyst with carbon nanotube support, along with Cs promoter and micro porous absorbents including Molecular Sieve 13X and Amberlyst 15 yield the highest ammonia efficiency in this process. Results further indicated that frequency and applied voltage of 10,000 Hz and 6000 V, with N₂:H₂ feed ratio of 3:1 provided the optimized efficiency of ammonia synthesis of 2.3 gNH₃/kWh.     

On the uptake of ammonia by the water/vapor interface

The passage of a single ammonia molecule from an infinitely dilute gas through the water/vapor interface is studied by constrained molecular dynamics simulations. The free energy of the system as a function of the distance between the ammonia and the interface has a minimum in the interfacial region. It is found that the preference of the ammonia for the interface is mainly due the disruption of the solvent structure caused by the ammonia in the bulk region, which results in an increase of the solvent internal energy.     

A new evanescent wave ammonia sensor based on polyaniline composite

A single-mode TE(0)-TM(0) optical planar waveguide ammonia sensor based on polyaniline/polymethyl methacrylate (PANI/PMMA) composite is designed and developed. The sensing properties of the photonic sensor to ammonia at room temperature are studied. A significant change is observed in the guided light output power of the sensor after it is exposed to ammonia gas. The metrological parameters (sensitivity, response time and recovery time) of the sensor are strongly influenced by the interaction length (length of sensing region). Compared with the conventional optical ammonia sensor based on absorption spectroscopy, the integrated optical sensor is more sensitive to ammonia.     

氨燃烧及反应机理研究进展

现今的一系列环境和能源问题迫使人类急需寻找清洁的燃料以替代传统的化石燃料。氨作为一种富氢的无碳燃料,具有能量密度高、成本低、储运安全等优势,近年来受到了越来越多学者的关注,成为了一个研究热点。本文介绍了氨燃料的物化特性及燃烧特性,分析了氨与各种燃料混合燃烧在燃烧速度、火焰结构、污染物形成等方面的表现以及在发动机的应用情况,详述了氨燃烧机理及动力学模型的研究现状,指出有待进一步研究的问题并展望了氨燃烧研究的发展方向。     

Homogeneous precipitation of mullite precursors

The synthesis of mullite powders or gels from an aqueous precursor solution has been studied. The starting solution is made by hydrolyzing TEOS into an aqueous solution of aluminium nitrate. When this solution is sprayed into a solution of ammonia in isopropanol, a nearly monophasic mullite precursor is obtained, whereas if this precipitation is made into an aqueous solution of ammonia, or ammonium carbonate, a diphasic colloidal precipitate is formed. By a slow and homogeneous precipitation in aqueous solution, induced by in-situ generation of ammonia by thermal hydrolysis of urea, a monophasic gel is also obtained. The samples have been studied by DTA, DSC, TGA, XRD and dilatometry.     

An infrared spectroscopy study of the phase transition in solid ammonia

The infrared spectra of solid ammonia at different phases and the existence of a metastable phase have been in controversy for the last fifty years. In order to address this problem, we studied the infrared spectra of solid ammonia in an ultrahigh vacuum chamber at distinct temperatures. Having prepared amorphous ammonia at 10 K, we observed a transition from the amorphous phase to the cubic crystalline phase at 57 K; successive re-cooling from 85 K back to 10 K confirms the presence of crystalline ammonia. No metastable phase has been detected.     

Mo活化NH3的自旋禁阻反应机理

采用密度泛函理论的UB3LYP方法,计算研究了气相中Mo活化NH3的反应机理。为了理解由Mo活化NH3过程中自旋翻转行为,对自旋态分别为七、五、三和单等4个反应势能面进行了计算研究,其结果表明,Mo活化NH3的过程是通过各自旋态势能面交叉产生的典型的自旋禁阻反应,最低能量交叉点(MECPs)附近的系间窜越导致2步H转移和脱H2反应能垒降低。此外运用自然键(NBO)轨道理论分析了反应中较为重要的几个物种的成键特性。通过计算在最低能量交叉点(MECPs)附近不同自旋态之间的自旋-轨道耦合常数,再运用Landau-Zener跃迁几率公式估算了MECPs处系间窜越几率。所确定的最低能量反应路径为:7Mo+NH3→7IM1→7/5MECP1→5TS12→5IM2→5/3MECP2→3TS23→3IM3→3TS34→3IM4→3HMoN+H2。