Advancements in Catalysts for Electrochemical Nitrate Reduction: A Sustainable Approach for Mitigating Nitrate Pollution: A Review

Nitrate pollution is of great importance in both the environmental and health contexts, necessitating the development of efficient mitigation strategies. This review provides a comprehensive analysis of the many catalysts employed in the electrochemical reduction of nitrate to ammonia, and presents a viable environmentally friendly approach to address the issue of nitrate pollution. Hence, the electrochemical transformation of nitrate to ammonia serves the dual purpose of addressing nitrate pollution in water bodies, and is a useful agricultural resource. This review examines a range of catalyst materials such as noble and non-noble metals, metal oxides, carbon-based materials, nitrogen-doped carbon species, metal complexes, and semiconductor photocatalysts. It evaluates catalytic efficiency, selectivity, stability, and overall process optimization. The performance of catalysts is influenced by various factors, including reaction conditions, catalyst structure, loading techniques, and electrode interfaces. Comparative analysis was performed to evaluate the catalytic activity, selectivity, Faradaic efficiency, current density, stability, and durability of the catalysts. This assessment offers significant perspectives on the structural, compositional, and electrochemical characteristics that affect the efficacy of these catalysts, thus informing future investigations and advancements in this domain. In addition to mitigating nitrate pollution, the electrochemical reduction of nitrate to ammonia is in line with sustainable agricultural methods, resource conservation, and the utilization of renewable energy resources. This study explores the factors that affect the catalytic efficiency, provides new opportunities to address nitrate pollution, and promotes the development of sustainable environmental solutions.

A novel fused iron catalyst for ammonia synthesis promoted with rare earth gangue

Rare earth gangue, which mainly consists of mixtures of light rare earths such as lanthana, ceria, neodymium oxide and praseodymium oxide, was used as the promoter of fused iron catalysts for ammonia synthesis. The result showed that the activity of the catalyst promoted with rare earth gangue was comparable with those of commercial iron catalysts with high amount of cobalt. The role of rare earths was owed to their advantages for favoring the deep reduction of the main composite in catalyst, i.e., iron oxide. This fmding indicated that the use of rare earth gangue could decrease the content of cobalt or even completely replace cobalt, which was used to be regarded as unsub- stitutable promoters for high performance ammonia catalyst; therefore, the cost of fused iron catalysts would decrease significantly.

Effect of Activated Carbon as a Support on Metal Dispersion and Activity ofRuthenium Catalyst for Ammonia Synthesis

Ten kinds of activated carbon from different raw materials were used as supports to prepare ruthenium catalysts. N_2 physisorption and CO chemisorption were carried out to investigate the pore size distribution and the ruthenium dispersion of the catalysts. It was found that the Ru dispersion of the catalyst was closely related to not only the texture of carbon support but also the purity of activated carbon. The activities of a series of the carbon-supported barium-promoted Ru catalysts for ammonia synthesis were measured at 425 ℃, 10 0 MPa and 10 000 h -1. The result shows that the same raw material activated carbon, with a high purity, high surface area, large pore volume and reasonable pore size distribution might disperse ruthenium and promoter sufficiently, which activated carbon as support, could be used to manufacture ruthenium catalyst with a high activity for ammonia synthesis. The different raw material activated carbon as the support would greatly influence the catalytic properties of the ruthenium catalyst for ammonia synthesis. For example, with coconut shell carbon(AC1) as the support, the ammonia concentration in the effluent was 13 17% over 4%Ru-BaO/AC1 catalyst, while with the desulfurized coal carbon(AC10) as the support, that in the effluent was only 1 37% over 4%Ru-BaO/AC10 catalyst.

Effect of the graphitic degree of carbon supports on the catalytic performance of ammonia synthesis over Ba-Ru-K/HSGC catalyst

A series of high surface area graphitic carbon materials （HSGCs） were prepared by ball-milling method. Effect of the graphitic degree of HSGCs on the catalytic performance of Ba-Ru-K/HSGC-x （x is the ball-milling time in hour） catalysts was studied using ammonia synthesis as a probe reaction. The graphitic degree and pore structure of HSGC-x supports could be successfully tuned via the variation of ball-milling time. Ru nanoparticles of different Ba-Ru-K/HSGC-x catalysts are homogeneously distributed on the supports with the particle sizes ranging from 1.6 to 2.0 nm. The graphitic degree of the support is closely related to its facile electron transfer capability and so plays an important role in improving the intrinsic catalytic performance of Ba-Ru-K/HSGC-x catalyst.

Role of surface defects of carbon nanotubes on catalytic performance of barium promoted ruthenium catalyst for ammonia synthesis

Carbon nanotubes(CNTs) with abundant surface defects are prepared by a liquid oxidation and thermal annealing method. The defective CNTs-D supported Ba–Ru/CNTs-D catalysts exhibit superior catalytic performance in ammonia synthesis with a TOF be increased up to 0.30 s-1, which is 2.5 times of oxidized CNTs-O supported Ba–Ru/CNTs-O catalysts and 5 times of the Ba–Ru/CNTs. The characterizations by CO chemisorption, transmission electron microscope, Raman, and X-ray photoelectron spectroscopy revealed that the uniformly well dispersed Ru NPs can be stabilized on the defective sites of CNTs-D. The great improvement of the catalytic performance and stability of the Ba–Ru/CNTs-D is contributed to the strong interaction between Ru NPs and surface defect of the CNTs.

Characterization and performance of Cu/ZnO/Al_2O_3 catalysts prepared via decomposition of M(Cu,Zn)-ammonia complexes under sub-atmospheric pressure for methanol synthesis from H_2 and CO_2

Methanol synthesis from hydrogenation of CO2 is investigated over Cu/ZnO/Al2O3 catalysts prepared by decomposition of M（Cu,Zn）-ammonia complexes （DMAC） at various temperatures.The catalysts were characterized in detail,including X-ray diffraction,N2 adsorption-desorption,N2O chemisorption,temperature-programmed reduction and evolved gas analyses.The influences of DMAC temperature,reaction temperature and specific Cu surface area on catalytic performance are investigated.It is considered that the aurichalcite phase in the precursor plays a key role in improving the physiochemical properties and activities of the final catalysts.The catalyst from rich-aurichalcite precursor exhibits large specific Cu surface area and high space time yield of methanol （212 g/（Lcat·h）;T=513 K,p=3MPa,SV=12000 h-1）.

RAMAN SPECTRA OF HYDROGEN ADSPECIES ON AMMONIA SYNTHESIS IRON CATALYST

Raman peaks at 1951 and 2165 cm^(-1) can be confirmed further by H_2/D_2 isotope exchange as H-adspecies on the doubly promoted iron catalyst for ammonia synthesis and are probably ascribed to two terminally adsorbed H-species.

不同测试循环轻型汽油车氨排放特性研究

随着人们环保意识的提高,道路车辆产生的氨(NH3)排放问题越来越受到重视。为了掌握某些特定场景下轻型汽油车NH3排放的实际状况,以2辆国六标准和1辆国五标准轻型汽油车为研究对象,分别对车辆在不同负荷、不同测试循环(包括WLTC循环和RDE循环)、不同排放标准、采用特殊技术路线(清氧功能)下进行了NH3排放测试。结果表明:车辆在WLTC循环低速段的NH3最高瞬时排放速率为RDE循环市区路段的2.7倍。在前1500 s内,空调开启状态,NH3排放因子较空调关闭状态升高了1.47倍,NH3最高瞬时排放速率较空调关闭状态增加了26.7倍;且当空调开启后,NH3的高排放区域分布更加集中。在RDE循环的总行程,国六标准车辆,NOx排放因子较国五标准车辆降低了56.1%,但NH3排放因子较国五标准车辆升高了12.8倍。车辆执行清氧操作后,NOx和NH3的生成规律都发生了明显改变,NOx排放得到了较好的控制,但增加了NH3产生的概率。

CuPc/FeNC双组分催化剂协同催化硝酸盐转化为氨

氨(NH_(3))作为重要的化学品和能源储存介质,需求量与日俱增.本文旨在通过电化学硝酸根还原反应(NO_(3)^(−)RR),将NO_(3)^(−)转化为NH3,不仅解决了NO_(3)^(−)引起的环境污染问题,又可以满足对NH_(3)的迫切需求.然而,NO_(3)^(−)RR涉及多个电子和质子转移过程,其中,NO_(2)^(−)是NO_(3)^(−)活化转化和深度还原合成NH_(3)的重要中间体.酞菁铜(CuPc)能够高效地活化转化NO_(3)^(−)为NO_(2)^(−),但在低过电位时无法有效地将NO2−还原为NH3,难以获得较高的氨法拉第效率(FENH3)和分电流密度.而氮配位的铁单原子催化剂(FeNC)则有较好的NO_(2)^(−)吸附活化特性.因此,利用双组分催化剂之间的协同作用以实现高效NO_(3)^(−)RR的活性和选择性是本文的主要研究思路.本文设计了CuPc/FeNC串联催化剂,利用CuPc和FeNC对NO_(3)^(−)和NO_(2)^(−)的吸附活化能力的差异,实现了高效的协同催化转化.X射线衍射、高角环形暗场扫描透射电镜、X射线光电子能谱及X射线吸收谱结果表明,FeNC催化剂中Fe原子均匀分布于ZIF-8热解后的基底.通过将FeNC和CuPc负载于气体扩散电极,在流动电解池中完成NO_(3)^(−)RR.CuPc/FeNC催化剂在较低电势区间中能够实现接近100%的NH3法拉第效率,同时在−0.57 V vs.RHE时达到273 mA cm–2的NH3分电流密度,并且在整个电势范围内有效地抑制了NO_(2)^(–)聚集.与单组分催化剂CuPc和FeNC对比结果表明,在−0.53 V vs.RHE时,CuPc/FeNC催化剂表现出较高的FE(NH_(3))/FE(NO_(2)^(−))比值,是CuPc催化剂的50倍;同时CuPc/FeNC催化剂上NH3分电流密度是FeNC催化剂的1.5倍.进一步研究了NO_(3)^(–)RR中的串联反应机制,其中FeNC催化剂表现出较高的NO_(2)^(–)RR活性,并且有效抑制了析氢反应.此外,CuPc/FeNC催化剂和FeNC催化剂在NO_(2)^(−)RR中表现出类似的NH3分电流密度,这表明在NO_(3)^(−)RR中,CuPc/FeNC催化剂性能的提高来源于FeNC位点能够进一步还原CuPc位点产生的NO_(2)^(–).理论计算结果表明,FeNC比CuPc表现出更强的NO_(2)^(–)吸附活化能力,说明NO_(2)^(−)在FeNC上更容易进行加氢还原.NO_(3)^(−)RR反应全路径分析结果表明,对于^(*)NO_(3)还原到*NO2过程,CuPc相对于FeNC位点具有明显降低的反应自由能,说明CuPc有利于NO_(2)^(−)的生成;而FeNC位点在后续的^(*)NO_(2)还原合成^(*)NH_(3)过程中具有更低的反应自由能,这与实验结果一致.一系列非原位和原位表征证明了CuPc催化剂在高电位下存在少量金属颗粒析出,与CuPc催化剂在高电位下NH_(3)分电流密度快速增加结果一致.综上,本工作中CuPc和FeNC催化剂之间的协同作用弥补了各自的不足,通过串联反应机制,在低过电位下有效增加了NH_(3)的法拉第效率和电流密度,实现了高效的协同催化转化,为设计和合成高效催化剂提供了新思路.

Ru/Ba-MgO氨合成催化剂模板棉纤维的盐酸处理对催化性能的影响

采用不同浓度的盐酸对棉纤维进行预处理,并以其为生物模板,制备具有纤维条状的仿生Ru/Ba-MgO氨合成催化剂。通过XRD、FTIR、FE-SEM、EDS、BET、H_(2)-TPR和TG等表征技术,分别对棉纤维、Ba-MgO载体和Ru/Ba-MgO催化剂进行分析,探讨了棉纤维中纤维素氢键对Ru/Ba-MgO催化剂的影响机理。结果表明,盐酸溶液中的H+会破坏棉纤维中纤维素分子内氢键,使得纤维素内大量高反应性的羟基暴露出来,增强了棉纤维对Mg^(2+),尤其是对Ba^(2+)的吸附,以其为模板制备的Ba-Mg O载体比表面积明显增加,孔径明显减小;棉纤维经过适宜浓度的盐酸预处理可以有效调控催化剂中活性组分Ru的颗粒尺寸及其分散度;助催化剂Ba的掺入抑制了RuO_(x)的产生,改善了Ru/Ba-MgO催化剂的还原性能,最终使得Ru/Ba-MgO催化剂氨合成活性和热稳定性提高。当棉纤维经过3mol/L盐酸溶液预处理时,以其为模板制备的Ru/Ba-MgO-3催化剂在425℃、10MPa和10000h^(-1)反应条件下具有最佳的活性,其出口氨体积分数为18.37%。

3-羟基丙酸甲酯加氢合成1,3-丙二醇反应中La对Cu/SiO_(2)催化剂的修饰作用

[目的] 3-羟基丙酸酯加氢制备1,3-丙二醇(1,3-PDO)过程中存在β-羟基脱除等副反应,导致1,3-PDO的选择性和收率不高,其中高效催化剂的开发是解决该问题的关键.[方法]采用蒸氨法制备了不同添加量La修饰的20Cu/SiO_(2)催化剂,对其进行催化性能评价,并通过H_(2)程序升温还原(H_(2)-TPR)、X射线衍射(XRD)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)和N_(2)物理吸附-脱附对其进行表征.[结果] 20Cu-0.50La/SiO_(2)的催化性能最佳,它显著地提高了3-羟基丙酸甲酯(3-HMP)加氢制1,3-PDO的催化活性和稳定性,其中3-HMP转化率为91.8%,1,3-PDO的选择性和收率分别为85.2%和78.2%.这是在高液时空速(LHSV=0.10 h^(-1))的条件下取得的最佳结果.[结论] La的加入与Cu产生了强相互作用,增强了催化剂中Cu的分散性,同时提高了Cu^(+)物种表面浓度,使活性Cu的比表面积增加,从而提高了加氢反应的活性和稳定性.

氨分解催化剂研究进展

氢能作为清洁环保的可再生能源受到全世界的关注。但氢极低的体积能量密度及易燃易爆的特点,给氢气的大规模储运带来困难和危险。氨是一种无碳的氢载体,不仅具有较高的体积和质量能量密度,还有较成熟的储存和运输技术。氨的现场制氢可以解决氢气储存和运输问题,所以氨气储氢正受到人们的广泛关注。氨分解最高效的催化剂是Ru基催化剂,但由于其高昂的价格无法实现大规模应用。在非贵金属基催化剂中,Ni基催化剂的活性最高,且其成本相对较低,被认为十分具有应用潜力。然而,Ru基和Ni基催化体系在活性和稳定性等方面仍存在一些挑战。本文综述了氨分解催化剂的最新研究进展,包括Ru基催化剂、非贵金属Fe基和Ni基催化剂及双金属催化剂等,并对目前文献中的反应机理进行了梳理。

层状多孔炭片负载钌催化剂的制备及其催化氨硼烷水解制氢性能研究

本研究以煤沥青为炭材料,氯化钠为模板剂,碳酸钾为活化剂,在氩气气氛下高温煅烧得到载体层状多孔炭片(LPCS),通过浸渍法向其中加入RuCl3金属溶液,将活性组分Ru负载到LPCS载体上合成Ru/LPCS催化剂,并对其催化氨硼烷水解制氢的性能进行了研究。结果表明,Ru/LPCS催化剂中,当煅烧温度为1123 K时,Ru的负载量为2%时,催化剂的反应转化频率(TOF)值最大,此时有光下催化剂的TOF为334.8 min^(-1),是无光照时TOF的1.38倍。在光照下,催化剂的活化能(Ea)从90.60 kJ/mol下降到70.33 kJ/mol。氨硼烷水解制氢速率相对于其浓度的级数为0.75,而相对于催化剂的用量满足于一级动力学关系。

Fe/Co/Ni基催化剂制备及氨分解制氢性能

氢能因具有高效、清洁、可持续等优点,被认为是最具发展潜力的化石燃料替代能源。氨气作为一种储氢材料,具有高储氢密度、易液化等优点,因此氨分解制氢是一种理想的氢气制备方法。开发中低温下高选择性、高活性、廉价的氨分解催化剂具有重要意义。Ru基催化剂是氨分解活性最高的单金属催化剂,但成本较高,Fe、Co、Ni等过渡金属是Ru的合适替代品。与此同时,催化剂载体的选择是制备高效催化剂的关键因素。采用浸渍法制备了以γ-Al_(2)O_(3)、SiO_(2)、MgO、TiO_(2)为载体,Fe、Co、Ni为活性组分的系列氨分解催化剂,在氨催化裂解反应平台开展了反应温度400~700℃、空速比18000 h^(-1)条件下的催化剂活性评估试验,并在此基础上对合成的催化剂进行了XRD、BET、SEM、TEM等表征分析,探究不同活性组合、载体种类、反应温度等因素对氨催化裂解的影响。结果表明,Ni/Al_(2)O_(3)催化剂活性最高,空速为18000 h^(-1)、600℃时的氨分解率达91.67%,650℃时可基本实现氨的完全分解。除SiO_(2)载体外,Ni基催化剂的活性整体高于Fe和Co基催化剂。表征发现在Ni/γ-Al_(2)O_(3)催化剂存在NiO与γ-Al_(2)O_(3)形成的复合氧化物结构,同时γ-Al_(2)O_(3)载体更大的比表面积和孔体积有利于提高氨分解转化率。

电催化硝酸盐合成氨催化剂研究进展

总结了电催化硝酸盐合成氨工艺的反应机理,通过掺杂合适的杂原子、不同金属复合、金属与非金属材料杂化等方式来提高催化剂活性并抑制析氢反应。综述了近几年金属基催化剂、碳基催化剂的合成方法和性能表现,以期为研制高催化活性的环境友好型硝酸盐电化学合成氨催化剂提供参考。

Co_(0.5)Cu_(0.5)/CNR催化剂制备及其氨硼烷水解制氢性能研究

以硝酸钴和硝酸铜制备溶液A,苯二甲酸(PTA)和N,N-二甲基甲酰胺(DMF)制备溶液B,两种溶液通过溶剂热法制备Co/Cu拉瓦希尔骨架系列材料(Co/Cu-MIL前驱体),进一步直接碳化前驱体制备出MOFs衍生物,即双金属碳纳米棒(CoxCu_(1-x)/CNR)催化剂。通过SEM、TEM、XRD、XPS等表征手段探究其形貌和组成。结果表明,Co/Cu-MIL经过高温焙烧后成功得到CoxCu_(1-x)/CNR,当x=0.5、溶剂热温度为120℃、焙烧温度为650℃时得到的催化剂催化活性最优,Co_(0.5)Cu_(0.5)/CNR催化剂催化氨硼烷(AB)水解制氢的TOF值为2718.21 h^(-1),反应的活化能为51.64 kJ/mol,且催化剂的循环稳定性较好,在循环10次后催化活性虽然有所下降,但对AB仍然保持100%的转化率。

碳材料在催化氨硼烷水解释氢中的应用

碳材料因其独特的化学和结构特性,在催化领域包括催化氨硼烷水解释氢中有广泛的应用。以碳材料的结构为侧重点,综述了不同维度形态的碳材料在催化氨硼烷水解释氢中的作用,并对其在催化氨硼烷水解释氢中所存在的问题以及今后的发展进行了总结和展望。

化学链合成氨中载氮体的设计与应用研究进展

氨不仅是氮肥生产的主要原料,也是可再生能源储存与转化过程中的能源载体之一。因此,开发温和条件下的合成氨技术是近年来重要的研究课题。化学链合成氨技术通过载氮体的传递作用,将合成氨反应解耦为固氮与释氨等多步反应,具有操作简便、反应温和、能耗低等优点。载氮体作为化学链合成氨的关键,起到传递能量及氮物种的作用,目前,载氮体固氮效率低,极大地限制了化学链合成氨技术的发展。基于此,本工作对化学链合成氨中载氮体的设计与应用研究进行综述。首先,对载氮体的设计理论进行了归纳与总结;其次,介绍了载氮体的研究现状,重点对如何提高载氮体的产氨速率以及如何提升晶格氮利用率等问题进行了综述;最后,对化学链合成氨技术所面临的机遇与挑战进行了研究,为今后载氮体的设计与开发提供了参考依据。

合成氨用钌催化剂研究进展

传统的Haber-Bosch法合成氨工艺存在能耗大、污染严重等问题,低能耗、清洁绿色合成氨技术是当前研究热点。在清洁低碳背景下电化学还原合成氨是一种有效的固氮转化方法,其技术核心在于如何通过电化学催化剂的研究调控合成氨产率及电流效率。本文综述了不同氮源的合成氨机理及用于电化学合成氨钌基催化剂制备与改性的最新研究进展,对不同钌基催化剂的性能进行比较。综合分析催化剂形貌及尺寸的影响,钌金属、载体及助催化剂间协同作用,为理解电化学还原合成氨中钌的催化作用提供参考。

大型氨合成塔催化剂钝化与卸出实践

介绍大型氨合成塔催化剂钝化流程配置,在卸催化剂时,先对塔内催化剂进行钝化,然后将催化剂由氮气保护氛围转换为空气氛围,将原来因无催化剂钝化而必须无氧卸出的操作转变成为了有氧卸出操作,消除了无氧卸催化剂作业的安全风险,提出了钝化过程的工艺参数控制、操作调整以及异常情况处置等实践经验。