Heterogeneous photocatalytic synthesis of ammonia from water and nitrogen

Photocatalytic synthesis of ammonia from water and nitrogen was performed. Binary wafered catalysts prepared with semiconductor powder (TiO₂, SrTiO₃, CdS or GaP) and platinum black, where the copolymer of ethylene and vinylalcohol was used as a binder, were found to be more effective to yield ammonia than the semiconductor powders alone.     

Highly efficient photocatalytic reduction of nitrogen into ammonia by single Ru atom catalyst supported by BeO monolayer

Ammonia（NH₃） is one of the most important building blocks of the chemical industry and a promising sustainable energy carrier. Conventional production of NH₃ via the Haber-Bosch process requires high temperature and high pressure, which is energy demanding and suffers safety issues. Photocatalytic nitrogen reduction reaction（NRR） is a green and sustainable route for NH₃ production, and has been expected to be an alternative for NH₃ production under mil...     

Electrochemical reduction of nitrogen to ammonia: Progress,challenges and future outlook

Ammonia is an important chemical used in the production of fertilizers. The electrochemical nitrogen reduction reaction (NRR) to synthesize ammonia has emerged to be a potential alternative approach. Here, we provide a short opinion of the current progress and challenges of nitrogen reduction reaction from the recent literature. Different types of electrocatalysts with their performances and design principles are briefly outlined. However, most of the electrocatalysts showed unsatisfactory catalytic performance for NRR because of various factors, such as the competing side reactions and the large thermodynamic energy barrier. Hence, the concept of conducting NRR should be re-evaluated. We provide our opinion on the future possible outlook on how to improve the NRR performance. Alternative external energy input should be coupled with the electrochemical reduction of nitrogen to help with the activation of nitrogen to ammonia. Some possible energy input could be the use of cold plasma and surface plasmon resonance.     

Quantum chemical analysis of the process of reduction of nitrogen oxide by ammonia

We have carried out a quantum chemical analysis of the electronic structure of the nitroprusside ion [Fe(CN)₅NO]^2– and also the transition complex [Fe(CN)₅NO· NH₃]^2– arising in the course of the reaction of reduction of coordinated nitrogen oxide with a nucleophile (ammonia). We consider the characteristics of the redistribution of electron density in the nitroprusside accompanying the nucleophilic attack. We discuss the role of the central iron ion and the CN-ligands during nucleophilic reduction.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 4, pp. 432–439, July–August, 1989.     

In situ localization of BiVO4 onto two-dimensional MXene promoting photoelectrochemical nitrogen reduction to ammonia

The existing industrial ammonia synthesis usually adopts the Haber-Bosch process, which requires harsh conditions of high temperature and high pressure, and consumes high energy. Under this circumstance, photoelectrochemical (PEC) catalysis is regarded as a promising method for N₂ reduction reaction (NRR), but bears problems of low efficiency and yield. Thus, exploring active catalysts remains highly desirable. In this work, BiVO₄@MXene hybrids have been facilely synthesized by a hydrothermal route. The heterojunctions by the in situ growth of BiVO₄ onto two-dimensional (2D) MXene greatly increase the NRR efficiency: under photoelectric conditions, the optimized NH₃ yield is 27.25 µg h ^{? 1} cm^?2, and the Faraday efficiency achieves 17.54% at ?0.8 V relative to the reversible hydrogen electrode (RHE), which are higher than most state-of-the-art NRR (photo) electrocatalysts. The mechanism speculation shows the enhanced light absorption range and the heterojunction formation largely promote the separation and the transfer efficiency of photogenerated carriers, thereby improving the PEC catalytic ability. Therefore, this work provides a hybrid route to combine the advantages of photo and electric catalysis for effective artificial nitrogen fixation.     

Mechanisms of electrochemical nitrogen gas reduction to ammonia under ambient conditions: a focused review

Journal of Solid State Electrochemistry - Electrocatalytic nitrogen reduction reaction (E-NRR) to ammonia is becoming a major topic of interest in the field of large-scale energy storage from...     

Selective catalytic oxidation of ammonia to nitrogen

The activity of catalysts of different nature in ammonia partial oxidation has been studied. Vanadium-titanium, copper-titanium catalysts and copper-substituted zeolites are the most active in the reaction. These catalysts are promising if used as honeycomb monoliths.     

Uncovering the synergistic photocatalytic behavior of bimetallic molecular catalysts

Bimetallic catalysts usually exhibit better performance than monometallic catalysts due to synergistic effect. However, there is a lack of exploring the synergistic effect on catalytic performance caused by the introduction of inactive metal ion. In this work, we design a molecular model system that can precisely regulate the metal site number and catalytic property. When these molecular metal compounds are used as homogeneous catalysts for photocatalytic CO₂ reduction, the dinuclear heterometallic CuNi-L² shows the highest CO₂-to-CO conversion, which is 2.1 and 3.0 times higher than that of dinuclear homometallic Ni₂-L² and mononuclear Ni-L¹. Density functional theory calculations demonstrate that, in CuNi-L², the introduction of inactive Cu^II is easier to promote the photo-generated electrons transferring to the coupled active Ni^II site to achieve the highest activity. In addition, this work also provides insights to design and construct more efficient bimetallic catalysts in future.     

粉煤灰基NaA/NaX双晶型沸石分子筛构建及其协同吸附氨氮性能

以粉煤灰为原料,采用“联合改性三步合成法”——超声辅助碱熔微波晶化法联合废旧玻璃/13X晶种/NaH₂PO₄浸渍三阶段改性合成沸石分子筛(GFS);作为对比,采用传统碱熔水热法合成沸石分子筛(FS);采用“三步合成法”——超声辅助碱熔微波晶化法合成沸石分子筛(WFS)。并采用X射线衍射(XRD)、扫描电镜(SEM)、傅里叶变换红外光谱(FTIR)、能量色散光谱(EDS)、N₂吸附-脱附等方法对材料的组成、形貌和结构进行了表征。结果表明,WFS和GFS较FS具有更高的比表面积和发达的介孔、微孔,且沸石分子筛晶型从NaA单晶型转为NaA/NaX双晶型。氨氮吸附实验结果表明,GFS (56.01 mg·g^-1)较WFS (49.17 mg·g^-1)和FS (39.75 mg·g^-1)吸附性能更优,吸附动力学和热力学数据符合二级动力学模型和Langmuir模型,氨氮吸附过程为以离子交换为主的吸附,且为自发放热过程,低温促进氨氮吸附。     

Boosting the stability of protein emulsions by the synergistic use of proteins and clays

The preparation and the properties of high-pressure emulsions based on five different proteins are reported. As proteins, we used the well-studied bovine serum albumin (BSA), a biotechnical produced hydrophobin called H Star Protein B? (HPB), a protein isolate from soybeans, a wheat protein isolate (Plantasol W), and a commercially available yeast extract. All emulsions were characterized by visual appearance, light microscopy, conductivity, and rheological measurements. Beside the emulsion based on soy protein isolate, all other samples showed phase separation under the used conditions (0.5 wt.% protein; 50 wt.% oil). Plantasol W and yeast extract formed the most unstable emulsions showing typical instability processes like coalescence. Gel-like properties have been observed for emulsions based on BSA, soy protein isolate, and HPB. The same proteins were also used to stabilize emulsions after their adsorption on clay particles. Interestingly, all emulsions had gel-like properties with a yield stress value and were stable to the used conditions. It is concluded that the gel character results from the stickiness of the protein covered oil droplets and is independent from the used protein type. The proteins which are adsorbed on the oil droplets can still interact and bind to proteins on other oil droplets.     

Selective photocatalytic reduction of nitrate to nitrogen molecules in an aqueous suspension of metal-loaded titanium(IV) oxide particles

Nitrate was photocatalytically reduced to nitrogen molecules with a high selectivity in a basic aqueous suspension of palladium and copper-loaded titanium(IV) oxide powders in the presence of oxalate anion as a hole scavenger.     

Enhancing ammonia production rates from electrochemical nitrogen reduction by engineering three-phase boundary with phosphorus-activated Cu catalysts

Electrochemical N₂ reduction reaction(eNRR) over Cu-based catalysts suffers from an intrinsically low activity of Cu for activation of stable N₂ molecules and the limited supply of N₂ to the catalyst due to its low solubility in aqueous electrolytes.Herein,we propose phosphorus-activated Cu electrocatalysts to generate electron-deficient Cu sites on the catalyst surface to promote the adsorption of N₂ molecules.The eNRR system is further modified using...     

Controlled reduction of the deleterious effects of photocatalytic activity of ZnO nanoparticles by PVA capping

Nanoparticles of uncapped and PVA (poly vinyl alcohol) capped zinc oxide were synthesized by precipitation method. The synthesized ZnO nanoparticles were characterized by fourier transform infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and thermogravimetric-differential thermal analysis. The photocatalytic activity of bare and modified ZnO nanoparticles was studied by monitoring the degradation of Rhodamine B. The results show that PVA capped ZnO nanoparticles has reduced photocatalytic activity than the bare ZnO nanoparticles. The reduction in the chemical oxygen demand and total organic carbon results also revealed the reduced photocatalytic activity of PVA capped ZnO. The UV-shielding property was evaluated by measuring the transmittance which shows that both bare and PVA capped ZnO nanoparticles possess good UV-shielding ability.     

New technology for selective catalytic oxidation of ammonia to nitrogen

The selective catalytic oxidation (SCO) of ammonia to N₂ was studied by using a series of noble metal-V₂O₅-WO₃ catalysts supported on titania-silica (TS) prepared by coprecipitation method. In the V₂O₅-WO₃ catalyst system, the use of TS as a support was very effective to enhance catalytic activity compared with TiO₂ or SiO₂ alone. The addition of a slight amount of Pd and Ir to V₂O₅-WO₃/TS catalyst caused also remarkable enhancement of the catalytic activity without decreasing the selectivity to N₂. The present catalysts provide remarkably high catalytic performance for SCO of ammonia to N₂ under the practical reaction conditions for an industrial application.     

Activation of MoS2 monolayer electrocatalysts via reduction and phase control in molten sodium for selective hydrogenation of nitrogen to ammonia

Electrochemical nitrogen fixation under ambient conditions is promising for sustainable ammonia production but is hampered by high reaction barrier and strong competition from hydrogen evolution, leading to low specificity and faradaic efficiency with existing catalysts. Here we describe the activation of MoS₂ in molten sodium that leads to simultaneous formation of a sulfur vacancy-rich heterostructured 1T/2H-MoS_x monolayer via reduction and phase transformation. The resultant catalyst exhibits intrinsic activities for electrocatalytic N₂-to-NH₃ conversion, delivering a faradaic efficiency of 20.5% and an average NH₃ rate of 93.2 μg h⁻¹ mg_cat⁻¹. The interfacial heterojunctions with sulfur vacancies function synergistically to increase electron localization for locking up nitrogen and suppressing proton recombination. The 1T phase facilitates H–OH dissociation, with S serving as H-shuttling sites and to stabilize . The subsequently couple with nearby N₂ and NH_x intermediates bound at Mo sites, thus greatly promoting the activity of the catalyst. First-principles calculations revealed that the heterojunction with sulfur vacancies effectively lowered the energy barrier in the potential-determining step for nitrogen reduction, and, in combination with operando spectroscopic analysis, validated the associative electrochemical nitrogen reduction pathway. This work provides new insights on manipulating chalcogenide vacancies and phase junctions for preparing monolayered MoS₂ with unique catalytic properties.

We describe the activation of MoS₂ in molten sodium that leads to the simultaneous formation of a sulfur vacancy-rich heterostructured 1T/2H-MoS_x monolayer electrocatalyst via reduction and phase transformation.     

氰基修饰石墨相氮化碳构建高效的活性位点用于光催化还原CO2

作为影响光催化反应的关键因素,光催化剂的活性位点数量直接决定了光催化活性.传统石墨相氮化碳(g-C3N4)由于活性位点不足而表现出较弱的光催化活性.为了增加g-C3N4的活性位点数量,研究人员采取了各种策略,包括杂原子掺杂、表面改性和空位工程.其中,表面改性是增加催化剂活性位点的有效策略之一.氰基具有很强的吸电子能力,可在光催化反应中作为活性位点.然而,关于氰基作为CO2光还原活性位点的研究并不多,特别是对于氰基修饰增强g-C3N4活性的机理尚不清楚.构建多孔结构是暴露催化剂活性位点的有效措施之一.多孔结构可以有效改善纳米片的团聚,促进活性位点暴露,增大反应物与活性位点间的接触机会;并且相互连接的多孔网络可形成独特的传输通道,进一步促进载流子迁移.本文通过分子自组装和碱辅助策略合成了氰基改性的多孔g-C3N4纳米片(MCN-0.5).氰基由于具有良好的吸电子特性,促进了局部载流子分离,并充当了光催化反应的活性位点.受益于活性位点的影响,MCN-0.5表现出显著增强的光催化CO2还原活性.在不添加牺牲剂和助催化剂的条件下,MCN-0.5样品上CO和CH4产率达到13.7和0.6μmol·h–1·g–1,分别是传统煅烧法制备的g-C3N4(TCN)产生CO和CH4产率的2.5和2倍.通过盐酸处理MCN-0.5除去氰基,并没有破坏样品的形貌结构,但催化剂的光催化活性显著降低,证实了氰基活性位点的作用.光还原Pt纳米颗粒的实验结果表明,与对照样品相比,氰基修饰的样品上还原的Pt纳米颗粒更多,进一步证实了引入氰基为光还原反应提供了更多活性位点.CO2等温吸附测试结果表明,MCN-0.5对CO2的吸附能力不如对照样品,间接证明氰基能成为活性位点是由于其良好的吸电子能力促进了局部载流子分离.瞬态荧光光谱、光电化学表征结果表明,氰基修饰增强了载流子迁移和分离能力.根据理论计算和原位红外光谱提出了氰基修饰增强g-C3N4光催化还原CO2活性的作用机理.以三聚氰胺为前驱体接枝氰基的g-C3N4也表现出比体相g-C3N4明显增强的光催化还原CO2活性,这证明了氰基改性增强g-C3N4活性策略的通用性.本文通过在光催化剂材料中设计活性位点为太阳能高效转化提供了一个有效途径.     

氰基修饰石墨相氮化碳构建高效的活性位点用于光催化还原CO2

作为影响光催化反应的关键因素,光催化剂的活性位点数量直接决定了光催化活性.传统石墨相氮化碳(g-C3N4)由于活性位点不足而表现出较弱的光催化活性.为了增加g-C3N4的活性位点数量,研究人员采取了各种策略,包括杂原子掺杂、表面改性和空位工程.其中,表面改性是增加催化剂活性位点的有效策略之一.氰基具有很强的吸电子能力,可在光催化反应中作为活性位点.然而,关于氰基作为CO2光还原活性位点的研究并不多,特别是对于氰基修饰增强g-C3N4活性的机理尚不清楚.构建多孔结构是暴露催化剂活性位点的有效措施之一.多孔结构可以有效改善纳米片的团聚,促进活性位点暴露,增大反应物与活性位点间的接触机会;并且相互连接的多孔网络可形成独特的传输通道,进一步促进载流子迁移.本文通过分子自组装和碱辅助策略合成了氰基改性的多孔g-C3N4纳米片(MCN-0.5).氰基由于具有良好的吸电子特性,促进了局部载流子分离,并充当了光催化反应的活性位点.受益于活性位点的影响,MCN-0.5表现出显著增强的光催化CO2还原活性.在不添加牺牲剂和助催化剂的条件下,MCN-0.5样品上CO和CH4产率达到13.7和0.6μmol·h–1·g–1,分别是传统煅烧法制备的g-C3N4(TCN)产生CO和CH4产率的2.5和2倍.通过盐酸处理MCN-0.5除去氰基,并没有破坏样品的形貌结构,但催化剂的光催化活性显著降低,证实了氰基活性位点的作用.光还原Pt纳米颗粒的实验结果表明,与对照样品相比,氰基修饰的样品上还原的Pt纳米颗粒更多,进一步证实了引入氰基为光还原反应提供了更多活性位点.CO2等温吸附测试结果表明,MCN-0.5对CO2的吸附能力不如对照样品,间接证明氰基能成为活性位点是由于其良好的吸电子能力促进了局部载流子分离.瞬态荧光光谱、光电化学表征结果表明,氰基修饰增强了载流子迁移和分离能力.根据理论计算和原位红外光谱提出了氰基修饰增强g-C3N4光催化还原CO2活性的作用机理.以三聚氰胺为前驱体接枝氰基的g-C3N4也表现出比体相g-C3N4明显增强的光催化还原CO2活性,这证明了氰基改性增强g-C3N4活性策略的通用性.本文通过在光催化剂材料中设计活性位点为太阳能高效转化提供了一个有效途径.     

Regioselective bond cleavage and coordination effects in the reduction of some acetals with lithium in ammonia

Some benzylic-type acetals possessing the 2,8-dioxa-bicyclo [3.2.1]octane ring system are cleaved in a regioselective manner when treated with lithium in ammonia. The results f rom various reductions implicate coordination of lithium as a significant factor involved in reduction mechanisms.