碳化硅和碳化硼在电催化中的应用

燃料电池是具有广泛应用前景的新能源技术。碳载铂基催化剂（Pt/C）是最常用的燃料电池电极催化剂,不过Pt/C稳定性较差、且成本高昂,严重限制了燃料电池的规模化应用。共价型碳化物碳化硅和碳化硼,由于具有极强的共价键,其物化稳定性优异,成为制备高稳定性、低成本的燃料电池催化剂的重要基础材料。本文总结了相关研究成果,介绍了碳化硅和碳化硼的独特优势,讨论了相关研究的发展方向。     

碳化硅和碳化硼在电催化中的应用

燃料电池是具有广泛应用前景的新能源技术。碳载铂基催化剂(Pt/C)是最常用的燃料电池电极催化剂,不过Pt/C稳定性较差、且成本高昂,严重限制了燃料电池的规模化应用。共价型碳化物碳化硅和碳化硼,由于具有极强的共价键,其物化稳定性优异,成为制备高稳定性、低成本的燃料电池催化剂的重要基础材料。本文总结了相关研究成果,介绍了碳化硅和碳化硼的独特优势,讨论了相关研究的发展方向。     

Hollow and Threadlike Nanostructures of Boron Carbide

An original low-temperature method is proposed for the synthesis of boron carbide from simple materials. It made it possible to obtain a powdered product in the form of hollow and threadlike nanostructures. The boron carbide nanotubes are shorter than bundles of nanotubes. The boron carbide nanostructures are grown from vapor-phase reagents at a high-temperature nanocenter, the enhanced reactivity of which is maintained as a result of the exothermic effect of the reaction.     

碳化硼成分分析标准物质的研制

介绍碳化硼成分分析标准物质的制备方法。以硼酸和蔗糖为原材料,酯化反应得到硼酸酯沉淀,经过烧结制备碳化硼粉体。用低温前驱体裂解法制备碳化硼成分分析标准物质,并进行了均匀性检验、稳定性考察,采用8家实验室协作定值,对定值结果的不确定度进行了评定。结果表明,研制的碳化硼成分分析标准物质具有良好的均匀性和稳定性,量值准确可靠,定值结果的相对扩展不确定度为0.003 1%~0.13%(k=2)。     

ICP–AES法测定硼铝复合材料中的硼

建立电感耦合等离子体发射光谱法(ICP–AES)测定辐照后硼铝复合材料中元素的方法。用氢氧化钠将辐照后的硼铝复合材料溶解过滤,滤纸和滤渣采用碱熔法制样。采用基体匹配法消除基体干扰,仪器工作条件:RF发生器功率为1 150 W,雾化器压力为151.7 kPa,辅助气流量为0.5 L/min,硼元素的分析线为249.678 nm,积分时间为5 s。硼的质量浓度在15~28 mg/L范围内与光谱强度呈良好的线性关系,线性相关系数为0.999 7。方法的回收率为99.1%~100.8%,测定结果的相对标准偏差为0.76%(n=10)。该方法快速,准确度和精密度高,能够满足样品测量需要。     

Determination of Chloride in Nuclear-Grade Boron Carbide by Ion Chromatography

This paper describes the use of ion chromatography with conductivity detection to determine chloride in nuclear-grade boron carbide. Samples were fused with sodium carbonate and fused mass was dissolved in hot water. The accuracy of the fusion method was evaluated by means of spike-recovery tests. Anion chromatography in suppressed-conductivity mode was performed with a mixed solution of Na₂CO₃ and NaHCO₃ as mobile phase. The detection limit for chloride was 33 mg kg^–1 and the recovery of added chloride was 98–104%. The relative standard deviation was 6% for the overall method.     

等离子发射光谱法测定碳化硼颗粒增强铝基复合材料中6种元素

采用等离子发射光谱法同时测定碳化硼颗粒增强铝基复合材料中Al,Si,B,Mg,Cu,Fe等元素的含量。分析了各元素之间以及基体的光谱谱线相互干扰情况,对标准溶液采取与样品大致相同的基体匹配方式,消除了基体干扰,使测定结果更加准确。     

石墨基底对碳/碳化硼复合纳米绳形成的影响

利用邻碳硼烷(C₂H₁₂B₁₀)作为反应原料,二茂铁(C₁₀H₁₀Fe)作为催化剂,通过化学气相沉积法在石墨基片上生长出一种新颖的碳化硼纳米绳。用X射线衍射仪分析纳米绳的相结构,用场发射扫描电子显微镜(FESEM)和高分辨透射电子显微镜(HRTEM)观察纳米绳的微观形貌和结构,结果发现纳米绳的中心部分是碳化硼纳米线,在线的表面有非晶碳绳结,故纳米绳为碳/碳化硼复合物。研究了绳状产物的生长机理,表明石墨基片对产物的形成有至关重要的作用。     

Amorphous Boron Dispersed in LaCoO3 with Large Oxygen Vacancies for Efficient Catalytic Propane Oxidation

Unsatisfactory oxygen mobility is a considerable barrier to the development of perovskites for low-temperature volatile organic compounds (VOCs) oxidation. This work introduced small amounts of dispersed non-metal boron into the LaCoO₃ crystal through an easy sol-gel method to create more oxygen defects, which are conducive to the catalytic performance of propane (C₃H₈) oxidation. It reveals that moderate addition of boron successfully induces a high distortion of the LaCoO₃ crystal, decreases the perovskite particle size, and produces a large proportion of bulk Co²⁺ species corresponding to abundant oxygen vacancies. Additionally, surface Co³⁺ species, as the acid sites, which are active for cleaving the C−H bonds of C₃H₈ molecules, are enriched. As a result, the LCB-7 (molar ratio of Co/B=0.93:0.07) displays the best C₃H₈ oxidation activity. Simultaneously, the above catalyst exhibits superior thermal stability against CO₂ and H₂O, lasting 200 h. This work provides a new strategy for modifying the catalytic VOCs oxidation performance of perovskites by the regulation of amorphous boron dispersion.     

Synergistic Effect of Boron Nitride and Carbon Domains in Boron Carbide Nitride Nanotube Supported Single-Atom Catalysts for Efficient Nitrogen Fixation

Developing the low-cost and efficient single-atom catalysts (SACs) for nitrogen reduction reaction (NRR) is of great importance while remains as a great challenge. The catalytic activity, selectivity and durability are all fundamentally related to the elaborate coordination environment of SACs. Using first-principles calculations, we investigated the SACs with single transition metal (TM) atom supported on defective boron carbide nitride nanotubes (BCNTs) as NRR electrocatalysts. Our results suggest that boron-vacancy defects on BCNTs can strongly immobilize TM atoms with large enough binding energy and high thermal/structural stability. Importantly, the synergistic effect of boron nitride (BN) and carbon domains comes up with the modifications of the charge polarization of single-TM-atom active site and the electronic properties of material, which has been proven to be the essential key to promote N₂ adsorption, activation, and reduction. Specifically, six SACs (namely V, Mn, Fe, Mo, Ru, and W atoms embedded into defective BCNTs) can be used as promising candidates for NRR electrocatalysts as their NRR activity is higher than the state-of-the art Ru(0001) catalyst. In particular, single Mo atom supported on defective BCNTs with large tube diameter possesses the highest NRR activity while suppressing the competitive hydrogen evolution reaction, with a low limiting potential of −0.62 V via associative distal path. This work suggests new opportunities for driving NH₃ production by carbon-based single-atom electrocatalysts under ambient conditions.     

碳化硼纳米线的制备和结构

以碳纳米管为模板，通过加热碳纳米管与硼粉的混合物，获得了笔直的硼碳纳米线.对纳米线的结构和成分进行研究，结果表明纳米线主要为B4C纳米线.在部分B4C纳米线的端部存在Ni颗粒，这些端部具有Ni颗粒的纳米线构成了纳米磁针.讨论了B4C纳米线的生长机制，B4C纳米线的生长主要为硼原子在碳纳米管中扩散并发生化学反应，使得碳纳米管晶格结构发生重组，形成B4C纳米线.反应后，硼原子部分取代了碳纳米管中碳原子，修补了碳纳米管中的晶格缺陷，获得了形态笔直的B4C纳米线.     

高比表面SiC的合成及其在CO氧化反应中的应用

采用蔗糖为碳源, 正硅酸乙酯(TEOS)为硅源, 分别以草酸、硝酸铁、硝酸镍为催化剂, 用溶胶-凝胶法制备碳化硅前驱体, 考察了制备过程中催化剂的种类以及反应温度和时间对凝胶形成的影响. 发现以硝酸铁为催化剂最有利于凝胶的形成, 碳/硅物质的量比为4的前驱体在氩气气氛1350 ℃下加热10 h, 碳热还原反应趋于完成. 以该条件下合成的多孔碳化硅(比表面积133 m2·g-1)作为催化剂载体, 通过等量浸渍法获得Pt/SiC催化剂, 将其应用于一氧化碳氧化的模型反应中. 研究结果表明该催化剂有较好的催化活性和稳定性. 引入镍助剂的PtNi/SiC催化剂能进一步提高一氧化碳催化氧化反应的活性.     

Why Boron Nitride is such a Selective Catalyst for the Oxidative Dehydrogenation of Propane

Boron‐containing materials, and in particular boron nitride, have recently been identified as highly selective catalysts for the oxidative dehydrogenation of alkanes such as propane. To date, no mechanism exists that can explain both the unprecedented selectivity, the observed surface oxyfunctionalization, and the peculiar kinetic features of this reaction. We combine catalytic activity measurements with quantum chemical calculations to put forward a bold new hypothesis. We argue that the remarkable product distribution can be rationalized by a combination of surface‐mediated formation of radicals over metastable sites, and their sequential propagation in the gas phase. Based on known radical propagation steps, we quantitatively describe the oxygen pressure‐dependent relative formation of the main product propylene and by‐product ethylene. Free radical intermediates most likely differentiate this catalytic system from less selective vanadium‐based catalysts.     

单取代杂多化合物在以分子氧为氧化剂的环己烯氧化反应中的催化作用

单取代杂多化合物在以分子氧为氧化剂的环己烯氧化反应中的催化作用秦笃捷,王国甲,吴越（吉林大学化学系,长春,１３００２３）关键词杂多化合物,环己烯,催化氧化单取代杂多化合物作为＂卟啉无机同系物＂而用于均相及相转移催化已引起人们的关注［１～３］．由于这类...     

Investigation on the Performance of Supported Molybdenum Carbide for the Partial Oxidation of Methane

The performance of uspported and unsupported molybdenum carbide for the partial oxidation of methane (POM) to syngas was investgated.An evaluation of the catalysts indicates that bulk molybdenum carbied has a higher methane conversion during the initial stage but a lower selectivity to CO and H2/CO ratio in the products.The rapid deactivation of the catalyst is also a significant problem.However,the supported molybdenum carbide catalyst shows a much higher methane conversion,increased selectivity and significantly improved catalytic stability.The characterization by XRD and BET specific area measurements depict an improved dispersion of molybdenum carbide when using alumina as a carrier.The bulk or the supported molybdenum carbide exists in the β-Mo2C phase,while it is transformed into molybdenum dioxide postcatalysis which is an improtant cause of molybdenum carbide deactivation.     

Bioinspired Synthesis of Lepidocrocite‐Containing Material and Its Catalytic Behaviour in CO Oxidation

Leptothrix sp. was cultivated in Lieske 's medium in the presence of Al foil covered by anodic Alumina . Samples of biomass deposited on lamellae were studied by the methods of infrared, Mössbauer , and X‐ray photoelectron spectroscopy. Sole deposition of γ‐FeOOH on the lamellae was found to take place. This result is explained by the influence of γ‐AlOOH ingredient in the used support due to crystal structure similarity. Thus, iron oxyhydroxide crystallisation could be directed during bacteria cultivation. The catalytic activity of deposited γ‐FeOOH was examined in CO oxidation.     

碳化钨用作质子交换膜燃料电池催化剂载体的抗氧化性能

 采用还原碳化法制备了碳化钨样品,并用原位还原法担载Pt粒子得到Pt/WxCy催化剂. 利用计时电流技术对Pt/WxCy和常规Pt/C催化剂进行氧化处理,并用循环伏安法测试了氧化前后两种催化剂的电化学活性面积. 将两种催化剂制成单电池,对比研究了其氧化后的性能衰减. 结果表明, Pt/WxCy催化剂制成的单电池抗氧化能力显著高于普通Pt/C制成的单电池.     

碳化钨和Vulcan XC-72炭黑载钯催化剂对甲酸氧化的电催化性能

研究了碳化钨(WC)和Vulcan XC-72炭黑(XC)作混合载体的Pd/WC-XC催化剂对甲酸氧化的电催化性能.发现Pd/WC-XC催化剂对甲酸氧化的电催化性能优于Pd/XC催化剂.而且,Pd/WC-XC催化剂的电催化性能与WC和XC的质量比有关,当质量比为3:1时,催化剂对甲酸氧化的电催化活性最好,当质量比为2:1时,催化剂对甲酸氧化的电催化稳定性性最好.     

Synthesis of Ultrafine Mesoporous Tungsten Carbide by High‐energy Ball Milling and Its Electrocatalytic Activity for Methanol Oxidation

Ultrafine mesoporous tungsten carbide (WC) was prepared from as‐synthesized mesoporous WC using high‐energy ball milling treatment. X‐ray diffraction (XRD), scanning electron microscopy (SEM), and nitrogen adsorption‐desorption techniques were used to characterize the samples. Brunauer‐Emmett‐Teller (BET) surface areas of WC samples increased with the increasing ball milling time and kept constant at 10–11 m²·g^?1 for over 9 h. The electrocatalytic properties of methanol electro‐oxidation at WC powder microelectrodes were investigated by cyclic voltammetry, chronoamperometry, and quasi‐steady‐state polarization techniques. The results reveal that ball‐milled WC exhibits higher activity for methanol electro‐oxidation than as‐synthesized mesoporous WC. The suitability of ball‐milled WC for methanol electro‐oxidation is better than platinum (Pt) micro‐disk, although the current peak is not as high as the Pt micro‐disk. Moreover, increasing the methanol concentration and reaction temperature promotes methanol electro‐oxidation on ultrafine mesoporous WC.