氮掺杂有序介孔碳负载超小尺寸铂纳米颗粒催化硝基苯类化合物选择加氢

氮掺杂有序介孔碳材料不仅具有高的比表面积、大的孔容和均一可调的孔径等优点,其骨架中丰富的氮原子还可以对材料的物理化学性质、配位金属电荷密度等进行调控,是一类优异的催化剂载体.本文利用软模板(嵌段共聚物F127为模板),以间氨基苯酚为碳源和氮前体,制备出较高含氮量(9.58 wt%)和比表面积(417 m2/g),以及规则孔径分布的介孔碳材料.结果表明,制备的材料具有三维立方相结构.以该碳材料作为载体,使用传统浸渍氢气还原的策略负载纳米铂颗粒.发现氮掺杂的载体能够有效控制金属纳米颗粒的尺寸,可实现超小尺寸Pt纳米颗粒的有效负载(1.0±0.5 nm),且纳米颗粒均匀分布于介孔碳材料的孔道中.相比而言,使用相同负载方法的情况下,以不掺氮的介孔碳材料为载体,纳米粒子的尺寸较难控制(4.4±1.7 nm)且会发生孔道外颗粒聚集的情况.研究表明,骨架中的氮原子与金属间弱的相互作用对纳米粒子有稳定作用.这对制备超小尺寸的金属纳米粒子催化剂具有一定的指导意义.此外,由于纳米粒子的尺寸将大大影响催化剂活性中心的暴露程度,进而影响催化剂活性.因此,我们以硝基苯类化合物的氢化反应来评价该催化剂的催化性能.在室温和1 MPa H2的温和条件下,氮掺杂的介孔碳负载催化剂表现出了优异的催化性能.反应0.5 h,对氯硝基苯可完全转化,且选择性高达99%.相比而言,商业化的Pt/C催化剂上反应的转化率和选择性分别为89%和90%.其它传统催化剂的比较,如Pt/SiO2,Pt/TiO2,同样表明,氮掺杂介孔碳负载的催化剂具有更优异的催化性能.在相同反应条件下,Pt/SiO2催化剂只能得到46%的转化率和93%的选择性,而Pt/TiO2催化剂虽然能够实现完全转化,但选择性也仅为91%.由此可见,氮掺杂的负载催化剂可大大提高反应活性和选择性,能有效抑制脱氯现象的发生.这种高的催化性能可能与催化剂的介孔结构、氮功能化载体以及超小尺寸的Pt纳米粒子的稳定有关.由于氮原子和介孔孔道的限域作用,氮掺杂介孔碳负载的催化剂也具有良好的催化稳定性,循环使用10次后,催化活性和选择性几乎没有下降.结果表明,循环使用后的催化剂金属粒子尺寸变化不大,进一步表明氮掺杂介孔碳载体对金属纳米颗粒的稳定作用.     

氮掺杂有序介孔碳负载超小尺寸铂纳米颗粒催化硝基苯类化合物选择加氢（英文）

氮掺杂有序介孔碳材料不仅具有高的比表面积、大的孔容和均一可调的孔径等优点,其骨架中丰富的氮原子还可以对材料的物理化学性质、配位金属电荷密度等进行调控,是一类优异的催化剂载体.本文利用软模板(嵌段共聚物F127为模板),以间氨基苯酚为碳源和氮前体,制备出较高含氮量(9.58 wt%)和比表面积(417 m~2/g),以及规则孔径分布的介孔碳材料.结果表明,制备的材料具有三维立方相结构.以该碳材料作为载体,使用传统浸渍氢气还原的策略负载纳米铂颗粒.发现氮掺杂的载体能够有效控制金属纳米颗粒的尺寸,可实现超小尺寸Pt纳米颗粒的有效负载(1.0±0.5 nm),且纳米颗粒均匀分布于介孔碳材料的孔道中.相比而言,使用相同负载方法的情况下,以不掺氮的介孔碳材料为载体,纳米粒子的尺寸较难控制(4.4±1.7 nm)且会发生孔道外颗粒聚集的情况.研究表明,骨架中的氮原子与金属间弱的相互作用对纳米粒子有稳定作用.这对制备超小尺寸的金属纳米粒子催化剂具有一定的指导意义.此外,由于纳米粒子的尺寸将大大影响催化剂活性中心的暴露程度,进而影响催化剂活性.因此,我们以硝基苯类化合物的氢化反应来评价该催化剂的催化性能.在室温和1 MPaH_2的温和条件下,氮掺杂的介孔碳负载催化剂表现出了优异的催化性能.反应0.5 h,对氯硝基苯可完全转化,且选择性高达99%.相比而言,商业化的Pt/C催化剂上反应的转化率和选择性分别为89%和90%.其它传统催化剂的比较,如Pt/SiO_2,Pt/TiO_2,同样表明,氮掺杂介孔碳负载的催化剂具有更优异的催化性能.在相同反应条件下,Pt/SiO_2催化剂只能得到46%的转化率和93%的选择性,而Pt/TiO_2催化剂虽然能够实现完全转化,但选择性也仅为91%.由此可见,氮掺杂的负载催化剂可大大提高反应活性和选择性,能有效抑制脱氯现象的发生.这种高的催化性能可能与催化剂的介孔结构、氮功能化载体以及超小尺寸的Pt纳米粒子的稳定有关.由于氮原子和介孔孔道的限域作用,氮掺杂介孔碳负载的催化剂也具有良好的催化稳定性,循环使用10次后,催化活性和选择性几乎没有下降.结果表明,循环使用后的催化剂金属粒子尺寸变化不大,进一步表明氮掺杂介孔碳载体对金属纳米颗粒的稳定作用.     

介孔碳负载铂催化剂的分散性和电催化活性

以介孔硅SBA-15为模板, 糠醇为碳源制备了高度有序的介孔碳(CMK-5), 并用微波法合成碳负载的铂纳米粒子的催化剂. 为改善铂微粒的分散性能, 在微波碳载过程中添加了适量的阳离子表面活性剂(CTAB). XRD和TEM测试结果表明, CTAB的加入改善了铂催化剂的分散性, 且使铂微粒的平均粒径降至2.9 nm左右. 循环伏安测试结果显示, 加入CTAB后所得Pt/CMK-5催化剂的电化学活性面积大于未加CTAB的以及商业Johnson Matthey公司的Pt/C催化剂的活性面积.     

新型负载碳点的介孔有机硅纳米粒子的制备与研究

本文将介孔有机二氧化硅纳米颗粒(MONs)与碳点(CDs)结合,制备新型负载碳点的介孔有机硅纳米粒子(CD@MONs).结果表明成功制备出负载碳点的介孔有机硅复合纳米粒子,详细表征显示产物呈球形,分散性较好,直径为40～60 nm,大小较为均一,孔道大,产物在415 nm激发下,荧光发射波长为670 nm,该复合材料既...     

纳米碳材料负载铂催化剂在环己烷脱氢反应中的催化性能研究

制备了纳米碳材料负载铂的催化剂,通过N₂吸附、TEM、XRD技术分别对载体的BET比表面积和催化剂结构、形貌和粒径大小进行了表征。考察了不同催化剂在环己烷脱氢反应中的催化性能以及温度对纳米碳颗粒负载铂催化剂活性的影响。结果表明,锚定在不同碳载体上的铂有较好的分散性,粒径较小,粒度分布范围较窄并且具有相同的晶型结构。孔状纳米碳颗粒负载铂催化剂的活性高于碳纳米管和高比表面的活性炭负载铂催化剂,并且在低温条件下已经显示了较高的活性,尤其是中空碳颗粒负载铂催化剂在环己烷脱氢反应中显示了好的活性和稳定性。     

氮掺杂碳材料负载Pd纳米催化剂在有机反应中的最新研究进展

氮掺杂碳材料负载Pd纳米催化剂因其具有反应活性高、反应完成后便于分离和重复使用等优点,在催化领域引起了极为广泛的关注.简要综述了基于氮掺杂多孔/介孔碳NC、氮掺杂石墨烯NG、氮掺杂碳纳米管NCNT和氮掺杂碳纳米片NCNS等不同类型碳材料载体制备的负载型Pd纳米催化剂的合成与应用的最新研究进展,同时对氮掺杂碳材料负载Pd纳米催化剂的发展方向进行了展望.     

Pt/CNT纳米催化剂的微波快速合成及其对甲醇电化学氧化的电催化性能

碳纳米管 (CNT)作为制备新型催化剂载体已有广泛的研究 [1～ 8] ,例如 ,在其表面负载 Pt,Ru和Pt Ru后则具有良好的催化性能[1,2 ,6～ 8] .但在 CNT表面负载金属微粒的方法难以获得尺寸和形状均匀的纳米粒子 .因此 ,如何制备超细和均匀的纳米粒子是一项具有重要的学术意义和技术价值的工作 .我们利用微波加热的多元醇工艺合成了 XC-72碳负载铂纳米粒子的催化剂 ,并发现它对甲醇的氧化具有较高的电催化活性 [9] .本文进一步以 CNT作为载体 ,利用微波加热法快速合成了 Pt/ CNT纳米催化剂 ,并对其对甲醇电化学氧化的性能进行了初步研究 …     

微波合成碳负载纳米铂催化剂及其对甲醇氧化的电催化性能

利用微波辐射快速加热含有XC—72碳的H2PtCl6的乙二醇混合液合成了碳负载的纳米铂,铂负载的质量分数在10％～20％,实验结果表明纳米铂粒子具有均匀的尺寸和形状,其平均粒径在3．6nm,并均匀地分散在纳米碳的表面,循环伏安和恒电位极化表明微波合成的Pt/C比以KBH4作为还原剂制备Pt/C和商业得到E-TEK Pt／C催化剂对甲醇的电化学氧化具有更高的催化活性。     

介孔Al2O3负载纳米Au催化剂用于低温催化氧化CO

 用不同模板剂合成了具有较高比表面积和较多表面碱性位的介孔Al2O3载体,并采用均相沉积-沉淀法制备了Al2O3负载纳米Au催化剂,对制备的介孔Al2O3载体及相应催化剂采用低温N2吸附法、TEM和XPS等手段进行了表征,考察了载体表面碱性对纳米Au粒子在载体表面的沉积及相应催化剂在CO氧化反应中催化性能的影响. 以CO2-TPD法测定载体表面碱性,结果表明,介孔氧化铝的表面碱性与其合成过程中所用的模板剂有关. 以表面碱性位较丰富的介孔Al2O3为载体制备的催化剂表面Au粒子分布较均匀且粒径(3.1～3.2 nm)较小,在CO完全氧化反应中催化活性最高,表明载体表面的碱性位有利于稳定其表面沉积的纳米Au粒子. XPS分析结果表明,催化剂表面的Au主要以Au0金属态形式存在,它在CO氧化反应中表现出较高的催化活性.     

不同载体负载的铂催化剂在丙酮酸乙酯不对称氢化反应中的活性及其铂流失率比较

以介孔树脂材料FDU-14和介孔碳材料CMK-3为载体制备了两种负载型铂催化剂, 用N₂气吸附、X射线衍射及CO化学吸附等手段对这两种催化剂进行了表征, 并将这两种不同的负载型铂催化剂在丙酮酸乙酯不对称氢化反应中的催化性能及其铂流失率与商品化Pt/Al₂O₃催化剂进行了比较. 研究结果表明, 尽管Pt/Al₂O₃催化剂的初始活性和光学选择性均较高, 然而相同反应条件下乙酸溶剂中Pt/FDU-14和Pt/CMK-3催化剂的铂流失率比Pt/Al₂O₃催化剂的低. 通过对催化剂进行CO吸附原位傅里叶变换红外漫反射光谱(DRIFTS)表征, 从载体的不同表面电子性质角度解释了不同载体负载的铂催化剂在丙酮酸乙酯不对称氢化反应中的活性和铂流失率的差异.     

PEFC catalyst layers: Effect of support microstructure on both distributions of Pt and ionomer and cell performance and durability

In order to improve the performance and durability of polymer electrolyte fuel cells (PEFCs), various improvements in the microstructures of cathode catalyst layers (CLs) were initiated in the early 1990s. More recent advances in CL materials are highlighted, including carbon supports for improved accessibility of Pt nanoparticles (NPs), adsorption of ionomer on the Pt surface, high-oxygen-permeability ionomers, corrosion resistance of mesoporous and microporous carbons, and conductive ceramic supports with a fused-aggregate network structure. These approaches are summarized as stepwise improvements. The influences of the support structure on the distribution of Pt NPs and ionomer are reviewed, as well as their effects on performance and durability. These approaches for carbon supports are extended to conductive ceramic supports and the unique advantages are discussed.     

Preparation and electrochemical behaviors of platinum nanoparticles impregnated on binary carbon supports as catalyst electrodes of direct methanol fuel cells

Binary carbon-supported platinum (Pt) nanoparticles were prepared by a chemical reduction method of Pt precursor on two types of carbon materials such as carbon blacks (CBs) and graphite nanofibers (GNFs). Average sizes and loading levels of Pt metal particles were dependent on a mixing ratio of two carbon materials. The highest electroactivity for methanol oxidation was obtained by preparing the binary carbon supports consisting of GNFs and CBs with a weight ratio of 30:70. Furthermore, with an increase of GNFs content from 0% to 30%, a charge-transfer resistance changed from 19 Ohm cm² to 11 Ohm cm². The change of electroactivity or the resistance of catalyst electrodes was attributed to the changes of specific surface area and morphological changes of carbon-supported catalyst electrodes by controlling the mixing ratio of GNFs and CBs.     

Ordered mesoporous platinum@graphitic carbon embedded nanophase as a highly active, stable, and methanol-tolerant oxygen reduction electrocatalyst

Highly ordered mesoporous platinum@graphitic carbon (Pt@GC) composites with well-graphitized carbon frameworks and uniformly dispersed Pt nanoparticles embedded within the carbon pore walls have been rationally designed and synthesized. In this facile method, ordered mesoporous silica impregnated with a variable amount of Pt precursor is adopted as the hard template, followed by carbon deposition through a chemical vapor deposition (CVD) process with methane as a carbon precursor. During the CVD process, in situ reduction of Pt precursor, deposition of carbon, and graphitization can be integrated into a single step. The mesostructure, porosity and Pt content in the final mesoporous Pt@GC composites can be conveniently adjusted over a wide range by controlling the initial loading amount of Pt precursor and the CVD temperature and duration. The integration of high surface area, regular mesopores, graphitic nature of the carbon walls as well as highly dispersed and spatially embedded Pt nanoparticles in the mesoporous Pt@GC composites make them excellent as highly active, extremely stable, and methanol-tolerant electrocatalysts toward the oxygen reduction reaction (ORR). A systematic study by comparing the ORR performance among several carbon supported Pt electrocatalysts suggests the overwhelmingly better performance of the mesoporous Pt@GC composites. The structural, textural, and framework properties of the mesoporous Pt@GC composites are extensively studied and strongly related to their excellent ORR performance. These materials are highly promising for fuel cell applications and the synthesis method is quite applicable for constructing mesoporous graphitized carbon materials with various embedded nanophases.     

Iron Carbide Nanoparticles Encapsulated in Mesoporous Fe‐N‐Doped Carbon Nanofibers for Efficient Electrocatalysis

Exploring low‐cost and high‐performance nonprecious metal catalysts (NPMCs) for oxygen reduction reaction (ORR) in fuel cells and metal–air batteries is crucial for the commercialization of these energy conversion and storage devices. Here we report a novel NPMC consisting of Fe₃C nanoparticles encapsulated in mesoporous Fe‐N‐doped carbon nanofibers, which is synthesized by a cost‐effective method using carbonaceous nanofibers, pyrrole, and FeCl₃ as precursors. The electrocatalyst exhibits outstanding ORR activity (onset potential of ?0.02 V and half‐wave potential of ?0.140 V) closely comparable to the state‐of‐the‐art Pt/C catalyst in alkaline media, and good ORR activity in acidic media, which is among the highest reported activities of NPMCs.     

High loading Pt nanoparticles on ordered mesoporous carbon sphere arrays for highly active methanol electro-oxidation

Three-dimensionally (3D) ordered mesoporous carbon sphere arrays (OMCS) are explored to support high loading (60 wt%) Pt nanoparticles as electrocatalysts for the methanol oxidation reaction (MOR). The OMCS has a unique hierarchical nanostructure with ordered large mesopores and macropores that can facilitate high dispersion of the Pt nanoparticles and fast mass transport during the reactions. The prepared Pt/OMCS exhibits uniformly dispersed Pt nanoparticles with an average size of 2.0 nm on the mesoporous walls of the carbon spheres. The Pt/OMCS catalyst shows significantly enhanced specific electrochemically active surface area (ECSA) (73.5 m² g^-1) and electrocatalytic activity (0.69 mA cm^-2) for the MOR compared with the commercial 60 wt% Pt/C catalyst.     

Fast preparation of PtRu catalysts supported on carbon nanofibers by the microwave-polyol method and their application to fuel cells

PtRu alloy nanoparticles (24 +/- 1 wt %, Ru/Pt atomic ratios = 0.91-0.97) supported on carbon nanofibers (CNFs) were prepared within a few minutes by using a microwave-polyol method. Three types of CNFs with very different surface structures, such as platelet, herringbone, and tubular ones, were used as new carbon supports. The dependence of particles sizes and electrochemical properties on the structures of CNFs was examined. It was found that the methanol fuel cell activities of PtRu/CNF catalysts were in the order of platelet > tubular > herringbone. The methanol fuel cell activities of PtRu/CNFs measured at 60 degrees C were 1.7-3.0 times higher than that of a standard PtRu (29 wt %, Ru/Pt atomic ratio = 0.92) catalyst loaded on carbon black (Vulcan XC72R) support. The best electrocatalytic activity was obtained for the platelet CNF, which is characterized by its edge surface and high graphitization degree.     

纳米碳纤维载铂作为质子交换膜燃料电池阳极催化剂

采用化学还原法合成了微结构不同的纳米碳纤维(板式、鱼骨式、管式)载铂催化剂(分别记为Pt/p-CNF、Pt/f-CNF、Pt/t-CNF). 通过高分辨透射电镜(HRTEM)和X射线衍射(XRD)等分析技术对催化剂的微观结构进行了表征, 并利用循环伏安(CV)法分析了催化剂的电化学比表面积(ESA). 在此基础上, 制备了膜电极(MEA), 通过单电池测试了催化剂的电催化性能. 结果表明: 铂纳米粒子在不同的纳米碳载体上表现出不同的粒径, 在板式、鱼骨式和管式纳米碳纤维上的铂纳米粒子平均粒径分别为2.4、2.7和2.8 nm. 板式纳米碳纤维载铂催化剂作单电池阳极时表现出良好的电催化性能, 其对应的最高功率密度可达0.569 W·cm^-2, 高于鱼骨式纳米碳纤维载铂催化剂和管式纳米碳纤维载铂催化剂对应的最高功率密度(分别为0.550和0.496 W·cm^-2). 同时, 也制备了碳黑(Pt/XC-72)载铂催化剂. 相比于Pt/XC-72, 纳米碳纤维载体上的铂纳米颗粒有较小的粒径、较好的分散和较高的催化活性, 说明纳米碳纤维是质子交换膜燃料电池(PEMFCs)催化剂的良好载体.     

碳材料中多层次孔对负载铂电催化活性的影响

分别以商用碳黑XC-72、介孔碳CMK-5和含多层次孔的碳气凝胶HCA为载体, 微波法负载Pt纳米粒子, 在硫酸和甲醇溶液中进行循环伏安测试, 考察碳材料中多层次孔对其电催化活性的影响. 结果显示, Pt/HCA电极表现出较高的峰电流(7.5 mA·cm-2)和电化学活性面积(128.0 m2·g-1). 这可能是因为碳气凝胶具有连续但非周期性的介孔结构, 有利于Pt纳米粒子的分散以及反应物质的传质.