Ni3V2O8催化性能与X射线光电子能谱分析

文章采用微波加热,草酸盐共沉淀法制备了Ni3V2O8催化剂,并对催化剂进行了BET,XRD,H2-TPR,XPS,TEM和电导等技术表征,分析研究了Ni3V2O8催化剂的丙烷氧化脱氢(ODH)制丙烯催化性能与其表面物种的关系.XRD,TEM和电导实验结果表明本方法制得的Ni3V2O8催化剂晶粒均匀,平均粒径为30 nm,具有p-型半导体性质.TPR和XPS实验结果显示Ni3V2O8催化剂中,晶格氧可以较容易转换成未完全还原氧,使催化剂内各种价态的钒之间易于进行氧化还原反应并形成氧缺位,从而催化剂的表面含有较多未充分还原氧物种O-和V4 物种.催化活性结果显示当丙烷的转化率为18.60%,丙烯选择性达到60.02%,在相同转化率条件下,比文献报道的NiO和Ni3V2O8共存催化体系中的丙烯选择性高,说明Ni3V2O8催化剂中存在未充分还原的O-和V4 物种有利于提高丙烯的选择性.     

氮掺杂碳载钴催化剂制备及其TG-FTIR和XRD光谱分析

以三聚氰胺甲醛树脂预聚体为氮源、碳源,以乙酸钴为金属前驱体,制备氮掺杂碳载钴氧还原电催化剂。利用傅里叶变换红外光谱与热重联用(thermogravimetry-fourier transform infrared spectroscopy,TG-FTIR)、X射线衍射光谱分析(X-ray diffraction spectra,XRD)等研究了催化剂的制备过程和结构,采用旋转圆盘电极测试(rotating disc electrode,RDE)考察了制备过程中不同炭化温度对催化剂氧还原催化活性的影响。结果显示,在惰性气氛中,随炭化温度升高,样品中部分有机基团以CO,CO2,HCHO,NH3,NO2等形态随保护气流失,催化剂结构出现明显变化,形成典型的面心立方结构。旋转圆盘电极测试结果表明,所制备的催化剂都具有较好的电催化活性,氮掺杂碳载钴催化剂的氧还原起始电位在0.5V(vs.SCE)左右,炭化温度为700℃时制备的催化剂具有最高电催化氧还原活性。     

氮掺杂碳制备氧还原反应催化剂及保护气流动对催化剂活性的影响

在氮气氛围中热处理含氯化锰、六次甲基四胺和乙炔黑的前驱体制备非贵金属氧还原反应催化剂MnHMTA/C. 考察了热处理温度和保护气流动对催化剂活性的影响. 在700 ℃下热处理2 h所得催化剂具有良好的催化活性. 在热处理过程中,Mn(II)离子转变为MnO,改进了催化剂活性. 六次甲基四胺以其气体分解产物参与催化剂活性位的生成,保护气的流动会将气体分解产物带出,从而减弱MnHMTA/C催化剂的性能.     

基于片层结构钴卟啉金属有机骨架的高效氧还原反应电催化剂

使用片层结构的金属有机骨架作为前驱物,通过高温煅烧制备出氮掺杂的介孔碳材料,同时在片层碳骨架上均匀分布着石墨化碳包裹的钴纳米粒子.电化学测试表明,800℃制备的样品具有与铂炭（Pt/C）催化剂相接近的氧还原反应催化活性,催化稳定性和甲醇耐受性良好,显著超越商品化Pt/C催化剂.     

纳米碳管作为氧扩散电极催化层第二相碳载体的电极特性

以纳米碳管和活性碳二元碳材料为催化层碳载体制备了氧扩散电极,采用稳态极化和电化学阻抗技术对其在碱性介质中氧还原反应的电催化活性进行了研究.结果表明,双载体电极比单载体纳米碳管、活性炭电极具有更高的电催化活性,纳米碳管和活性炭质量比为50∶50时双载体电极的催化活性最好;电极动力学参数测试表明,催化层中引入第二相纳米碳管载体提高了电极比表面积、电子导电性和氧还原反应速度;采用浸渍还原法在第二相纳米碳管载体中负载纳米级Pt催化剂,即使在低Pt负载量下(45.7μg/cm2)也明显改善了双载体电极的催化活性.阻抗测试表明,载Pt与未载Pt催化剂的双载体电极均受氧在薄液膜中的扩散控制.     

碳纳米纤维负载Pd-Pt 催化剂的萘加氢耐硫性能

通过催化加氢来降低柴油中芳烃含量是提高油 品质量的一个重要过程.贵金属催化剂,如Pd或 Pt,具有非常高的反应活性,但易被原料油中的含硫 有机化合物毒化[1].因此,提高贵金属催化剂的耐 硫性能是一个重要的课题.已有的研究结果表明,贵 金属催化剂硫中毒的主要原因是硫在金属中心上产 生强化学吸附,因此,调节金属中心和硫之间的电子 相互作用可以改进催化剂的耐硫性能[2,3]. 催化生长的碳纳米纤维(CNF)是一种新型的碳 材料,其石墨层沿轴线方向闭合的特殊结构使它具 …     

葡萄糖催化氧化反应用Pd-Co/C催化剂的XPS研究

活性炭为载体，制备了Pd/C、Pd-Co/C催化剂，并进行了活性评价和XPS表征。在Pd-Co／C催化剂上反应3h后，葡萄糖的转化率达92％，选择性为94％，较Pd/C催化剂有显著提高。Co的添加及焙烧过程改变了Pd/C催化剂的表面组成及结构，提高了贵金属Pd在催化剂表面的分散程度，有利于Pd的还原，使Pd-Co/C催化剂表现出良好的催化活性和选择性。     

原位漫反射红外光谱研究NO在Ag/SAPO-34催化剂上的选择性催化还原

原位漫反射红外光谱研究NO在Ag/SAPO 34催化剂上的选择性催化还原过程。考察了以丙烯为还原剂 ,在富氧及 573～ 773K温度条件下的反应。通过比较初始混合气中加氧或不加氧时反应的原位光谱 ,探讨了氧在NO还原过程中的作用。结果表明 ,氧能充分促进丙稀活化以及增加NOx 吸附态含量 ,并且氧的存在是有效产生有机 氮氧化物 (R NO2 ,R ONO)不可缺少的条件。基于光谱实验 ,认为反应机理为 :NO ,丙烯和氧反应 ,在Ag/SAPO 34催化剂上生成吸附的有机 氮氧化物 ,再由这些吸附物种分解成N2 ,催化还原的关键是形成有机 氮氧化物中间体。     

压-电-化学耦合增强策略及机理研究进展

压电材料能够收集环境中存在的微小的机械能,具有将机械信号转换为电信号的强大能力.利用压电材料的压电效应与电化学氧化还原效应二者的耦合可以实现压-电-化学耦合.近年来,压-电-化学耦合在收集清洁能源和处理废水保护环境方面受到国内外研究人员的广泛关注.本文综述了增强压-电-化学耦合的策略,从构建异质结、负载贵金属、构筑相界、混合碳或石墨烯和调控缺陷方面出发进行了总结梳理.从电子的运输和转移、材料相变和氧空位的角度解释不同策略中的物理机理,并对研究前景进行了展望.     

异丁烷部分氧化V-P-O/SiO2催化剂的研究

采用溶胶 凝胶法制备了V2 O5 /SiO2 和V2 O5 P2 O5 /SiO2 催化剂 ,用XRD、TPR、IR、TPD和微反应等技术研究了催化剂的表面结构、晶格氧活泼性、化学吸附和异丁烷部分氧化反应性能 .结果表明 ,催化剂的活性组份在无定型的SiO2 表面上呈超细粒子均匀分布 ,表面活性位主要由Lewis碱位 (V =O键的端氧、V -O -V键的桥氧 )和Lewis酸位 (Vn + )构成 ,PO43 - 的引入可以降低表面Lewis碱位V =O键端氧的活泼性 ;异丁烷分子主要通过两个甲基中H双位吸附在催化剂表面Lewis碱位V =O的端氧上 ,PO43 - 的引入使异丁烷的吸附强度略有下降 ;异丁烷在V2 O5 P2 O5 /SiO2 催化剂上反应产物主要是i C4H8、MAL、MAA和COx,PO43 - 的引入可以明显的提高部分氧化产物的选择性     

Dealloyed PtCu catalyst as an efficient electrocatalyst in oxygen reduction reaction

Pt-transition metal alloy catalysts with an active Pt surface have exceptional properties for use in oxygen electro-reduction reactions in fuel cells. Herein, we report the simple synthesis of dealloyed PtCu catalysts and their catalytic performance in oxygen reduction. The dealloyed PtCu catalysts consisted of a Pt-enriched shell with a Pt–Cu alloy core and were synthesized through a chemical co-reduction process followed by thermal annealing and chemical dealloying. During synthesis, thermal annealing leads to a high degree of formation of PtCu alloy particles (e.g., PtCu or PtCu₃), and chemical dealloying causes selective dissolution of unstable Cu species from the surface layers of the PtCu alloy particles, resulting in a PtCu alloy@Pt-enriched surface core–shell configuration. Our PtCu₃/C catalyst exhibits a great improvement in the oxygen reduction reaction with a mass activity of 0.501 A/mg_Pt, which is 2.24 times greater than that of a commercial Pt catalyst. In this article, the synthesis details, characteristics and performance improvements in ORR of chemically dealloyed PtCu catalysts are systemically explained.     

Direct pyrolysis and ultrasound assisted preparation of N,S co-doped graphene/Fe3C nanocomposite as an efficient electrocatalyst for oxygen reduction and oxygen evolution reactions

Bifunctional electrocatalysts to enable efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential for fabricating high performance metal–air batteries and fuel cells. Here, a defect rich nitrogen and sulfur co-doped graphene/iron carbide (NS-GR/Fe₃C) nanocomposite as an electrocatalyst for ORR and OER is demonstrated. An ink of NS-GR/Fe₃C is developed by homogeneously dispersing the catalyst in a Nafion containing solvent mixture using an ultrasonication bath (Model-DC150H; power − 150 W; frequency − 40 kHz). The ultrasonically prepared ink is used for preparing the electrode for electrochemical studies. In the case of ORR, the positive half-wave potential displayed by NS-GR/Fe₃C is 0.859 V (vs. RHE) and for the OER, onset potential is 1.489 V (vs. RHE) with enhanced current density. The optimized NS–GR/Fe₃C electrode exhibited excellent ORR/OER bifunctional activities, high methanol tolerance and excellent long-term cycling stability in an alkaline medium. The observed onset potential for NS–GR/Fe₃C electrocatalyst is comparable with the commercial noble metal catalyst, thereby revealing one of the best low-cost alternative air–cathode catalysts for the energy conversion and storage application.     

可控合成Pd-Pt八面体框架结构作为高效的氧还原反应催化剂

Pt-based nanoframes represent a class of promising catalysts towards oxygen reduction reaction. Herein, we, for the first time, successfully prepared Pt-Pd octahedral nanoframes with ultrathin ridges less than 2 nm in thickness. The Pt-Pd octahedral nanoframes were obtained through site-selected deposition of Pt atoms onto the edge sites of Pd octahedral seeds, followed by selective removal of the Pd octahedral cores via chemical etching. Due to that a combination of three-dimensional opens geometrical structure and Pt-skin surface compositional structure, the Pt-Pd octahedral nanoframes/C catalyst shows a mass activity of 1.15 A/mg_Pt towards oxygen reduction reaction, 5.8 times enhancement in mass activity relative to commercial Pt/C catalyst (0.20 A/mg_Pt). Moreover, even after 8000 cycles of accelerated durability test, the Pt-Pd octahedral nanoframes/C catalyst still exhibits a mass activity which is more than three times higher than that of pristine Pt/C catalyst.     

基于XRD和FITR的Ce-V-Ti催化剂减排烧结烟气二噁英的活性分析

二噁英是一类含氯挥发性有机污染物,具有环境持久性、生物蓄积性和长期残留性等特性,可造成致畸、致癌和致突变等危害。铁矿烧结过程中含氯前驱物在碱性环境下通过Ullman反应或经飞灰中某些催化性成分催化生成二噁英;碳、氢、氧和氯等元素可通过基元反应“从头合成”(de novo)二噁英,是二噁英最主要的排放源之一。物理吸附技术仅能实现污染物由气相向固相转移,加重了飞灰处理负担,并存在特定温度条件下(250～350 ℃)二噁英再生风险。催化降解技术能彻底矿化有机污染物,生成CO₂,H₂O和HCl/Cl₂,是一种避免二次污染高效节能、成本较低的方法。但由于传统催化剂活性温度区间较高,无法达到烧结烟气末端温度。选择合适的催化剂,提高催化剂低温降解活性,能实现低温、高效催化降解烧结烟气中有机污染物的目标。过渡金属Ce具有稀土金属的4f轨道配位效应和路易斯酸活性位点,对有机污染物C-H和C-Cl键活化起到至关重要的作用,掺杂过渡金属、调整活性组分比例可进一步提高铈基催化剂的抗中毒性能和降解活性。因此,本文采用溶胶凝胶法制备Ce-V-Ti复合催化剂,以氯苯为二噁英模型分子,研究了不同活性组分比例对铈基催化剂降解烧结烟气中二噁英活性影响。利用X射线衍射仪、比表面积及孔径测定仪和拉曼光谱仪对催化剂进行表征,研究Ce-V-Ti催化剂的相组成、比表面积和分子结构,并推测铈基催化剂的降解机理。结果表明,在实验室模拟烧结烟气气氛下,反应条件为GHSV=30 000 h-1、20%O₂和100 ppm CB,当Ce质量分数为15%、V质量分数为2.5%时,Ce-V-Ti催化降解氯苯活性最高,150 ℃能达到约60%转换率,300 ℃能实现95%降解率。催化剂载体与活性组分之间化学交互作用,影响催化剂的降解活性。通过光谱学分析发现,Ce-V-Ti催化剂XRD图谱主要为锐钛矿相的TiO₂,比表面积为95.53 m2·g-1,孔容0.29 cm3·g-1,孔径6.5 nm。表面官能团主要为C-H基团和H-O官能团。引入V作为Ce-Ti催化剂助剂,促进了Ce元素固溶,增加了催化剂表面氧空位,有利于提升催化剂降解活性。通过对催化剂机理分析,认为反应物首先通过发生亲核取代而垂直吸附于催化剂表面,再被活性组分Ce活化,活化后氯苯分子被表面活性氧分解矿化。同时,过渡金属V的低价态氧化物发生氧化反应,促进Ce的还原反应。     

A rational design of bimetallic PdAu nanoflowers as efficient catalysts for methanol oxidation reaction

Methanol fuel cells have been intensively developed as clean and high-efficiency energy conversion system due to their high efficiency and low emission of pollutants. Here, we developed a simple aqueous synthetic method to prepare bimetallic Pd Au nanoflowers catalysts for methanol oxidation reaction(MOR) in alkaline environment. Their composition can be directly tuned by changing the ratio between Pd and Au precursors. Compared with commercial Pd/C catalyst, all of the Pd Au nanoflowers catalysts show the enhanced catalytic activity and durability. In particular, the Pd Au nanoflowers specific activity reached 0.72 m A/cm2, which is 14 times that of commercial Pd/C catalyst. The superior MOR activity could be attributed to the unique porous structure and the shift of the d-band center of Pd.     

NiFe LDH-CoPc/CNTs as novel bifunctional electrocatalyst complex for zinc–air battery

A new type of composite electrocatalyst was designed and prepared with NiFe layered double hydroxides (LDHs) for oxygen evolution reaction (OER) and CoPc for oxygen reduction reaction (ORR) supported on carbon nanotubes (CNTs). The NiFe LDH–CoPc/CNT composite exhibits higher electrocatalytic activity and stability than the commercial precious metal catalyst Pd/C + Ru/C in 6 M KOH electrolyte. The resulting rechargeable Zn–air battery showed high discharge voltage at 195 mW cm^?2. The discharge voltage is around 1.08~0.95 V and the charge voltage is lower, 2.07 V, after the cycle of 300 h at 80 mA cm^?2, indicating that zinc–air battery possessed high reversibility and durability over long charge and discharge cycles.     

Nitrogen‐Doped Carbon with Mesopore Confinement Efficiently Enhances the Tolerance,Sensitivity, and Stability of a Pt Catalyst for the Oxygen Reduction Reaction

Electrocatalysts for the oxygen reduction reaction (ORR) present some of the most challenging vulnerability issues reducing ORR performance and shortening their practical lifetime. Fuel crossover resistance, selective activity, and catalytic stability of ORR catalysts are still to be addressed. Here, a facile and in situ template‐free synthesis of Pt‐containing mesoporous nitrogen‐doped carbon composites (Pt‐m‐N‐C) is designed and specifically developed to overcome its drawback as an electrocatalyst for ORR, while its high activity is sustained. The as‐prepared Pt‐m‐N‐C catalyst exhibits high electrocatalytic activity, dominant four‐electron oxygen reduction pathway, superior stability, fuel crossover resistance, and selective activity to a commercial Pt/C catalyst in 0.1 m KOH aqueous solution. Such excellent performance benefits from in situ covalent incorporation of Pt nanoparticles with optimal size into N‐doped carbon support, dense active catalytic sites on surface, excellent electrical contacts between the catalytic sites and the electron‐conducting host, and a favorable mesoporous structure for the stabilization of the Pt nanoparticles by pore confinement and diffusion of oxygen molecules.     

Highly Strong Interaction between Fe/Fe3C Nanoparticles and N-Doped Carbon toward Enhanced Oxygen Reduction Reaction Performance

Transition metal compounds anchored on N-doped carbon (NC) show intrinsic activity and stability for oxygen reduction reaction (ORR). However, the interaction between the transition metal compounds and NC still needs to be strengthened for electron transfer at the compounds/carbon interface. Herein, Fe/Fe₃C hybrid nanoparticles encapsulated into N-doped carbon (Fe@NC) are used as high-performance ORR catalysts. Benefiting from the strong interaction at Fe/Fe₃C nanoparticles/NC interface, the electrons can transfer from Fe/Fe₃C hybrid nanoparticles to NC, redistributing the electron density of active sites and promoting the ORR process. The as-synthesized Fe@NC exhibits outstanding ORR catalytic activity with an onset potential of 1.01 V and a half-wave potential of 0.92 V in alkaline media. It also shows prominent cycling stability and tolerance to methanol crossover, superior to Pt/C catalyst. The theoretical analysis reveals that the Fe nanoparticles have regulated the electron distributions at the heterojunction interface. The Gibbs free energy diagrams for ORR illustrate that the rate-determining step is the conversion of OH* to OH⁻. In situ Raman spectra give evidence of O-containing intermediates to prove the ORR process.     

A facile sonochemical route for the synthesis of MoS2/Pd composites for highly efficient oxygen reduction reaction

For the alkaline fuel cell cathode reaction, it is very essential to develop novel catalysts with superior catalytic properties. Here, we report the synthesis of highly active and stable MoS₂/Pd composites for the oxygen reduction reaction (ORR), via a simple, eco-friendly sonochemical method. The bulk MoS₂ was first transformed into single and few layers MoS₂ nanosheets through ultrasonic exfoliation. Then the exfoliated MoS₂ nanosheets served as supporting materials for the nucleation and further in-situ growth of Pd nanoparticles to form MoS₂/Pd composites via ultrasonic irradiation. Cyclic voltammetry and rotating disk voltammetry measurements demonstrate that as-prepared MoS₂/Pd composites which provides a direct four-electron pathway for the ORR, have better electrocatalytic activity, long-term operation stability than commercial Pt/C catalyst. We expect that the present work would provide a promising strategy for the development of efficient oxygen reduction electrocatalyst. In addition, this study can also be extended to the preparation of other hybrid with desirable morphologies and functions.     

Engineering beneficial structures and morphologies of M-N-C oxygen-reduction catalysts derived from different metal-containing precursors

Morphologies and structures of M-N-C catalysts are the key factor for controlling the formation of catalytic active sites, which are directly connected with the electrocatalytic activities for oxygen reduction reaction (ORR). By combining different metal sources (metal-free, Co, and Fe) with polyaniline (PANI) and para-phenylenediamine functionalized GO (PGO), morphologies and structures are tuned to accelerate the ORR activity. Compared with metal-free catalyst, metal-containing catalysts show better ORR performance because of the possible synergistic effect between metal and N atoms. In particular, the improved ORR activity of Fe-PANI-PGO catalyst is obtained by rotating disc electrode (RDE) at 1600 rpm in 0.1 M KOH electrolyte. The Fe-PANI-PGO electrocatalyst has the enhanced half-wave potential of 0.89 V and the high stability with only decreasing 7 mV of half-wave potential after 10,000 cycles, implying increased number and strengthened structures of active sites. Combined with various means of characterization, advantageous morphologies and structures including large electrochemically active surface area, high graphitization degree, and thick carbon structure with more pyridinic nitrogen boned with metal atoms can greatly enhance the ORR activity and stability of the catalyst.

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