制备方法对直接乙醇燃料电池阳极PtSn/C催化剂性能的影响

 对比研究了用三种液相沉积还原法制备的PtSn/C催化剂,并用X射线衍射、透射电镜和程序升温还原等技术表征了催化剂的形貌、结构及组成. 用乙二醇还原法制备的PtSn/C(EG)催化剂的平均粒径最小(约为1.8 nm), 且分布均匀, Sn以多种价态存在于PtSn/C(EG)中. 采用循环伏安法和直接乙醇燃料电池单池评价了三种PtSn/C催化剂对乙醇氧化反应的催化活性,探索了单池性能与催化剂粒径及组成的关系. 结果表明, PtSn/C(EG)催化剂具有较高的催化乙醇氧化活性. 这可能是因为PtSn/C(EG)催化剂的金属粒径较小, Pt晶格发生了适当的扩张以及SnO2能够在较低电位下提供含氧物种的缘故.     

添加锡组分对Pt/ZSM-5催化剂丙烷脱氢反应性能的影响

丙烷脱氢制丙烯是优化利用炼厂气和油田伴生气资源的一条重要途径,这方面的研究已日益引起研究者的关注[1～5].对γ-Al2O3为载体的负载型铂催化剂丙烷脱氢催化性能已进行了深入的研究.通过引入特定的助剂,可以提高负载型铂催化剂低碳烷烃脱氢选择性和稳定性[6,7].与Ce、Zn、V、La、Cr、Fe、Zr、Mn等助剂比较,Sn助剂更有利于提高催化剂丙烷脱氢的反应稳定性[8].     

Effect of thermal treatment on phase composition and ethanol oxidation activity of a carbon supported Pt50Sn50 alloy catalyst

A carbon supported Pt–Sn electrocatalyst in the Pt/Sn atomic ratio 50:50 was prepared by the reduction of Pt and Sn precursors with formic acid and thermally treated at 200 °C (i.e., in the presence of solid tin) and 500 °C (in the presence of molten tin) in flowing hydrogen. In the absence of thermal treatment, X-ray diffraction (XRD) analysis showed a solid solution of Sn in the face centered cubic (fcc) Pt and SnO₂. After thermal treatment, the formation of a main phase of hexagonal PtSn (niggliite) and a secondary phase of cubic Pt₃Sn was observed in the Pt50Sn50 catalyst. The relative amount of the PtSn phase increased with increasing thermal treatment temperature. The presence of molten tin gave rise to the formation of some big particles during annealing at 500 °C. The activity for the ethanol oxidation reaction (EOR) of the as-prepared catalyst was higher than that of both thermally treated catalysts and Pt75Sn25/C and Pt50Ru50/C by E-TEK. The higher activity for the EOR of the as-prepared Pt–Sn catalysts was ascribed to the presence of a large amount of SnO₂. Dedicated to Teresa Iwasita’s 65th birthday.     

PtSn/Al2O3/MCM-41催化剂的丙烷脱氢催化性能

用微型催化反应装置评价, 并结合X射线粉末衍射(XRD)、表面积和孔结构测试、程序升温还原(TPR)、氢化学吸附和热重分析等方法研究了负载型PtSn/γ-Al2O3, PtSn/MCM-41和PtSn/Al2O3/MCM-41催化剂的丙烷脱氢反应催化性能. 发现PtSn/Al2O3/MCM-41催化剂具有较PtSn/MCM-41催化剂高的丙烷脱氢反应活性和较PtSn/γ-Al2O3催化剂高的反应稳定性. 实验结果表明, 纯硅MCM-41载体表面的锡物种因与载体相互作用较弱故易被还原, 导致铂金属分散度和催化剂的丙烷脱氢活性较低. 用Al2O3修饰MCM-41可以增强Sn物种与Al2O3/MCM-41载体之间的相互作用, 提高PtSn/Al2O3/MCM-41催化剂铂金属分散度和丙烷脱氢催化活性. 并且, 积炭后的PtSn/Al2O3/MCM-41催化剂具有较高的铂金属表面裸露度, 故具有较高的丙烷脱氢反应稳定性. PtSn/Al2O3/MCM-41催化剂优良的丙烷脱氢催化性能可能不仅与Sn-载体Al2O3/MCM-41较强的相互作用有关, 而且与Al2O3/MCM-41载体的介孔结构有关.     

A novel precursor system and its application to produce tin doped indium oxide

A new type of precursor has been developed by molecular design and synthesised to produce tin doped indium oxide (ITO). The precursor consists of a newly developed bimetallic indium tin alkoxide, Me(2)In(O(t)Bu)(3)Sn (Me = CH(3), O(t)Bu = OC(CH(3))(3)), which is in equilibrium with an excess of Me(2)In(O(t)Bu). This quasi single-source precursor is applied in a sol-gel process to produce powders and coatings of ITO using a one-step heat treatment process under an inert atmosphere. The main advantage of this system is the simple heat treatment that leads to the disproportionation of the bivalent Sn(II) precursor into Sn(IV) and metallic tin, resulting in an overall reduced state of the metal in the final tin doped indium oxide (ITO) material, hence avoiding the usually necessary reduction step. Solid state (119)Sn-NMR measurements of powder samples confirm the appearance of Sn(II) in an amorphous gel state and of metallic tin after annealing under nitrogen. The corresponding preparation of ITO coatings by spin coating on glass leads to transparent conductive layers with a high transmittance of visible light and a low electrical resistivity without the necessity of a reduction step.     

Theoretical evidence of PtSn alloy efficiency for CO oxidation

The efficiency of PtSn alloy surfaces toward CO oxidation is demonstrated from first-principles theory. Oxidation kinetics based on atomistic density-functional theory calculations shows that the Pt3Sn surface alloy exhibits a promising catalytic activity for fuel cells. At room temperature, the corresponding rate outstrips the activity of Pt(111) by several orders of magnitude. According to the oxidation pathways, the activation barriers are actually lower on Pt3Sn(111) and Pt3Sn/Pt(111) surfaces than on Pt(111). A generalization of Hammer's model is proposed to elucidate the key role of tin on the lowering of the barriers. Among the energy contributions, a correlation is evidenced between the decrease of the barrier and the strengthening of the attractive interaction energy between CO and O moieties. The presence of tin modifies also the symmetry of the transition states which are composed of a CO adsorbate on a Pt near-top position and an atomic O adsorption on an asymmetric mixed PtSn bridge site. Along the reaction pathways, a CO2 chemisorbed surface intermediate is obtained on all the surfaces. These results are supported by a thorough vibrational analysis including the coupling with the surface phonons which reveals the existence of a stretching frequency between the metal substrate and the CO2 molecule.     

Reacting the unreactive: a toolbox of low-temperature solution-mediated reactions for the facile interconversion of nanocrystalline intermetallic compounds

Metallurgical materials, including intermetallic compounds, are notoriously inert toward low-temperature reactivity. However, as nanocrystals, their reactivity is significantly enhanced. Here we show that intermetallic PtSn and AuCu nanocrystals can be converted, in solution at low temperatures, into derivative intermetallics. For example, PtSn can be converted into PtSn2 and Pt3Sn by reaction with SnCl2 and K2PtCl6, respectively. The reactions are also reversible, for example, the sequences PtSn --> PtSn2 --> PtSn and PtSn --> Pt3Sn --> PtSn are all readily achievable. The strategy also allows nanocrystalline AuCu to be successfully converted into AuCu3 via reaction with Cu(C2H3O2)2.H2O, suggesting that this approach may be general.     

Catalysts of ethanol anodic oxidation for ethanol-air fuel cell with a proton-conducting polymer electrolyte

Synthesis techniques for binary PtSn, PdM (M = Sn, V, Mo) and ternary PtSnNi, PtRuSn catalysts of ethanol electrooxidation on highly dispersed carbon materials are suggested. The highest activity in the 0.5 M H₂SO₄ solution containing 1 M C₂H₅OH corresponds to the system of PtSn (3: 1, 40 wt % Pt) with the particle size of 2–4 nm and tin content in the alloy with platinum of about 6%. It was shown that the catalyst efficiency as regards ethanol oxidation depth decreases in the series of Pt > PtRu ≈ PtSn, and the catalyst activity by current forms the series of PtSn > PtRu > Pt. The membrane-electrode assembly (MEA) with the anodes on the basis of the PtSn (3: 1, 40 wt % Pt) catalyst had stable characteristics for 220 h at the current density of ∼50 mA/cm².     

锡负载量对PtSn/Al2O3催化丙烷脱氢性能的影响

采用羰基合成-浸渍法制备了不同Pt/Sn摩尔比(3:1, 1:1, 1:2和1:3)的PtSn/Al₂O₃催化剂, 利用N₂吸附-脱附实验、 X射线衍射(XRD)、 透射电子显微镜(TEM)、 吡啶吸附红外光谱(Py-IR)和热重-差热分析(TG-DTA)等手段对其进行了表征, 研究了Sn负载量对PtSn/Al₂O₃的结构性质及催化丙烷脱氢性能的影响. 结果表明, 制备的PtSn/Al₂O₃具有较高的丙烯选择性和稳定性. 当Pt/Sn摩尔比为3:1和1:1时, 铂和锡在催化剂上主要以Pt₃Sn和PtSn合金形式存在, 合金的形成明显改善了催化剂的脱氢性能, 可抑制金属颗粒的高温烧结; 当Pt/Sn摩尔比为1:2和1:3时, 铂主要以金属形式存在. 随着Sn负载量的增加, 催化剂上L酸性位逐渐减少, 丙烷转化率降低, 丙烯选择性增加, 同时促使反应积炭从金属表面向载体迁移, 改善了催化剂的稳定性.     

Extractive separation and spectrophotometric determination of palladium and platinum with dithizone in the presence of stannous chloride

The conditions [acid used, presence of chloride and tin(II)] for the extractive separation and spectrophotometric determination of palladium and platinum as the dithizonates Pd(HDz)(2) and Pt(HDz)(2) have been examined. In the absence of stannous chloride platinum does not undergo extraction. Conditions for the separation and determination of these metals in the presence of mercury, gold and copper, which are also extracted with dithizone into carbon tetrachloride or chloroform under the conditions suitable for palladium (1M sulphuric acid/0.1M hydrochloric acid), have been defined. The mercury and gold dithizonates are formed quickly and can be removed before the palladium and platinum compounds have had time to form. They can be decomposed with iodide. Copper dithizonate is decomposed by reduction with tin(II). The proposed procedure has been applied to the determination of palladium in technical platinum metal.     

Crystal structure and chemical bonding in tin(II) acetate

Tin(II) acetate was prepared and its crystal structure was solved from X-ray powder diffraction data. Tin(II) acetate adopts a polymeric structure consisting of infinite Sn(CH₃COO)₂ chains running along the c-axis which are packed into groups of four. The acetate groups bridge the Sn atoms along the chains. The Sn atoms are asymmetrically surrounded by four oxygen atoms with two short Sn–O distances (2.170(6), 2.207(6) Å) and two longer ones (2.293(7), 2.372(8) Å). The coordination environment of the Sn atoms is completed up to a strongly distorted trigonal bipyramid SnO₄E by the sterically active lone electron pair E. The coordination environment of the Sn atoms is virtually identical for Sn(CH₃COO)₂ in the gaseous and solid phase: the two short Sn–O bonds and the lone electron pair are located in the equatorial plane of the trigonal bipyramid and the two longer Sn–O bonds are directed towards the apical vertexes. Localization of the lone electron pair on Sn(II) was confirmed by electron localization function (ELF) analysis. The polymeric nature of the tin(II) acetate crystal structure was confirmed by a MALDI-TOF experiment.     

Determination of trace tin by stripping potentiostatic coulometry

On the basis of voltammetric and coulometric studies of the behavior of tin(II) in a 2 M HCl solution at a carbon-graphite bulky electrode made of fibrous porous felt (FPF), we have found the optimum conditions for the stripping potentiostatic coulometric determination of 10–1000 μg tin(II) by the reaction Sn(0)-ē ? Sn(I) after preconcentrating Sn(0) at the electrode surface. The relative standard deviation varied from 0.5 to 4%. The results of the coulometric determination of the number of electrons involved in the oxidation of Sn(0) suggest that the stripping Sn(0) from the surface of the FPF electrode proceeds in two stages. The first stage Sn(0) → Sn(I) was electrochemical, and the second stage Sn(I) → Sn(II) was chemical. The procedure was applied to the determination of ～1% tin in a jewelry alloy based on gold, silver, platinum, and copper.     

水蒸汽对PtSn／Al2O3催化剂结构及反应性能的影响

比较研究了Ａｌ２Ｏ３负载的铂及ＰｔＳｎ催化剂在氮气及水蒸汽稀释条件下的丙烷脱氢性能,并利用ＸＰＳ及氢脉冲吸附对催化剂进行了表征。结果表明,水蒸汽可促使Ｐｔ／Ａｌ２Ｏ３催化剂的铂晶粒烧结。与在氮气氛中相比,在水蒸汽存在下反应显著提高了Ｐｔ／Ａｌ２Ｏ３的丙烷转化率,却降低了丙烯的选择性。另一方面,水蒸汽可调变ＰｔＳｎ／Ａｌ２Ｏ３催化剂的结构,破坏了ＰｔＳｎ／Ａｌ２Ｏ３中与锡相互作用的铂簇团结构。从而导     

B修饰的ZrO2及其制备p H值对PtSn/B-ZrO2丙烷脱氢反应性能的影响（英文）

丙烯作为一种重要的石油化工基础原料,传统上是从石脑油蒸汽裂解或催化裂化过程中作为副产物生产的.随着原油的枯竭和页岩气开发技术的成熟,通过乙烷蒸汽裂解制备乙烯更具吸引力并已得到广泛的工业应用,但该路线乙烯选择性高,而副产物丙烯数量有限.为满足不断增加的丙烯需求量,利用油田气和页岩气中低附加值的丙烷为原料,将其直接脱氢制丙烯(PDH)具有重要的现实意义.目前已开发成功的PDH技术采用的催化剂主要为负载PtSn型催化剂和Cr基催化剂.其中,Pt基催化剂较Cr基催化剂更加环境友好,因此得到了更广泛的应用.由于Pt元素的昂贵和稀有,制备低Pt含量和良好性能的催化剂极具吸引力.UOP Oleflex工艺开发的最新一代催化剂DEH-16仅含有0.3 wt%Pt,相对于前一代催化剂Pt含量降低30%.然而,许多文献报道,随着Pt含量的降低,催化剂的稳定性很容易恶化,降低Pt含量并保持催化剂性能仍具有一定的挑战.研究表明,含有更多Lewis酸性位点和更少Bronsted酸位点的催化剂显示出较好的丙烷脱氢活性和丙烯选择性.此外,源自缺陷位或配位不饱和位的Lewis酸性位也可为负载的金属颗粒提供锚定位点.BASF对ZrO2作为载体的丙烷脱氢催化剂进行了广泛研究,但其催化剂尚未完全商业化.有文献报道,ZrO2负载的PtSn催化剂在脱氢反应中的稳定性较差.将元素硼(B)加入到ZrO2中可以极大地抑制Bronsted酸性而提高Lewis酸量和酸强度,因此我们推测含有适量配位不饱和Zr位点的ZrO2作为PtSn丙烷脱氢催化剂载体可能具有优异的性能.载体的合成pH值对催化剂PDH性能也会有影响.然而,目前还没有硼改性的ZrO2(B-ZrO2)合成pH值对PDH催化性能影响的研究.本文研究了B-ZrO2的合成pH值(9,10和11)对PtSn/B-ZrO2在丙烷脱氢反应中催化性能的影响.Py-IR结果表明各pH值下合成的B-ZrO2均只有Lewis酸,NH3-TPD结果则表明B-ZrO2的Lewis酸量和强度随合成pH值的增加而增加.XPS结果显示,载体对Pt和Sn电子性质的影响不容忽视.由于OSC与CO氧化活性之间没有线性关系,因此Pt和Sn之间的相互作用程度在CO氧化反应中可能起主要作用,并有如下递增趋势:PtSn/B-ZrO2-9相似文献   

Zn对Pt-Sn/γ-Al2O3催化剂中Sn的活性状态及丙烷脱氢反应的影响

将少量Zn添加到催化剂Pt-Sn/γ-Al2O3中, 可显著提高催化剂的丙烷脱氢稳定性和丙烯的选择性. 程序升温还原(H2-TPR)和程序升温电导(TPEC)测试结果表明, Zn的存在使Sn在强还原气氛中不易被还原, Sn的氧化态的稳定存在是Sn发挥助剂作用和保持催化剂稳定性的重要条件.     

钒化合物对酸性镀锡溶液的稳定作用

研究了钒化合物稳定剂对酸性SnSO4 溶液稳定性的影响 .可见光谱分析表明稳定剂中主要含有VO2 + 和少量的V3+ ,循环伏安实验显示在 - 0 .2 0～ - 0 .55V(vs .SCE)电位范围内VO2 + 能够在阴极上还原为V3+ ,在更负的电位下V3+ 能进一步还原到V2 + .实验结果说明稳定剂中的低价钒离子有效地清除了镀液中的溶解氧 ,因而防止了Sn2 + 离子的氧化 ,显著地提高了酸性锡镀液的稳定性 .     

直接乙醇燃料电池PtSn/C电催化剂的合成表征和性能

采用多元醇法制备了n(Pt)/n(Sn)比为2:1,3:1,4:1的PtSn/C电催化剂.通过XRD,TEM、循环伏安和氢化学吸附技术对催化剂进行了表征.TEM和XRD结果表明,不同比例的PtSn/C金属粒子的平均粒径均小于4nm,且粒径分布较窄;该系列催化剂中Pt具有fcc结构;PtSn间的相互作用使Pt晶格参数增大.循环伏安和氢化学吸附实验结果表明,加入Sn可抑制Pt对氢的吸附,Pt3Sn/C对乙醇的氧化电流比Pt4Sn/C高约1倍.用不同n(Pt)/n(Sn)比的催化剂作为直接醇类燃料电池阳极电催化剂,在相同条件下,随着Sn含量的增加,单电池最大输出功率逐渐增大,当Sn含量继续增大时,单池性能反而下降.导致不同比例PtSn催化剂活性差别的原因可能是由于Sn与Pt间的合金化程度不同和催化剂粒子尺寸效应及Sn含量对电池阻抗等几方面因素所致.对40h寿命测试前后的阳极Pt3Sn/C催化剂的分析(EnergydispersiveX-rayanalysis,EDX)结果表明,PtSn含量在测试前后均有所降低,PtSn催化剂的寿命尚有待改善.     

用于锂离子电池负极材料的锡/碳复合材料研究

采用分散聚合的方法在氧化锡的表面包覆聚对位二乙烯基苯,再热解制备了锡基颗粒在碳基体中均匀分散的锡/碳复合材料.该复合材料具有良好的循环性能.在该复合材料中无定形碳起到了至关重要的作用,它一方面保证了复合材料的导电性能,另一方面有效地抑制了锡基颗粒的团聚与粉化.只有当小尺寸的锡基颗粒均匀地分散在碳基体中时,锡/碳复合材料才具有稳定的电化学性能.     

High stability three-dimensional porous PtSn nano-catalyst for ethanol electro-oxidation reaction

In addition to the theoretical research, direct ethanol fuel cells have great potential in practical applications. The performance of direct ethanol fuel cells largely depends on the electrocatalysts. Pt-based electrocatalysts have been promising candidates for advancing direct ethanol fuel cells for its high catalytic activity and great durability. Here, a PtSn catalyst with unique three-dimensional porous nanostructure has been designed and synthesized via a two-step liquid phase reduction reaction. Sn formed a self-supporting framework in PtSn alloy particles (∼3.5 nm). In ethanol electro-oxidation reaction, the PtSn catalyst exhibited high mass activity and excellent recycling time compared with that of Pt/C. After the morphology characterization before and after potential cycling, the PtSn alloy-based nano-catalyst showed good stability. The PtSn catalysts effectively avoid structural instability due to the external carriers, and prolong the leaching time of Sn. In addition, the introduction of a certain amount of Sn can also solve the poisoning phenomenon of active sites on Pt surface. The design strategy of porous alloy nano-catalyst sheds light on its applications in direct ethanol fuel cells.     

Modification of a Pt surface by spontaneous Sn deposition for electrocatalytic applications

In the present communication we explored a simple dip-coating method for spontaneous (without applying an external current or additional reducing agents) modification of Pt surface by both tin oxy-species and tin metal based on hydrolysis of tin chloride complex and autocatalytic (electroless) deposition of tin for fabrication of the fuel cell catalysts with improved CO tolerance. It consisted of (i) Pt immersion into SnCl₂/HCl solution under open-circuit conditions; (ii) subsequent rinsing of the surface by pure water. The resulting Sn-modified Pt surfaces were characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry (CV). Two types of tin species, namely, tin oxide/hydroxide species and metallic tin were identified at Pt surface. Tin oxide/hydroxide species were assumed to be derived as a result of Sn(II) chloride complex hydrolysis, while tin metal particles were most likely deposited spontaneously on Pt surface due to disproportionation of Sn(II) to Sn(IV) and metallic tin, competing with dissolution of the Sn deposit in strongly acidic medium. Modifying tin species show a satisfactory stability in 0.5-M H₂SO₄ solution at potentials relevant to low-temperature fuel cell operating conditions (below 0.6 V vs. a standard hydrogen electrode, SHE).