碱性介质中异丙醇在铂电极表面的吸附和电化学氧化

运用电化学循环伏安、原位FTIR反射光谱和石英晶体微天平(EQCM)等方法研究了碱性介质中异丙醇在Pt电极表面吸附和氧化行为. 结果表明：碱性介质中异丙醇电氧化过程不存在自毒化现象. 虽然电化学原位FTIR反射光谱未能检测到CO等毒性物种, 但EQCM结果证明异丙醇或其解离产物吸附于铂电极上. 在实验条件下, 碱性介质中异丙醇在铂电极上氧化的最终产物只有丙酮, 预示着碱性介质中异丙醇通过脱氢步骤氧化成丙酮. EQCM研究还从电极表面质量定量变化的角度提供了异丙醇吸附和电氧化反应机理的新数据.     

镀Pd的GC电极上HCOOH的电催化氧化

在玻璃碳 (GC)基底上电沉积Pd ,应用SEM观测Pd沉积层的表面形貌 ,用循环伏安法研究了Pd/GC电极上HCOOH在HClO4溶液中的电氧化行为 .结果表明 ,Pd的电沉积条件影响电极的催化性能 .在高电流密度下制得的Pd/GC电极对HCOOH的电氧化具有比纯Pd电极更高的催化活性 .当电极表面生成PdO时 ,HCOOH被电氧化的活性很低 ,而在PdO还原后生成的Pd表面 ,HCOOH的电氧化显示极高的活性 .本文还讨论了Pd(Ⅱ )离子对HCOOH电氧化过程的影响 .     

酸性溶液中钯催化醇电化学氧化的研究

应用电化学循环伏安法(CV)和现场红外光谱(FTIR),研究了酸性溶液中钯催化甲醇、乙二醇电氧化的过程.结果表明:在酸性和中性介质中,甲醇和乙二醇在多晶Pd电极上氧化须在1.5V以上才能发生.随着溶液pH值的降低,过电位减小且峰电流密度上升.溶液的pH值以及电极表面形成的吸附含氧物种对Pd电催化氧化醇有显著的影响.现场红外光谱电化学测试显示,在高电位和强酸性介质中,乙二醇在Pd电极上的氧化产物主要是CO2和少量的乙二酸.在酸性和中性介质中,无论在低电位或高电位,甲醇和乙二醇在Pd上氧化的主要产物是CO2,没有发现CO的存在,说明该氧化过程CO2是经过非毒化的路径产生的.     

乙醇在钯电极上的电氧化机理

利用循环伏安与现场傅里叶变换红外(FTIR)光谱对乙醇在Pd电极上的电氧化机理进行了研究. 循环伏安测量表明, 乙醇在Pd上氧化的性能受pH值与乙醇浓度的影响. 当溶液pH>11.0时, Pd对乙醇才具有催化性能, 而且乙醇在Pd上氧化的性能随着pH值和乙醇浓度的增加而提高. 现场红外光谱电化学测量结果证明, 乙醇在不同pH 溶液中的氧化反应机理和产物不同. 当溶液pH>13.0 时, 产物只有乙酸盐, 说明乙醇仅发生部分氧化, 乙醇中的C—C键没有断裂. 当溶液pH≤13.0时, 尽管乙醇在Pd电极上的氧化活性受到抑制, 却发生完全氧化而产生二氧化碳, 说明乙醇的C—C键在低碱环境中容易断裂, 最后乙醇被完全氧化. 实验中没有检测到CO, 表明该反应途径是一个非毒化过程.     

浸渍法制备硅钨酸修饰的炭载钯催化剂电催化甲酸氧化

用浸渍的方法制备了硅钨酸（SiWA）修饰的炭载Pd(Pd/C-SiWA)催化剂。 计时电流曲线研究表明,在Pd/C和Pd/C-SiWA催化剂电极上,3000 s时的电流密度分别为0.013和0.082 A/mg,分别为10 s时电流密度的2.5%和14.1%。 结果表明,Pd/C-SiWA催化剂对甲酸氧化的电催化稳定性要远远优于Pd/C催化剂。 这是因为Pd/C催化剂上SiWA的修饰抑制了甲酸的自分解, 从而减小了CO的毒化作用,改进了Pd/C催化剂对甲酸氧化的电催化和稳定性。     

纳米钯催化剂对甲醇的电催化氧化

采用水热法,以甲醛作还原剂还原Pd2+-EDTA络合物,制得钛基纳米钯颗粒电极(nanoPd/Ti).扫描电子显微镜(SEM)显示,纳米钯颗粒直径约为60 nm,形成三维立体网状结构.在碱性溶液中,循环伏安及交流阻抗测试分别表明:nanoPd/Ti电极对甲醇氧化有极高的阳极电流、较低的起始氧化电位和较强的抗CO毒化能力.在nanoPd/Ti电极上甲醇电氧化反应的阻抗值较低,增加甲醇浓度,电极阻抗更低.电极对甲醇氧化具有极好的电催化活性.     

金属化聚邻甲苯胺膜修饰电极的性能研究

在聚邻甲苯胺 (POT)膜修饰电极上用电化学法沉积Pt微粒 ,由SEM与XRD表征其表面形态与晶面取向 ,同时研究异丙醇在金属化POT膜电极上的氧化行为 .结果表明 ,Pt在POT膜上的沉积呈现晶面择优取向的现象 ,况且POT质子掺杂后 ,由于电化学活性增强 ,影响了沉积铂微粒的尺寸和粒径分布 .异丙醇的电氧化可发生在POT的电化学活性区 ,当电位大于 0 .70V(SCE)时 ,POT不再呈氧化还原活性 ,异丙醇的电氧化主要在铂微粒上进行 .聚合物不仅作为铂微粒的载体而且自身参加反应 ,这种微异相催化体系需用新的模型描述     

碱性介质中葡萄糖在铂电极上的阳极氧化

为了进一步探明葡萄糖在铂电极上的氧化机理,用循环伏安法(CV)在-0.9～0.4 V(相对于饱和甘汞参比电极)内研究了葡萄糖在铂电极上催化氧化行为,首次详细报道了葡萄糖在电化学氧化过程中的电位振荡现象,并用电流扫描法表征了葡萄糖的电位振荡情况.电流扫描结果表明,在较慢的电流扫描速度下,电极过程出现了明显的电位振荡.说明电极上产生了毒化中间物,电位振荡是由于毒化中间物在电极上的吸附和在高电位下氧化除去引起的.     

PmClAn基膜修饰电极的电化学及催化性质研究

聚苯胺作为电极修饰材料 ,已在传感器上显示出广泛的应用前景[1～ 4 ] .异丙醇 ( i- P)氧化[5,6 ] 是个较简单的反应 ,被广泛作为电催化研究的模型反应 .目前 ,i- P电化学氧化的研究集中于 Pt的多晶或单晶电极[7～ 9] ,Gonzales等 [10 ] 报道了 Pt- Sn共沉积的 PAn膜修饰电极上的异丙醇电氧化 ,但对复合材料的微观结构仍欠研究 .本文讨论 Pm Cl An基质性质对 Pt电沉积的影响 ,并探讨了 i- P在沉积 Pt微粒的 Pm Cl An功能膜电极上的氧化情况 .1　实验部分1 .1　电极的制备　聚间氯苯胺 ( Pm Cl An,本征态 ud,HCl掺杂态 d)采用乳液聚…     

Synthesis and structure of colloids and films from Pd–Ag in organic solvents

Pd/Ag bimetallic particles are dispersed in acetone, 2-propanol and 2-methoxyethanol. The colloids are prepared by codeposition of the vapors of metals and solvents at 77 K. The stabilities of the Pd/Ag colloids are in the order acetone>2-methoxyethanol~2-propanol. The particles are studied by transmission electron microscopy to determine their size and also by electron diffraction to study their crystal structure. The Pd/Ag samples exhibit more than one metallic phase in the different solvents, these being Pd, Ag and Pd/Ag. The crystallinity is controlled by the Pd/Ag ratio; the crystalline phases in the bimetallic particles can be observed using the dark field technique. The differential scanning calorimetry of Pd/Ag-2-methoxyethanol solids shows three exothermic peaks in which phase transformation, microcrystal growth and solvent decomposition of the solvent in the solid are observed. However, the differential scanning calorimetry of Pd/Ag-acetone solids shows two exothermic peaks.     

Electrooxidation of 2-propanol on Pt, Pd and Au in alkaline medium

Pd and Au are investigated as electrocatalysts for 2-propanol oxidation and compared with the conventional catalyst of Pt in alkaline medium. The current density for 2-propanol oxidation on Pd electrode is much higher than that on Pt electrode. The onset potential for 2-propanol oxidation on Pd electrode is more negative compared with that on Pt electrode. The results show that Pd is a good electrocatalyst for 2-propanol oxidation and the activity for the electrooxidation of 2-propanol is higher than Pt and Au in alkaline medium. Pd has higher electrocatalytic activity and better stability for the electrooxidation of 2-propanol. The present study shows a promising choice of Pd as effective electrocatalyst for 2-propanol electrooxidation in alkaline medium.     

Palladium nanoparticles from solvated atoms—stability and HRTEM characterization

Palladium particles of nanometric dimensions were synthesized by the chemical liquid deposition method in which the Pd atoms were co-deposited at 77 K with 2-propanol, acetone, and tetrahydrofurane vapor to obtain colloidal dispersions. The colloidal dispersions were characterized by UV–visible spectrophotometry, transmission electron microscopy (TEM) and high-resolution TEM (HRTEM). The palladium colloids synthesized by use of these solvents are very stable. A strong absorption band in the UV region suggests that quantum confinement occurs in the nanoparticles obtained by this procedure. Studies of TEM micrographs reveal average size distributions between 1 and 5 nm for all Pd colloids. Whereas particle sizes in Pd–2-propanol colloids are not very sensitive to concentration change, the particle-size average in Pd–acetone and Pd–THF increases by 0.5 nm when the concentration increases from 10^–3 to 10^–2 mol l^–1. The HRTEM results show the high crystallinity of Pd nanoparticles and three low-energy structure shapes were found: cuboctahedron, tetrakaidecahedron, and icosahedron.     

Pd/C promoted by Au for 2-propanol electrooxidation in alkaline media

Pd/C catalysts promoted by Au are investigated as electrocatalysts for the direct 2-propanol fuel cells in alkaline media. The results show that Pd is a good electrocatalyst for 2-propanol oxidation and the activity for 2-propanol electrooxidation is higher than that for methanol electrooxidation on the Pd/C electrocatalysts in alkaline media. Addition of Au can significantly increase the palladium catalytic activity and stability for the 2-propanol oxidation. PdAu4:1/C has higher electrocatalytic activity and better stability for the electrooxidation of 2-propanol than Pd/C and E-TEK Pt/C electrocatalysts. The present study shows the promising properties of Au promoted Pd/C as effective electrocatalysts for 2-propanol fuel based direct alcohol fuel cells.     

TPR studies on steam reforming of 2-propanol on Rh/Al2O3, Ru/Al2O3 and Pd/Al2O3

Reaction pathways for steam reforming of 2-propanol (isopropyl alcohol, IPA) on Rh/Al₂O₃, Ru/Al₂O₃ and Pd/Al₂O₃ have been studied by temperature-programmed reactions (TPRs) of IPA and acetone in the presence of steam. The results of TPRs suggest that that of IPA on Rh/Al₂O₃ and Ru/Al₂O₃ proceeds via acetone, while the steam reforming of IPA on Pd/Al₂O₃ takes place via propene from acetone. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ion association of lithium bromide,chloride and picrate and of sodium picrate in 2-propanol at 25°C. I. Conductance measurements

The molar conductances of lithium bromide, chloride and picrate, and of sodium picrate have been determined as a function of salt concentration in 2-propanol solvent at 25°C. Values of the limiting molar conductance, Λ₀, and ion pair formation constant K_A have been calculated for each of these salts using both the Fuoss 1978 and the Lee and Wheaton conductance equations. Both of these equations yield comparable results for the present systems. The limiting conductances found here are compored with those reported for lithium chloride in 1-propanol and acetone and with those for the picrates in acetone and 2-butanone, all solvents of comparable dielectric constants. The Rasaiah-Friedman square mound potential, h_+?/kT, has been calculated for each salt using the approach of Justice and Justice. These values for 2-propanol have been compared with those for lithium chloride in 1-propanol and in acetone and for the picrates in acetone and 2-butanone.     

CW-CO2激光引发异丙醇反应

近年来,醇类的红外光化学反应及其红外多光子解离的研究日益受到人们的重视。Farneth等报道了用TEACO_2激光器引发气相异丙醇反应,得到丙烯产物。我们用CW-CO_2激光引发气相和液相异丙酮反应,主要得到丙酮,以及少量的丙烯,甲烷和CO。我们曾经研究了CW-CO_2激光引发NH_3 CH_3OH反应得到产物六次甲基四胺,而此产物是由CH_2O和NH_3反应生成的。据此,我们认为在无氧条件下,CW-CO_2激光引发气相异丙醇反应或引发NH_3敏化甲醇的多     

The conductance of electrolytes in acetone-2-propanol and acetone-1,1,1,3,3,3-hexafluoro-2-propanol mixtures at 25°C1

Precise conductance measurements are reported for tetrabutylammonium chloride, bromide, iodie, and perchlorate and lithium chloride in acetone-2-propanol (2-PrOH) and acetone-1,1,1,3,3,3-hexafluoro-2-propanol (HFP) mixtures at 25°C. Densities, viscosities and dielectric constants of the mixtures were determined. The dielectric constant vs mole % acetone curve for the acetone (ε=19.4)-2-propanol (ε=20.5) goes through a minimum at 40% acetone (ε=17.4), while that for acetone-HFP (ε=16.8) goes through a maximum at 50% acetone (ε=26.87). The variations ofK _A with ε in acetone-HFP are in accord with the predictions of electrostatic theory, while those for acetone-2-PrOH show more complex behavior. Ionic association in these mixtures is discussed in terms of an interplay between solvent structure and a multiple-step association process.     

Effect of mercaptan on photoreduction of acetone. Non-repair hydrogen transfer reactions

Abstract— Ultraviolet (u.v.) irradiation of solutions of benzhydrol in acetone leads to formation of -2-propanol, benzpinacol and some benzophenone, apparently from the free radicals (CH₃)₂COH, II, and (C₆H₅)₂COH, I. 2-Propanol is formed more rapidly and benzophenone is formed to a much larger extent and persists longer when the solution contains mesityl mercap-tan, as radical II is reduced by mercaptan and radical I is oxidized by thiyl radical. The same hydrogen atom transfer reactions, which retard by a repair mechanism the photoreduction of benzophenone by 2-propanol, accelerate and alter the course of photoreduction of acetone by benzhydrol. Irradiation of acetone leads to 2-propanol, and this is formed more rapidly in the presence of mercaptan. Irradiation of benzophenone in acetone leads to no apparent reaction. The courses of reaction of the several systems are discussed.     

The Enol of Acetone during Photochemical Reactions of 3-Hydroxy-3-methyl-2-butanone and of Acetone

The enol of acetone, formed by disproportionation reactions of 1-hydroxy-1-methylethyl radicals, is detected by NMR, spectroscopy during photoreactions of 3-hydroxy-3-methyl-2-butanone in acetonitrile and of acetone in 2-propanol and slowly tautomerizes to acetone. The photolysis of 3-hydroxy-3-methyl-2-butanone is shown to proceed via Type I cleavage, predominantly from an excited triplet state.