Catalytic wet air oxidation of oleic acid on ceria-supported platinum catalyst.effect of pH

Summary Catalytic wet air oxidation (CWAO) of oleic acid was carried out in a batch reactor on platinum supported ceria catalyst (Pt/CeO₂). Oleic acid is a water insoluble linear unsaturated fatty acid of 18 carbon atoms. To increase the homogeneity of the solution by saponification, the influence of NaOH additions in oleic acid CWAO mechanism and catalyst performances have been investigated. The oxidation of such molecule occurs by two types of mechanisms: successive carboxy-decarboxylation which leads essentially to CO₂and/or C-C bonds splitting in the alkyl chain inducing a high formation of acetic acid. With or without NaOH, the 5%Pt/CeO₂catalyst is active in the conversion of oleic acid and selective to carbon dioxide. In alkaline medium, oleic acid is initially saponified which increases the solubility of the reactant before it to be oxidized. Finally the oxidation is slightly delayed by the presence of NaOH. The catalyst characterizations show no significant difference before and after reaction.</o:p>     

Impedance study of Ni–Co electro-deposition on Fe powder particles in fluidised bed systems

The electrochemical impedance method was applied during the electrochemical deposition of a binary Ni–Co coating on iron powder in a fluidised bed electrode system. The influence of the suspension density on the charge transfer in the course of the electro-deposition process was studied. At a potential of −900 mV (vs. Ag/AgCl/3 M KCl), when the binary Ni–Co layer was formed, the impedance data were characterised by two semicircles with the semicircle at high frequencies being larger in magnitude. A contribution of the diffusion process to the overall current was observed. The optimal suspension density for the charge transfer in the bed was 10×10⁻³–15×10⁻³ (i.e., 4–6 g of iron powder in 50 ml of electrolyte). The most probable mechanism of the charge transfer for the studied concentrations of powder particles is the convective mechanism. The iron particles dispersed in the electrolyte were considered to act as either a depolariser or an additional working electrode depending on the applied electrode potential and on the suspension density.     

Peculiarities of interactions between the DNA molecule and different isomers and modifications of binuclear coordination compounds of platinum(II)

A comparison has been made of conformational changes in the DNA molecule during its interaction in solution with different binuclear coordination compounds of platinum [Pt(NH₃)₂Cl-R-Pt(NH₃)₂Cl]Cl₂ in cis and trans conformations, which contain cytosine, pyrazine, and carboxypyrazine as the common ligand (R). The influence of concentration of the components, and in particular, of ionic strength of the solution on the complexation process was studied. The influence of the nature of the common ligand, and of cis and trans conformations of coordination compounds on the character of their interaction with DNA was considered. A comparison was made between the structures of DNA complexes with mono-and binuclear compounds with the same set of ligands in the platinum coordination sphere.     

Geometrical characteristics of four-coordinate complexes of Ni,Pd, and Pt containing triphenylphosphine as ligand

A statistical analysis based on crystal structure results of 4-coordinated complexes of Ni, Pd, and Pt containing triphenylphosphine as ligand has been performed using the Cambridge Structural Data Base. Distorted square-planar coordination appears as the most probable one presented by these metals.

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Geometrische Charakteristika von vier-koordinierten Komplexen des Ni, Pd und Pt mit Triphenylphosphin als Ligand

Zusammenfassung Es wurde unter Verwendung der Cambridge Strukturdatenbank eine statistische Analyse von Resultaten an vier-koordinierten Komplexen des Ni, Pd und Pt mit Triphenylphosphin-Ligand durchgeführt. Dabei ergab sich eine verzerrte quadratisch-planare Koordination als die am meisten wahrscheinliche Geometrie.

     

Pt/HM和Pd/HM催化剂表面氧的恢复与供出活化能测定

催化氧化是最重要的工业催化反应之一。七十年代以来,关于氧化催化剂的基础研究取得了长足的进步,采用各种手段对氧化催化剂的表面及体相氧种进行了考察。本文作者根据研究实用氧化催化剂的经验,结合控制论方法,亦提出了多相催化氧化反应的集团结构适应性规律。近年来,作者用TPD和吸附平衡法研究了V_2O_5/SiO_2催化剂表面氧的种类、数目和供出活性,较好地关联了催化氧化的一些事实,使以上规律更趋于半定量化。在多相氧化反应中,催化剂表面活性氧不断处于供出和恢复的循环之中,催化剂表面氧中心的供     

Pt/TiO_2催化剂上的氢—氧作用 Ⅰ.氢、氧的吸咐—脱附行为以及相互促进作用

本文采用程序升温脱附(TPD)技术研究了光沉积方法制备的Pt/TiO_2催化剂经过氧化、还原后氧、氢的脱附行为.光沉积过程中,Pt/TiO_2表面上可以生成大量的吸咐氢,在TPD中脱附;同时Pt/TiO_2表面上化学吸附的水在TPD过程中也可以分解释氢.氧化处理的Pt/TiO_2在TPD过程中于550～750K温区出现氧脱附峰,随着氧化温度升高,脱附峰位向高温移动,经实验证明,这种可脱附活泼氧物种的生成是由样品前身中留存氢引起的.还原处理的Pt/TiO_2在TPD过程中分别在300～600和大于600K出现两个氢脱附峰,认为是由于表面羟基和钛—氢(Ti~(4+)—H~-)物种的分解释氢引起的Pt/TiO_2上活泼氧物种的存在,增加了样品在室温条件下的吸氢量;在中温(473～573K)这种活泼氧物种则和氢发生反应,减少了TPD过程中的脱氢量;Pt/TiO_2在大于673K温度还原,可以消除活泼氧物种的影响.     

Pt/TiO_2催化剂上的氢—氧作用——Ⅱ. 程序升温还原和程序升温氧化研究

本文采用TPR、TPO技术分别考察了氧处理Pt/TiO_2上氧物种的还原行为和氢还原样品的氧化过程.TPR结果表明,表面含有活泼氧物种的Pt/TiO_2样品对氢很活泼,室温条件下可以吸附大量氢,并且这些吸附氢又可以在TPR过程中脱附.表面活泼氧物种与氢的反应温度在500—673K之间,当大于673K时,Pt/TiO_2继续耗氢,可能是氢与还原产生的表面Ti~(3+)离子进一步反应生成钛—氢物种,并向TiO_2体相扩散与TiO_2体相晶格氧发生反应.对于773K还原的Pt/TiO_2作品,室温吸附氧在TPD过程中可以与表面吸附氢反应;473K氧化处理可以消除表面的吸附氢,但并不能完全去除体相储氢;573K氧化处理则基本上恢复了原样品的氧化状态.不同温度氢还原处理的Pt/TiO_2样品在动态氧化过程(TPO)中,在300-600K温区,气相氧与样品上表面吸附氢和表面氧空位反应;在大于600K温区,氧主要与表面钛—氢物种发生反应,并向体相扩散,与体相氢发生反应.文中描述了气相氢、氧分别与Pt/TiO_2催化剂存在的氧或氢物种作用的形式.     

新型重整催化剂的研究—Pt／BaKL型沸石中钡的作用

本文采用XRD,NH_3-TPD,IR以及TEM等方法考察了Pt/BaKL沸石中Ba~(2+)的作用。NH_3-TPD结果表明,交换Ba~(2+)后的L型沸石的酸性,由于阳离子的作用仅在弱酸范围内有些改变,但与载铂的沸石的催化活性无明显的对应关系。IR及XRD谱线表明,BaKL沸石中Ba~(2+)在最佳交换度(26.3%)时,随预培烧温度的提高,使Ba~(2+)处于沸石孔道中B、C、D位置,接近于最佳分布,此时IR谱线上1421cm~(-1)处有一新峰。当沸石负载铂后,因铂与Ba~(2+)的相互作用,新峰消失,导致铂粒在沸石上分布更加均匀;铂粒在1.5—3.0nm之间占有最大比例,使得Pt/BaKL沸石呈现芳构化活性及选择性高于Pt/KL沸石,分别为～98%和～95%。     

负载Pt,Pd催化剂上NO—TPD和NO催化还原性能

负载Ｐｔ、Ｐｄ催化剂上ＮＯ－ＴＰＤ和ＮＯ催化还原性能１）钟依均（浙江师范大学化学系金华３２１００４）罗孟飞周碧袁贤鑫（杭州大学催化研究所杭州３１００２８）关键词负载Ｐｔ、Ｐｄ催化剂ＮＯ－ＴＰＤＣＯ－ＮＯ反应分类号Ｏ６４３．３２氮氧化物（ＮＯｘ）污染是...     

甲醇在欠电位沉积Ru修饰Pt电极上的催化氧化

采用欠电位沉积(upd)方法在Pt 表面沉积亚单层的Ru制备出upd-Ru/Pt 电极. 通过欠电位沉积前后电极在0.5 mol·L-1 H2SO4溶液中循环伏安图-152 - 128 mV(vs Ag/AgCl)电位范围内对氢区的数值积分确定Pt表面Ru 的覆盖度. 用电化学方法测试了甲醇在upd-Ru/Pt电极上的催化氧化, 并讨论分析了欠电位沉积电位和Ru的表面覆盖度对甲醇氧化的影响. 结果表明, Ru能够欠电位沉积到Pt表面. Pt表面欠电位沉积少量的Ru 即能大大促进甲醇的氧化.只要控制upd-Ru的沉积量, upd-Ru原子就能大大促进甲醇氧化而与沉积电位无关. Ru原子对甲醇氧化的促进作用与Ru和Pt是否形成合金无关, 而取决于Ru 在Pt表面的百分含量.