Chemisorption of Probe Molecules on Metal Oxides

A more complete understanding of the structural and mechanistic details of a catalyzed heterogeneous reaction leads both directly and indirectly to the development of new and better catalysts. For catalyst technology, the most sensitive probe of catalysts performance will continue to be the rate and selectivity of a chemical reaction. However, these macroscopic observations, adequate for determining how good a catalyst is, require supplementary microscopic information to remove ambiguity in the deduction of a catalytic mechanism. This information, almost down to the atomic level, concerning the structure and reactivity of the intermediates, the nature of adsorption sites (and sometimes the active sites) and their number, is the main objective of the science of catalysis. The most promising approach to this problem is the use of suitable probe molecules for the quantitative titration of site density and qualitative characterization of their nature by means of surface spectroscopies of the chemisorbed probe molecules [1, 21. This framework of action is schematically represented in Fig.1.     

金属氧化物催化环己基苯过氧化反应的研究

环己基苯的过氧化是环己基苯法生产苯酚、环己酮工艺中最重要的一步反应。该文考察了4种金属氧化物对环己基苯过氧化反应的催化活性,反应温度383 K时,以环己基苯转化率为指标,4种催化剂活性大小顺序为:MnO2CuOCaOZnO。研究了以MnO2为催化剂时反应温度和催化剂用量等不同因素对环己基苯催化过氧化反应的影响,得出了优化的反应条件为:常压,反应温度393 K,催化剂用量0.01 g,通氧速率100 mL/min,反应时间10 h,在该条件下,环己基苯的转化率和过氧化氢环己基苯的选择性分别为33.58%和80.09%。     

Oxygen in Catalysis on Transition Metal Oxides

Reactions of catalytic oxidation over oxide catalysts have been extensively studied in recent years following expansion of their applications in petrochemistry as well as their wide theoretical interest. Studies in this field have also contributed greatly to our understanding of the general mechanisms of catalyst action.     

Catalysis of Gold Nanoparticles Deposited on Metal Oxides

Gold in bulk is chemically inert and has often been regarded to be poorly active as a catalyst. However, when gold is small enough—with particle diameters below 10 nm—it turns out to be surprisingly active for many reactions, such as CO oxidation and propylene epoxidation. This is especially so at low temperatures. Here, a summary of the catalysis of Au nanoparticles deposited on base metal oxides is presented. The catalytic performance of Au is defined by three major factors: contact structure, support selection, and particle size, the first of which being the most important because the perimeter interfaces around Au particles act as the site for reaction.     

Catalytic Decomposition of Formic Acid on Metal Oxides

Studies on the decomposition of formic acid were initiated during the first decade of the present century by Mailhe and Sabatier [1], using metals and metal oxides. These authors were concerned primarily with the selectivity of their catalysts, i.e., their ability to favor one of the reactions possible for the decomposition of formic acid (Eq. 1).     

Catalytic Decomposition of Formic Acid on Metal Oxides

Studies on the decomposition of formic acid were initiated during the first decade of the present century by Mailhe and Sabatier [1], using metals and metal oxides. These authors were concerned primarily with the selectivity of their catalysts, i.e., their ability to favor one of the reactions possible for the decomposition of formic acid (Eq. 1).     

金属氧化物对甲基乙烯基硅橡胶胶料性能的影响

研究金属氧化物MgO,ZnO,Fe₂O₃和Al₂O₃对甲基乙烯基硅橡胶（MVQ）胶料性能的影响。结果表明,金属氧化物种类对MVQ胶料的硫化特性和MVQ硫化胶的拉伸性能影响不大;加入MgO的MVQ硫化胶的压缩永久变形最小（6%）,Fe₂O₃使MVQ硫化胶的压缩永久变形明显增大;加入ZnO和MgO的MVQ硫化胶的耐油性能较好;加入MgO降低了MVQ硫化胶的橡胶分子主链的分解速率,将分解温度提高至647 ℃;与空白样相比,加入MgO的MVQ硫化胶的最终分解温度上升40 ℃,耐热性能显著提高;加入MgO的MVQ胶料的综合性能最佳。     

Metal Oxides for Dye-Sensitized Solar Cells

The incessant demand for energy forces us to seek it from sustainable resources; and concerns on environment demands that resources should be clean as well. Metal oxide semiconductors, which are stable and environment friendly materials, are used in photovoltaics either as photoelectrode in dye solar cells (DSCs) or to build metal oxide p – n junctions. Progress made in utilization of metal oxides for photoelectrode in DSC is reviewed in this article. Basic operational principle and factors that control the photoconversion efficiency of DSC are briefly outlined. The d -block binary metal oxides viz. TiO₂, ZnO, and Nb₂O₅ are the best candidates as photoelectrode due to the dissimilarity in orbitals constituting their conduction band and valence band. This dissimilarity decreases the probability of charge recombination and enhances the carrier lifetime in these materials. Ternary metal oxide such as Zn₂SnO₄ could also be a promising material for photovoltaic application. Various morphologies such as nanoparticles, nanowires, nanotubes, and nanofibers have been explored to enhance the energy conversion efficiency of DSCs. The TiO₂ served as a model system to study the properties and factors that control the photoconversion efficiency of DSCs; therefore, such discussion is limited to TiO₂ in this article. The electron transport occurs through nanocrystalline TiO₂ through trapping and detrapping events; however, exact nature of these trap states are not thoroughly quantified. Research efforts are required not only to quantify the trap states in mesoporous metal oxides but new mesoporous architectures also to increase the conversion efficiency of metal oxide-based photovoltaics.     

Defect Equilibria in Transition Metal Oxides

This paper assesses the importance of vacancy aggregates in transition metal oxides. It presents the predictions of quantitative atomistic calculations and discusses them in relation to observed structural, diffusion, thermodynamic, and other data. The results indicate that vacancy complexes constitute the major defect species at high nonstoichiometry. The commonly discussed vacancy-hole complexes appear to be unimportant except, perhaps, over a very limited composition range.     

纳米金属氧化物吸附金属离子的研究现状

纳米材料由于具有较大的比表面积及许多未饱和的原子,对金属离子具有很强的吸附性,纳米金属氧化物由于价格低廉、容易合成,近年来,在研究其对金属离子吸附方面受到关注。对纳米金属氧化物吸附金属离子的机理、影响因素、及应用进行了综述,提出了目前纳米金属氧化物在吸附金属离子方面存在的问题以及对其发展前景进行了展望。     

Pathways for Carboxylic Acid Decomposition on Transition Metal Oxides

The concept of structure sensitivity is well established for reactions catalyzed by metals as it has been generally demonstrated by the use of supported metal catalysts exhibiting different particle size [l-71. The con-cept of structure sensitivity in catalysis by metal oxides is considerably less well developed than in catalysis by metals, in spite of the growing number of examples of such reactions. Characterization of oxide catalyst is generally more problematical than that of metal; it is difficult, for example, to titrate the active surface areas of supported oxides by chemisorption techniques. Carboxylic acid decomposition could be used as a probe to establish struc-tural dependence and selectivity on metal oxides. For example, in the case of formic acid decomposition, bimolecular decomposition of two adsorbed formates occurs on a surface with Ti4+ cation of fourfold oxygen coordi-znation while unimolecular decomposition occurs in the case of formates adsorbed on Ti4+ fivefold coordinated cations [8]. Similarly, acetic acid adsorbed on Ti02 with Ti0,(011) leads to the production of ketene by unimolecular dehydration whereas on the Ti02(l 14) faceted surface, bi-molecular reaction of surface acetate takes place to form acetone [9, 101. Thus understanding the pathway of decomposition of carboxylic acid is likely not only to throw light on the new catalyst search for ketene formation but also to establish the use of this molecular decomposition model as a probe for the study of the structural property of metal oxide catalysts.     

金属掺杂改性钙钛矿型氧化物的研究进展

钙钛矿型氧化物由于其具有独特物理性质、化学性质和高的结构稳定性,日益成为材料科学领域的研究热点。但由于催化活性偏低,并且带隙能较高,不能高效利用太阳光谱中所含丰富的可见光,因此限制了该技术的推广应用。金属元素掺杂钙钛矿型氧化物可以有效改善其光催化性能,目前采用的方法主要有溶胶-凝胶法、水热法、固相反应法及微乳液法等,最后提出掺杂改性钙钛矿型氧化物的研究发展。     

Pathways for Carboxylic Acid Decomposition on Transition Metal Oxides

The concept of structure sensitivity is well established for reactions catalyzed by metals as it has been generally demonstrated by the use of supported metal catalysts exhibiting different particle size [l-71. The con-cept of structure sensitivity in catalysis by metal oxides is considerably less well developed than in catalysis by metals, in spite of the growing number of examples of such reactions. Characterization of oxide catalyst is generally more problematical than that of metal; it is difficult, for example, to titrate the active surface areas of supported oxides by chemisorption techniques. Carboxylic acid decomposition could be used as a probe to establish struc-tural dependence and selectivity on metal oxides. For example, in the case of formic acid decomposition, bimolecular decomposition of two adsorbed formates occurs on a surface with Ti4+ cation of fourfold oxygen coordi-znation while unimolecular decomposition occurs in the case of formates adsorbed on Ti4+ fivefold coordinated cations [8]. Similarly, acetic acid adsorbed on Ti02 with Ti0,(011) leads to the production of ketene by unimolecular dehydration whereas on the Ti02(l 14) faceted surface, bi-molecular reaction of surface acetate takes place to form acetone [9, 101. Thus understanding the pathway of decomposition of carboxylic acid is likely not only to throw light on the new catalyst search for ketene formation but also to establish the use of this molecular decomposition model as a probe for the study of the structural property of metal oxide catalysts.     

金属(氢)氧化物对氟醚橡胶耐热老化性能的影响

考察了金属（氢）氧化物对氟醚橡胶耐热老化性能的影响,并从理论上进行了探讨。热重分析结果表明,在氟醚橡胶的热老化过程中没有明显的氧化裂解发生,但氧对其热老化有一定的促进作用;金属（氢）氧化物可以促进氟醚橡胶的硫化,并可使其生成热稳定性更高的交联结构,有利于提高氟醚橡胶的耐热老化性能,特别是长时间耐热老化性能     

金属氧化物对硅橡胶和氟硅橡胶耐热性的影响

着重研究了金属氧化物对甲基乙烯基硅橡胶、甲基苯基乙烯基硅橡胶、三氟丙基甲基乙烯基硅橡胶耐热性的影响。结果表明,Ｆｅ２Ｏ３、ＦｅＯ３／ＳｎＯ２、ＳｎＯ２、ＣｅＯ２等可以显著提高硅橡胶的耐热性;光电子能谱分析结果说明,ＳｎＯ２、ＣｅＯ２在热空气老化过程中从高价态被还原到低价态,发生了多个（或单个）电子转移的氧化还原反应,从而阻止了硅橡胶的热氧化自由基链增长,提高了硅橡胶的耐热空气老化性能。     

超级电容器金属氧化物电极材料的研究进展

超级电容器具有功率高,使用寿命长,无污染等优点,具有广阔的应用前景和巨大的经济价值。电极材料是决定超级电容器性能的关键因素,因而备受关注。主要论述了应用于超级电容器的多种金属氧化物电极材料的研究进展。     

纳米金属氧化物去除水体重金属的研究进展

简要介绍了用于吸附水体重金属的几种纳米金属氧化物,包括:纳米铁氧化物、纳米锰氧化物、纳米铝氧化物、纳米钛氧化物、纳米锌氧化物、纳米镁氧化物、纳米铈氧化物以及纳米金属氧化物复合材料,讨论了各种纳米金属氧化物处理水体重金属的优缺点,并展望了其应用前景。     

硫酸化金属氧化物固体酸催化剂的研究进展

概述了国内外金属氧化物负载硫酸根固体酸催化剂研究进展及其改性研究。展望了固体酸催化剂在酯化反应在其今后的研究发展方向。     

MOFs荧光探针检测炸药分子研究

烈性炸药的探测是一项重要的研究课题,基于金属有机骨架化合物（MOFs）的荧光探针近年来受到研究者的广泛关注。本文采用密度泛函理论（DFT）和含时密度泛函理论（TDDFT）研究了金属有机骨架化合物[Zn（sfdb）（bpy）（H2O）]n的发光机理及其与硝基苯分子之间的氢键相互作用。运用TDDFT方法探究氢键在激发态下的行为,结果表明分子间氢键在激发态下增强,促进分子间电荷转移,导致荧光淬灭。这项研究工作表明分子间氢键对于荧光过程具有重要影响,这为设计合成探测炸药分子的MOFs荧光探针提供了新的思路。