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1.
There is a general desire to improve the configuration of industrial catalysts to take advantage of the intrinsic properties of metal oxides. In recent years, a series of studies has been published examining the growth of oxide nanoparticles on metal substrates. These studies have revealed structures for the supported oxide which are different from those found in bulk phases. In addition, the oxide ? metal interactions can alter the electronic states of the oxide producing new chemical properties. On an inverse oxide/metal catalyst, the reactants can interact with defect sites of the oxide nanoparticles, metal sites, and the metal–oxide interface. In these systems, one can couple the special reactivity of the oxide nanoparticles to the reactivity of the metal to obtain high catalytic activity. Furthermore, an oxide/metal system is also an attractive model for fundamental studies. It can be used to investigate the role of the oxide in a catalytic process, and how the stability of different reaction intermediates depends on the nature of the oxide.  相似文献   

2.
利用共沉淀法制备了几种稀土金属氧化物改性的氧化镍催化剂 ,考察了其乙烷氧化脱氢 (ODE)制乙烯的催化性能 ,讨论了不同稀土金属氧化物掺杂浓度对催化剂催化性能的影响 ,利用Raman光谱技术初步表征反应在该类催化剂上的活性氧物种为Raman谱带出现在 1 0 60cm- 1 的表面双原子超氧物种O-2 ,该谱峰的大小与催化剂的ODE性能有很好的对应关系。  相似文献   

3.
The search for more efficient catalytic systems that might combine the advantages of both homogeneous (catalyst modulation) and heterogeneous (catalyst recycling) catalysis is one of the most exciting challenges of modern chemistry. More recently with the advances of nanochemistry, it has been possible to prepare soluble analogues of heterogeneous catalysts. These nanoparticles are generally stabilized against aggregation into larger particles by electrostatic or steric protection. Herein we demonstrate the use of room temperature ionic liquid for the stabilization of palladium nanoparticles that are recyclable catalysts for the hydrogenation of carbon–carbon double bonds and application of these catalysts to the selective hydrogenation of internal or terminal C=C bonds in unsaturated primary alcohols. The particles suspended in room temperature ionic liquid show no metal aggregation or loss of catalytic activity even on prolonged use.  相似文献   

4.
Successive electropolymerization of dopamine and electrodeposition of Pd and/or Pt on a graphene oxide (GO) support were used to prepare anode catalysts for low-temperature fuel cells. Transmission electron microscopy images were used to investigate the morphologies and distribution of the prepared catalysts, which showed the metal formed as nanoparticles on the catalysts. The GO surface was favorable for the modification with electropolymerized polydopamine (PDA) and the electrodeposition of metal catalyst nanoparticles using a simple preparation process. The PDA-loaded GO composite was used as a matrix for the dispersion of Pt and Pd nanoparticles. GO could be simultaneously modified by PDA and reduced without using reducing agents. The electrocatalytic performance of the catalysts for the oxidation of selected small molecule fuels (e.g., methanol, ethanol and formic acid) was examined. An outstanding catalytic activity and stability was found for the prepared Pt/Pd/PDA/GO composite, which was attributed to the high active surface area.  相似文献   

5.
The direct epoxidation of propylene to propylene oxide (PO) using molecular oxygen is an attractive alternative to current production methods using chlorohydrin or hydroperoxide-mediated processes, which are environmentally harmful and expensive. Although direct ethylene epoxidation using Ag-based catalysts has been practiced industrially for decades, due to the presence of allylic hydrogen in propylene the selectivity toward epoxide is generally much lower for propylene than for ethylene. Mechanistic understanding on well-characterized surfaces of model catalysts can potentially provide guidance to effectively alter the electronic properties of the catalyst in order to increase PO selectivity. This review summarizes both experimental and theoretical studies on model catalysts for propylene epoxidation and their contributions to elucidating the reaction mechanism, intermediates, and active sites. We first show examples of experimental studies on Cu, Ag, and Au surfaces, and compare the reaction pathways and intermediates on these surfaces. Novel approaches including plasmon-mediated catalysis and utilization of shape-controlled crystal facets that open new opportunities for improving PO selectivity will also be discussed. We then describe how density functional theory (DFT) calculations have provided important insights into the reaction mechanism and active sites on Cu, Ag, and Au surfaces and clusters. Propylene oxidation pathways on other relevant metal surfaces will also be discussed. The combined experimental and computational studies elucidate the nature of surface oxygen species and the role of the oxametallacycle intermediate. We conclude by highlighting design principles and insights for guiding further development of active and selective propylene epoxidation catalysts.  相似文献   

6.
用于HCOOH分解制氢的贵金属催化剂存在着反应选择性差和资源稀缺等问题. 单原子催化可以有效改善催化剂性能并降低成本,C2N作为一种新型二维材料可为过渡金属原子提供良好的结合位点. 本文利用密度泛函理论,设计了Pd@C2N 单原子催化剂,研究了HCOOH在Pd@C2N表面上的吸附和分解制氢反应机理. 结果表明,HCOOH可在Pd原子顶位吸附,并在C2N表面N原子的协同作用下通过甲酸盐路径生成氢气. 通过比较,Pd@C2N具有比Pd (111)表面更好的催化反应活性与选择性.  相似文献   

7.
Surface state and reactivity of vanadium-tin mixed oxide nanoparticles (V/Sn ratios 0.05-0.2) were characterized by spectroscopic techniques and catalytic measurements. Analyses by X-ray photoelectron spectroscopy (XPS) and diffuse reflectance spectroscopy (DRS) revealed that the oxidation state and surface structure of vanadium oxide species and the electronic interaction between Sn and V atoms are dependent upon the vanadium content. These oxides were evaluated as catalysts for methanol oxidation in a fixed-bed reactor. Both reaction rate and formaldehyde selectivity increased with increasing the vanadium amount in catalyst. Results demonstrate that the V5+ site in the bridging V-O-Sn structure exhibits a high redox activity to facilitate the transformation of adsorbed methoxy to formaldehyde and that the vanadium dispersion plays a crucial role in the surface reactivity. A mechanism that elucidates the catalytic redox process is proposed.  相似文献   

8.
Model low-percentage metal oxide palladium catalysts are prepared from acetate complexes of Pd and Mn to study the nature of the activity and the genesis of nanostructured membrane catalyst Pd-Mn systems. A comprehensive study of the prepared model precursor compounds; specific features of their metal components in gels and oxides; and the genesis of the active component, local structure, and charge state is performed by EXAFS and XANES. Possible versions of structural models for the stabilization of metals on oxide supports aare discussed.  相似文献   

9.
Preparative methods for the reduction of simple and complex metal oxides by supercritical isopropanol (SCI) were developed. Procedures for effective work with SCI under usual laboratory conditions were suggested. Optimum reaction conditions (temperature and pressure) and reagent ratios for reactions between SCI and metal oxides were found. Disperse oxides coated by fine-dispersity metals that could be used as catalysts were prepared. Simple methods for obtaining metal nanoparticles by the reduction in situ of metal oxide nanoparticles stabilized in polyethylene and synthetic silica (opal) matrices with SCI were developed.  相似文献   

10.
The synergetic effect in multicomponent catalysts is a topic of profound industrial importance and intense academic interest. On a newly identified multicomponent catalyst, Au/IrO(2)/TiO(2), first-principles density-functional theory is analyzed to clarify the outstanding catalytic activity of the system for oxidative reactions at high temperatures. By comparing CO oxidation on interfaces and single-component surfaces, it is revealed that a high dispersion of a more active oxide (IrO2), on a more inert oxide (TiO2) is the key. It preserves the sintering resistance of Au supported on less active oxides, while at the same time promoting oxidative reactions that occur at the Au/active-oxide interface.  相似文献   

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