Hydrogen Effects in Metal Catalysts

The interaction of hydrogen with metals is the cause or basis of a host of phenomena ranging from the chemisorption of hydrogen on the surface, its dissolution in the metal, catalytic reactions involving hydrogen as a reactant or as an astoichiometric component, etc., to the formation of metal hydrides. Hydrogen -induced corrosion and hydrogen embrittlement of steel are well known in chemical process industry and metallurgy. Catalytic reactions on metal or metal-oxide catalysts in the presence of hydrogen, often under pressure, are some of the major chemical, petroleum, and petrochemical processes of today, e.g., ammonia, methanol, Fischer-Tropsch, Oxo and other syntheses, hydrogenation of oils and fats, catalytic reforming, hydrode-sulfurization/hydrotreating, hydrocracking, and hydrogenation/ dehydrogenation.     

Activation of Supported Pd Metal Catalysts for Selective Oxidation of Hydrogen to Hydrogen Peroxide

Catalytic activity of supported Pd metal catalysts (Pd metal deposited on carbon, alumina, gallia, ceria or thoria) showing almost no activity in the liquid-phase direct oxidation of H₂ to H₂O₂ (at 295 K) in acidic medium (0.02 M H₂SO₄) can be increased drastically by oxidizing them using different oxidizing agents, such as perchloric acid, H₂O₂, N₂O and air. In the case of the Pd/carbon (or alumina) catalyst, perchloric acid was found to be the most effective oxidizing agent. The order of the H₂-to-H₂O₂ conversion activity for the perchloric-acid-oxidized Pd/carbon (or alumina) and air-oxidized other metal oxide supported Pd catalysts is as follows: Pd/alumina < Pd/carbon < Pd/CeO₂ < Pd/ThO₂ < Pd/Ga₂O₃. The H₂ oxidation involves lattice oxygen from the oxidized catalysts. The catalyst activation results mostly from the oxidation of Pd metal from the catalyst producing bulk or sub-surface PdO. It also caused a drastic reduction in the H₂O₂ decomposition activity of the catalysts. There exists a close relationship between the H₂-to-H₂O₂ conversion activity and/or H₂O₂ selectivity in the oxidation process and the H₂O₂ decomposition activity of the catalysts; the higher the H₂O₂ decomposition activity, the lower the H₂-to-H₂O₂ conversion activity and/or H₂O₂ selectivity.     

Precious Metal Catalysts Supported on Ceramic and Metal Monolithic Structures for the Hydrogen Economy

Distributed hydrogen for the hydrogen economy will require new catalysts and processes. Existing large-scale hydrogen plants can not simply be reduced in size to meet the economic, safety, and frequent duty cycle requirements for applications for fuel cells, hydrogen fueling stations, and industrial uses such as hydrogenation reactions, gas turbine cooling, metal processing, etc 1, 2. Consequently, there is a need to completely reassess how hydrogen can be made for the emerging hydrogen economy. This article presents some of the technological advantages of precious metal monoliths over traditional base metal particulate catalysts for reforming hydrocarbons, such as natural gas, for the generation of distributed hydrogen.     

有机合成中的三氟甲磺酸金属盐催化剂

三氟甲磺酸金属盐催化剂有极强的热力学及化学稳定性,在温和的反应条件下具有活性高、选择性好、收率高、低毒性和可循环使用等特点而广受关注,能够催化亲电取代、亲核取代和加成等多种反应,而且可以用于全水相高效催化。简要总结了三氟甲磺酸金属盐在有机合成中的应用情况,包括傅克反应、缩醛反应、氢烷氧化与氢胺化反应、烯丙基化反应、成环开环反应、氧化与还原反应、重排反应等多种合成领域。     

Aging-Induced Metal Redistribution in Bimetallic Catalysts

Alloy particles were detected by XRD in bimetallic catalysts, made from physical mixtures of powders comprising distinct metal-support combinations (e.g., Pd on alumina and Rh on ceria-zirconia), following high-temperature redox aging. The morphology of the catalysts was examined by TEM, and the compositional structure of some of the alloy particles was determined. Two different effects of the redistribution of metals on oxygen-storage capacity were identified, one due to Pd enrichment of the surface of Pd-Rh alloy particles and the other due to loss of contact between metal and ceria-zirconia.     

Metal Particle Size Determination of Supported Metal Catalysts

The variety of supported metal catalysts utilized in the operations of the petroleum and chemical industries emphasizes the importance of metal-catalyzed reactions. As a result, many scientific investigators have attempted to characterize and follow closely the changes in the crystallite size and shape of supported metal particles in commercial and simulated environments. From these efforts a massive production of experimental facts has emerged.     

Molecular Metal Clusters as Catalysts

Abstract

In earlier analyses [1–8] we have established a correlation between metal clusters and metal surfaces with chemisorbed molecules in the specific contexts of (1) the metal frameworks wherein the metal cluster core structures are fragments of cubic and hexagonal close packed or body centered cubic metal bulk structures; (2) ligand stereochemistry where the geometric features of ligands bound to clusters and to metal surfaces are similar; (3) thermodynamic features where the average bond energies for ligand-metal and metal-metal bonds are comparable, for a specific metal, in the metal cluster and the metal surface regime; and (4) mobility of ligands bonded to metal cluster frameworks and to metal surfaces. Nevertheless, there are sharp distinctions between surfaces and clusters. The average coordination numbers for metal-metal interactions and for metal-ligand interactions are distinctly different for clusters and for surfaces: generally, the former are larger for surfaces and the latter are larger for clusters. Additionally, the surface state is typically differentiated from the cluster state in the degree of coordination saturation—the metal atoms in the surface state are typically less coordinately saturated even for the states in which molecules or molecular fragments are chemisorbed at the surface than those metal atoms at the periphery of a molecular metal cluster. In the crucial chemical issue, metal surfaces are far more reactive than metal clusters. Metal surfaces exhibit a wide range and high level of catalytic activity whereas most metal clusters are catalytically inert, at least under modest reaction conditions, Most reported clusters are relatively stable and nonreactive; they are not the products of sophisticated synthesis procedures designed to generate highly reactive metal clusters. They commonly have been the products of reaction mixtures run at forcing conditions and are thermodynamically controlled, not kinetically controlled, products.     

Molecular Metal Clusters as Catalysts

In earlier analyses [1-8] we have established a correlation between metal clusters and metal surfaces with chemisorbed molecules in the specific contexts of (1) the metal frameworks wherein the metal cluster core structures are fragments of cubic and hexagonal close packed or body centered cubic metal bulk structures; (2) ligand stereochemistry where the geometric features of ligands bound to clusters and to metal surfaces are similar; (3) thermodynamic features where the average bond energies for ligand-metal and metal-metal bonds are comparable, for a specific metal, in the metal cluster and the metal surface regime; and (4) mobility of ligands bonded to metal cluster frameworks and to metal surfaces. Nevertheless, there are sharp distinctions between surfaces and clusters. The average coordination numbers for metal-metal interactions and for metal-ligand interactions are distinctly different for clusters and for surfaces: generally, the former are larger for surfaces and the latter are larger for clusters. Additionally, the surface state is typically differentiated from the cluster state in the degree of coordination saturation—the metal atoms in the surface state are typically less coordinately saturated even for the states in which molecules or molecular fragments are chemisorbed at the surface than those metal atoms at the periphery of a molecular metal cluster. In the crucial chemical issue, metal surfaces are far more reactive than metal clusters. Metal surfaces exhibit a wide range and high level of catalytic activity whereas most metal clusters are catalytically inert, at least under modest reaction conditions, Most reported clusters are relatively stable and nonreactive; they are not the products of sophisticated synthesis procedures designed to generate highly reactive metal clusters. They commonly have been the products of reaction mixtures run at forcing conditions and are thermodynamically controlled, not kinetically controlled, products.     

Metal Particle Size Determination of Supported Metal Catalysts

The variety of supported metal catalysts utilized in the operations of the petroleum and chemical industries emphasizes the importance of metal-catalyzed reactions. As a result, many scientific investigators have attempted to characterize and follow closely the changes in the crystallite size and shape of supported metal particles in commercial and simulated environments. From these efforts a massive production of experimental facts has emerged.     

The Sintering of Supported Metal Catalysts

Metal catalysts are commonly employed in the form of metal dispersed as small crystallites on high surface area supports. The use of these supported metal catalysts increases the utilization of the metal as a catalyst since a large fraction of the metal atoms are at the surface of the small metal crystallites. Another important function of the support is to physically separate the small metal crystallites and thereby hinder the agglomeration of the small metal crystallites into larger crystallites. This agglomeration would decrease the number of surface metal atoms per unit mass of metal, and thereby decrease the utilization of the metal and the activity of the catalyst.     

负载型纳米贵金属催化剂的催化氢化反应研究

研究了负载型的高分散纳米贵金属催化剂和含钌的双金属催化剂对2-吡啶甲酸甲酯加氢反应的催化活性.结果表明,单金属催化剂Ru(5 %)/C对吡啶及其衍生物具有较好的催化活性.用XRD、HRTEM和XPS对还原后的Ru/C催化剂表征,表明钌处于高分散零价态,其平均粒径小于5 nm.在50 ℃、5.0 MPa的条件下,催化2-吡啶甲酸甲酯,其加氢转化率达100 %,TOF达到了10.     

制氢转化催化剂的使用与维护

总结了制氢转化催化剂的装填、运行情况,针对催化剂运行过程中存在的问题提出了预防措施。     

Separation by Diffusion of Hydrogen Clusters in a Metal Hydrogen System

Abstract

Dynamical problems facing hydrogen diffusion in metal hydrogen systems at low temperature are surveyed. A microscopic model is constructed based on the assumption that the functional units are clusters of Fermi or Bose particles, collectively referred to as spin clusters. Critical behavior of metal hydrogen systems provides a key approximation which makes our model soluble. The time-dependent autocorrelation functions are obtained by solving the Heisenberg equation of motion using a new mathematical technique called the recurrence relations. The dynamical solutions shed light on the reversed isotope effect in diffusion. The nature of interstitial spin clusters is examined and compared with atomic and nuclear spin clusters. The spin clusters show striking resemblance to the superfluid component in the two-fluid theory of liquid ⁴He.     

贵金属催化剂的研究进展

贵金属因其完美的质感和独特的金属色泽,自古便被人们视为财富和高贵的象征。随着科技水平的不断进步,贵金属优良物化特性逐渐引起了人们的关注,并将其广泛地应用于工业催化领域,收到了良好的效果。综述了钯(Pd)、金(Au)、铂(Pt)系和银(Ag)这4类贵金属在催化领域的研究进展,并进行了展望。     

Propane Oxidative Dehydrogenation over Metal Pyrophosphates Catalysts

Metal pyrophosphates (M–P₂O₇, where M is V, Zr, Cr, Mg, Mn, Ni or Ce) have been found to catalyze the oxidative dehydrogenation of propane to propene. The reaction was conducted at 1 atm, 450–550°C and feed flowrate of 75 cm³/min (20 cm³/min propane, 5 cm³/min oxygen and the balance is helium). All catalysts showed increase in degrees of conversion and decrease in olefins selectivity with increase in reaction temperature. At 550°C, MnP₂O₇ exhibited the highest activity (40.7% conversion) and total olefins (C₃H₆ and C₂H₄) yield (29.3%). The other catalysts, indicated by their respective metals, may be ranked (based on olefins yield) as V (16.9%) < Cr (17.5%) < Ce (25.1%) < Zr (26.2%) < Ni (26.8%) < Mg (27.9%). The reactivity of the lattice oxygen was estimated from energy of formation of the corresponding metal oxides. Correlation between the selectivity to propene and the standard energy of formation was attempted. Although there was no clear correlation, the result suggested that the lattice oxygen play a key role in the selectivity-determining step.     

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%。     

高分子金属络合物催化剂新进展

简述高分子金属络合物催化剂的发展历史。着重介绍其在加氢反应、氧化反应和硅氢加成等中的应用和特点,以及高分子金属络合物催化剂的发展趋势。     

过渡金属硫化物催化剂的研究进展

金属硫化物通常被人们普遍认定为一种有害物质,但随着科学的发展,过渡金属硫化物在催化方面的应用引起了人们广泛的关注。本文介绍了过渡金属硫化物催化剂在加氢、合成醇、还原SO2等反应中的应用研究。