Chemisorption Complexes on Alloy Surfaces

Three factors have greatly promoted the recent revival of interest in catalysis by alloys.

The first was the finding that in industrial catalysis certain bimetallic systems are superior to monometallic catalysts. Sinfelt [1-5] had a particularly important share in the pioneering work supporting this finding. He showed that the selectivity for catalyzing nondestructive hydrocarbon reactions is often significantly tighter for a bimetallic catalyst than for its most active monometallic constituent. Even more important was the finding that bimetallic catalysts are frequently less susceptible to poisoning by, e.g., carbonaceous residues [1-6], As a consequence, their steady-state activity will be superior to that of monometallic catalysts even if the initial activity was lower.     

Enantiospecific Chemisorption of Amino Acids on Step Decorated Chiral Cu Surfaces

Highly stepped metal surfaces can define intrinsically chiral structures, and can potentially be used to separate chiral molecules. The decoration of steps on these surfaces with additional metal atoms may be one potential avenue for improving the enantiospecificity of those surfaces. Density functional theory (DFT) calculations have been performed to study the enantiospecific chemisorption of amino acids adsorbed on the pure, Pd-decorated, and Au-decorated Cu(643) ^S surfaces. Negligible differences in adsorption energies for the most stable minima of enantiomers of alanine were found on these surfaces. There are, however, measureable energy differences between the two enantiomers of both serine and cysteine in their most stable states for all surfaces. For serine and cysteine in ?? ₃ adsorption geometries, no enhancement in enantiospecificity upon the step decoration is observed, while for those in ?? ₄ geometries, it is improved, especially on Au-decorated surface. Our results provide initial information on how tuning the chemistry of intrinsically chiral surfaces can affect the enantiospecific adsorption of amino acids on these surfaces.     

铝合金基体上超疏水表面的制备

采用简单化学刻蚀的方法制备出多晶铝合金基体上的超疏水表面.刻蚀后的铝合金表面经过氟化处理后具有了超疏水的性质,水滴与表面的接触角达到156°,接触角滞后为5°.通过对表面进行扫描电镜分析可知,超疏水铝合金表面上具有了由长方体状的凸台和凹坑构成的深浅相间的微纳米结构,这些微纳米结构相互连通形成凹凸不平的“迷宫”结构,这种结构经氟化修饰后,可捕获空气,形成水与基底之间的气垫,对表面超疏水性的产生起到了关键的作用.文中对铝合金基体上的超疏水现象以Cassie 理论进行了分析,结果表明,水与表面形成了非均匀接触,约12%的面积是水滴和基体接触,而有约88%的面积是水滴和空气接触.研究中考查了不同刻蚀时间以及不同刻蚀液浓度对表面疏水效果的影响.最佳制备条件为:盐酸溶液浓度为4.0 molL1,刻蚀时间为12 min.     

Stimuli-Responsive Cucurbit[n]uril-Mediated Host-Guest Complexes on Surfaces

Supramolecular functional surfaces are at the heart of many materials and medical applications. Increasing interest can be seen for devising new supramolecular functionalization strategies of surfaces. In this review we place particular emphasis on the use of cucurbit[n]uril-mediated host-guest complexation as surface functionalization strategy. The state of the art of cucurbit[n]uril-mediated host-guest complexes on surfaces is reviewed. Cucurbit[n]urils (CB[n]) are able to form strong host-guest complexes with affinities that span several orders of magnitudes up to the regime of the biotin-streptavidin pair and that can be modulated by applying remote stimuli provided suitably sensitive guests were selected. Strategies to fabricate stimuli-responsive surfaces creates versatile supramolecular systems and several applications of these types of surfaces are outlined.     

Titanium and Alloy Surfaces for Adhesive Bonding

The nature of the oxide on the surface of titanium and the Ti-6Al-4 V alloy after a number of recommended treatments has been examined by x-ray and electron diffraction. No evidence for material other than titania in its rutile form was obtained even though anatase and fluoride have been reported. The most efficient surface for adhesive bonding is a rough surface of the black oxide such as is produced by treatment of the metal in alkaline hydrogen peroxide.     

Titanium and Alloy Surfaces for Adhesive Bonding

The nature of the oxide on the surface of titanium and the Ti-6Al-4 V alloy after a number of recommended treatments has been examined by x-ray and electron diffraction. No evidence for material other than titania in its rutile form was obtained even though anatase and fluoride have been reported. The most efficient surface for adhesive bonding is a rough surface of the black oxide such as is produced by treatment of the metal in alkaline hydrogen peroxide.     

纳米改性环氧底漆在铝材及其合金表面的应用研究

研究了一种使用纳米浓缩浆改性的环氧底漆,可以直接涂装在铝材及其合金表面,大大提高涂层对铝材表面的防护性。探讨了环氧固化剂、颜料体积浓度及纳米浓缩浆添加量对涂膜性能的影响。     

铝合金表面微弧氧化涂层制备工艺

用微弧氧化技术对铝合金表面进行强化处理,利用正交试验设计优化试验方案,按五因素四水平得到正交表,合理安排微弧氧化试验,达到优化工艺条件的目的;并用综合平衡法评价各因素对陶瓷膜硬度和厚度影响的主次顺序和最优水平.结果表明:铝合金微弧氧化陶瓷膜的硬度和厚度受各因素水平的影响显著,其中硅酸钠的质量浓度对陶瓷膜硬度和厚度的影响最大;在最优工艺条件下,陶瓷膜致密层硬度达1 700 HV,膜层总厚度达到约200μm.     

Chemisorption of oxygen on cellulose char

Investigation of a series of chars prepared by rapid pyrolysis of cellulose in the temperature range of 400–800°C has shown that they have a high chemisorptive affinity for oxygen. Maximum chemisorption occured on chars prepared at a HTT of 550°C. The Elovich equation was used to describe the kinetics of the process. The extent of chemisorption decreased with increasing HTT of the chars, although the surface area of the chars stayed approximately constant; indicating the presence of less reactive areas on the surface of chars formed at higher temperatures. As chemisorption progressed there was a corresponding increase in the intensity of several IR absorption bands, which were attributed to the formation of stable oxygen-containing functional groups. The chemisorption process, preceded by physical adsorption, does not influence the gasification reaction. The presence of impurities from pre-pyrolysis doping of cellulose could promote or inhibit the rate of gasification but had negligible effect on the initial rate of chemisorption. The role of these two processes in char combustion was discussed in the light of known concepts for the carbon-oxygen reaction.     

Chemisorption of Yttrium Nitrate on AlN Particles

Homogenization of Y₂O₃ as a sintering additive in AlN green compact has been achieved by chemisorption of Y(NO₃)₃ on AlN particles in isopropanol suspension. Substantial adsorption of Y(NO₃)₃ equivalent to a Y₂O₃ content up to a maximum of 1.4 wt% of AlN has been observed. Electrokinetic mobility measurements of the coated particles and the adsorption studies show that the adsorption takes place in isopropanol suspension. SEM shows a good homogeneous distribution of Y₂O₃ in the green ceramic compacts, and no trace of secondary crystallization has been observed.     

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.     

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.     

Chemisorption of alkenes on copper-exchanged ZSM-5 zeolite

On Cu-ZSM-5 zeolite at room temperature, propane is physisorbed, while propene shows characteristics of chemisorption. The chemisorption mode has certain advantages for the catalytic control of automotive emissions. Alkane and alkene adsorption equilibria and kinetics are compared on Cu-ZSM-5 and on ZSM-5 free of alumina. The results are discussed in terms of the Langmuir adsorption isotherm.     

Heats of Chemisorption of O2, H2, CO, CO2, and N2 on Polycrystalline and Single Crystal Transition Metal Surfaces

One of the important physical-chemical properties that characterizes the interaction of solid surfaces with gases is the bond energy of the adsorbed species. The determination of the bond energy is usually performed indirectly by measuring the heat of adsorption (or heat of desorption) of the gas [1, 2], In order to define the heat of adsorption, let us consider the chemisorption of a diatomic molecule, X₂, onto a site on a uniform solid surface, M. The molecule may adsorb without dissociation to form MX₂. M represents the adsorption site where bonding occurs to a cluster of atoms or to a single atom. In this circumstance, the heat of adsorption, ΔH_ads, is defined as the energy needed to break the MX₂ bond:     

Heats of Chemisorption of O2, H2, CO,CO2, and N2 on Polycrystalline and Single Crystal Transition Metal Surfaces

Abstract

One of the important physical-chemical properties that characterizes the interaction of solid surfaces with gases is the bond energy of the adsorbed species. The determination of the bond energy is usually performed indirectly by measuring the heat of adsorption (or heat of desorption) of the gas [1, 2], In order to define the heat of adsorption, let us consider the chemisorption of a diatomic molecule, X₂, onto a site on a uniform solid surface, M. The molecule may adsorb without dissociation to form MX₂. M represents the adsorption site where bonding occurs to a cluster of atoms or to a single atom. In this circumstance, the heat of adsorption, ΔH_ads, is defined as the energy needed to break the MX₂ bond:     

Chemisorption of Nitrogen Monoxide on Size-Selected Cobalt Cluster Ions

Collisional reactions of NO with Co_n⁺ (n = 2–10) were studied by measuring the absolute cross sections for creating the product ions in a beam-gas geometry at different collision energies and internal temperatures of Co_n⁺. The dominant reaction is chemisorption of NO on Co_n⁺ (formation of Co_nNO⁺ and Co_n–1NO⁺). As n increases, the chemisorption cross section starts to rise sharply at n = 4 and soon reaches the highest possible value, which is the Langevin cross section. The chemisorption cross section practically does not change with the internal temperature, while the branching fraction for the production of Co_nNO⁺ with respect to the sum of Co_nNO⁺ and Co_n–1NO⁺ decreases with the internal temperature in the size range of n = 6–10. A statistical model based on the RRK theory explains the dependences of the chemisorption cross section and the branching fraction on the size (n), the collision energy, and the internal temperature. The energies of the NO chemisorption derived from the dependences of the chemisorption cross section and the branching fraction on the collision energy and the internal temperature show that (1) the NO chemisorption is dissociative for n ≥ 4 and (2) more than one isomer is involved in the chemisorption of NO on Co₉⁺.     

Corrosion of Platinum Metals and Chemisorption

As the theoretical corrosion (potential-pH) diagram shows, palladium metal is thermodynamically stable at all pH's in the presence of aqueous solutions free from strong oxidizing, reducing, or com-plexing agents [1]. In practice, palladium is acted upon by water only at high temperatures [2] and it does not tarnish when exposed to moist air. Moreover, at ordinary temperatures this metal is not attacked by nonoxidizing acidic solutions.     

Corrosion of Platinum Metals and Chemisorption

As the theoretical corrosion (potential-pH) diagram shows, palladium metal is thermodynamically stable at all pH's in the presence of aqueous solutions free from strong oxidizing, reducing, or com-plexing agents [1]. In practice, palladium is acted upon by water only at high temperatures [2] and it does not tarnish when exposed to moist air. Moreover, at ordinary temperatures this metal is not attacked by nonoxidizing acidic solutions.