Formation,composition, and catalytic activity of multicomponent oxide structures on aluminum

Possibility is considered of obtaining multicomponent oxide systems as afterburning catalysts for automobiles by flame-electrolytic oxidation and impregnation of oxide structures on aluminum.     

Formation,structure, composition,and catalytic properties of Ni-, Cu-, Mn-, Fe-, and co-containing films on aluminum

Layers containing oxygen compounds of copper and nickel and(or) of one of transition metals (manganese, cobalt, iron) were formed on an aluminum alloy by the plasma-electrolytic oxidation method. The layers were characterized by means of X-ray phase analysis, X-ray fluorescence microanalysis, and scanning electron microscopy and tested in the reaction of CO oxidation to CO₂.     

Composition,structure, and catalytic activity of Ni- and Cu-containing plasma-electrolytic coatings on titanium

Unmodified and modified nickel- and copper-containing oxide layers were formed on a titanium support and their composition, structure, and catalytic activity in a model reaction of CO oxidation were studied.     

Preparation,properties, and catalytic activity of platinum-modified plasma electrolytic oxide structures on aluminum

Catalytically active Pt-containing oxide composites on aluminum have been prepared by plasma electrolytic oxidation (PEO) and by additional modification of the resulting coating by impregnation with an aqueous solution of chloroplatinic acid followed by calcination. The oxide film/metal composites have been characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and electron microscopy. The modified films contain the γ-Al₂O₃ and Pt crystalline phases. Platinum in the surface and subsurface layers is in the Pt⁰ state. There are platinum-rich areas on the surface of the PEO films. A higher catalytic activity in CO oxidation into CO₂ is shown by the samples whose oxide film contains nickel and copper along with platinum.     

Electrochemical synthesis of Cu-containing polyheteroarylenes and study of their catalytic properties

Method of electrochemical synthesis of new Cu-containing polyheteroarylenes that have biquinolyl units in their main chain is developed on the base of the soluble anode technique. The study of electrochemical properties of thus obtained Cu-containing polymer and the corresponding monomer complex revealed existence of two types of coordination environment: (1) copper Cu(I) in the tetrahedral surrounding of two biquinolyl ligands and (2) copper Cu(I) bound with only one biquinolyl fragment. The complexes with one biquinolyl polymer ligand showed high activity as catalysts for O₂ reduction in the presence of hydroquinone that is converted to quinone in the course of the reaction.     

Adsorption and catalytic properties of sulfated aluminum oxide modified with cobalt ions

The adsorption properties of sulfated aluminum oxide (9% SO ₄ ^2- /γ-Al₂O₃) and a cobalt-containing composite (0.5%Сo/SO ₄ ^2- /γ-Al₂O₃) based on it are studied via dynamic sorption. The adsorption isotherms of such test adsorbates as n-hydrocarbons (C₆–C₈), benzene, ethylbenzene, chloroform, and diethyl ether are measured, and their isosteric heats of adsorption are calculated. It is shown that the surface sulfation of aluminum oxide substantially improves its electron-accepting properties, and so the catalytic activity of SO ₄ ^2- /γ-Al₂O₃ in the liquid-phase alkylation of benzene with octene-1 at temperatures of 25–120°C is one order of magnitude higher than for the initial aluminum oxide. It is established that additional modification of sulfated aluminum oxide with cobalt ions increases the activity of this catalyst by 2–4 times. It is shown that adsorption sites capable of strong specific adsorption with both donating (aromatics, diethyl ether chemosorption) and accepting molecules (chloroform) form on the surface of sulfated γ-Al₂O₃ promoted by cobalt salt.     

Formation of superhydrophobic cerium oxide surfaces on aluminum substrate and its corrosion resistance properties

Superhydrophobic cerium oxide film was introduced to aluminum substrate by an in‐situ growth process and surface modification. Different molar ratios between Ce(NO₃)₃ · 6H₂O and C₆H₁₂N₄ were involved in this research. The morphologies, chemical compositions and wetting properties of the films were analyzed by scanning electron microscopy (SEM), energy dispersive X‐ray detector, Fourier transfer infrared spectrometer and water contact angle (WCA) measurement, respectively. A great WCA of 158.8^o with a low angle hysteresis of about 3^o was obtained. Combination of uniform hierarchical micro‐nanostructure as revealed by SEM together with the hydrophobic alkyl groups from stearic acid was found to be responsible for the superior superhydrophobic property. The corrosion resistance performance of the superhydrophobic surface was evaluated by immersing in sodium chloride aqueous solution, the WCA kept as high as 152.1^o after immersion for 21 days, indicating our superhydrophobic surfaces had high chemical stability and durability in corrosive medium. Copyright © 2013 John Wiley & Sons, Ltd.     

Formation of oxide layers modified with polytetrafluoroethylene or graphite on aluminum and titanium alloys by plasma electrolytic oxidation

For one-stage formation of coatings containing polytetrafluoroethylene or graphite, it was proposed to use Na₂SiO₃ + NaOH aqueous electrolyte containing siloxane-acrylate emulsion and dispersed powders of polytetrafluoroethylene or graphite. The phase and elemental composition and surface morphology of the formed coatings were determined. It was shown that the introduction of polytetrafluoroethylene markedly increases the hydrophobic and wear-resistant properties of coatings.     

Study of the self-assembling of n-octylphosphonic acid layers on aluminum oxide

The deposition of n-octylphosphonic acid on aluminum oxide was studied. The substrate was pretreated in order to achieve a root-mean-square roughness of <1 nm, a hydroxyl fraction of 30%, and a thickness of approximately 170 nm. It was proven using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) that, rather than a monolayer, an organic multilayer was formed. The growth mechanism was identified as a Stranski-Krastanov one. It was also shown that the use of AFM, probing the surface topography, is essential for a reliable quantification and interpretation of data obtained with XPS.     

Deposition,composition, and activity in CO oxidation of anodic layers with platinum on aluminum and titanium

Pt + TiO₂/Ti(Al) and Pt + CeO₂ + ZrO₂ + TiO₂/Ti composites were formed by plasma electrolytic oxidation and their surface composition and catalytic activity in CO oxidation to CO₂ were studied.     

Formation and properties of composite coatings on aluminum alloys

A study was made into the morphology, composition, and electrochemical and mechanical properties of protective composite coatings on various aluminum alloys, including those doped with Sc, Cu, and Ni. It was established that protective coatings significantly increase the corrosion resistance of the alloys in a 3% NaCl solution. Composite coatings produced by triple dip coating in an superdispersed polytetrafluoroethylene suspension have unique corrosion-resistance properties, reducing the corrosion current density for all the protected alloys to 3.1 × 10^–11–4.0 × 10^–12 A/cm², which is more than three orders of magnitude lower than that for coatings formed by plasma electrolytic oxidation and five orders of magnitude lower than that for alloys without coating.     

Fabrication of polytetrafluoroethylene- and graphite-containing oxide layers on aluminum and titanium and their structure

Stable aqueous electrolyte emulsions with negatively charged micelles containing dispersed particles of polytetrafluoroethylene (PTFE) or graphite are obtained using siloxane-acrylate emulsion as an emulsifier. The oxide coatings formed in such electrolytes contain carbon, polytetrafluoroethylene, or graphite. The coatings with PTFE particles are similar to monolithic polytetrafluoroethylene with respect to its hydrophobic characteristics. According to X-ray photoelectron spectroscopy data, the surface of the formed coatings predominantly contains aliphatic carbon (C-C and C-H bonds) and some fraction of oxidized (or, in the case of PTFE-containing electrolytes, fluorinated) carbon.     

Formation and properties of halogenated aluminum clusters

The fast-flow tube reaction apparatus was employed to study the halogenation of aluminum clusters. For reactions with HX (X=Cl, Br, and I), acid-etching pathways are evident, and we present findings for several reactions, whereby Al(n)X(-) generation is energetically favorable. Tandem reaction experiments allowed us to establish that for Al(n)Cl(-), Al(n)I(-), and Al(n)I(2) (-), species with n=6, 7, and 15 are particularly resistant to attack by oxygen. Further, trends in reactivity suggest that, in general, iodine incorporation leaves the aluminum clusters' electronic properties largely unperturbed. Ab initio calculations were performed to better interpret reaction mechanisms and elucidate the characteristics of the products. Lowest energy structures for Al(13)X(-) were found to feature icosahedral Al(13) units with the halogen atom located at the on-top site. The charge density of the highest occupied molecular orbital in these clusters is heavily dependent on the identity of X. The dependence of reactivity on the clusters' charge state is also discussed. In addition, we address the enhanced stability of Al(13)I(-) and Al(13)I(2) (-), arguing that the superhalogen behavior of Al(13) in these clusters can provide unique opportunities for the synthesis of novel materials with saltlike structures.     

Nanoscale lanthanum oxide catalysts for self-condensation of acetone: preparation via self-assembly on anodic aluminum oxide,structure, and properties

A novel structured La₂O₃/AAO solid base catalyst was prepared by supporting lanthanum oxide (La₂O₃) on the surface of anodic aluminum oxide (AAO) under hydrothermal conditions. Catalytic activity of the catalyst was tested using self-condensation of acetone to diacetone alcohol as a probe reaction. The conversion of acetone reached 4.14% with the diacetone alcohol selectivity of 98%. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy disperse spectroscopy (EDS), thermogravimetric analysis (TGA), N₂ adsorption-desorption (BET), and temperature programmed desorption (CO₂-TPD). XRD patterns and SEM images indicated that La₂O₃ nanoscale particles with high crystallinity were uniformly distributed over the AAO surface. The results of CO₂-TPD showed that the calcination temperature led to the formation of medium-strength basic sites, strong basic sites, and to an increase of the basic strength. The strong basic sites and large basic strength are an important factor that influences the catalytic activity in the self-condensation of acetone to diacetone alcohol.     

Oxidation of Carbon Monoxide on Co-, Ni-, and Cu-containing Catalysts Prepared by Pyrolysis of Metal β-Diketonates on Synthetic Foamed Ceramics

Catalytic systems containing Co, Ni, and Cu composite coatings prepared by gas-phase thermolysis of metal acetylacetonates and hexafluoroacetylacetonates on synthetic foamed ceramics were suggested for oxidation of CO to CO₂. The relative activities of the catalysts and the kinetic and activation parameters of CO oxidation were determined. The catalytic activity depends on the catalyst preparation procedure.     

Structure and function of oxide nanostructures: catalytic consequences of size and composition

Redox and acid-base properties of dispersed oxide nanostructures change markedly as their local structure and electronic properties vary with domain size. These changes give rise to catalytic behavior, site structures, and reaction chemistries often unavailable on bulk crystalline oxides. Turnover rates for redox and acid catalysis vary as oxide domains evolve from isolated monomers to two-dimensional oligomers, and ultimately into clusters with bulk-like properties. These reactivity changes reflect the ability of oxide domains to accept or redistribute electron density in kinetically-relevant reduction steps, in the formation of temporary acid sites via reductive processes, and in the stabilization of cationic transition states. Reduction steps are favored by low-lying empty orbitals prevalent in larger clusters, which also favor electron delocalization, stable anions, and strong Br?nsted acidity. Isomerization of xylenes and alkanes, elimination reactions of alkanols, and oxidation of alkanes to alkenes on V, Mo, Nb, and W oxide domains are used here to demonstrate the remarkable catalytic diversity made available by changes in domain size. The reactive and disordered nature of small catalytic domains introduces significant challenges in their synthesis and their structural and mechanistic characterization, which require in situ probes and detailed kinetic analysis. The local structure and electronic properties of these materials must be probed during catalysis and their catalytic function be related to specific kinetically-relevant steps. Structural uniformity can be imposed on oxide clusters by the use of polyoxometalate clusters with thermodynamically stable and well-defined size and connectivity. These clusters provide the compositional diversity and the structural fidelity required to develop composition-function relations from synergistic use of experiments and theory. In these clusters, the valence and electronegativity of the central atom affects the acid strength of the polyoxometalate clusters and the rate constants for acid catalyzed elementary steps via the specific stabilization of cationic transition states in isomerization and elimination reactions.     

Adsorption properties of Ni-Pd catalysts supported on aluminum oxide

The surface composition of Ni-Pd/Al₂O₃ catalysts has been studied using XPES and adsorption methods. The bimetallic catalysts differ from the single-metal Ni and Pd catalysts in the dispersivity of the metal phase which depends on the method of preparation and the presence of K⁺ promoter. A catalyst produced by the immersion method is strongly enriched in Pd compared with impregnated catalysts.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1746–1751, August, 1991.     

Acid-base and catalytic properties of iron-antimony oxide catalysts

Iron antimonate, whose strongest acidic sites (Fe³⁺) are blocked by weak acidic aprotic centers Sb³⁺, is an active and selective catalyst for the ammoxidation of propylene.

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, (Fe⁺³) Sb⁺³, .