Effect of metal oxides on electrochemical performances of La–Mg–Ni-based alloys

Metal oxides (TiO₂, Er₂O₃ and ZnO) were added to La–Mg–Ni-based hydrogen storage alloy electrodes and their effects on the structural and electrochemical properties were studied. The charge efficiency, especially at high charge current density was greatly ameliorated, and the high rate charge capability at 1440 mA g⁻¹ increased from 85.1% (blank) to 94.1% (TiO₂), 93.3% (Er₂O₃) and 90.5% (ZnO). The high temperature dischargeability was also improved in case of TiO₂, Er₂O₃ and ZnO additives. These additives suppressed formation of Mg(OH)₂ and La(OH)₃ during charge/discharge process and therefore the cycling stability was improved. The discharge capacity retention at the 200th cycle increased from 72.9% (blank) to 79.6% (TiO₂), 87.5% (Er₂O₃) and 77.9% (ZnO).     

Glycerol steam reforming over Ni/γ-Al2O3 catalysts modified by metal oxides

The metal oxides modified Ni/γ-Al₂O₃ catalysts for glycerol steam reforming were prepared by impregnation. Characterization results of fresh catalysts indicated that the molybdates modification abated the acidity and the stronger metal-support interaction of Ni/γ-Al₂O₃ catalysts, leading to a stable catalytic activity. Especially, NiMoLa-CaMg/γ-Al₂O₃ (NiMoLa/CMA) catalyst exhibited no deactivation along with glycerol complete conversion to stable gaseous products containing 69% H₂, 20% CO and 10% CO₂ during time-on-stream of 42 h. TPO of spent Ni/γ-Al₂O₃ catalysts modified by different components showed that the carbon deposit on acidic sites and NiAl₂O₄ species led to catalysts deactivation. A lower reforming temperature and a higher LHSV and glycerol content were helpful to the production of syngas from GSR over NiMoLa/CMA; the reverse conditions would improve the formation of H₂.     

Electrochemical absorption of hydrogen in transition metal oxides—II. Sorption of hydrogen in titanium monoxide TiO

The absorption of hydrogen in titanium “monoxide” was studied electrochemcially by potential-step and ac techniques. The absorption equilibrium obeys the Crandall—Faughnan—Armand isotherm and the chemical diffusion coefficient is a linear function of concentration. The heat of absorption is 80 kJ (g atom H)⁻¹ and the true diffusion coefficient D₀ is 4 × 10⁻¹³ cm²s⁻¹ at 20°C. The absorption occurs in oxygen vacancies.     

Baeyer–Villiger oxidation of cyclic ketones with aqueous hydrogen peroxide catalyzed by transition metal oxides

The Baeyer–Villiger oxidation of cyclic ketones to the corresponding lactones using aqueous hydrogen peroxide as an oxidant over transition metal oxides was investigated. MoO₃ and WO₃ were found to exhibit higher catalytic activity than TiO₂, Fe₂O₃, Co₃O₄, ZnO and ZrO₂. The high catalytic activity was attributed to the interaction of MoO₃/H₂O₂ and WO₃/H₂O₂. Additionally, the reaction mechanism on MoO₃ and WO₃ was proposed.     

Water gas shift reaction over Cu–Mn mixed oxides catalysts: Effects of the third metal

Highly efficient Cu–Mn spinel catalysts for water gas shift (WGS) reaction were achieved by a single step urea-nitrate combustion method. A series of doped Cu–Mn-M catalysts (M = Ce, Zr, Zn, Fe, Al) were prepared by the same method. Effects of dopants on WGS activity and stability of doped Cu–Mn catalysts were investigated. The doped catalysts were characterized by BET, XRD and TPR. XRD results showed that non-doped samples and Zr-doped samples are mainly composed of Cu_1.5Mn_1.5O₄ phase, while CuO, Cu₂O and Cu_1.5Mn_1.5O₄ for other doped samples. It was further found that WGS activities depend strongly on the natures of the dopant employed despite of their lower content, varying in the order of Zr > Fe > non-doped > Ce > Al > Zn. TPR profiles revealed that all dopants shift the reduction peaks to lower temperature region, indicating no direct correlation between WGS activity and the reducibility. In addition, Zr-doped Cu–Mn catalyst with 5 wt.% content showed the best catalytic performance and, optimal stability exposed to oxygen-stream and on-stream operation. It indicates that ZrO₂ is an effective promoter for Cu–Mn catalyst, and the catalytic performances are related to the existence of a Cu_1.5Mn_1.5O₄ phase and ease reducibility of the catalysts.     

An interpretation of the Zech–Podlaha–Landolt model of metal codeposition via queuing theory

The electrode kinetics of anomalous codeposition of iron group metals is interpreted by queuing theory applied to the recently proposed Zech–Podlaha–Landolt model which postulates an adsorbed mixed–metal species existing temporarily as an electrochemically activated complex. The complex acts as an intermediate in a consecutive reaction leading to enhanced deposition of the more electronegative metal. Numerical illustrations for the codeposition of iron and nickel, and cobalt and nickel from a sulphate electrolyte are provided.     

An electric model of a vapour anode, multitube alkali–metal thermal-to-electric converter

A two-dimensional electric model of vapour anode, multitube alkali–metal thermal-to-electric conversion (AMTEC) cells was developed. These cells are being developed to power the Pluto/Kuiper Express and Europa Orbiter spacecrafts, at NASA which are scheduled for launch early in the next century. Model results of several cells tested at the Air Force Research Laboratory showed that electric losses in the current collector networks and the connecting leads were negligible. The charge-exchange polarization/concentration losses in the TiN electrodes were the major losses, amounting to 25–50% of the cell's total theoretical power, while the contact losses and the beta-alumina solid electrolyte ionic losses amounted to less than 16% of the cell theoretical power. Results also showed that a cell with advanced Rh₂W electrodes could have delivered from 14% to 25% more electrical power.     

Inhomogeneous electrodes—a polarization model of the partially blocked reversible metal ion electrode

A small-signal response equation of reversible metal ion electrodes is derived based on partial blockade, non-linear diffusion and surface activation. Congruence with ac impedance of the Ag/Ag⁺ system is checked.     

Microcalorimetric and infrared spectroscopic studies ofγ-Al2O3 modified by tin oxides

Microcalorimetric and infrared spectroscopic studies of ammonia and carbon dioxide adsorption have been used to study the effects on the acid/base properties of adding tin oxide to-Al₂O₃. The addition of SnO₂ to-Al₂O₃ decreases the number of strong acid sites (heats of ammonia adsorption higher than 140 kJ/mol), increases the number of weaker acid sites (heats from 110 to 130 kJ/mol), and decreases slightly the number of basic sites (heats of carbon dioxide adsorption from 70 to 150 kJ/mol). In contrast, the presence of SnO on-Al₂O₃ decreases the total number of acid sites (heats of ammonia adsorption higher than 70 kJ/mol) and eliminates most of the basic sites. Infrared spectroscopy of adsorbed ammonia reveals interactions between aluminum cations and stannous ions, leading to a decrease in the strength of the Lewis acid sites associated with aluminum cations.     

Studies of metal–support interactions with “real” and “inverted” model systems: reactions of CO and small hydrocarbons with hydrogen on noble metals in contact with oxides

Two types of model catalysts are compared: thin film catalysts consisting of polyhedral noble metal nanocrystals (Rh and Pt) supported by reducible and non‐reducible oxides, and their inverted pendants, submonolayers of titania and vanadia deposited under UHV conditions on the respective metal surfaces (Pd and Rh(111) and Rh (polycrystalline)). The structure and composition of the inverse catalysts were examined in situ by LEED and AES and the nanoparticles were characterized by HRTEM. The activity of thin film and inverse catalysts was studied in a series of reactions, such as the ring opening of methylcyclopentane and methylcyclobutane, the dissociation of CO and the CO methanation. Reaction conditions comprise atmospheric pressure but also molecular beam experiments. The reaction rates are related to the oxidation state of the supporting oxide, to the free metal surface area and to the number of sites at the interface between metal and support. This revised version was published online in June 2006 with corrections to the Cover Date.     

Development of an ionic polymer–metal composite stepper motor using a novel actuator model

A novel ionic polymer–metal composite (IPMC) actuated stepper motor was developed in order to demonstrate an innovative design process for complete IPMC systems. The motor was developed by utilizing a novel model for IPMC actuators integrated with the complete mechanical model of the motor. The dynamic, nonlinear IPMC model can accurately predict the displacement and force actuation in air for a large range of input voltages as well as accounting for interactions with mechanical systems and external loads. By integrating this geometrically scalable IPMC model with a mechanical model of the motor mechanism an appropriate size IPMC strip has been chosen to achieve the required motor specifications. The entire integrated system has been simulated and its performance verified. The system has been built and the experimental results validated to show that the motor works as simulated and can indeed achieve continuous 360° rotation, similar to conventional motors. This has proven that the model is an indispensable design tool for integrated IPMC actuators into real systems. This newly developed system has demonstrated the complete design process for smart material actuator systems, representing a large step forward and aiding in the progression of IPMCs towards wide acceptance as replacements for traditional actuators.     

Investigations on the promoting effect of metal oxides on La–V–O catalyst in propane oxidative dehydrogenation

The addition of reducible metal oxides as promoters shows a positive effect on the catalytic behavior of lanthanum vanadate (LaVO₄). A C₃H₆ yield increase of 6.5% is observed at 500°C on molybdenum-promoted LaVO₄, which can be attributed to the change of the redox properties, the blocking of the strong oxidation sites of the catalysts and to an increase of the accessibility of the labile oxygen toward the reactant. The influence of the catalyst preparation method and of the Mo loading as well as the additional promoting effect of CO₂ in the gas feed was also examined.     

Synergistic interaction of metal–acid sites for phenol hydrodeoxygenation over bifunctional Ag/TiO_2 nanocatalyst

The use of silver metal for hydrodeoxygenation(HDO) applications is scarce and different studies have indicated of its varying HDO activity. Several computational studies have reported of silver having almost zero turnover frequency for HDO owing to its high C\\O bond breaking energy barrier and low carbon and oxygen binding energies.Herein this work, titania supported silver catalysts were synthesized and firstly used to examine its phenol HDO activity via experimental reaction runs. BET, XRD, FESEM, TEM, EDX, ICP–OES, Pyridine-FTIR, NH_3-TPD and H_2-TPD analyses were done to investigate its physicochemical properties. Phenomena of hydrogen spillover and metal–acid site synergy were examined in this study. With the aid of TiO_2 reducible support, hydrogen spillover and metal–acid site interactions were observed to a certain extent but were not as superior as other Pt, Pd, Ni-based catalysts used in other HDO studies. The experimental findings showed that Ag/TiO_2 catalyst has mediocre phenol conversion but high benzene selectivity which confirms the explanation from other computational studies.     

Surface science approach to the preparation and characterization of model Ziegler–Natta heterogeneous polymerization catalysts

Ziegler–Natta heterogeneous catalytic systems are extensively used to polymerize ethylene and propylene. Some industrial catalysts consist of TiCl₄ chemisorbed on activated MgCl₂ and subsequently reduced and alkylated by reaction with an aluminum alkyl (generally AlEt₃). Lewis bases are added to the catalytic systems to control the enantio-selectivity for the production of isotactic polypropylene. Our aim is to clarify the chemical composition of the active centers by modern surface science methods. Model catalysts are prepared in the form of ultra-thin films by gas-phase deposition on a gold foil in ultrahigh vacuum. Under these conditions, MgCl₂ films grow to controlled thickness via a layer-by-layer mechanism, as revealed by AES and XPS. TiCl₄ can be deposited on these films near room temperature by both electron irradiation-induced and metallic magnesium-induced chemical vapor deposition. Angle-resolved XPS studies indicate that these films consist of a few layers of TiCl₂ with one monolayer of TiCl₄ chemisorbed on its surface. The exposure of these titanium chloride films to the co-catalyst AlEt₃ produces an active model Ziegler–Natta catalyst. XPS analysis reveals the presence of TiCl₂Et on the catalyst surface: this is believed to be the active site. Prolonged reaction with the co-catalyst reduces the titanium sites to TiClEt_n (n = 1 and/or 2). High molecular weight polyethylene and polypropylene are synthesized on these catalysts, as shown by Raman spectroscopy. Highly isotactic polypropylene is produced without need for stereo-regulating Lewis bases. This revised version was published online in June 2006 with corrections to the Cover Date.     

Surface potentials of metal–gas interfaces compared with analogous electrochemical systems as probed by adsorbate vibrational frequencies

The dependence of adsorbate vibrational frequencies on the surface potential, φ (“Stark-tuning” effect), observed in electrochemical systems is exploited for the same metal surfaces in contact with ambient-pressure gases so to estimate φ values in the latter environment. Saturated CO adlayers on palladium and platinum films are examined along these lines by using surface-enhanced Raman spectroscopy (SERS) to obtain frequencies for both the C–O (ν_CO) and metal–carbon stretching (ν_M--CO) vibrations in CO-containing aqueous electrochemical and gaseous environments. The effective gas-phase surface potentials extracted by matching the vibrational frequencies with the corresponding potential-dependent electrochemical spectra are substantially (ca. 1–1.5 V) lower than the work functions for such interfaces under “clean” (ultrahigh vacuum) conditions. These disparities are ascribed to the occurrence of electrochemical-like redox half-reactions in the ambient-pressure gas-phase environment, leading to surface charging, and, hence, marked alterations in the surface potential as controlled by potential-dependent redox kinetics. The possible implications of these and related findings to ambient-pressure adsorption and catalysis are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Antibacterial Surface Treatment of Aluminum Materials

Aluminum specimens were anodized in a sulfuric acid bath, then silver was electrodeposited in pores of the anodized aluminum by using alternating current . The anodized aluminum with deposited silver was tested for its antibacterial performance. The results show that the antibacterial rates of the specimens are above 95% against the growth of E. coli, P. aeruginasa, S. faecalis and S. aureus. The morphology of the silver in pores of anodized aluminum is characterized by transmission electron microscopy, and the micrographs indicate that silver is assembled in the form of nanowires with a diameter of 10 nm or 25 nm. The nanowires have a structure of parallel bright stripes alternating with parallel dark stripes.     

The Surface Coatings Industry of China

It had ever sinee been several thousand yearsthat the art of emPloying natural laequers anddrying ofis for Protection and decoration waswidely Praetised in Qljna,a land of aneient eivi-lization. Ninetee     

Basicity–FAME yield correlations in metal cation modified MgAl mixed oxides for biodiesel synthesis

In this paper Zn^2 +, Co^2 +, Fe^3 + and La^3 + were respectively introduced into Mg₃Al₁ mixed oxides to prepare Mg₁Zn₂Al₁, Mg₁Co₂Al₁, Mg₃Al_0.6Fe_0.4 and Mg₃Al_0.6La_0.4 oxides by calcinations at 773 K. The XRD, XPS, BET, ICP-AES and CO₂-TPD characterizations of samples exhibited that the effects of the substitution of trivalent cations (Fe^3 +, La^3 +) for Al^3 + on the basicity of samples were stronger than the substitution of divalent cations (Zn^2 +, Co^2 +) for Mg^2 + because of high O^2 − concentration which were coincident with the FAME yield for these catalysts. La^3 + modified catalyst exhibited highest activity in transesterification.     

Effect of low activation rare-earth oxides on sintering of β-SiC

The feasibility of sintering β-SiC at 1850 ℃ with using low-activation rare-earth oxides as sintering additives was studied. Thermodynamic calculation suggested that all five rare-earth oxides (Y₂O₃, Sc₂O₃, CeO₂, La₂O₃, and Pr₆O₁₁) were suitable sintering additives. Comprehensive microstructure characterization further revealed that Pr₆O₁₁ was the most effective sintering additive as it suffered the least influence from the content effect. A mechanism based on liquid phase sintering was proposed based on microstructure observations. The radiation stability of sintered SiC was investigated as well. The intergranular phases (rare-earth oxides and silicates) and SiC grains remained after being irradiated to 17 dpa at 750 ℃.     

Selective catalytic reduction of nitrogen oxides with hydrocarbons over Zn–Al–Ga complex oxides

Selective reduction of NO with hydrocarbons was studied using metal oxide catalysts having a spinel structure. A Zn–Al–Ga complex oxide was found to be very active and selective for the catalytic reduction of NO with both C₃H₆ and CH₄. It was revealed that the role of oxygen at the initial stage of the reaction strongly depends on the reductants; oxygen is mainly used for NO oxidation to NO₂ in the reduction with CH₄, whereas it is used both for NO oxidation to NO₂ and oxidation of C₃H₆ to an active intermediate in the reduction with C₃H₆. This revised version was published online in July 2006 with corrections to the Cover Date.