Morphology effects of Co3O4 on the catalytic activity of Au/Co3O4 catalysts for complete oxidation of trace ethylene

Au/Co₃O₄ catalysts with different morphologies (nanorods, nanopolyhedra and nanocubes) were successfully synthesized and evaluated for ethylene complete oxidation. We found that support morphology has a significant effect on catalytic activity, which is related to the exposed planes of different morphological Co₃O₄. HRTEM revealed the Co₃O₄-nanorods predominantly exposes {110} planes, while the dominant exposed planes of Co₃O₄-nanopolyhedra and -nanocubes are {011} and {001} planes, respectively. Compared with {011} and {001} planes, {110} planes exhibit the maximum amount of oxygen vacancies, which play a major role in ethylene oxidation. Therefore, Au/Co₃O₄-nanorods exhibits extraordinary catalytic activity, yielding 93.7% ethylene conversion at 0 °C.     

Catalysis at the toluene/water interface: shape-selective hydrolysis of esters having some rings and lactones promoted by octadecyl immobilized H-ZSM-5 catalyst

Shape-selective properties of octadecyltrichlorosilane-treated H-ZSM-5, abbreviated as H-ZSM-5-C₁₈, have been observed in the hydrolysis of esters having some rings and lactones in toluene-water solvent system. The shape-selectivity for the reaction has been evaluated by the ratio of the relative rate constants in comparison with the rate constant of methyl acetate. The selectivity became higher with increase in bulkiness of the substrate. Substrates having the minimum diameter larger than 6.5 Å, significantly larger in size than the pore openings of ZSM-5, could not react in this system.     

Facet-Dependent SERS Activity of Co3O4

Surface-enhanced Raman spectroscopy (SERS) is an ultra-sensitive and rapid technique that is able to significantly enhance the Raman signals of analytes absorbed on functional substrates by orders of magnitude. Recently, semiconductor-based SERS substrates have shown rapid progress due to their great cost-effectiveness, stability and biocompatibility. In this work, three types of faceted Co₃O₄ microcrystals with dominantly exposed {100} facets, {111} facets and co-exposed {100}-{111} facets (denoted as C-100, C-111 and C-both, respectively) are utilized as SERS substrates to detect the rhodamine 6G (R6G) molecule and nucleic acids (adenine and cytosine). C-100 exhibited the highest SERS sensitivity among these samples, and the lowest detection limits (LODs) to R6G and adenine can reach 10⁻⁷ M. First-principles density functional theory (DFT) simulations further unveiled a stronger photoinduced charge transfer (PICT) in C-100 than in C-111. This work provides new insights into the facet-dependent SERS for semiconductor materials.     

The origin of photochemical anisotropy in SrTiO<Subscript>3</Subscript>

Photochemical reactions that deposit insoluble products on catalytic surfaces have been used to probe the anisotropy of the reactivity of SrTiO₃ microcrystals. Both reduced and oxidized products are formed preferentially on {100} surfaces. It is proposed that the anisotropic photochemical reactivity can be explained by the electronic band structure. Because direct optical transitions for charge carriers having momentum vectors in the <100> direction overlap well with the spectral distribution of the absorbed photons, more photogenerated carriers are moving toward {100} surfaces than other surfaces and, as a result, {100} surfaces are more active. Knowledge of the electronic band structure and the spectral distribution of the light allows predictions to be made about the anisotropic reactivity of photocatalysts with other crystal structures.     

The preparation of Mg3Si2O5(OH)4 nanotubes under solvothermal conditions

With magnesium carbonate hydroxide and nanoporous silica as the starting materials, chrysotile (Mg₃Si₂O₅(OH)₄) nanotubes were prepared by using a solvothermal method at 400^∘C within four hours. This new method needs no strong alkali medium and the reaction time is very short. EDX analysis showed a molar ratio of 3Mg:2Si:9O of the product. Selected Area Electron Diffraction (SAED) pattern indicated that the tube axis is along [100] direction. HRTEM image showed the nanotubes were multi-walled and the distance between the two close layers was about 0.75 nm, which is very near to the distance of {001} planes. Thus, combining the results of SAED and HRTEM, we can conclude that the {001} planes of serpentine roll up along the [100] direction to form the tubular structure. The effects of various reaction conditions and the formation mechanism were also discussed.     

Preparation and characterization of V2O3 micro-crystals via a one-step hydrothermal process

Phase pure V₂O₃ micro-crystals with a hexagonal dipyramid morphology were fabricated for the first time via a facile one-step hydrothermal method. The crystals were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). A hexagonal dipyramid structure of V₂O₃ enclosed by well-grown {012} facets was obtained by hydrothermally reducing VO(acac)₂ precursor with N₂H₄·H₂O at 220 °C for 48 h. The results indicated that V₂O₃ can be well crystallized up to micron size with distinguished facets by only one step hydrothermal treatment. The formation mechanism and morphology evolution for V₂O₃ micro-crystals were discussed. Based on our experiments, the V₂O₃ nuclei formed and grew by a phase transformation through a dissolution–recrystallization process of VOOH, and the formation of the hexagonal dipyramids was ascribed to the specific adsorption of Hacac to the {012} facets restraining the growth in the directions normal to the {012} facets. The present work provides a facile method for preparing phase pure V₂O₃ micro-crystals with hexagonal dipyramid morphology, which can be used as a new powder material for ceramic fabrication.     

Synthesis and Characterization of Bowl-Like Single-Crystalline BaTiO3 Nanoparticles

Novel bowl-like single-crystalline BaTiO₃ nanoparticles were synthesized by a simple hydrothermal method using Ba(OH)₂·8H₂O and TiO₂ as precursors. The as-prepared products were characterized by XRD, Raman spectroscopy, SEM and TEM. The results show that the bowl-like BaTiO₃ nanoparticles are single-crystalline and have a size about 100–200 nm in diameter. Local piezoresponse force measurements indicate that the BaTiO₃ nanoparticles have switchable polarization at room temperature. The local effective piezoelectric coefficient d₃₃ ^* d_{33}^{ * } is approximately 28 pm/V.     

Water–Gas Shift Reaction Over Aluminum Promoted Cu/CeO2 Nanocatalysts Characterized by XRD, BET, TPR and Cyclic Voltammetry (CV)

A series of aluminum promoted Cu/CeO₂ nanocatalysts with aluminum content in the range of 0–5wt.% were prepared by co-precipitation method and examined with respect to their catalytic performance for the water–gas shift (WGS) reaction. The catalysts were characterized by XRD, BET, H₂-TPR and cyclic voltammetry (CV) techniques. The results indicate that catalytic activity increases with the aluminum content at first, but then decreases with the further increase of aluminum content. Hereinto, Cu/CeO₂ catalyst doped with 1 wt.% of aluminum shows the highest catalytic activity (CO conversion reaches 84.4% at 200 °C) and thermal stability for WGS reaction. Correlation to the results from above characterization, it is found that the variation of catalytic activity is in very agreement with that of the surface area, the area of peak γ (i.e., the reduction of surface copper oxide (crystalline forms) interacted with surface oxygen vacancies on ceria), and the area of peak C₂ and in cyclic voltammetry process), respectively. Enough evidence was found for the fact that the metallic copper (Cu⁰) interacted with surface oxygen vacancies on ceria is the active site for WGS reaction over Cu/CeO₂ catalysts.     

A simple and efficient oxidation system for the oxidation of alcohols utilizing Oxone® as oxidant catalyzed by polymer-supported 2-iodobenzamide

$\begin{array}{l}{\hbox{R}^1\hbox{R}^2\hbox{CHOH}} \\ {\hbox{RCH}_2\hbox{OH} }\end{array} \dynrightarrow{Oxone}{\hbox{CH}_3\hbox{CN/H}_2\hbox{O}, 70^{\circ}\hbox{C}} \begin{array}{l}{\hbox{R}^1\hbox{R}^2\hbox{CO}} \\ {\hbox{RCOOH}} \end{array} A simple and environmentally friendly procedure for the oxidation of alcohols is presented utilizing Oxone^? (2KHSO₅ · KHSO₄ · K₂ SO₄) as oxidant and polymer-supported 2-iodobenzamide as catalyst in CH₃CN/H₂O mixed solvents.     

Novel dual heterojunction between MoS2 and anatase TiO2 with coexposed {101} and {001} facets

This work prepared an anatase TiO₂ by controlling coexposed {101} and {001} facets. The anatase TiO₂ was composited with MoS₂, and the photocatalytic behavior was studied. The relationship between the exposed ratio of {001} facets and the enhancement proportion by the composite was compared. An appropriate exposed ratio of {001} facets, instead of a high ratio, can cause the highest enhancement proportion for photocatalytic activity. This finding confirmed that exposed {001} facets are not the main factors for improving photocatalytic activity. Dual heterojunction was observed to form between MoS₂ and anatase TiO₂ with coexposed {101} and {001} facets, which is a crystal‐face heterojunction between {101} and {001} facets and a semiconductor heterojunction between MoS₂ and {001} facets of TiO₂. In this dual heterojunction, photo‐induced electrons in TiO₂ will flow into {101} facets of TiO₂, instead of MoS₂, whereas the photo‐induced holes in TiO₂ will flow into MoS₂ to reach a high separation efficiency. This finding further revealed the elevating mechanism of constructing heterojunction based on coexposed crystal faces.     

Evaluation of strategies for the subsequent use of CO2

If substantial amounts of CO₂, which according to actual scenarios may in the future be captured from industrial processes and power generation, shall be utilized effectively, scalable energy efficient technologies will be required. Thus, a survey was performed to assess a large variety of applications utilizing CO₂ chemically (e.g., production of synthesis-gas, methanol synthesis), biologically (e.g., CO₂ as fertilizer in green houses, production of algae), or physically (enhancement of fossil fuel recovery, use as refrigerant). For each of the processes, material and energy balances were set up. Starting with pure CO₂ at standard conditions, expenditure for transport and further process specific treatment were included. Based on these calculations, the avoidance of greenhouse gas emissions by applying the discussed technologies was evaluated. Based on the currently available technologies, applications for enhanced fossil fuel recovery turn out to be most attractive regarding the potential of utilizing large quantities of CO₂ (total capacity > 1000 Gt CO₂) and producing significant amounts of marketable products on one hand and having good energy and material balances on the other hand $ \left( {{{t_{CO_2 - emitted} } \mathord{\left/ {\vphantom {{t_{CO_2 - emitted} } {t_{CO_2 - utilized} < 0.2 - 0.4}}} \right. \kern-\nulldelimiterspace} {t_{CO_2 - utilized} < 0.2 - 0.4}}} \right) $ \left( {{{t_{CO_2 - emitted} } \mathord{\left/ {\vphantom {{t_{CO_2 - emitted} } {t_{CO_2 - utilized} < 0.2 - 0.4}}} \right. \kern-\nulldelimiterspace} {t_{CO_2 - utilized} < 0.2 - 0.4}}} \right) . Nevertheless, large scale chemical fixation of CO₂ providing valuable products like fuels is worth considering, if carbon-free energy sources are used to provide the process energy and H₂ being essential as a reactant in a lot of chemical processes (e.g., production of DME: $ {{t_{CO_2 - emitted} } \mathord{\left/ {\vphantom {{t_{CO_2 - emitted} } {t_{CO_2 - utilized} > 0.34}}} \right. \kern-\nulldelimiterspace} {t_{CO_2 - utilized} > 0.34}} $ {{t_{CO_2 - emitted} } \mathord{\left/ {\vphantom {{t_{CO_2 - emitted} } {t_{CO_2 - utilized} > 0.34}}} \right. \kern-\nulldelimiterspace} {t_{CO_2 - utilized} > 0.34}} ). Biological processes such as CO₂ fixation using micro-algae look attractive as long as energy and CO₂ balance are considered. However, the development of effective photo-bioreactors for growing algae with low requirements for footprint area is a challenge.     

Zur kinetik der acrylnitril-polymerisation

The heterogeneous bulk polymerization of acrylonitrile initiated by AIBN has been studied by means of an improved dilatometric technique and a new method of analysis, where the initial reaction rate (v_w)₀ results from the intercept of a straight line in a \documentclass{article}\pagestyle{empty}\begin{document}$ \frac {\ln \left( 1 \hbox{---} {\rm U} \right)} {{\rm e}^{{- 0,5} {\rm k}_{\rm s}{\rm t} \hbox{---} 1}}$\end{document} versus t plot. It has been found that the initial reaction rate is proportional to the square root of the initial catalyst concentration S₀. The ratio of the rate coefficients of propagation and termination\documentclass{article}\pagestyle{empty}\begin{document}$\frac { {\rm k}_{\rm a} } { {\rm k}_{ {\rm w}^{2} } } $\end{document} could be calculated from the slope of a straight line passing through the origin in a plot of (v_w)₀ versus \documentclass{article}\pagestyle{empty}\begin{document}$\sqrt { {\rm S}_{0} }$\end{document} and yielded a value of 280 mol 1^?1.     

Two New Organic–Inorganic Hybrids Based on [SiW12O40]4? Anion: Hydrothermal Syntheses, Crystal Structures, and Electrochemical Properties

Two new organic–inorganic hybrid compounds [\textCu^\textI ( \texten ) ₂ ( \textH ₂ \textO )] ₂ { ( \textSiW^\textVI _{1 1} \textW^\textV ₁\textO ₄₀ ) ₂ [ \textCu^\textII ( \texten ) ₂ ( \textH ₂ \textO )] ₂ [\textCu^\textII ( \texten ) ₂ ] ₂ }·6 \textH ₂ \textO [{\text{Cu}}^{\text{I}} \left( {\text{en}} \right)_{ 2} \left( {{\text{H}}_{ 2} {\text{O}}} \right)]_{ 2} \left\{ {\left( {{\text{SiW}}^{\text{VI}}_{ 1 1} {\text{W}}^{\text{V}}_{ 1}{\text{O}}_{ 40} } \right)_{ 2} \left[ {{\text{Cu}}^{\text{II}} \left( {\text{en}} \right)_{ 2} \left( {{\text{H}}_{ 2} {\text{O}}} \right)\left] {_{ 2} } \right[{\text{Cu}}^{\text{II}} \left( {\text{en}} \right)_{ 2} } \right]_{ 2} } \right\}{\cdot}6 {\text{H}}_{ 2} {\text{O}} (1) and (H₂ L)₂[SiW₁₂O₄₀]·H₂O (2) [en = ethylenediamine, L = 1,4-bis(3-pyridinecarboxamido)benzene], have been hydrothermally synthesized and characterized by IR, elemental analyses, TG analysis, and single-crystal X-ray diffraction. Structural analyses indicate that compound 1 exhibits an interesting three-dimensional(3D) cross-like supramolecular network through arrangement of a 1D organic–inorganic hybrid chain { ( \textSiW^\textVI _{1 1} \textW^\textV ₁ \textO ₄₀ ) ₂ [ \textCu^\textII ( \texten ) ₂ ( \textH ₂ \textO )] ₂ [\textCu^\textII ( \texten ) ₂ ] ₂ } ^2- . \left\{ {\left( {{\text{SiW}}^{\text{VI}}_{ 1 1} {\text{W}}^{\text{V}}_{ 1} {\text{O}}_{ 40} } \right)_{ 2} \left[ {{\text{Cu}}^{\text{II}} \left( {\text{en}} \right)_{ 2} \left( {{\text{H}}_{ 2} {\text{O}}} \right)\left] {_{ 2} } \right[{\text{Cu}}^{\text{II}} \left( {\text{en}} \right)_{ 2} } \right]_{ 2} } \right\}^{ 2- } . The compound 2 consists of protonated L ligand and [SiW₁₂O₄₀]⁴⁻ anion. The protonated L ligands have been extended into a 2D network via hydrogen-bonding interactions. The guest [SiW₁₂O₄₀]⁴⁻ clusters have been incorporated into the square voids of the 2D host network as templates. The electrochemical behavior and electrocatalysis of compound 2 bulk-modified carbon paste electrode (2-CPE) have been studied.     

Regulating Photocatalytic Selectivity of Anatase TiO2 with {101}, {001}, and {111} Facets

In this work, we demonstrate a novel approach to control the photocatalytic selectivity of TiO₂ though different dominant crystal facets. {101}, {111}, and {001} facets exposed nanoscale anatase TiO₂ were obtained by a simple hydrothermal route with different ratio of NH₄⁺ and F^?, then a calcined progress to clear surface adsorbent atoms. Results reveal that {101} exposed TiO₂ has some remain binding N with a mode of unsaturated N_3c exhibits selectively photocatalytic degradation of methylene orange (MO) in a methylene blue (MB) and methyl orange (MO) mixed solution, whereas TiO₂ with exposed {111} and {001} facets exhibits photocatalytic selectivity for MB. The {111} facets of anatase TiO₂ exhibit a better photocatalytic selective ability than {001} facets. It confirms that the photocatalytic selectivity can be affected by different dominant crystal facets. In a deeper analysis, there are many unsaturated O_2c on the surface of {001} and {111} facets, which enhances adsorbent selectivity and relevant photocatalytic activity of MB, at the same time, the unsaturated O_2c on the surface of {111} facets is much more than that on the surface of {001} facets results in a better photocatalytic selectivity of {111} facets. This research hopes that developing a new strategy for photocatalytic selectivity and providing a deeper understanding of different crystal facets of TiO₂.     

Influence of electrolytes on the absorption of nitrogen oxide components N2O4 and N2O3 in aqueous absorbents

The influence of electrolytes, which are dissolved in the aqueous absorbent and do not react with nitrogen oxides, on the absorption kinetics of both these components was investigated experimentally. In addition to demineralized water, various salt solutions of different concentrations as well as sodium hydroxide solution were used as absorbents. The term H \documentclass{article}\pagestyle{empty}\begin{document}$ H\sqrt {k_1 D} $\end{document} for N₂O₄ and N₂O₃, which is important for the design of industrial absorbers, was determined as a function of composition and concentration of the absorbents. In the case of N₂O₄, the chosen measuring and evaluation methods permitted a separate determination of the rate constant k of the pseudo first order reaction and of the solubility H. The diffusion coefficient D of the gas in the absorbent can be obtained only by calculation. Experimental results showed that \documentclass{article}\pagestyle{empty}\begin{document}$(H\sqrt {k_1 D} )\,_{{\rm N}_{\rm 2} {\rm O}_{\rm 4} } $\end{document} decreases with increasing ionic strength I, however, without a clear indication of any ion-specific effects. This decrease does not appear to be caused simply by a reduction in solubility (salting out effect), or in diffusion coefficient, but at least, to the same extent, through a decrease of the rate constant k with increasing electrolyte content in the absorbent. The measurements permitted the determination of the gas-based salting out parameter for N₂O₄. The investigations on the absorption of N₂O₃ in water and in an Na₂SO₄ solution showed no experimentally detectable influence of dissolved salts on \documentclass{article}\pagestyle{empty}\begin{document}$(H\sqrt {k_1 D} )\,_{{\rm N}_{\rm 2} {\rm O}_{\rm 3} } $\end{document}. The numerical value of \documentclass{article}\pagestyle{empty}\begin{document}$(H\sqrt {k_1 D} )\,_{{\rm N}_{\rm 2} {\rm O}_{\rm 3} } $\end{document} is six times that of \documentclass{article}\pagestyle{empty}\begin{document}$(H\sqrt {k_1 D} )\,_{{\rm N}_{\rm 2} {\rm O}_{\rm 4} } $\end{document}.     

Conduction in Bi2O3-based oxide ion conductor under low oxygen pressure. II. Determination of the partial electronic conductivity

In order to investigate the partial electronic conduction in the high oxide ion conductor of the system Bi₂O₃-Y₂O₃ under low oxygen pressure, e.m.f. and polarization methods were employed. Although the electrolyte was decomposed when the \(P_{{\text{O}}_{\text{2}} }\) was lower than the equilibrium \(P_{{\text{O}}_{\text{2}} }\) of Bi, Bi₂O₃ mixture at each temperature, the ionic transport number was found to be close to unity above that \(P_{{\text{O}}_{\text{2}} }\) . The hole conductivity (σ _p) and the electron conductivity (σ _p) could be expressed as follows, $$\begin{gathered} \sigma _p \Omega cm = 5 \cdot 0 \times 10^2 \left( {P_{O_2 } atm^{ - 1} } \right)^{{1 \mathord{\left/ {\vphantom {1 4}} \right. \kern-\nulldelimiterspace} 4}} \exp \left[ { - 106 kJ\left( {RT mol} \right)^{ - 1} } \right] \hfill \\ \sigma _p \Omega cm = 3 \cdot 4 \times 10^5 \left( {P_{O_2 } atm^{ - 1} } \right)^{ - {1 \mathord{\left/ {\vphantom {1 4}} \right. \kern-\nulldelimiterspace} 4}} \exp \left[ { - 213 kJ\left( {RT mol} \right)^{ - 1} } \right] \hfill \\ \end{gathered} $$ These values were much lower than the oxide ion conductivity under ordinary oxygen pressure.     

Formation Energies of Antiphase Boundaries in GaAs and GaP: An ab Initio Study

Electronic and structural properties of antiphase boundaries in group III-V semiconductor compounds have been receiving increased attention due to the potential to integration of optically-active III-V heterostructures on silicon or germanium substrates. The formation energies of {110}, {111}, {112}, and {113} antiphase boundaries in GaAs and GaP were studied theoretically using a full-potential linearized augmented plane-wave density-functional approach. Results of the study reveal that the stoichiometric {110} boundaries are the most energetically favorable in both compounds. The specific formation energy γ of the remaining antiphase boundaries increases in the order of γ_{113} ≈ γ_{112} < γ_{111}, which suggests {113} and {112} as possible planes for faceting and annihilation of antiphase boundaries in GaAs and GaP.     

The Effect of CO2 and H2O on the Kinetics of NO Reduction by CH4 Over Sr-Promoted La2O3

The influence of CO₂ and H₂O on the activity of 4% Sr-La₂O₃ mimics that observed with pure La₂O₃, and a reversible inhibition of the rate is observed. CO₂ causes a greater effect, with decreases in rate of about 65% with O₂ present and 90% in its absence, while with H₂O in the feed, the rate decreased around 35-40% with O₂ present or absent. The influence of these two reaction products on kinetic behavior can be described by assuming competitive adsorption on the surface, incorporating adsorbed CO₂ and H₂O in the site balance, and using rate expressions previously proposed for this reaction over Sr-promoted La₂O₃. In the absence of O₂, the rate expression is $$r_{N_2 } = \frac{{k'P_{{\text{NO}}} P_{{\text{CH}}_{\text{4}} } }}{{{\text{(1 + }}K_{{\text{NO}}} P_{{\text{NO}}} {\text{ + }}K_{{\text{CH}}_{\text{4}} } P_{{\text{CH}}_{\text{4}} } {\text{ + }}K_{{\text{CO}}_{\text{2}} } P_{{\text{CO}}_{\text{2}} } {\text{ + }}K_{{\text{H}}_{\text{2}} {\text{O}}} P_{{\text{H}}_{\text{2}} {\text{O}}} {\text{)}}^{\text{2}} }},$$ which yields a good fit to the experimental data and gives optimized equilibrium adsorption constants that demonstrate thermodynamic consistency. With O₂ in the feed, nondifferential changes in reactant concentrations through the reactor bed were accounted for by assuming integral reactor behavior and simultaneously considering both CH₄ combustion and CH₄ reduction of NO, which provided the following rate law for total CH₄ disappearance: $$(r_{{\text{CH}}_{\text{4}} } )_{\text{T}} = \frac{{k'_{{\text{com}}} P_{{\text{CH}}_{\text{4}} } P_{{\text{O}}_{\text{2}} }^{{\text{0}}{\text{.5}}} + k'_{{\text{NO}}} P_{{\text{NO}}} P_{{\text{CH}}_{\text{4}} } P_{{\text{O}}_{\text{2}} }^{{\text{0}}{\text{.5}}} }}{{{\text{(1 + }}K_{{\text{NO}}} P_{{\text{NO}}} {\text{ + }}K_{{\text{CH}}_{\text{4}} } P_{{\text{CH}}_{\text{4}} } {\text{ + }}K_{{\text{O}}_{\text{2}} }^{{\text{0}}{\text{.5}}} P_{{\text{O}}_{\text{2}} }^{{\text{0}}{\text{.5}}} {\text{ + }}K_{{\text{CO}}_{\text{2}} } P_{{\text{CO}}_{\text{2}} } {\text{ + }}K_{{\text{H}}_{\text{2}} {\text{O}}} P_{{\text{H}}_{\text{2}} {\text{O}}} {\text{)}}^{\text{2}} }}.$$ The second term of this expression represents N₂ formation, and it again fit the experimental data well. The fitting constants in the denominator, which correspond to equilibrium adsorption constants, were not only thermodynamically consistent but also provided entropies and enthalpies of adsorption that were similar to values obtained with other La₂O₃-based catalysts. Apparent activation energies typically ranged from 23 to 28 kcal/mol with O₂ absent and 31-36 kcal/mol with O₂ in the feed. With CO₂ in the feed, but no O₂, the activation energy for the formation of a methyl group via interaction of CH₄ with adsorbed NO was determined to be 35 kcal/mol.     

Selective electrodeposition of PbO2 on anodised-polycrystalline titanium

Electrochemical experiments on titanium electrodes were coupled with electron backscattered diffraction (EBSD) experiments. The substrates were thermally treated and electropolished in order to have flat and reproducible polycrystalline surfaces, leading to EBSD orientation mapping. Afterwards, the samples were anodised by a galvanostatic procedure. It was shown that electrodeposition of PbO₂ from a 0.5 M Pb(NO₃)₂+2.5 M HNO₃ solution occurs selectively on the near {0 0 0 1} grains, whereas lead electrodeposition occurs on all the grains, whatever their orientation. These results are discussed, taking into account the fact that on {0 0 0 1} grains, the oxide layers are thinner than on other grains. It was concluded that electrodeposition is observed locally on Ti/TiO₂ electrodes for (i) cathodic electrodeposition of metals at low overvoltage; (ii) anodic electrodeposition of PbO₂, in potentiostatic or galvanostatic conditions.     

Oxygen isotope equilibration and exchange as probes for differing dioxygen interactions with pure and rhodia-promoted CeO2 and Al2O3

Comparisons are made between the catalytic activities of CeO₂, Al₂O₃ and Rh₂O₃ when pure, or in the case of CeO₂ and Al₂O₃ when promoted by rhodia dispersed thereon, in respect of: (a) activity at 290 K for homomolecular oxygen isotope equilibration of an equimolar (¹⁸O₂ + ¹⁶O₂) probe gas, the so-called R₀ process, (b) activity under T-ramp for heterophase oxygen isotope exchange between surface lattice and O₂ highly enriched in ¹⁸O, which is shown to occur predominantly by single-stay exchange of both oxygen atoms of dioxygen (the so-called R₂ process). This revised version was published online in June 2006 with corrections to the Cover Date.