Understanding heterogeneous catalysis on an atomic scale: a combined surface science and reactivity investigation for the dehydrogenation of ethylbenzene over iron oxide catalysts

In order to study the dehydrogenation of ethylbenzene to styrene, epitaxial iron oxide model catalyst films with Fe₃O₄(111), -Fe₂O₃(0001) and KFe _x O _y (111) stoichiometry were prepared in single crystal quality on Pt(111). They were investigated using surface science techniques before and after atmospheric pressure reaction experiments in a newly designed single crystal flow reactor. As expected from low-pressure measurements, Fe₃O₄(111) is catalytically inactive. The catalytic activity of -Fe₂O₃(0001) starts after an activation period of about 45 min. After that, the surface is essentially clean but shows a high concentration of defects. On the potassium-promoted films, however, the activation period is much longer, the activity then is higher and the surface gets covered completely with carbon and oxygen during reaction. This indicates a different reaction pathway on the promoted films with a carbon–oxygen species as catalytically active species.     

Comportement électrochimique des variétés alpha et beta PbO2 et influence de l'antimoine sur leur reactivité électrochimique en milieu H2SO4, 8N

Résumé L'expérience a montré qu'il est possible d'obtenir par l'oxydation anodique des variétés- et-PbO₂ parfaitement pures au point de vue cristallographique, et que la réduction de-PbO₂ se déroule à un potentiel plus élevé et plus constant que celui observé sur-PbO₂. La réactivité électrochimique de-PbO₂ est plus importante que celle de-PbO₂. L'introduction de Sb dans les réseaux cristallins de ces variétés diminue fortement leur cristallinité et dans le cas de-PbO₂ on obtient toujours simultanément- et-PbO₂. Du point de vue réactivité électrochimique, l'accroissement dû à la présence de Sb est de l'ordre de 33%.

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The results demonstrate the possibility of preparing through anodic oxidation rigorously pure, from the crystallographic point view,- and-PbO₂ phases, and that the reduction of-PbO₂ takes place at a potential which is more positive and more constant than the one obtained with-PbO₂. In a battery, the electrochemical reactivity of-PbO₂ is more important. The introduction of Sb into the lattice of these forms of PbO₂ decreases their crystallinity, and for the case of-PbO₂ we obtained simultaneously- and-PbO₂. Their electrochemical reactivity can increase by about 33%.

     

Small Amounts of Rh-Promoted Ni Catalysts for Methane Reforming with CO2

Small amounts of Rh-promoted Ni/-Al₂O₃ catalysts possessed higher activity than pure Ni/-Al₂O₃, Rh-Al₂O₃ catalysts and exhibited excellent coke resistance ability in methane reforming with CO₂. XRD, H₂-TPR, CO₂-TPD and coking reaction (via CH₄ temperature-programmed decomposition) indicated that Rh improved the dispersion of Ni, retarded the sintering of Ni and increased the activation of CO₂ and CH₄ on the surface of catalyst.     

Kinetics and Mechanism of Copolymerization of α-terpineol with Methylmethacrylate in Presence of Azobisisobutyronitrile as an Initiator

The radical copolymerization of -terpineol with methyl-methacrylate in xylene at 80±0.1C for 50 minutes in the presence of azobisisobutyronitrile (AIBN) follows ideal kinetics and results in the formation of a functional and random copolymer. The activation energy is 33 KJ/mole. The IR spectrum and NMR spectra of the copolymer(s) shows the bands at 1750 and 3400 cm^–1 for ester group of methylmethacrylate and alcoholic group of -terpineol and peaks at 3 to 4 for methoxy group and at 6.5 to 7.5 due to alcoholic group of methylmethacrylate and -terpineol repectively. The values of reactivity ratios, calculated by Kelen–Tüdos method, are r ₁ (MMA) = 0.18 and r ₂ (-terpineol) = 0.046. The Alfrey-Price; Q–e parameters for -terpineol has been calculated as 0.149 and 2.486. The mechanism of copolymerization has been elucidated and it is concluded that the double bond present in the monocyclic ring of -terpineol is an active site for copolymerization and the alcoholic group of -terpineol remain to give functional copolymer.     

Grinding kinetics of calcined alumina

Conclusions If it is necessary to obtain a mineral powder with a high dispersion (_mean 1 ), it is technically-undesirable and economically unsuitable to increase the quantity of grinding bodies by more than four times with respect to the weight of -Al₂O₃.Silicone oil is a suitable surface active agent for carrying out effective dry grinding of -Al₂O₃.With the dry grinding of -Al₂O₃ using metal grinding bodies, the iron pickup is approximately ten times greater than with wet grinding. During the dry grinding of -Al₂O₃ with an addition of silicone oil, and corundum grinding bodies, the rate of grinding is the same as with wet grinding using metal grinding bodies.Translated from Ogneupory, No. 8, pp. 71–72, August, 1971.     

The use of alkali carbonates in carbon concentration cells

The feasibility of using alkali carbonates as electrolytes in carbon concentration cells has been investigated. The following cell was set up: The test electrode (LHS) was a carbon-permeable-iron membrane in contact with a gaseous or liquid metal environment whose carbon activity could be varied. Experiments involving argon and liquid sodium environments at 970 K showed that the potential of the-Fe test electrode was a function of its carbon activity.The potential of the electrode,-Fe, C ¦ CO ₃ ^2– , was also measured as a function of carbonate ion activity and current.It was concluded that the predominant electrode reaction at the iron electrode was reversible and involved carbon and carbonate species or species with which they were in equilibrium.     

Some Factors Influencing the Morphology of α-Zirconium Phosphate and its Intercalation Reactions with a Bifunctional Thioether Amine

Crystalline samples of -zirconium phosphate, (-ZrP, -Zr(HPO₄)₂·H₂O) have been prepared by decomposition of zirconium fluoride complexes in the presence of phosphoric acid under a variety of conditions. The crystallinity and morphology have been shown to depend on a number of factors including the F^–/Zr⁴⁺ ratio, the concentration of Zr⁴⁺ ions, the material of the reaction vessel and the reaction temperature. Under conditions of rapid precipitation small plate-like crystals of -ZrP are produced whereas under conditions of slow crystallisation larger crystals with a lower aspect ratio are formed. The relative intensities of the d ₀₀₂, d ₁₁₀ and d ₁₁₂ reflections observed by X-ray powder diffraction show a correlation with the crystal morphology as determined by SEM.The intercalation reaction of 4-(methylmercapto)aniline with different samples of -ZrP under a variety of conditions has been studied. Incomplete intercalation is observed in each case, with the extent of intercalation depending on both the morphology of the -ZrP and the reaction conditions. The intercalated amine has been shown to exist as a mixture of protonated cations and neutral molecules.     

Mechanisms of Iron Activation on Fe-Containing Zeolites and the Charge of α-Oxygen

According to previous Mössbauer data [1] -sites formation at the activation of Fe-containing zeolites is accompanied by irreversible self-reduction of the iron, proceeding without participation of an external reducing agent. Reduced Fe²⁺ ions are inert to O₂ but are reversibly oxidized to Fe³⁺ by N₂O, generating the -oxygen species, O, which provide selective oxidation of hydrocarbons.In this work, the mechanism of -sites formation was studied via quantitative measurement of the dioxygen amount desorbed into the gas phase at the step of self-reduction. A prominent role of the zeolite matrix chemical composition has been revealed. For example, with zeolites of Al–Si composition (FeZSM-5 and Fe-), heating to 900 °C in a closed vacuum space leads to irreversible evolution of O₂, which is accompanied by the immediate formation of -sites. Similar heating of B–Si and Ti–Si zeolites also leads to dioxygen evolution; however, this evolution is reversible and is not accompanied by formation of -sites. Activation of these zeolites occurs only in the presence of water vapor. Stoichiometric measurements showed that in terms of charge one regular O^2- ion, removed at the activation, is equivalent to two -oxygen atoms. So, -oxygen is identified as an ion-radical species O ^-., whose unique oxidation properties still distinguish it from the generally observed O^-. radicals.The mechanism of -sites formation is proposed, in which the process of strong chemical stabilization of reduced Fe²⁺ atoms in the zeolite structure is a key step, making impossible the reoxidation of the iron with O₂.     

Occurrence and Correlations of Monoterpene Hydrocarbon Enantiomers in Pinus sylvestris and Picea abies

The relative amounts and enantiomeric compositions of monoterpene hydrocarbons in branch and trunk xylem, in needles, and in resin from apical buds in 18 Pinus sylvestris trees have been determined and compared with the terpene content in branch xylem and needles of Picea abies. Besides the high amount of (+)-3-carene, an excess of (+)--pinene has been found in P. sylvestris, whereas in P. abies (–)--pinene dominates over (+)--pinene. In P. sylvestris, clear positive correlations were found between (+)--pinene and (+)-camphene in the four tissues analyzed. Good positive correlations were also observed between (–)--pinene and (–)-camphene in the two types of xylem, between (+)--pinene and (+)--pinene in the resin, and between tricyclene and (–)-camphene in resin and needles. In P. abies, positive correlations were found between (+)--pinene and (+)-camphene in the branch xylem and between tricyclene and (–)-camphene as well as between (–)--pinene and (–)-camphene in the needles. Complex relationships between (–)--pinene and (–)--pinene were found both in the P. abies and in the P. sylvestris tissues. The importance of the enantiomeric composition of -pinene for the host selection of Ips typographus, Tomicus piniperda, and Hylobius abietis is discussed.     

Current distribution in a two-dimensional narrow gap cell composed of a gas evolving electrode with an open part

On the basis of the observation of gas bubbles evolved by electrolysis, a two-dimensional vertical model cell composed of electrodes with open parts for releasing gas bubbles to the back side is proposed. The model cell consists of two layers. One layer forms a bubble curtain with a maximum volume fraction of gas bubbles in the vicinity of the working electrode with open parts. The other. being located out of the bubble layer, is a convection layer with a small volume fraction distributed in the vertical direction under forced convection conditions. The cell resistance and the current distribution were computed by the finite element method when resistivity in the back side varied in the vertical direction along the cell. The following three cases for overpotential were considered: no overpotential, overpotential of the linear type and overpotential of the Butler-Volmer type. It was found that the cell resistance was determined not only by the interelectrode gap but also by the percentage of open area and in some cases by the superficial surface area. The cell resistance varied only slightly with the distribution of the bubble layer in the back side.Nomenclature b linear overpotential coefficient given byb=/i - C proportionality constant given by Equation 15 - d ₁ distance between front side of working electrode and separator - d ₂ thickness of separator - F Faraday constant - I total current per half pitch - i current density at working electrode - i ₀ exchange current density - L length of a real electrolysis cell - n number of electrons transferred in electrode reaction - O _p percentage of open area given by Equation 1 - p pitch, i.e. twice the length of the unit cell, defined by 2(BC) in Fig. 4 - q thickness of bubble curtain, defined by (AM) in Fig. 4 - R gas constant - r _t total cell resistance - r unit-cell resistance defined by (V – V _eq)/I - r _rs residue ofr from sum ofr ₀ andr - r ₀ ohmic resistance of solution when0 _p=0 - r resistance due to overpotential when0 _p=0 - s electrode surface ratio or superficial surface area given by Equation 2 for the present model - T absolute temperature - t thickness of working electrode defined by EF in Fig. 4 - V cell voltage - V _eq open circuit potential difference between working and counter electrodes - solution velocity in cell - ₀ solution velocity at bottom of cell - w width of working electrode, defined by 2(DE) in Fig. 4 - x abscissa located on cell model - y ordinate located on cell model - anodic transfer coefficient - linear overpotential kinetic parameter defined byb/[_bc(p/2)] - d infinitesimally small length on the boundary - volume fraction of gas bubbles in cell - dimensionless cell voltage defined bynF(V – V _eq)/RT - overpotential at working electrode - Butler-Volmer overpotential kinetic parameter defined by [nFi _0bc(p/2)]/RT - coordinate perpendicular to boundary of model cell - ₁ resistivity of bubble-free solution - ₂ resistivity of separator - _bc resistivity of bubble curtain - potential in cell     

Preparation of supported gold catalysts from gold complexes and their catalytic activities for CO oxidation

A phosphine-stabilized mononuclear gold complex Au(PPh₃)(NO₃) (1) and a phosphine-stabilized gold cluster [Aug(PPh₃)₈](NO₃)₃ (2) were used as precursors for preparation of supported gold catalysts. Both complexes 1 and 2 supported on inorganic oxides such as -Fe₂O₃, TiO₂, and SiO₂ were inactive for CO oxidation, whereas the 1 or 2/ oxides treated under air or CO or 5% h₂/Ar atmosphere were found to be active for CO oxidation. The catalytic activity depended on not only the treatment conditions but also the kinds of the precursor and the supports used. The catalysts derived from 1 showed higher activity than those derived from 2. -Fe₂O₃ and TiO₂ were much more efficient supports than SiO₂ for the gold particles which were characterized by XRD and EXAFS.     

Dose and enantiospecific responses of white pine cone beetles,Conophthorus coniperda,to alpha-Pinene in an eastern white pine seed orchard

The white pine cone beetle, Conophthorus coniperda, exhibited dose and enantiospecific responses to -pinene in stands of mature eastern white pine, Pinus strobus, in a seed orchard near Murphy, North Carolina, USA. (–)--Pinene significantly increased catches of cone beetles to traps baited with (± )-trans-pityol. (+)--Pinene did not increase catches of beetles to pityol-baited traps and interrupted the response of beetles to traps baited with (±)-trans-pityol and (–)--pinene. Maximal attraction of cone beetles to pityol-baited traps was obtained with lures releasing (–)--pinene at a rate of 103 mg/day at 23^°C. Lures releasing (–)--pinene at rates lower or higher than 103 mg/day resulted in reduced catches to traps baited with (±)-trans-pityol. The sex ratio in all catches was heavily male biased. Attraction of the clerid predator, Thanasimus dubius, to traps baited with (±)-trans-pityol increased significantly with the presence of -pinene, irrespective of enantiomeric composition. Maximal attraction of T. dubius to pityol-baited traps occurred with devices releasing (–)--pinene at the highest rate tested, 579 mg/d at 23^°C, a sub optimal rate for cone beetles.     

The active dissolution of tin in acidic chloride electrolyte solutions — a rotating disc study

The anodic dissolution of tin in acidic chloride electrolyte has been investigated using the rotating disc technique. The dissolution reaction has a Tafel slope of 64 ±5 mV dec^–1 after the effects of diffusion are eliminated. The order of reaction with respect to Cl^– ion has been found to be unity. The measured currents were also found to depend onC _H+. The suggested mechanism involves quasi-reversible charge transfer.A possible explanation is given for the observed current-time behaviour at low anodic current densities.Notation i Current density - i ₍₎ Current density at infinite rotation speed - i _d ,Cl^– Limiting current density due to Cl^– diffusion - C _cl ^– Concentration of chloride ion - C _H+ Concentration of hydrogen ion - d ₀ Diffusion coefficient of oxidised species - k _b Rate constant for reduction of oxidised species - Kinematic viscosity - Angular velocity - Anodic transfer coefficient - Rate constant at standard equilibrium potential - Direction of reaction     

Bruchins,plant mitogens from weevils: structural requirements for activity

Bruchins are 3-hydroxypropanoate esters of long-chain ,-diols from pea weevils and cowpea weevils that have been shown to initiate callus formation on pea pods at extremely low application rates. Synthetic analogs have been prepared and examined to evaluate structural requirements for inducing this unusual neoplastic response. Chain length (optimum length C₂₂–C₂₄) is important, whereas unsaturation within the chain is relatively unimportant. Difunctionality is required for maximum activity, but the ,-diols themselves are inactive. Most critical is the ester portion(s) of the molecules; 3-hydroxypropanoate esters are far more active than any analogs examined.     

Anisotropic structure analysis for cobalt oxides on α-Al2O3(0001) by polarized total-reflection fluorescence extended X-ray absorption fine structure

Anisotropic structure analyses for [CoO_x]/-Al₂O₃ (0001) and [Co₃O₄]_n /-Al₂O₃ (0001) which were derived from Co₂(CO)₈/-Al₂O₃ (0001) were performed by a polarized total-reflection fluorescence extended X-ray absorption fine structure (EXAFS) technique. Both s- and p-polarized EXAFS data revealed that the cobalt atoms of [CoO_x] were located on three-fold hollow sites of -Al₂O₃ (0001) in a monomer form and that a thin spinel structure [Co₃O₄] grew with the (001) plane parallel to -Al₂O₃ (0001).     

Preparation of α,ω-bis(p-vinylbenzyl)-terminated polystyrene and α-methylstyrene tetramer

Summary Telechelic macromers composed of only hydrocarbon were prepared by the end-capping reactions of two-ended living polystyrenes and dianion of -methylstyrene tetramer with p-vinylbenzyl chloride. ,-bis(p-vinylbenzyl)polystyrene obtained was found to have a narrow molecular weight distribution and high functionality. In the end-capping reaction of the tetrameric dianion, the yield of ,-(p-vinylbenzyl)-methylstyrene tetramer was 84 % at most, profoundly depending on the concentration of the dianion. To isolate the functionalized tetramer, the fractional dissolution of a crude product was performed with H₂O/MeOH and the result was desirable.     

Cluster Model DFT Study of the Intermediates of Benzene to Phenol Oxidation by N2O on FeZSM-5 Zeolites

An Fe(II) ion at an -cation exchange position of ZSM-5 zeolite (Fe/Z) was taken as a model for the active site in the nitrous oxide decomposition and in the selective oxidation of phenol with nitrous oxide. The oxygen deposited by decomposition of N₂O is commonly referred to as -oxygen (OFe/Z). Cluster model DFT calculations show that the interaction of the OFe/Z center with benzene resulted easily in arene oxide formation. The results indicate a rather low activation energy for this step. Possible transformations of the adsorbed arene oxide are considered and the experimental evidence for the absence of the kinetic H/D isotope effect in phenol formation is discussed. It is concluded that the rate-limiting step for the in situ oxidation of benzene to phenol is the desorption of the product.     

Catalytic oxidation of methanol to methyl formate over silver – a new purpose of a traditional catalysis system

Catalytic reaction was performed in the unregarded temperature region over silver catalysts with long catalytic lifetime for the conversion of methanol to methyl formate. O-saturated or O-saturated silver catalysts were studied individually to identify the roles of O, O in the oxidative esterification of methanol over an unsupported polycrystalline silver catalyst. A synergic process is proposed based on the coexistence of -oxygen species and -oxygen species on the surface of polycrystalline silver at about 573 K.     

α-Copaene, A Potential Rendezvous Cue for the Mediterranean Fruit Fly, Ceratitis Capitata?

-Copaene, a potent attractant for male Mediterranean fruit flies, Ceratitis capitata, is found as a minor component in the essential oils of various plant species, including its hosts such as orange, guava, and mango. Despite the specific attraction of male flies and the wide distribution of the compound in host plants, the biological significance of -copaene remains unknown. In a laboratory test, leklike behavior of C. capitata was induced artificially by using a plastic leaf model treated with (+)--copaene. It was also found that (+)--copaene affected virgin females, provoking "pseudomale" courtship behavior in the short-range bioassay. Mating occurred exclusively on the artificial leaves treated with -copaene, suggesting the compound potentially serves as a chemical cue to facilitate orientation of flies to the rendezvous site.     

Soldier defense secretions of malaysian free-ranging termite of the genusLacessititermes (Isoptera,Nasutitermitinae)

Soldiers of free-ranging termites of the genusLacessititermes (Isoptera, Nasutitermitinae) secrete from their frontal glands a mixture of monoterpenes, sesquiterpenes, and diterpenes.Lacessititermes ransoneti, L. laborator, andL. species A produce species-specific secretions, the composition being most complex forL. laborator. Apart from known mono- and dihydroxytrinervitadienes, the following new diterpenes were isolated and tentatively assigned as trinervita-1(15),8(19)-dien-2,3,9,14-tetraol 2,3,14-O-triacetate, trinervita-1(15),8(19)-dien-2,3,9,14-tetraol 2,3,14-O-triacetate, 2,3,9, 14-tetraacetoxy-1 (15), 8(19)-trinervitadiene, and 2,3,11,13-tetraacetoxy-1(15),8(19)-trinervitadiene. Data on intragenus chemical variations were subjected to canonical discriminant analysis and genetic distances among the species were calculated to depict intragenus identities and affinities.