Vapour phase deposition and thermal decarbonylation of Re2(CO)10 on gamma-alumina: infrared studies

Dirheniumdecacarbonyl vacuum sublimed onto mesoporous -alumina forms Lewis type adducts where an axial CO group is coordinated to an A1³⁺ ion at the metal oxide surface, as revealed by IR spectroscopy. Vacuum heating of the surface adduct at 773 K brings about decarbonylation, with intermediate formation of a surface-bound mononuclear tricarbonyl which was completely decarbonylated on prolonged heating at the same temperature. The resulting material strongly chemisorbs CO to yield mainly a surface-bound pentacarbonyl species. This suggests that the supported metal remains primarily in a zero-valent and well dispersed state.     

Determination of the high-pressure phase equilibria of Polystyrene/p-Cymene in presence of CO2

An environmentally friendly technology to recycle Polystyrene (PS) wastes from a solution of p-Cymene using CO₂ as antisolvent was proposed. In this process, the study of equilibrium of the ternary mixtures CO₂/p-Cymene/Polystyrene is crucial, and particularly, the solubility of p-Cymene in CO₂ and the sorption of CO₂ in the solution are the key factors since the recovered polymer should be precipitated while the solvent should be fully solubilized in CO₂. In this work, the effect of pressure (50–100–150 bar), temperature (25–30–40 °C) and polymer concentration (0.05–0.80 g PS/ml p-Cymene) on the solubility of p-Cymene and CO₂ were studied to determine the most suitable conditions to perform the precipitation of Polystyrene. The experimental data were correlated as a function of density and polymer concentration according to modifications of well-known semi-empirical expressions (Chrastil's equation and Dual-Mode model). The optimum conditions to carry out the precipitation process of Polystyrene were calculated from the application of the fitted parameters obtained from the previous proposal. The most suitable conditions to precipitate Polystyrene from its solution in p-Cymene were reached at high values of density, it means, high pressure, low temperature and moderated concentration.     

The mechanism of CO oxidation over Cu(110): Effect of CO gas energy

The effect of the temperature of gas phase CO upon the kinetics of the oxygen titration reaction: CO_g +O_a CO_2,g, has been studied. It is found that the reaction's rate is independant of CO gas temperature between 300 and 623 K. The activation energy (6.5 kcal/mole), dependence upon CO pressure (first-order), and independence upon oxygen coverage for 0.1 _o 0.4 are all independant of the CO gas phase temperature. This result rules out any Eley-Rideal type mechanism whereby CO reacts directly from the gas phase with an oxygen adatom without first being accommodated to the surface temperature in an absorbed state. The result is instead interpretable in terms of a Langmuir-Hinshelwood mechanism.Camille and Henry Dreyfus Foundation Teacher-Scholar Fellowship.     

Promotion through gas phase induced surface segregation: methanol synthesis from CO, CO2 and H2 over Ni/Cu(100)

We have studied the rate of methanol formation over Cu(100) and Ni/Cu(100) from various mixtures of CO, CO₂ and H₂. It is found that the presence of submonolayer quantities of Ni leads to a strong increase in the rate of methanol formation from mixtures containing all three components whereas Ni does not influence the rate from mixtures of CO₂/H₂ and CO/H₂, respectively. The influence of the partial pressures of CO and CO₂ on the rate indicates that the role of CO is strictly promoting. From temperature-programmed desorption spectra it follows that the surface concentration of Ni depends strongly on the partial pressure of CO. In this way the increase in reactivity is interpreted as a CO-induced structural promotion introduced by the stronger bonding of CO to Ni as compared to Cu. It is suggested that this type of promotional behavior will be of general importance in existent catalysts and perhaps even more relevant in the development of new or improved bimetallic catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Simulation of kinetics of nitrogen desorption from Rh(111)

Associative desorption of N atoms from the Rh(111) surface is simulated in the framework of the lattice-gas model. The Arrhenius parameters and nearest-neighbour lateral interaction employed to describe the measured thermal desorption spectra are as follows:v=10¹³ s^–1,E _d=40 kcal/mol, and ₁=1.7 kcal/mol. The results obtained are used to clarify the role of nitrogen desorption in the NO + CO reaction on Rh(111) atT=400–700 K andP _NOP _CO0.01 atm.     

The dependence of catalytic carbon filament growth kinetics upon gas phase carbon activity

Previous studies using an α-iron catalyst showed that the rate of carbon filament growth was linearly proportional to the gas-phase carbon activity (a_c) at lower a_c. At higher a_c the rate then became nearly independent of the gas-phase carbon activity. It was also reported that γ-iron did not show two regions of linear behavior, but instead a smooth transition from low a_c where the rate was strongly dependent, to high a_c where it was nearly independent. In the present study, nickel has been observed to behave in a manner similar to that of γ-iron. A model is presented which explains this behavior. The model includes the effect of concentration upon the diffusivity of carbon in the metal. It predicts qualitatively the observed dependence of rate upon gas-phase carbon activity.     

Vanadia/titania catalysts for gas phase partial toluene oxidation: Spectroscopic characterisation and transient kinetics study

Formation of vanadia species during the calcination of ball milled mixture of V₂O₅ with TiO₂ was studied by Raman spectroscopy in situ and at ambient conditions. It is found that calcination in air leads to fast (1–3 h) spreading of vanadia over TiO₂ followed by a slower process leading to the formation of a monolayer vanadia. The calcinated catalyst showed higher activity during toluene oxidation than the uncalcinated one, but the selectivity towards C₇-oxygenated products (benzaldehyde and benzoic acid) remains unchanged. The activity of the catalysts is ascribed to the formation of vanadia species in the monolayer. The details of the parallel–consecutive reaction scheme of toluene oxidation are presented from steady-state and transient kinetics studies. Different oxygen species seem to participate in the deep and partial oxidation of toluene. Coke formation was observed during the reaction presenting an average composition C_2nH_1.1n. The amount of coke on the catalyst was not dependent on the calcination step and the vanadium content in the catalyst. Coke formation was seen to be responsible for the deactivation of the catalyst.     

Hreels characterization of the room temperature phase of propene adsorbed on ruthenium (001)

Room temperature adsorption of propene on ruthenium (001) was studied by HREELS and UPS. Adsorption was mainly dissociative, with cleavage of both C-H and C-C bonds, and resulted in a mixture of surface species: naked carbon atoms, CH fragments, metal carbynes, ethylidyne, di- adsorbed alkene, and -adsorbed alkene in order of their relative abundance.     

The kinetics of photocatalytic degradation of trichloroethylene in gas phase over TiO2 supported on glass bead

In this investigation, a packed bed filled with coated titanium dioxide glass beads to study the kinetics of photocatalytic degradation of trichloroethylene under irradiation of 365 nm UV light. In the range of 100–500 ml/min of flowrate, the reaction rate for 6 μM TCE increased with an increasing flowrate upto 300 ml/min, while was not affected by the flowrate at the values higher than 300 ml/min. For moisture in the range of 9.4–1222.2 μM, the reaction rate of TCE was decreased with an increasing humidity. The adsorbed water on the catalyst surface could compete with the adsorption of TCE on the sites. The reaction rate of 6 μM TCE increased as the light intensity increased, and was proportional to the 0.61 order of the light intensity. Among the three L–H bimolecular form models, the experimental data had the best fit for one of models:

     

Effect of phase transfer catalyst on CO substitution of Mo(CO)6

The effect of Q⁺ OH^- was studied, which is formed in NaOH solution used for anion exchange with PTC, on CO substitution of molybdenum hexacarbonyl complex by strong electron donating ligand, 2,2’-bipyridine. The change of product yield was discussed according to the amount and types of solvent and PTC, their compositions, reaction temperature and time, and different cation and anion of PTC.     

Sorption/desorption studies on polypropylene geomembrane in the presence of hazardous organic liquids

Experimental results of sorption/desorption obtained from a gravimetric method are presented for a polypropylene geomembrane with various organic liquids at 25, 50, and 70°C. The sorption data have been fitted to an Arrhenius relationship to obtain the heat of sorption. The sorption/desorption data have been analyzed using an empirical equation. The swelling of the PP geomembrane has also been studied for the chosen liquids. Experimental results and the derived quantities have been discussed to study the chemical resistivity of the geomembrane. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1291–1298, 1999     

Energy and Structure of (001) Coincident-Site Twist Boundaries and the Free (001) Surface in MgO: A Theoretical Study

A computer code is described which permits investigation of the energy and structure of coincident-site lattice (CSL) grain boundaries, stacking faults, and free surfaces in ionic crystals. The code uses computational techniques similar to those of Harwell's HADES code for the study of point defects in bulk ionic crystals. Two sets of short-range potentials are used to determine the energy and structure of the free (001) surface and of (001) CSL twist boundaries in MgO with values of Γ, the inverse density of CSL sites, ranging between Γ= 5 and Γ= 65. From comparison of the results obtained by means of the different potentials it is concluded that the Van der Waals attraction between oxygen ions on opposite sides of the interface is mainly responsible for the rather weak cohesion predicted for such bicrystals, whereas Coulombic interactions are found to play only a minor role. It then follows that (i) the (001) plane is not a favored plane for the formation of grain boundaries in pure oxides with NaCl structure and (ii) similarities should exist between (001) twist boundaries in ionic crystals with NaCl structure and in fee metals. These similarities are investigated by comparing calculated boundary structures and energy-vs-misfit angle curves for MgO with recent results for aluminum, copper, silver, and gold, in which a broad spectrum of different interatomic potentials was used. It is suggested that the rather strong cohesion of the pressure-sintered MgO bicrystals of Sun and Balluffi may be due to impurities which have migrated to the boundary during sintering.     

NO reduction by CO over automotive exhaust gas catalysts in the presence of O2

The reduction of NO by CO in absence and presence of O₂ has been investigated by transient experiments at automotive cold-start conditions over Pt/Rh/CeO₂/-Al₂O₃, and derived model catalysts. A high-resolution magnetic sector mass spectrometer was used for distinguishing CO/N₂ and CO₂/N₂O. Mechanistic comparisons are made between the catalyst formulations. A kinetic scheme of elementary reaction steps is proposed, which highlights the various contributions of the catalyst constituents.     

On the kinetics of CO oxidation by O2 over RhI(CO)2 catalytic species anchored to a zeolitic support

The reactivity of Rh^I(CO)₂ towards CO oxidation was studied on a model Rh(0.7 wt%)/HY material. The kinetic results show that Rh^I(CO)₂ exhibit a fairly low activity. It is therefore suggested that the catalytic species responsible for the enhanced activity of Rh/Ce_0.68Zr_0.32O₂ [Manuel et al., J. Catal. 224 (2004) 269] would rather be electron-deficient Rh clusters (Rh _n ^δ+ ).     

Sensitivity of SnO2 semiconductor gas sensors to CO in the presence of high concentrations of water vapour

Amongst future uses of semiconductor gas sensors, one important application could be the measurement of emission gases for the control of combustion processes. In such measurements, water vapour is always present as a factor that can cause interference. Combustion gases, depending on the fuel, can contain up to 20% by volume of water vapour. Therefore, it is important to elucidate the influence exercised by water vapour on the sensor. In this study, the sensitivities of SnO₂-based gas sensors to CO and water vapour were investigated in the laboratory. The concentration of water vapour was varied in the range of 0 to 19·9% by volume. The sensors tested were thick film sensors prepared in the laboratory as well as commercial TGS 812 sensors. Water vapour and CO were found to have a synergistic effect on the conductance of TGS sensor but not on the conductance of the thick film sensor. Due to the absence of the synergistic effect between CO and water vapour the thick film sensor is much less sensitive to the variation of the concentration of water vapour in the range of a few percent to 20% by volume than the TGS 812 sensor.     

Ozonation of cholesterol in the presence of ethanol: Identification of a cytotoxic ethoxyhydroperoxide molecule

Cholesterol ozonation was carried out in ethanol-containing aqueous or nonaqueous solvent, and the ozonized products were analyzed by chemiluminescence detection-HPLC with on-line electrospray MS (HPLC-CL-MS) and characterized on the basis of NMR and FABMS. After the ozonolysis of cholesterol in water/ethanol (aqueous system) as well as in chloroform/ethanol (nonaqueous system), a unique ethoxyhydroperoxide molecule (7α-ethoxy-3β-hydroxy-5α-B-homo-6-oxacholestane-5-hydroperoxide, termed “7α-ethoxy-5-OOH”) appeared as main ozonation product. In addition to structural analysis, we confirmed the remarkable cytotoxicity of 7α-ethoxy-5-OOH toward human lung adenocarcinoma A549 cells and found that its cytotoxicity is superior to that of the commonly known autoxidized cholesterol (3β-hydroxycholest-5-ene-7-one). Hence, 7α-ethoxy-5-OOH is a toxic molecule of primary importance, arising during cholesterol ozonation in the presence of ethanol.     

惰气存在下的热敏物料真空精馏

本文针对热敏物系精馏存在的问题,通过加入惰性气体以降低精馏温度,较全面地考察了惰性气体对精馏塔的影响,说明惰气真空精馏可以有效地解决热敏物质的精馏问题。