State of supported rhodium nanoparticles for methane catalytic partial oxidation (CPO): FT-IR studies

The effect of pretreatments as well as of rhodium precursor and of the support over the morphology of Rh nanoparticles were investigated by Fourier transform infrared (FT-IR) spectroscopy of adsorbed CO. Over a Rh/alumina catalyst, both metallic Rh particles, characterized by IR bands in the range 2070-2060 cm-1 and 1820-1850 cm-1, and highly dispersed rhodium species, characterized by symmetric and asymmetric stretching bands of RhI(CO)2 gem-dicarbonyl species, are present. Their relative amount changes following pretreatments with gaseous mixtures, representative of the catalytic partial oxidation (CPO) reaction process. The Rh metal particle fraction decreases with respect to the Rh highly dispersed fraction in the order CO approximately CO/H2 > CH4/H2O, CH4/O2 > CH4 > H2. The metal particle dimensions decrease in the order CH4/O2 > H2 > CH4/H2O > CO > CO/H2. Grafting from a carbonyl rhodium complex also increases the amount and the dimensions of Rh0 particles at the catalyst surface. Increasing the ratio (extended rhodium metal particles/highly dispersed Rh species) allows a shorter conditioning process. The surface reconstruction phenomena going on during catalytic activity are related to this effect.     

Buoyancy Effects on Upward Brine Displacement Caused by CO2 Injection

Upward displacement of brine from deep reservoirs driven by pressure increases resulting from CO₂ injection for geologic carbon sequestration may occur through improperly sealed abandoned wells, through permeable faults, or through permeable channels between pinch-outs of shale formations. The concern about upward brine flow is that, upon intrusion into aquifers containing groundwater resources, the brine may degrade groundwater. Because both salinity and temperature increase with depth in sedimentary basins, upward displacement of brine involves lifting fluid that is saline but also warm into shallower regions that contain fresher, cooler water. We have carried out dynamic simulations using TOUGH2/EOS7 of upward displacement of warm, salty water into cooler, fresher aquifers in a highly idealized two-dimensional model consisting of a vertical conduit (representing a well or permeable fault) connecting a deep and a shallow reservoir. Our simulations show that for small pressure increases and/or high-salinity-gradient cases, brine is pushed up the conduit to a new static steady-state equilibrium. On the other hand, if the pressure rise is large enough that brine is pushed up the conduit and into the overlying upper aquifer, flow may be sustained if the dense brine is allowed to spread laterally. In this scenario, dense brine only contacts the lower-most region of the upper aquifer. In a hypothetical case in which strong cooling of the dense brine occurs in the upper reservoir, the brine becomes sufficiently dense that it flows back down into the deeper reservoir from where it came. The brine then heats again in the lower aquifer and moves back up the conduit to repeat the cycle. Parameter studies delineate steady-state (static) and oscillatory solutions and reveal the character and period of oscillatory solutions. Such oscillatory solutions are mostly a curiosity rather than an expected natural phenomenon because in nature the geothermal gradient prevents the cooling in the upper aquifer that occurs in the model. The expected effect of upward brine displacement is either establishment of a new hydrostatic equilibrium or sustained upward flux into the bottom-most region of the upper aquifer.     

In situ Raman and in situ XRD analysis of PdO reduction and Pd° oxidation supported on γ-Al2O3 catalyst under different atmospheres

Reduction of Pd° and decomposition of palladium oxide supported on γ-alumina were studied at atmospheric pressure under different atmospheres (H(2), CH(4), He) over a 4 wt% Pd/Al(2)O(3) catalyst (mean palladium particle size: 5 nm with 50% of small particles of size below 5 nm). During temperature programmed tests (reduction, decomposition and oxidation) the crystal domain behaviour of the PdO/Pd° phase was evaluated by in situ Raman spectroscopy and in situ XRD analysis. Under H(2)/N(2), the reduction of small PdO particles (<5 nm) occurs at room temperature, whereas reduction of larger particles (>5 nm) starts at 100 °C and is achieved at 150 °C. Subsequent oxidation in O(2)/N(2) leads to reoxidation of small crystal domain at ambient temperature while oxidation of large particles starts at 300 °C. Under CH(4)/N(2), the small particle reduction occurs between 240 and 250 °C while large particle reduction is fast and occurs between 280 and 290 °C. Subsequent reoxidation of the catalyst reduced in CH(4)/N(2) shows that small and large particle oxidation of Pd° starts also at 300 °C. Under He, no small particle decomposition is observed probably due to strong interactions between particles and support whereas large particle reduction occurs between 700 and 750 °C. After thermal decomposition under He, the oxidation starts at 300 °C. Thus, the reduction phenomenon (small and large crystal domain) depends on the nature of the reducing agent (H(2), CH(4), He). However, whatever the reduction or decomposition treatment or the crystal domain, Pd° oxidation starts at 300 °C and is completed only at temperatures higher than 550 °C. Under lean conditions, with or without water, the palladium consists of reduced sites of palladium (Pd°, Pd(δ+) with δ < 2 or PdO(x) with x < 1) randomly distributed on palladium particles.     

Simultaneous Determination of Caffeine and Acetylsalicylic Acid in Pharmaceutical Formulations Using a Boron‐Doped Diamond Film Electrode by Differential Pulse Voltammetry

This work presents a simple, fast and low‐cost method for simultaneous determination of acetylsalicylic acid (ASA), without alkaline hydrolysis and caffeine (CF) in pharmaceutical formulations using a boron‐doped diamond as the working electrode through differential pulse voltammetry. A good repeatability was reached for 20 measurements, with a low relative standard deviation of less than 1.0 %. The calibration curves presented a great linear correlation coefficient for both drugs (R=0.999) with a limit of detection of 1.6×10^?7 mol L^?1 for CF and 2.3×10^?7 mol L^?1 for ASA. The system was validated in comparison with the official method.     

Katalytische Oxydation von 1-Buten - Einflu? des Sauerstoffdruckes

Ohne Zusammenfassung     

Liquid crystal behaviour of linear copolymers—I

The molar volumes of some mesophasic linear homo- and copolymers have been measured as a function of temperature. Both the liquid crystal phase (nematic) and the isotropic liquid have been examined. The polymer chain is characterized by an alternating sequence of rigid groups and flexible spacers. The molar volumes measured for the liquid crystal phase give evidence for a substantially disordered conformation taken by the flexible spacers in the nematic phase. Analogies between homo- and copolymers are discussed.     

Author index for volume 31

The solid state reactions of MMoO₄ (M = Mg²⁺, Fe²⁺, and Ni²⁺) and orthorhombic TeO₂ were investigated. A new metal telluromolybdate MgTeMoO₆ was obtained in the case of Mg; its structure belongs to the orthorhombic system with unit-cell dimensions a = 5.262Å, b = 5.028 Å, c = 8.880 Å. Fe₂(MoO₄)₃ and a new compound were formed in the case of Fe. The new compound is made up with Fe³⁺ ions and its chemical formula cannot be recognized as FeTeMoO₆. In the case of Ni a complex reaction mixture is obtained. An explanation is given of the ability of M²⁺ ions to form the metal telluromolybdates. The catalytic properties of MgTeMoO₆ are discussed and compared to those of the other metal telluromolybdates.     

On the deactivation of Fe2O3?MoO3/SiO2 catalysts in the oxidation of methanol to formaldehyde

The deactivation behavior of Fe₂O₃–MoO₃/SiO₂ catalysts with different Fe₂O₃+MoO₃ content in the oxidation of methanol to formaldehyde is investigated. A simplified reaction-deactivation kinetic model is presented and used to compare and discuss the different behaviors.

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Fe₂O₃–MoO₃/SiO₂ Fe₂O₃+MoO₃ . : -.

     

Oxidation of propylene over tellurium oxides and Cd?Te?Mo?O and Mn?Te?Mo?O systems

The catalytic behavior of the Cd–Te–Mo–O and Mn–Te–Mo–O systems in the selective oxidation of propylene to acrolein has been related to the MTeMoO₆ phases in the region rich in Te and to the MMoO₄ phases with Te as dopant in the region poor in Te. In view of the possible relevance of Te⁴⁺ and Te⁶⁺ ions to catalysis, the behavior of the different forms of tellurium oxide is also discussed.

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Cd–Te–Mo–O Mn–Te–Mo–O MTeMoO₆ Te MMoO₄ Te Te. Te⁺⁴ Te⁺⁶ .

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This work was supported by the Italian C.N.R. (Roma)