Catalytic Decomposition of Methane Over M–Co–Al Catalysts (M = Mg,Ni, Zn,Cu)

Abstract  

The catalytic decomposition of methane over M–Co–Al (M = Mg, Ni, Zn, Cu) was studied. The samples were prepared by co-precipitation and characterized by S_BET, TGA, DTA, TPR and XRD. The carbon produced in the reaction was characterized by SEM and TPO. Activity tests were carried out in a thermobalance between 500 and 750 °C. The results show that the textural properties of the calcined samples did not change significantly with the partial substitution of Co by Mg, Ni, Zn or Cu. On the other hand, there were marked differences in the reduced samples. There was a strong influence on the reducibility of cobalt oxides in the presence of Ni or Cu. Nickel promoted the reduction of Co₃O₄ at the same temperature as the NiO phase, whereas copper strongly decreased the reduction temperature of both Co₃O₄ and CoAl₂O₄ due to a synergistic effect between Cu and Co. The sample containing Cu resulted in low catalytic activity in the whole temperature range because the reduction conditions promoted the formation of a Cu–Co alloy. In the reaction carried out at 700 °C, the observed activity was Co–Al > Mg–Co–Al > Ni–Co–Al. All the samples were deactivated by encapsulation under these conditions due to high rates of carbon deposition. The carbon produced was mainly carbon nanotubes, except for the Cu–Co–Al sample, which produced mostly amorphous carbon.     

High-Stable Mesoporous Ni-Ce/Clay Catalysts for Syngas Production

Abstract  

A mesoporous-type catalytic support was synthesized through the modification of a smectite with polyvinyl alcohol (PVA) and microwaves. Texture and micro-morphology of the support was determined. Several techniques were employed in order to describe the chemical environment of active species on the surface. Ni⁰ particle sizes were dependent on the structural site of reducible species. High stable Ni-Ce catalysts (calcined at 800 °C) were evaluated in the CO₂ reforming of methane reaction at 700 °C (WHSV = 96 L g⁻¹ h⁻¹, without dilution gas and pre-reduction). The catalysts have presented CH₄ conversions between 40 and 65%, CO₂ conversion between 35 and 65% and H₂/CO ratios between 0.2 and 0.4.     

Electrodeposition of Zn in acid sulphate solutions: pH effects

The kinetics of zinc electrodeposition from acid sulphate solution on a platinum electrode was investigated by means of stationary polarization curves, interfacial pH measurement and electrochemical impedance spectroscopy. The effect of pH, namely pH 2, 3 and 4, was analyzed. A significant dependence of Zn electrodeposition with solution pH was verified. The results obtained cannot be predicted by the available models for Zn electrodeposition. A reaction model is then proposed based on the predominant steps as a function of the potential and the electrode surface nature.     

Current advances in the non‐chromatographic fractionation and characterization of PEGylated proteins

For more than 30 years, PEGylation has been used to improve the physicochemical properties of several proteins and therapeutic drugs having a major impact in the biopharmaceutical industry. The purification of PEGylated proteins usually involves two basic challenges: (1) the separation of PEG‐proteins from other reaction products; and (2) the sub‐fractionation of PEG‐proteins on the basis of their degree of PEGylation and positional isomerism. Currently, most PEGylated protein purification processes are based on chromatographic techniques, especially size exclusion chromatography (SEC) and ion exchange chromatography (IEX). Nonetheless, other less frequently used strategies based on non‐chromatographic techniques such as ultrafiltration, electrophoresis, capillary electrophoresis, and aqueous two‐phase systems have been developed in order to fractionate and analyze PEGylated derivates. This review presents current advances in some of the most widely used non‐chromatographic strategies for the fractionation and analysis of PEG‐protein conjugates. Copyright © 2010 Society of Chemical Industry     

Effect of the sintering additive content on the protective passive oxidation behaviour of pressureless liquid-phase-sintered SiC

The long-term oxidation behaviour in air of pressureless liquid-phase-sintered SiC was investigated as a function of the sintering-additive content (a mixture of Y₂O₃ and Al₂O₃ in the 3:5 molar ratio) at oxidizing temperatures in the interval 1100–1300 °C. It is shown that oxidation under these mild conditions is always passive, and with formation of protective oxide scales. However, the oxidation kinetics cannot be described appropriately by the parabolic-rate law. Instead, due to the gradual crystallization of the oxide scales during oxidation, it is more complex, exhibiting two different stretches given respectively by the arctan- and parabolic-rate laws. Furthermore, it was found that the rate-limiting mechanism of the initial arctan oxidation is the outward diffusion of metal cations from the secondary intergranular phase into the oxide scale, with the activation energy of the oxidation being very high and decreasing from 545 to 432 kJ/mol with increasing sintering-additive content from 5 to 20 wt%. The rate-limiting mechanism of the subsequent parabolic oxidation is however the inward diffusion of oxygen through the multicomponent oxide scale, with the activation energy being lower than before and also decreasing from 345 to 205 kJ/mol as the sintering-additive content increases from 5 to 20 wt%. It is also shown that the oxidation resistance decreases with increasing sintering-additive content, but that while the decrease is moderate up to 10 wt%, it is very marked for greater contents.     

Asymmetric Intermolecular Mizoroki-Heck Reaction: From Phosphine/Phosphinite-Nitrogen to Phosphite-Nitrogen Ligands

This review discusses the latest developments in ligand design for the Pd-catalyzed asymmetric intermolecular Mizoroki-Heck reaction, from the successful phosphine/phosphinite-nitrogen ligands to the recently reported phosphite-nitrogen ligands. The presence of a biaryl phosphite group offers several advantages as a ligand scaffold for this process.     

Residual stress versus microstructural effects on the strength and toughness of phase-separated PbO–B2O3–Al2O3 glasses

A few authors have reasonably proposed that liquid–liquid phase-separated (LLPS) glasses could show improved fracture strength, S_f, and toughness, K_Ic, as the second phase could provide a barrier to crack propagation via deflection, bowing, trapping, or bridging. Due to the associated tensile or compressive residual stresses, the second phase could also act as a toughening or a weakening mechanism. In this work, we investigated five glasses of the PbO–B₂O₃–Al₂O₃ system spanning across the miscibility gap: Four of them undergo LLPS—three are binodal (two B₂O₃-rich and one PbO-rich) and one is spinodal—and one does not show LLPS (composition outside the miscibility gap). Their compositions were designed in such a way that the amorphous particles are under compressive residual stresses in some and under tensile residual stresses in others. The following mechanical properties were determined: the Vickers hardness, ball on three balls (B3B) strength, and toughness, K_Ic-SEVNB (single-edge V-notch beam [SEVNB]). The microstructures and compositions were analyzed using scanning electron microscopy with energy-dispersive X-ray spectrometry. The spinodal glass showed, by far, the best mechanical properties. Its K_Ic-SEVNB = 1.6 ± 0.1 MPa m^1/2, which embodies an increase of almost 50% over the B₂O₃-rich binodal composition, and 90% considering the PbO-rich binodal composition. Moreover, its fracture strength, S_f = 166 ± 7 MPa, is one of the highest ones ever reported for an LLPS glass. Fracture analyses evidenced that the spinodal composition exhibited the lowest net stress at the fracture point. Moreover, calculations indicate that the internal residual stress level is the lowest in the spinodal glass. The overall results indicate that the microstructural effect of the spinodal glass is the most significant factor for its superior mechanical properties. This work corroborates the idea that LLPS provides a feasible and stimulating solution to improve the mechanical properties of glasses.     

Serendipitous Identification of a Covalent Activator of Liver Pyruvate Kinase

Enzymes are effective biological catalysts that accelerate almost all metabolic reactions in living organisms. Synthetic modulators of enzymes are useful tools for the study of enzymatic reactions and can provide starting points for the design of new drugs. Here, we report on the discovery of a class of biologically active compounds that covalently modifies lysine residues in human liver pyruvate kinase (PKL), leading to allosteric activation of the enzyme (EC₅₀=0.29 μM). Surprisingly, the allosteric activation control point resides on the lysine residue K282 present in the catalytic site of PKL. These findings were confirmed by structural data, MS/MS experiments, and molecular modelling studies. Altogether, our study provides a molecular basis for the activation mechanism and establishes a framework for further development of human liver pyruvate kinase covalent activators.     

Increased HDL Size and Enhanced Apo A-I Catabolic Rates Are Associated With Doxorubicin-Induced Proteinuria in New Zealand White Rabbits

The catabolism and structure of high‐density lipoproteins (HDL) may be the determining factor of their atheroprotective properties. To better understand the role of the kidney in HDL catabolism, here we characterized HDL subclasses and the catabolic rates of apo A‐I in a rabbit model of proteinuria. Proteinuria was induced by intravenous administration of doxorubicin in New Zealand white rabbits (n = 10). HDL size and HDL subclass lipids were assessed by electrophoresis of the isolated lipoproteins. The catabolic rate of HDL‐apo A‐I was evaluated by exogenous radiolabelling with iodine‐131. Doxorubicin induced significant proteinuria after 4 weeks (4.47 ± 0.55 vs. 0.30 ± 0.02 g/L of protein in urine, P < 0.001) associated with increased uremia, creatininemia, and cardiotoxicity. Large HDL2b augmented significantly during proteinuria, whereas small HDL3b and HDL3c decreased compared to basal conditions. HDL2b, HDL2a, and HDL3a subclasses were enriched with triacylglycerols in proteinuric animals as determined by the triacylglycerol‐to‐phospholipid ratio; the cholesterol content in HDL subclasses remained unchanged. The fractional catabolic rate (FCR) of [¹³¹I]‐apo A‐I in the proteinuric rabbits was faster (FCR = 0.036 h^?1) compared to control rabbits group (FCR = 0.026 h^?1, P < 0.05). Apo E increased and apo A‐I decreased in HDL, whereas PON‐1 activity increased in proteinuric rabbits. Proteinuria was associated with an increased number of large HDL2b particles and a decreased number of small HDL3b and 3c. Proteinuria was also connected to an alteration in HDL subclass lipids, apolipoprotein content of HDL, high paraoxonase‐1 activity, and a rise in the fractional catabolic rate of the [¹³¹I]‐apo A‐I.