纯相和镍取代的Co_3O_4尖晶石催化剂用于N_2O直接分解(英文)

A series of NixCo1-xCo2O4(0 ≤ x ≤ 1) spinel catalysts were prepared by the co-precipitation method and used for direct N2O decomposition. The decomposition pathway of the parent precipitates was characterized by thermal analysis. The catalysts were calcined at 500 °C for 3 h and characterized by powder X-ray diffraction, Fourier transform infrared, and N2 adsorption-desorption. Nickel cobaltite spinel was formed in the solid state reaction between NiO and Co3O4. The N2O decomposition measurement revealed significant increase in the activity of Co3O4 spinel oxide catalyst with the partial replacement of Co2+ by Ni2+. The activity of this series of catalysts was controlled by the degree of Co2+ substitution by Ni2+, spinel crystallite size, catalyst surface area, presence of residual K+, and calcination temperature.     

Efficiency of succinylated-olive stone biosorbent on the removal of cadmium ions from aqueous solutions

Chemical functionalization of olive stone wastes with succinate linkers can potentially improve the performance of wastewater treatment technologies via enhanced adsorption and high affinity of the covalently attached succinate groups for heavy metals. In this study, a novel reusable adsorbent material based on agricultural waste has been synthesized by esterifying the lignocellulosic matrix of olive stones with succinic anhydride in toluene under basic conditions. Characterization of the as-prepared material by FTIR and solid-state MAS ¹³C NMR spectroscopies and TGA confirmed that the heterogeneous esterification has proceeded very efficiently to yield the succinylated-olive stone (S–OS). Subsequent alkaline treatment of S–OS with saturated NaHCO₃ aqueous solution led to the resulting sodic material (NaS–OS), which was subjected to batch experiments in order to evaluate its cadmium-removing efficiency from aqueous solutions at realistic concentrations of cadmium found in industrial effluents. The results obtained from the sorption characteristics have revealed that NaS–OS material is highly effective in removing cadmium from aqueous solutions, with a maximum uptake capacity of 200 mg g⁻¹ (1.78 mmol g⁻¹). The Langmuir isotherm model was found to fit adequately the equilibrium isotherm data. Cadmium adsorption occurs rapidly and the adsorption mechanism is a chemical sorption via ionic exchange between the adsorbate and adsorbent. Thermodynamic parameters were also evaluated from the effect of temperature studies. Regenerability of NaS–OS material was ascertained by quantitative desorption of cadmium with 1 M aqueous NaCl and the reusability of the matrix after five repeated cycles led to nearly no attenuation in its performance (less than 2% in the sorption capacity), indicating that repeated use of NaS–OS is quite feasible. Compared to other low-cost adsorbents utilized for the removal of Cd(II) from water/wastewater, NaS–OS shows higher sorption capacity. These results have important implications for the design of low-cost adsorbents based on agricultural wastes.     

Study of photocrosslinkable polysiloxanes bearing gem di-styrenyl groups: Synthesis and thermal properties

The synthesis of photocrosslinkable polysiloxanes containing gem di-oxaalkylene styrenyl groups and gem di-urethane-α-methyl styrenyl groups has been performed by copolycondensation of α,ω-dihydroxy polydimethyl siloxanes and dichlorosilanes bearing either cyclic acetal groups or Si-H groups (onto which the cyclic acetal groups are further added) and dichlorosilanes bearing alkyl groups. The introduction of styrenyl groups was then achieved by hydrolysis of the acetal groups into the corresponding alcohols followed by reaction with chloromethyl styrene or with 3-isopropenyl-α,α- dimethylbenzyl isocyanate.The structure of the different products synthesized was determined by IR, ¹H, ¹³C and ²⁹Si NMR spectroscopies. The thermal properties of the polysiloxanes bearing gem di-styrenyl groups have been studied at low and high temperatures.These products have been crosslinked under UV, in the presence of a cationic photoinitiator, and showed very good release paper properties.     

Some new extragradient iterative methods for variational inequalities

In this paper, we suggest and analyze some new extragradient iterative methods for finding the common element of the fixed points of a nonexpansive mapping and the solution set of the variational inequality for an inverse strongly monotone mapping in a Hilbert space. We also consider the strong convergence of the proposed method under some mild conditions. Several special cases are also discussed. Results proved in this paper may be viewed as improvement and refinement of the previously known results.     

On locally <Emphasis Type="Italic">A</Emphasis>-convex <Emphasis Type="Italic">H</Emphasis>*-algebras

We endow any proper A-convex H*-algebra (E, τ) with a locally pre-C*-topology. The latter is equivalent to that introduced by the pre C*-norm given by Ptàk function when (E, τ) is a Q-algebra. We also prove that the algebra of complex numbers is the unique proper locally A-convex H*-algebra which is barrelled and Q-algebra.      

Approximating Unknown Mappings: An Experimental Evaluation

Different methodologies have been introduced in recent years with the aim of approximating unknown functions. Basically, these methodologies are general frameworks for representing non-linear mappings from several input variables to several output variables. Research into this problem occurs in applied mathematics (multivariate function approximation), statistics (nonparametric multiple regression) and computer science (neural networks). However, since these methodologies have been proposed in different fields, most of the previous papers treat them in isolation, ignoring contributions in the other areas. In this paper we consider five well known approaches for function approximation. Specifically we target polynomial approximation, general additive models (Gam), local regression (Loess), multivariate additive regression splines (Mars) and artificial neural networks (Ann).Neural networks can be viewed as models of real systems, built by tuning parameters known as weights. In training the net, the problem is to find the weights that optimize its performance (i.e. to minimize the error over the training set). Although the most popular method for Ann training is back propagation, other optimization methods based on metaheuristics have recently been adapted to this problem, outperforming classical approaches. In this paper we propose a short term memory tabu search method, coupled with path relinking and BFGS (a gradient-based local NLP solver) to provide high quality solutions to this problem. The experimentation with 15 functions previously reported shows that a feed-forward neural network with one hidden layer, trained with our procedure, can compete with the best-known approximating methods. The experimental results also show the effectiveness of a new mechanism to avoid overfitting in neural network training.     

Étude de l'écoulement plan d'un fluide visqueux et incompressible autour et au travers de coques cylindriques poreuses, á faibles nombres de Reynolds

Résumé On étudie par voies numérique et expérimentale l'écoulement plan engendré par la translation uniforme en régime de Stokes d'une coque poreuse cylindrique à mi-distance entre deux parois parallèles. On donne des résultats fiables et détaillés concernant le champ hydrodynamique en formulant avec précision les conditions de raccordement aux interfaces entre le milieu poreux et le milieu fluide.

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The two-dimensionnal flow induced by the uniform translation of a porous shell cylinder midway between two parallel plane walls is investigated, for the Stokes regime, both numerically and experimentally. Reliable and detailed results relative to the hydrodynamic field are given formulating the conditions of junction between porous and fluid media.

     

Thermodynamics of Mixtures Excess Volumes and Energies of Mixing of Cycloalkane Mixtures (Cyclopentane to Cyclooctane)

The volumes of mixing for the systems cyclopentane + cyclohexane, cyclopentane + cycloheptane, cyclohexane + cycloheptane (at 20°C), and cyclopentane + cyclooctane, cyclohexane + cyclooctane, cycloheptane + cyclooctane (at 30 °C) have been measured with a dilatometer. All systems show volume contractions, except the first. The energies of mixing are also given. They vary from 7 to 55 J/mol for equimolar solutions.