Characterization of NOx species in dehydrated and hydrated Na- and Ba-Y, FAU zeolites formed in NO2 adsorption

Adsorbed ionic NO_x species formed upon the interaction of NO₂ with dehydrated or hydrated Na- and Ba-Y, FAU zeolites were characterized using FT-IR/TPD, solid state NMR, and XANES techniques. NO₂ disproportionates on both dehydrated catalyst materials forming NO⁺ and NO₃⁻ species. These ionic species are stabilized by their interactions with the negatively charged zeolite framework and the charge compensating cations (Na⁺ and Ba²⁺), respectively. Although the nature of the adsorbed NO_x species formed on the two catalysts is similar, their thermal stabilities are strongly dependent on the charge compensating cations. In the presence of water in the channels of these zeolite materials new paths open for reactions between NO⁺ and H₂O, and NO₂ and H₂O, resulting in significant changes in the adsorbed ionic species observed. These combined spectroscopic investigations afforded the understanding of the interactions between water and NO₂ on these zeolite catalysts.     

Existence globale pour l'équation de Smoluchowski continue non homogène et comportement asymptotique des solutions

We prove global existence of solutions to the continuous nonhomogeneous Smoluchowski equation for coagulation rates satisfying a more general structure condition than the Galkin–Tupchiev monotony hypothesis considered in (Ph. Laurençot, S. Mischler, Arch. Rational Mech. Anal. 162 (1) (2002) 45–99). The Smoluchowski coagulation rate fulfils this condition as well as some rates which vanish on the diagonal. Under the condition of positivity of the coagulation rate outside of the diagonal we prove that solutions tend to 0 in the large time asymptotic. These results depend on a new estimate from below for the dissipation rate of the L^p-norm, p>1. To cite this article: S. Mischler, M. Rodriguez Ricard, C. R. Acad. Sci. Paris, Ser. I 336 (2003).     

An adaptive pruning algorithm for the discrete L-curve criterion

We describe a robust and adaptive implementation of the L-curve criterion. The algorithm locates the corner of a discrete L-curve which is a log–log plot of corresponding residual norms and solution norms of regularized solutions from a method with a discrete regularization parameter (such as truncated SVD or regularizing CG iterations). Our algorithm needs no predefined parameters, and in order to capture the global features of the curve in an adaptive fashion, we use a sequence of pruned L-curves that correspond to considering the curves at different scales. We compare our new algorithm to existing algorithms and demonstrate its robustness by numerical examples.     

Excited-state dynamics in Yb3+-Ho3+-doped fluoroindate glasses

This work has been partially supported by Gobierno Autonomo de Canarias under contact number 226–265/93.     

Decontamination treatment of uranium in tricarbonated solutions

It has been established that the coexistence of chemical species structurally different from cerium, is a direct consequence of the time taken for its preparation. Its practical applications, within the scope of purifying uranium, may constitute the most important technological aspect in the process of ionic exchange, to separate¹⁴¹Ce from uranium.     

Absorptiometric determination of micro- and submicroamounts of iron using an extractive method with pyridine-2-acetaldehyde salicyloylhydrazone

The formation and extraction into chloroform of iron complex with PASH (λ_max = 640 nm) was studied. Beer's law is obeyed between 2.7 and 16.0 μg · ml⁻¹ of iron, in organic phase (10 ml). The method can be applied to volume ratios V_aq.:V_org. from 1:1 to 20:1. The minimum concentration determinable in aqueous phase is 135 ng ml⁻¹ of iron. The interferences of 73 species were evaluated and eliminated when it was possible. The extraction method of the green complex was applied for the spectrophotometric determination of iron(II) in several standard, geochemical, and bromatological samples. A procedure based on the standard addition method was applied satisfactorily to the determination of as little as 25 ng of iron(II) per milliliter.     

Evaluation of enzymatic digestion and liquid chromatography-mass spectrometry peptide mapping of the integral membrane protein bacteriorhodopsin

A method for the complete peptide mapping of the model integral membrane protein bacteri-orhodopsin is demonstrated. Utilizing more effective enzymatic digestion, procedures with capillary liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) and tandem mass spectrometry (MS/MS), all predicted tryptic digestion products were detected, as well as peptides from all previously reported post-translational modifications of bacteriorhodopsin. A significant contribution of chymotryptic-like digestion products was also observed. A characterization of the behavior of hydrophobic integral membrane peptides in a reversed-phase liquid chromatographic separation is also provided. The method reported here offers improved compatibility of the solubilizing reagents with both the chromatography and mass spectrometry, rendering it suitable for high-throughput proteomic applications.     

Vitamin D: a concise synthesis of the C19 hydroxylated enyne A-ring, an interesting precursor for the preparation of C19 substituted vitamin D analogues

A new C₁₉ hydroxylated enyne 15, as potential A-ring building block of vitamin D analogues, was synthesized in enantiomerically pure form in nine steps from (−)-(S)-limonene. This short synthesis involved ozonolyzis of 1,2-limonene oxide followed by a Criegee rearrangement, epoxide trans diaxial ring opening by lithium acetylide, elimination, epoxidation and syn β-elimination of the resulting homopropargylic oxirane.     

Oligomérisation anionique de l'ethylène. I. Etude cinétique

A kinetic study of ethylene oligomerization in hexane, in the presence of n-BuLi–TMEDA complexes, allowed us to suggest a new mechanism for anionic ethylene oligomerization. n-BuLi and n-Bu(CH₂CH₂)Li species have the same reactivity. The RLi–TMEDA complex in a 1-to-1 stoichiometry is the active species. The following kinetic equation has been established: It reflects the intervention of associated species (n-BuLi–TMEDA)₂ as well as the influence of the concentration of the complexing agent on the kinetics of oligomerization.     

Studies on Ziegler-Natta catalysts. Part II. Reactions between α- or β-TiCl3 and AlMe3, AlMe2Cl,or AlEt3 at various temperatures

The following reactions, carried out in the absence of solvents, has been studied: α-TiCl₃ + Al(CH₃)₃ at 20°C., β-TiCl₃ + Al(CH₃)₃ at 65°C., α-TiCl₃ + Al(CH₃)₂Cl at 20 and 65°C., and α-TiCl₃ + Al(C₂H₅)₃ between 30 and 65°C. It appears that a general reaction mechanism, such as discussed in the preceding paper of this series, applies to all these reactions between TiCl₃ and aluminum alkyls. The differences in overall stoichiometry between some of these systems may be linked to differences in stability of the intermediate Ti? C bonds. In the case of α-TiCl₃ + Al(CH₃)₂Cl, alkylation is probably accompanied by fixation of the AlCH₃Cl₂ on the nonvolatile product.