Co6Al2-yCeyHT hydrotalcite like compounds were synthesized by co-precipitation method. Hydrotalcite structure as well as the mixed oxides obtained after calcination were studied by several physic-chemical techniques: N2-Sorption, XRD, H2-TPR. The mixed oxides were also tested for the toluene total oxidation. The physico-chemical studies revealed modifications in the structural characteristics (surface area, morphology) as well as in reducibility properties of the formed mixed oxides. The solid containing the higher cerium content was the most active in this reaction. Furthermore, relation between the reducibility and T50 for the toluene oxidation was demonstrated, suggesting a Mars Van Krevelen mechanism for the toluene total oxidation with Co-Al mixed oxide. The key factor of these solids is the dispersion of the ceria in the solid.

Series of V-Ce and Cu-V-Ce oxides with different atomic ratios were prepared by the incipient wetness impregnation of a ceria support. These solids were studied by TG–DTA in the oxidation of a model soot (carbon black (CB) Degussa N330). V-Ce oxides are active in the carbon black oxidation and an increase in the vanadium content enhances their catalytic activity. This observation is correlated with the presence of a V2O5 phase. However, this catalytic system (V-Ce) produces CO during the CB oxidation. Adding copper to the V-Ce oxide to form a ternary system (Cu-V-Ce) has a beneficial effect on the CO2 selectivity. A synergistic effect between copper and vanadium species on ceria is evidenced. The presence of the V2O5 phase on the catalyst enhances the activity for the CB oxidation while copper (II) species decrease the CO production significantly.

The influence of vanadyl and copper precursors, impregnated on ceria, was evaluated by X-ray diffraction (XRD), thermal analysis (TG-DSC), and electron paramagnetic resonance (EPR) of binary and ternary oxides. The formation of a copper oxalate phase from copper nitrate and vanadyl oxalate was revealed during the preparation of the ternary oxide (1Cu1V10Ce). Three types of Cu(II) species in the dried copper containing solids were evidenced: (i) Cu(II) cations with an elongated octahedral symmetry attributed to the copper nitrate precursor, (ii) a copper oxalate phase with a compressed octahedral symmetry and (iii) well-dispersed Cu 2+ ions on the ceria surface, located in a tetragonally distorted octahedral crystal field and surrounded by less than six ligands. The dispersion of the copper-(II) cations over the ceria support surface was facilitated by the copper nitrate precursor. The EPR intensities clearly show that the increase of the oxalate precursor content induces a large fraction of copper that escapes detection by EPR and could be consistent with the presence of large Cu(II) agglomerates. After the calcination of the solids at 300 °C, only one copper species was evidenced and assigned to Cu 2+ ions located in octahedral sites tetragonally distorted. The distortion was more pronounced in the presence of vanadium than in the case of the copper cerium oxide samples. The high dispersion of the copper(II) cations over the ceria support surface, owing to the copper nitrate precursor, was confirmed even after its thermal decomposition.

Vanadium–cerium oxide samples with different V/Ce atomic ratios were prepared using the impregnation method, and then calcined under air at 773 K, and characterized by XRD and 51V MAS NMR. Ceria is the only phase evidenced in low vanadium content samples while a CeVO4 phase and small amounts of V2O5 crystals appeared with the CeO2 phase for higher V contents. 51V MAS NMR study showed the presence of different V sites in solids: distorted sites in polymeric vanadates, highly tetrahedral sites in CeVO4 and octahedral sites in V2O5. The dependence of isotropic chemical shift line for both polymeric V sites and CeVO4 with temperature is evidenced and revealed the interaction of nuclear spin of V atoms with unpaired electrons associated to cerium species.

The combustion of diesel soot has been studied in presence of copper-cerium oxide catalysts. These catalysts were prepared by impregnation of copper nitrate on ceria and calcination under air up to 1073 K. The solids were widely characterised by electron paramagnetic resonance (EPR) technique. For an atomic ratio Cu/Ce=1 and a calcination temperature of 673 K, the catalyst seems to be the most active in the combustion of diesel soot, when compared to other catalysts. The Cu2+ monomers are more concerned than the dimers in this combustion.

The presence of copper and vanadium in ceria at di†erent concentrations gives solids with di†erent characteristics which varywith calcination temperature. At low copper and vanadium concentrations, only the phase is formed. When the concentra-CeO2tion of copper is relatively high compared to vanadium, a CuO phase appears alongside However, when the concentrationCeO2.of vanadium is relatively high compared to copper, and phases are formed along with The formation of theCeVO4V2O5CeO2.CeVO phase is due to the reaction between a trapped electron and leading to reduction of CeIV to CeIII.4V2O5~x/CeO2~yIn a recent work,1 it was shown that when is pre-Ce(OH)3pared at room temperature by precipitation from cerium(III)nitrate and NaOH, is partially formed with cerium(CeO III)2and cerium(IV) hydroxides whereas it is mainly produced whenit is calcined under air at high temperatures ([673 K). Thisproduct exhibits a large deviation from its stoichiomet-CeO2ric composition by the creation of oxygen vacancies.2h5In addition, it was demonstrated6h8 that when Cu2` ionsare added to the solid by coprecipitation or impregna-CeO2tion methods and subsequently calcined under air at di†erenttemperatures, monomers, dimers and clusters of Cu2` areformed in the solid. When the Cu/Ce atomic ratio is [0.5,two phases, and CuO, are formed starting from a cal-CeO2cination temperature of 673 K. In such an oxidised state, thevalences of copper and cerium are respectively ]2 and ]4.No trace of Ce3` is detected except when the solid is reducedunder hydrogen at low temperatures (\373 K). Under theseconditions Cu2` is transformed into Cu` and/or Cu0 species.Moreover, vanadyl introduced into ceria has also beenstudied.9 When this solid is treated under nitrogen at 1073 K,dimers of the form Ce3`EV4` are probably formed and theirconcentrations become more signiÐcant after a reductiontreatment under hydrogen.The purpose of this work is to study the formation mecha-nism of the phase during the preparation of CuVCeCeVO4oxide catalysts.

The presence of copper and vanadium in ceria at different concentrations gives solids with different characteristics which vary with calcination temperature. At low copper and vanadium concentrations, only the CeO2 phase is formed. When the concentration of copper is relatively high compared to vanadinmm a CuO phase appears alongside CeO2. However, when the concentration of vanadium is relatively high compared to copper, CeVO4 and V2O5 phases are formed along with CeO2. The formation of the CeVO4 phase is due to the reaction between a trapped electron and V2O5-x/CeO2-y leading to reduction of Ce-IV to Ce-III.

The oxidation behaviour of gentisic acid, from which a humic acid model was synthesized, was studied. Electrochemical investigation coupled with Electron Spin Resonance analysis revealed the complexity of the mechanism. Coupled chemical reactions appeared after the two electron oxidation, leading to trihydroxybenzoic acids, and to dimeric compounds. The presence of methylenic groups, particularly important to mimic the flexibility and aggregative properties of natural humic substance, was confirmed. Assuming a free radical mechanism for the chemical evolution of humic substances, metal ions could help the reaction process, leading to efficient spin-trapping matters to be considered in water treatments.

The oxidative cleavage of 2,5-dihydroxybenzoic acid (gentisic acid), presumably into maleylpyruvate in basic aqueous solution has been shown by ESR spectra of semiquinonic radicals bearing a methylenic group. One of these radicals has been unambiguously attributed to 2,4,5-trihydroxyphenylacetic acid semiquinonic radical. The formation of an hydroxylated homogentisic acid from gentisic acid (a metabolite of aspirin) is of particular importance in the treatment of alkaptonuria and related inflammatory arthritis.

The ability of hydroxylated metabolites of salicylic acid to scavenge reactive oxygen species and to inhibit arachidonic acid metabolism was investigated. The tested trihydroxybenzoic acids (THBAs) were potent scavengers of hydroxyl and superoxide anion radicals produced by Fenton reaction and xanthine/xanthine oxidase system or activated macrophages respectively. In the same tests, salicylic acid possessed moderate O2(-) and low OH'scavenging activities. Our results demonstrate that adding two hydroxyl groups to salicylic acid strongly increases the reactive oxygen species (ROS) scavenging activities. Adding two hydroxyl groups at position 4 and 5 (2,4,5-THBA) affords the most active ROS scavenging activity probably due to the ortho unsubstituted catechol moiety. In fact, we can consider that the ROS scavenging properties of salicylic acid are essentially due to its metabolic products such as 2,3- and 2,5-DHBAs, catechol and also to THBAs.

Reactions of 2-chloroformylhydrazones of aromatic aldehydes or ketones 2 with various hydrazines were converted to monocarbonohydrazone derivatives 3 or 5 and/or tetrahydro-1,2,4,5-tetrazin-3(2H)-one derivatives 6, 7. By oxidation with lead dioxide, compounds 6 were transformed into stable 3,4-dihydro-3-oxo-1,2, 4,5-tetrazin-1(2H)-yl radical derivatives 8.

The hydroxyl radical scavenging activity of salicylic acid, 2,5 (3,4 and 2,3)-dihydroxybenzoic acids and catechol was investigated. To quantify their antioxidative effects, a test system based on the inhibition of the ESR signal of 5,5-dimethyl-2-hydroxypyrrolidine-N-oxide (DMPO-OH) (obtained by addition of hydroxyl radical (generated by Fenton reaction) with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO)) by the tested compounds was applied. It was found that catechol was 6600 times more potent than salicylic acid, 2,5 or 2,3-dihydroxylbenzoic acids. This effect is discussed in terms of unfavourable ortho interactions between the phenolic and carboxylic acid functions.

The kinetics of the acylation of 2,3-dihydrobenzoxazol-2-one with dodecanoic acid in polyphosphoric acid were investigated. Two competitive reactions occurred at the 3- and 6-positions. The acylation reactions in polyphosphoric acid of 2,3-dihydrobenzoxazol-2-one and 2H-1,4-benzoxazin-3(4H)-one give 6- and 7-acyl derivatives. 4-Acetyl-2H-1, 4-benzoxazin-3(4H)-one rearranged in polyphosphoric acid exclusively to the 7-acetyl derivative. Two mechanisms are proposed to explain the different reaction sites for the acylation of 2H-1,4-benzoxazin-3(4H)-one.

A long‐lasting large‐amplitude pulsation event was observed on January 10, 1983, 0200–0600 UT (0411–0745 MLT) in the ionosphere and in the magnetosphere. In the ionosphere the characteristics of the pulsations changed from being Ps 6/auroral torches toward substorms and back to Ps 6 over the 4‐hour period. At the geostationary orbit (6.6 Re) the corresponding characteristics were a modulation of the high‐energy (≥20 keV) particle intensity and plasma dropouts. Following the work by Rostoker and Samson (1984), we propose an interpretation of the event in which the pulsations are caused by the Kelvin‐Helmholtz instability, during an interval of strong magnetospheric convection. The gradual transition between Ps 6 pulsations and substorm structures is interpreted as being different results of the Kelvin‐Helmholtz instability, caused by different states of the magnetospheric convection. The proposed explanation forms the basis for a discussion on a simplified scheme of the substorm sequence.