Cerium Oxidation Research Articles

The relationship between cerium and manganese oxidation in the marine environment

The microbially mediated oxidation of Ce(II1) and Mn(I1) in surface waters of Vineyard Sound, Massachusetts, has been studied to evaluate the relationship between these two processes under different experimental conditions. These data, combined with earlier observations showing that Ce(II1) and Mn(I1) specific oxidation rates covary over a wide range of environments, suggest a close mechanistic relationship between the two processes which contributes to the marked similarities in the geochemistry of each element. Oxidation of Ce(II1) and Mn(I1) at different oxygen concentrations, pH, and concentrations of Mn(II), Ce(III), and Pr(II1) was studied with radiotracers. For both elements, oxidation was inhibited in the absence of oxygen. Ce(II1) oxidation was inhibited by Mn(I1) and vice versa, probably due to competitive inhibition within a common oxidative pathway. Pr(III), a nonredox analog of Ce(III), did not inhibit Mn(I1) oxidation nearly as effectively as Ce(II1) did, indicating that inhibition was not exclusively due to competition at a common binding site but that a redox step must also be involved. Both reactions exhibited a modest dependence on pH which was much smaller than would be expected for nonbiological oxidation. The results are consistent with a common oxidative pathway for Ce and Mn and indicate that an alternative process, nonbiological Ce oxidation on freshly formed Mn oxides, is unlikely. The results also illustrate the potential usefulness of Ce(II1) and Pr(II1) as probes of Mn uptake and redox transformations in biological systems.

X-ray photoelectron spectroscopic study of the oxidation and reduction of a cerium(III) oxide/cerium foil substrate

X-ray photoelectron spectroscopy has been used to examine the nature of the oxide overlayers on a passivated cerium metal foil as a function of a variety of oxidation and reduction treatments. Oxidation of a clean uncontaminated cerium(III) oxide surface is facile at room temperature and produces non-stoichiometric ceria (CeO2−x) at oxygen doses as low as 10 L. At higher doses the overlayer thickens, and after a dose of 160 L the layer depth exceeds the Ce 3d photoelectron attenuation distance of about 20 A. High pressure treatment of the foil in oxygen (0.5 bar at RT and 473 K) produces CeO2 in a high degree of crystallographic order such that O 1s photoelectron intensities are increased above that expected from a randomly oriented powder. An attempt to reduce the CeO2 layer formed by controlled oxidation with CO (633 K, 14 h, 0.6 bar) results in the formation of a carbonated surface layer. Results following attempts to reoxidise this layer are discussed.

一方向凝固させたFe-C合金の成長形態に及ぼす硫黄の影響

Unidirectional solidification experiments were conducted on high purity iron-carbon alloys containing various amounts of sulphur or cerium in order to clarify the mechanism of spheroidization of graphite in cast iron. A self sealing method was used to prevent decarburization and oxidation of cerium. In the alloys containing 0.003 mass% sulphur or 0.2 mass% cerium, the graphite flakes at the interface were completely covered with austenite. At this time, the intergraphite spacing decreased suddenly at a critical solidification rate of 4 mm/h. In the alloys containing more sulphur (>0.006 mass%), the graphite flakes at the interface protruded into the liquid phase. In this case, there was a sudden increase in the intergraphite spacing at a solidification rate of 4 mm/h. It is considered that the change in the morphology at the interface was caused by lowering the graphite/liquid interfacial energy. The sudden increase in the intergraphite spacing was caused by the limiting effect of the adsorbed sulphur on the branching of graphite flakes. In addition, an equilibrium interface morphology was achieved by holding the furnace stationary for 5 h.

Effect of calcination temperature on Al2O3-supported CeO2: complementary results from XRD and XPS

X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) have been used to follow the effect of calcination temperature on CeO 2 particle size, relative CeO 2 concentration, and cerium oxidation state for CeO 2 supported on γ- Al 2 O 3. When the calcination temperature was increased from 500 to 900°C, XRD results indicated a decrease in the relative concentration of CeO 2 at the highest loading (15 wt%), while XPS results reflected an apparent reduction of Ce 4+ to Ce 3+ at the lowest loading (5 wt%). Together these results suggest a transformation of a portion of the CeO 2 particles to a more dispersed Ce 3+-like species following high-temperature calcination. The reduction of ceria under these conditions is thermodynamically unfavorable. The apparent reduction of Ce 4+ to Ce 3+ upon calcination may be the result of an electronic effect, rather than a true reduction of the ceria.

Oxidation of Cerium(III) during Solvent Extraction with Benzoyltrifluoroacetone into Carbon Tetrachloride in the Absence and Presence of Tetrabutylammonium Ions

Cerium(III) in aqueous 0.1mol dm-3 sodium nitrate solutions was extracted with benzoyltrifluoroacetone (Hbfa) into carbon tetrachloride in the absence and presence of tetrabutylammonium (tba+). In the absence of tba+, only the Ce(bfa)3 was extracted; in its presence, however, not only was the ternary complex (Ce(bfa)4-tba+) also extracted, and the extraction was much better. When the two-phase agitation was continued, the organic phase gradually changed from colorless to brown in the absence of tba+ due to the oxidation of the metal ions in the complex in the organic phase to the cerium(IV). However, in the presence of tba+, the organic phase remained colorless for a long time and, thus, oxidation of the cerium(III) was negligible. The rate of oxidation of cerium(III) in the Ce(bfa)3 complex in carbon tetrachloride to the cerium(IV) by forming the Ce(bfa)4 complex was measured by spectrophotometry. The rate of this oxidation was found not to be affected by the ligand concentration.

Metal valence and geometry: synthesis, structure and solution behaviour of the isomers of [Os(S2CNEt2)2(PPh3)2]0, +

The reaction of [Os(PPh3)3Br2] with Na(S2CNEt2) affords cis-[OsL2(PPh3)2](L = S2CNEt2) from which trans-[OsL2(PPh3)2]PF6 is isolated via cerium(IV) oxidation. Reduction of the latter complex by hydrazine hydrate furnishes trans-[OsL2(PPh3)2]. The X-ray structures of all the three complexes have been determined and their spectra and magnetic properties are reported. Solution equilibrium data show that the metal oxidation states strongly differentiate the isomeric co-ordination spheres—the more stable geometry is cis for the bivalent and trans for the trivalent metal. The metastable trans-bivalent complex (d6) can still be isolated because isomerisation is slow but the cis-trivalent complex (d5) isomerises rapidly and could not be isolated. Variable-temperature isomerisation rates, activation parameters and metal reduction potentials [E½(cis) > E½(trans)] of the isomers are reported. There is a progressive decrease in the Os–P bond length in going from trans-[OsL2(PPh3)2]PF6 to trans-[OsL2(PPh3)2] to cis-[OsL2(PPh3)2], the net change being a remarkable 0.15 A. This correlates with the 5dπ–3dπ back-bonding order cis-[OsL2(PPh3)2] > trans-[OsL2(PPh3)2]trans-[OsL2(PPh3)2]PF6. In cis-[OsL2(PPh3)2], PPh3⋯ PPh3 steric repulsion is present but it is more than offset by the strong back-bonding. In trans-[OsL2(PPh3)2] the steric factor is absent but the back-bonding is also weaker. In equilibrated solution both the isomers are present but the cis form predominates (85%). For the very weakly back-bonding trivalent metal, the steric factor becomes strongly controlling and in solutions very little of the cis isomer is present at equilibrium (≈0.002%).

1 H-cyclopropa(b)naphthalene-3,6-dione

Cerium ammonium nitrate demethylation and oxidation of 3,6-dimethoxy-1H-cyclopropa[b]-naphthalene 6 provides 1H-cyclopropa[b]naphthalene-3,6-dione 8 as the first stable cyclopropaquinone.

Anodic generation of cerium (IV) at glassy carbon in acetic acid and coulometric titrations with the generated reagent

Conditions for electrochemical generation of cerium(IV) at glassy carbon in acetic acid in the presence of alkali-metal acetates and sodium perchlorate, respectively, were investigated. A high current efficiency was achieved in anodic oxidation of cerium(III) in acetate supporting electrolytes. Coulometric titration methods for the determination of reducing substances with the generated oxidant were also developed. The end-points were determined by the biamperometric and bipotentiometric methods. The error of the determinations was less than + 2%.

Kinetics of cerium(IV) oxidation of propionic acid in perchloric acid: Role of solvent

The oxidation rate of propionic acid (PROA) by cerium(IV) in aqueous perchloric acid (1.0–6.0 mol/dm3) is proportional to the PROA concentration, the total order of the reaction being two. It was found that the rate is related to the values of Hammett's acidity function (H0) in agreement with both Zucker-Hammett's hypothesis and Bunnett-Olsen's criterion, the water acting as a proton transfer agent. A mechanism consistent with the findings is proposed.

Study of optical and electrophysical characteristics of cerium-containing glasses

The jumping conductivity ( σ c) on localized states close to the Fermi level at T < 200°C and the ionic conductivity ( σ i) at T > 250°C have been established in the alumina-silica alkalineless cerium-containing glasses. The charge transfer is realised by electron jumping on the scheme Ce 3+ ↔ Ce 4+ ( σ c and by the alkaline-earth cations ( σ i). In the 60Co γ-ray fields σ c increases according to the law σ c = AP Δ where P is the dose rate and Δ < 0.5 at P < 800 R/s and Δ > 1 at P > 800 R/s, while σ i decreases because of the decrease in the number of charge carriers owing to the electron-ion recombination, as P grows. Increase in the concentration ( C) of CeO 2 in the composition of the glass was found to enhance the degree of cerium oxidation and to cause the simultaneous presence of Ce 3+ and Ce 4+ in the structure with the predominant entry of Ce 4+ at a concentration of Ceo 2 > 4.5 mol%. The increase of the concentration of CeO 2 to 9 mol% and the substitution chain of Mg 2+ → Sr 2+ → Ba 2+ in the glass composition lead to a drop in the luminescence intensities, correlated with the decrease of σ due to the transition Ce 3+ → Ce 4+ and suppressive action of Sr 2+ and Ba 2+. The kinetics of Ce 3+ ↔ Ce 4+ transformation under the irradiation have been considered.

Secondary ion mass spectrometry and scanning transmission and transmission electron microscopy studies of the effects of reactive elements on nickel oxidation

Implantation of reactive elements (REs), such as cerium and yttrium, at doses of 0.5−5 × 10 16 ions cm −2 has been shown to reduce the NiO scale growth rate substantially during the oxidation of nickel in oxygen at 900 °C, at least during 5 h exposures. Understanding the mechanism involved necessitates establishing the location and form of the RE within the scale. These questions have now been addressed, primarily by secondary ion mass spectrometry (SIMS) and by scanning transmission and transmission electron microscopy (TEM/STEM) examination, on NiO scales formed on nickel implanted with either cerium or yttrium ions to 5 × 10 16 cm -2 during oxidation in oxygen at 900 °C for periods between 0.25 and 150 h. SIMS demonstrated that initially the peak RE concentration within the scale was located near the gas interface but with increasing time it became positioned at increasing depth. NiO growth on unimplanted nickel is controlled primarily by outward cation transport. Assuming the position of the RE peak concentration is indicative of the original nickel surface then, at least initially, RE ion implantation changed the scale growth such that inward oxidant movement was dominant. However, with time, growth reverted increasingly to outward cation transport control. The resurgence of cation transport occured earlier during the oxidation of cerium than yttrium implanted nickel. TEM/STEM has established that cerium was present as small oxide particles within both the NiO grains and grain boundaries and also that cerium and yttrium segregated along the scale grain boundaries. The segregant concentrations diminished with oxidation time, indicating diffusion along the boundaries, which was consistent with the SIMS observations. There would seem, therefore, to be a plausible correlation between the disposition of the REs within the NiO scale and their effect on the oxidation behaviour of nickel.

Role of solvent acidity in the cerium(IV) oxidation of butanoic acid

The oxidation of butanoic acid by cerium(IV) has been studied kinetically in aqueous perchloric acid (1.0–6.0 mol/dm3). It has been found that the reaction is first order with respect to both oxidant and the reductant. Analysis of the influence of the solvent acidity permits to clarify the role of water which acts as a proton transfer agent. A reaction mechanism is proposed.

Aerobic carbon cycling and cerium oxidation: significance for Archean oxygen levels and banded iron-formation deposition

The amounts of organic carbon and iron generally estimated to have been preserved in early Precambrian sediments suggest by implication that only the rapid, oxidative recycling of organic carbon by aerobic heterotrophy could plausibly have kept pace with the oxygen produced annually by net photosynthesis, even with a low global primary productivity of less than 1% of modern global values (Towe, 1990). A global aerobic recycling process would require at least a moderately oxygenated atmosphere to operate. The presence of such an atmosphere as far back in Earth history as 3.8 Ga ago is consistent with, but not proven by, the abundance of organic carbon and the “anomalous” distribution of rare earths in the banded iron-formations of the Isua sediments (Dymek and Klein, 1988). The absence of positive cerium anomalies and the presence of positive europium anomalies in these and other banded iron-formations (Klein and Beukes, 1989; Derry and Jacobsen, 1990) imply that iron oxidation during BIF deposition took place in waters at some depth below the zone of mixing rather than at the surface. A modified Klein-Beukes model using shallow, seasonal downwelling in an otherwise deep-water stratified basin under a moderately oxygenated atmosphere may help explain the origin of some of these enigmatic deposits.

Aerobic carbon cycling and cerium oxidation: significance for Archean oxygen levels and banded iron-formation deposition

The amounts of organic carbon and iron generally estimated to have been preserved in early Precambrian sediments suggest by implication that only the rapid, oxidative recycling of organic carbon by aerobic heterotrophy could plausibly have kept pace with the oxygen produced annually by net photosynthesis, even with a low global primary productivity of less than 1% of modern global values (Towe, 1990). A global aerobic recycling process would require at least a moderately oxygenated atmosphere to operate. The presence of such an atmosphere as far back in Earth history as 3.8 Ga ago is consistent with, but not proven by, the abundance of organic carbon and the “anomalous” distribution of rare earths in the banded iron-formations of the Isua sediments (Dymek and Klein, 1988). The absence of positive cerium anomalies and the presence of positive europium anomalies in these and other banded iron-formations (Klein and Beukes, 1989; Derry and Jacobsen, 1990) imply that iron oxidation during BIF deposition took place in waters at some depth below the zone of mixing rather than at the surface. A modified Klein-Beukes model using shallow, seasonal downwelling in an otherwise deep-water stratified basin under a moderately oxygenated atmosphere may help explain the origin of some of these enigmatic deposits.

Synthesis of substituted tetrahydronaphthalenes by manganese(III), cerium(IV), and iron(III) oxidation of substituted diethyl .alpha.-benzylmalonates in the presence of olefins

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSynthesis of substituted tetrahydronaphthalenes by manganese(III), cerium(IV), and iron(III) oxidation of substituted diethyl .alpha.-benzylmalonates in the presence of olefinsAttilio Citterio, Roberto Sebastiano, Antonio Marion, and Roberto SantiCite this: J. Org. Chem. 1991, 56, 18, 5328–5335Publication Date (Print):August 1, 1991Publication History Published online1 May 2002Published inissue 1 August 1991https://doi.org/10.1021/jo00018a023RIGHTS & PERMISSIONSArticle Views575Altmetric-Citations65LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (960 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Kinetics and Mechanism of the Cerium(IV) Oxidation of Arnold's Base and the Protonation and Hydroxylation of Michler's Hydrol Blue

AbstractIn aqueous H2SO4, Ce(IV) ion oxidizes rapidly Arnold's base((p‐Me2NC6H4)2CH2, Ar2CH2) to the protonated species of Michler's hydrol((p‐Me2NC6H4)2CHOH, Ar2CHOH) and Michler's hydrol blue((p‐Me2NC6H4)2CH+, Ar2CH+). With Ar2CH2 in excess, the rate law of the Ce(IV)‐Ar2CH2 reaction in 0.100 M H2SO4 is expressed ‐d[Ce(IV)]/dt = kapp[Ar2CH2]0[Ce(IV)] with kapp = 199 ± 8M−1s−1 at25°C. When the consumption of Ce(IV) ion is nearly complete, the characteristic blue color of Ar2CH+ ion starts to appear; later it fades relatively slowly. The electron transfer of this reaction takes place on the nitrogen atom rather than on the methylene carbon atom. The dissociation of the binuclear complex [Ce(III)ArCHAr‐Ce(III)] is responsible for the appearance of the Ar2CH+ dye whereas the protonation reaction causes the dye to fade. In highly acidic solution, the rate law of the protonation reaction of Michler's hydrol blue is ‐d[Ar2CH+]/dt = kobs[Ar2CH+] where Kobs = ((ac + 1)[H*] + bc[H+]2)/(a + b[H+]) (in HClO4) and kobs= ((ac + 1 + e[HSO4−])[H+] + bc[H+]2 + d[HSO4−] + q[HSO4−]2/[H+])/(a + b[H+] + f[HSO4−] + g[HSO4−]/[H+]) (in H2SO4), and at 25°C and μ = 0.1 M, a = 0.0870 M s, b = 0.655 s, c = 0.202 M−1s−1, d = 0.110, e = 0.0070 M−1, f = 0.156 s, g = 0.156 s, and q = 0.124. In highly basic solution, the rate law of the hydroxylation reaction of Michler's hydrol blue is ‐d[Ar2CH+]/dt = kOH[OH−]0[Ar2CH+] with kOH = 174 ± 1 M−1s−1 at 25°C and μ = 0.1 M. The protonation reaction of Michler's hydrol blue takes place predominantly via hydrolysis whereas its hydroxylation occurs predominantly via the path of direct OH attack.

Osmium(VIII)/palladium(II) catalysis of cerium(IV) oxidation of allyl alcohol in aqueous acid

Catalysis of the CeIV-allyl alcohol (AA) reaction in acid solution depends both on the of rate enhancement and product distribution on the catalyst used: OsVIII results mainly in acrolein, whereas PdII gives acrylic acid. The rate laws in the two cases also differ:viz., Equations 1 and 2K1 is the equilibrium constant of formation of the OsVIII-allyl alcohol complex and k1 is the rate constant of its oxidation by CeIV; K2 is the equilibrium constant for the formation of the CeIV-PdII-allyl alcohol complex and k2 is its rate constant of decomposition. Rate = K1k1[CeIV][AA][OsVIII]/(1+K1[AA]) (1) Rate = K1k1[CeIV][PdII]/(1+K2[CeIV]) (2)

Solubilization of doubly charged iron(II) complexes in aqueous neutral micellar aggregates. A kinetic investigation

The incorporation of doubly charged iron(II) complexes FeL2+3[with L = 4,4′-dimethyl-2,2′-bipyridine or 4,4′-bis(alkoxycarbonyl)-2,2′-bipyridine, where alkoxy = methoxy, ethoxy or propoxy] into micellar aggregates of non-ionic surfactants CiEj(C10E6, C12E6, C14E6, C12E10 and C12E23) has been studied at 20 °C by examining the kinetics of the cerium(IV) oxidation of these complexes. Binding of the iron(II) complexes to the neutral micelles increases as the co-ordinated ligand becomes increasing hydrophobic. Solubilization is also favoured by an increase (at constant i) in the number of ethoxy groups on the surfactant, while the extent of binding remains substantially unchanged when the hydrocarbon alkyl surfactant chain becomes longer (at constant j). Binding of the solubilized iron(II) complexes would occur at the interface of the hydrophobic core and the wet outer poly(ethoxy) sheath of the micelle with a probable large projection of the solubilizate into the latter micellar region.

Kinetics of Cerium(IV) Oxidation of Sailcylidene Aminophenols In Acidic Medium

Kinetics of Cerium(IV) Oxidation of Sailcylidene Aminophenols In Acidic Medium

ChemInform Abstract: Regioselective Introduction of a Methoxy Group at the Benzylic Position of Isochroman Derivatives by Cerium(IV) Oxidation in Methanol.

AbstractThe isochromans (III), prepared by cyclization of the arylethanols (I) with paraformaldehyde (II), and the isochromanones (X) and (XIII) are oxidized with ceric ammonium nitrate in methanol (IV) to produce regioselectively the methoxy derivatives (V), (VII), and (XIV), together with some other oxidation products as outlined in the reaction scheme.