Showing papers on "Oxidation state published in 1991"
TL;DR: In this paper, the authors characterized the phase composition of the NiO/Al 2 O 3 phase of a 25 wt% NiO+Al 2O 3 catalyst for complete oxidation of methane feed to CO 2 and H 2 O. The authors showed that the previously calcined catalyst bed consists of three different regions.
703 citations
TL;DR: In this paper, the relative roles of Fe(III) and dissolved oxygen (DO) in pyrite oxidation at circumneutral pH were investigated, and it was shown that Fe(II) is preferred as an adsorbate to Fe(3) due to both electrostatic and acid-base selectivity.
435 citations
TL;DR: In this article, a potential profiling technique was used to detect the intermediacy of the fully oxidized pernigraniline oxidation state (readily isolable as the base form).
122 citations
TL;DR: Thermodynamically, +2 and +2 are the most stable states, while the +3 and +6 oxidation states are themost common ones found in aqueous solution, and these factors must be considered in analyzing samples for total chromium and for the amounts of each oxidation state.
Abstract: Chromium, named for its many-colored compounds, exists in the oxidation states of -2 to +6 inclusively. The compounds exhibit a wide range of geometries including square planar, tetrahedral, octahedral, and various distorted geometries. Chromium is found in nature principally as the chromite ore FeCr2O4 in which chromium is in the +3 state. The existence of a particular oxidation state is dependent on many factors including pH, redox potentials, and kinetics. Thermodynamically, +3 and +2 are the most stable states, while the +3 and +6 oxidation states are the most common ones found in aqueous solution. Kinetically, chromium +3 is substitutionally inert: for water exchange k(sec-1) = 2.5 x 10(-6), due to the presence of the half-filled d(t2g)3.4A2g state. On the other hand, protonation/deprotonation is quite rapid. Polymerization is very slow but is promoted at higher pHs; acid cleavage of the protonated oligomers is also quite slow. Chromium +6 as the chromate ion is strongly oxidizing at low pHs and less so in basic solution. The chromate ion does form some polyacids and polyanions. These factors must be considered in analyzing samples for total chromium and for the amounts of each oxidation state.
94 citations
TL;DR: The most highly oxidized polyaniline, in the form of pernigraniline base, can be synthesized as an analytically and oxidatively pure solid (powder or large free-standing films) by the controlled oxidation of emeraldine base by m -chloroperbenzoic acid or directly from aniline by oxidative polymerization with (NH 4 ) 2 S 2 O 8.
90 citations
TL;DR: In this article, the dependence of shear viscosity on the oxidation state of six ferrosilicate melts has been measured using the concentric cylinder method and a gas mixing furnace.
Abstract: The dependence of shear viscosity on the oxidation state of six ferrosilicate melts has been measured using the concentric cylinder method and a gas mixing furnace. The measurements were performed under air, COr, and COr-CO mixtures at I atm and in a temperature range of 1345 to 1470"C. The experimental procedure involved a continuous
measurement of viscosity during stepwise reduction of the melts. Melt chemistry was controlled by dip sampling the tiquids at each oxidation state. The resulting glassesw ere
analyzed by electron microprobe, a volumetric FeO itration, and 57Fe Mdssbauer spectroscopy.
The electron microprobe data indicate Fe loss for some of the most reduced samples.T he wet chemical (+ microprobe) and spectroscopicd eterminations of theseF erich
samples yield oxidation states that are in excellent agreement. The viscosity of all melts investigated herein decreasesw ith melt reduction. The viscosity
decrease is, in general, a nonlinear function of oxidation state expressed as Fe2*/F€,o,.
89 citations
TL;DR: In this article, the electronic structures (effective oxidation states, delocalization) of the dioxolene complexes were discussed in terms of the electronic structure of the ligands, and the conflicts between results obtained using different techniques were resolved using a simple, qualitative MO model.
Abstract: : Complexes of the general formula (Ru(bpy)(dioxolene)2)n+ have been prepared where (bpy) is 2,2'-bipyridine, and n = 1, 0, +1. The dioxolene ligand is 1,2-dihydroxybenzene (catechol), 3,5-di-t-butyl- or 3,4,5,6-tetrachloro-1,2-dihydroxybenzene which may formally exist in the catecholate, semiquinone or quinone oxidation state. Redox series of up to five members have been prepared by controlled potential electrolysis of the parent species or, in some cases, by chemical oxidation or reduction. Electrochemistry, magnetism, X-ray structural data and ultraviolet, visible and near infrared electronic, resonance Raman, vibrational (FTIR), nuclear magnetic resonance, electron spin resonance and photoelectron spectra, for various members of the redox series, are discussed in terms of the electronic structures (effective oxidation states, delocalization) of the complexes. Apparent conflicts between results obtained using different techniques are resolved using a simple, qualitative MO model. Keywords: Quinone, Ruthenium, Delocalization, Redox series.
80 citations
TL;DR: In this paper, the mixed-valence states in Cs2AuIAuIIIX6 (X = Cl, Br or I) were systematically studied by X-ray photoelectron spectroscopy of the Au 4f region for the first time.
Abstract: The mixed-valence states in Cs2AuIAuIIIX6(X = Cl, Br or I) were systematically studied by X-ray photoelectron spectroscopy of the Au 4f region for the first time. The gold valence states in halogeno complexes of AuI and AuIII were also studied. In Cs2Au2X6 the difference between the oxidation state of AuI and that of AuIII decreases as the covalency of the –AuI–X–AuIII–X– bonds increases in the order X = Cl < Br < I, because the charge-transfer interaction between AuI and AuIII through the bridging halogen becomes stronger in this order. In the non-stoichiometric CsAu0.6Br2.6 the oxidation state of Au is considered to be almost homogeneous.
78 citations
77 citations
71 citations
TL;DR: The binding energy (BE) of ruthenium compounds has been measured with a monochromatic small spot XPS as discussed by the authors, and it has been shown that the BE of the 3d 5 2 level of RuCl3 is in the range 279.91 −282.88 eV.
TL;DR: In this article, a significant oxygen isotope fractionation is obtained between hematite and magnetite, which is attributed to the quantitative redox of iron in the experiments, that can in turn explain the nearly identical isotope composition of oxygen in coexisting hematites and magnetites pairs from the banded iron-formation in the Iron Quadrangle, Brazil.
Abstract: Thermodynamic oxygen isotope factors for hematite and magnetite are calculated using the modified increment method and incorporating the theoretical and experimental reduced partition function ratios determined for quartz and water in the temperature range 0 to 1200 o C. The obtained oxygen isotope fractionation factors between hematite, magnetite and water are expressed as 10 3 ln α Fe2O3-H2O =2.69×10 6 /T 2 -12.82×10 3 /T+3.78, 10 3 ln α Fe3 O 4- H 2 O=3.02×10 6 /T 2 -12.00×10 3 /T+3.31, and those between quartz and hematite or magnetite are expressed as 10 3 ln α Si O 2-FeO3 =1.55×10 6 /T 2 +9.05×10 3 /T-4.82, 10 3 ln α SiO2-Fe3O4 =1.22×10 6 /T 2 +8.22×10 3 /T-4.35. The present results are well in agreement with existing theoretical, experimental and empirical calibrations involving magnetite and hematite. A significant oxygen isotope fractionation is obtained between hematite and magnetite, whith hematite being depleted in 18 O relative to magnetite. This matches with the observation from Precambrian iron-formation in the Hamersley Range, Australia. The rule of effect of oxidation state on the oxygen isotope fractionation seems not to work for the two iron oxides. Previous experimental calibration of magnetite-water system by reduction of hematite to magnetite is concordant with the present result for hematite-water system. This is attributed to the quantitative redox of iron in the experiments, that can in turn explain the nearly identical isotope composition of oxygen in coexisting hematite and magnetite pairs from the banded iron-formation in the Iron Quadrangle, Brazil
TL;DR: In this article, the presence of vanadium in V-P-O catalysts before and after use has been examined using 31P NMR spin echo mapping and magnetic susceptibility measurements were used to confirm the presence in most catalysts which had been exposed to n-butane or 1-butene.
TL;DR: In this paper, X-ray photoelectron spectroscopy (XPS) and other surface and bulk characterization techniques were employed in the study of mixed oxides of Cu, Co, and Mn as catalysts for CO oxidation.
TL;DR: In situ X-ray absorption spectroscopy spectra of an electrochemically deposited monolayer of copper on gold (100) and (111) surfaces were obtained using fluorescence detection under gazing incidence, the X-rays being polarized parallel to the plane of the substrate surface as discussed by the authors.
TL;DR: The recently reported paramagnetic compounds (dbdab)2M and (bpy-˙)MIIIMe2(bpy = 2,2′-bipyridine) contain trivalent metal bound to one singly and one doubly reduced dbdab ligand as mentioned in this paper.
Abstract: The recently reported paramagnetic compounds (dbdab)2M (dbdab = 1,4-di-tert-butyl-1,4-diazabutadiene, M = Ga, Al), both contain trivalent metal bound to one singly and one doubly reduced dbdab ligand; the larger metal hyperfine coupling in the EPR spectrum of the gallium complex is not due to a gallium(II) oxidation state, it is simply a result Of the quite large isotropic hyperfine coupling constants of 69Ga and 71Ga as demonstrated previously for the related radicals (bpy–˙)MIIIMe2(bpy = 2,2′-bipyridine).
TL;DR: In this article, the stabilities and reactivities of cluster ions generated from fast-atom bombardment (FAB) or the direct laser vaporization (DLV) of the Group 13 metal oxides (Al2O3, Ga2O4, and In2O5) were examined by mass spectrometry.
Abstract: The stabilities and reactivities of cluster ions generated from the fast‐atom bombardment (FAB) or the direct laser vaporization (DLV) of the Group 13 metal oxides (Al2O3, Ga2O3, and In2O3) were examined by mass spectrometry. The nascent cluster ion distributions, fragmentations, and reactions were studied. The observed patterns of stability and reactivity were compared with the structures and heats of formation calculated from theoretical studies of aluminum oxide cluster ions using MNDO, Xα, and Born–Mayer pair potentials. The method of production of the metal oxide cluster ions, whether by FAB, DLV, or through the reaction of sputtered bare metal cluster ions with oxygen, had little influence on the abundance distribution observed. In agreement with the known M–O binding energies, a trend of increasing cluster oxidation state was observed in the abundance distributions of the cluster ions for decreasing metal atom z value. Dissociation of the oxide cluster ions occurred through the loss of particularly stable neutral fragments which together with theoretical considerations suggest a preference for particular parent cluster stoichiometries. Although gallium oxide and indium oxide cluster ions exhibited little reactivity toward oxidation agents, the aluminum oxide ions reacted readily with most oxidants. ‘‘Oxygen saturation’’ effects were observed for the ions with 2 and 3 aluminum atoms. These saturation effects could be explained by the formation of structures in which the Al atoms are three‐fold planar coordinated.
TL;DR: In this paper, a NiCo2O4 anode in aqueous base has been investigated, and it is shown that a range of compounds undergo oxidation at the same potential, that for the conversion of the oxide surface to a higher oxidation state, and that limiting current densities approach those expected for mass transfer control.
Abstract: The oxidation of alcohols and primary amines at a NiCo2O4 anode in aqueous base has been investigated. It is shown that a range of compounds undergo oxidation at the same potential, that for the conversion of the oxide surface to a higher oxidation state, and that the limiting current densities approach those expected for mass transfer control. Using a flow cell, it is confirmed that the conversation of primary alcohols to carboxylic acids, secondary alcohols to ketones and primary amines to nitriles can all be achieved with high selectivity and reasonable current efficiency at high current densities. The oxide coating appears to be quite stable during repeated electrolyses.
Abstract: The oxidation state of Fe and Ti ions implanted in yttria stabilized zirconia (YSZ) was studied by XPS (X-ray photoelectron spectroscopy) in combination with depth profiling using Ar+ sputtering. In the “as-implanted” state of the sample Fe was found to be present as Fe3+, Fe2+ and as metallic Fe0. This is in agreement with earlier conversion electron Mossbauer Spectroscopy measurements. For Ti-implanted YSZ in the “as-implanted” state the majority of the Ti is present as Ti4+, Ti3+, and Ti2+ ions, while a part of the Zr cations is present in the divalent oxidation state (Zr2+). After oxidation in air, the Fe and Ti ions are present only in the valence three and four oxidation states, respectively.
TL;DR: In this article, a simple method is proposed to correlate the oxidation states of 1,2-diaminobenzene derivatives with their structural parameters, and it thus becomes possible to deduce the oxidation state of a 1, 2-Diaminibenzene derivative just by considering its crystal structure.
Abstract: The known crystal structures of metal complexes containing 1,2-diaminobenzene derivatives in the form of the benzenediamine dianion I, benzosemiquinone diimine monoanion II or neutral benzoquinone diimine III have been examined. Since the forms I–III differ both in oxidation state and structural features, a simple method is proposed to correlate the oxidation states of these ligands with their structural parameters. It thus becomes possible to deduce the oxidation state of a 1,2-diaminobenzene derivative just by considering its crystal structure. The available data indicate that the 1,2-diaminobenzene derivatives considered, once complexed to a metal ion, generally do not assume charge-localized structures, like I–III, but intermediate ones. In most cases, these forms are near to II or intermediate between II and III. The results are compared with literature oxidation-state assignments, and discussed in terms of the back-bonding ability of the ligands.
TL;DR: In this article, an aerated open-aqueous system where a continuous influx of mixed Mn 2+ and Cd 2+ solution was supplied and pH was maintained with an automated pH-stat adding dilute NaOH X-ray diffraction and electron diffraction identified the solids produced as mixtures of cd 2 Mn 3 4+ O 8 and MnO 2.
TL;DR: In this article, the behavior of polycrystalline Ag-Mn alloys from room temperature to 650 °C in high vacuum and in 5 m Torr O2 has been investigated by x-ray photoelectron spectroscopy.
Abstract: The oxidation of several compositions (5, 9 and 14% Mn) of polycrystalline Ag-Mn alloys from room temperature to 650 °C in high vacuum and in 5 m Torr O2 has been investigated by x-ray photoelectron spectroscopy (XPS). The behavior of the oxidation and the nature of the oxide films are controlled by tempearature, oxygen pressure, bulk alloy composition and the stability of the oxide overlayers. At low temperatures and pressures, the oxidation process is controlled by the relative free energies of oxide formation of the alloy components. At high temperatures the oxide of stabilities play a large role in determining the oxidation state of the oxide overlayer. The chemical state and the morphology of the oxide of manganese formed during the alloy oxidation has been examined. The chemical state and the morphology of the oxide overlayers have been studied by XPS, x-ray diffraction (XRD) and scanning electron microscopy (SEM). The complex oxidation process has been delineated.
TL;DR: In this article, the catalytic properties of PrO x and Li/PrO x for the oxidative coupling of methane have been studied in fixed bed reactors and the results obtained, combined with those of the reaction of oxygen with methane, ethane, ethene and carbon monoxide in an empty reactor, allow us to suggest a reaction scheme for catalytic process.
TL;DR: In this paper, an infrared technique was used to observe the formation of Mo(0) on moderately reduced conventional alumina-supported molybdenum catalysts under more extreme reduction conditions (1,173 K) and benzene hydrogenation.
TL;DR: A new non-stoichiometric mixed-valence compound CsAu06Br26 has been prepared, and its powder X-ray diffraction profile, ESR spectra, and electrical conductivity determined from its empirical formula the average valence of Au is + 267 powder diffraction data indicate that the compound has a cubic perovskite structure as discussed by the authors.
Abstract: A new non-stoichiometric mixed-valence compound CsAu06Br26 has been prepared, and its powder X-ray diffraction profile, ESR spectra, and electrical conductivity determined From its empirical formula the average valence of Au is + 267 Powder diffraction data indicate that the compound has a cubic perovskite structure [cubic lattice, space group Pm3m, a= 5462(2)A] This means that the AuBr6 octahedra are crystallographically equivalent ESR measurements show the existence of a +II formal oxidation state for Au The conductivity is four orders of magnitude higher than that of the AuI–AuIII mixed-valence compound Cs2Au2Br6
TL;DR: In this paper, the K absorption edge of Si in matrix isolated SiO molecular clusters was studied for various dilutions R(Ar/SiO) and the spectra from the clusters at different dilutions showed a dramatic evolution in their relative intensity.
Abstract: TheK absorption edge of Si in matrix isolated SiO molecular clusters was studied for various dilutionsR(Ar/SiO). The spectra from the clusters at different dilutions show a dramatic evolution in their relative intensity. Two types of spectral features from Si atoms present in the clusters could be detected in the spectra. The first is due to the Si atoms which are tetrahedrally coordinated to Si and O atoms responsible for the presence of different Si oxidation states. The Si+, Si3+ and Si4+ oxidation states in SiO clusters and in bulk were readily identified. The Si2+ oxidation state whose abundance in SiO clusters is predicted by structural considerations is not clearly observed. The second type of feature, whose intensity decreases with the dilution R, can be attributed to the presence of Si atoms possessing unsaturated bonds. In order to explain this the clustering of 4–6 SiO molecules is simulated to yield different tetrahedral bonding microstructures in which the well coordinated as well as under coordinated Si atoms are present. The behaviour of the spectral features resulting from these microstructures is discussed.
Patent•
21 May 1991TL;DR: Novel bleach and oxidation catalysts, a method of bleaching substrates using these catalysts and bleaching (detergent) compositions containing the catalysts are reported in this article.
Abstract: Novel bleach and oxidation catalysts, a method of bleaching substrates using these catalysts and bleaching (detergent) compositions containing the catalysts are reported. The catalysts are manganese complexes of formula: [L.sub.n Mn.sub.m X.sub.p ].sup.z Y.sub.q wherein Mn is manganese or iron or mixtures thereof, which can be in the II, III, IV or V oxidation state or mixtures thereof; n and m are independent integers from 1-4; X represents a co-ordination or bridging species; p is an integer from 0-12; Y is a counter-ion, the type of which is dependent upon the charge z of the complex which can be positive, zero or negative; q=z/[charge Y]; and L is a ligand being a macrocylic organic molecule.
TL;DR: In this article, the location of lead on a promoted commercial palladium/carbon catalyst was studied and the role of lead ad-atoms on the surface of the promoted catalysts was investigated.