Showing papers on "Oxidation state published in 2003"
TL;DR: In this paper, it was shown that a substantial quantity of Li (at least 1.39 Li) may be removed at 55 °C by oxidation of the nonaqueous electrolyte, thus generating H+ which exchange one-for-one with Li+ to form Li2-xHxMnO3.
Abstract: Lithium intercalation compounds based on lithium manganese oxides are of great importance as positive electrodes for rechargeable lithium batteries. It is widely accepted that Li+ may be extracted (deintercalated) from such lithium manganese oxides accompanied by oxidation of Mn up to a maximum oxidation state of +4. However, it has been suggested recently that further Li+ removal may be possible. Among the mechanisms that have been proposed to charge balance the removal of Li+ are Mn oxidation beyond +4 or loss of O2-. To investigate this phenomenon we have selected Li2MnO3, a layered compound Li[Li1/3Mn2/3]O2 with a ready supply of mobile Li+ ions but with all Mn already in the +4 oxidation state. We show that a substantial quantity of Li (at least 1.39 Li) may be removed. At 55 °C this occurs exclusively by oxidation of the nonaqueous electrolyte, thus generating H+ which exchange one-for-one with Li+ to form Li2-xHxMnO3. The presence of H+ between the oxide layers results in a change of the layer stac...
484 citations
TL;DR: The new compounds were found to have properties well-suited for use as precursors for atomic layer deposition (ALD) of thin films, and have high volatility, high thermal stability, and high and properly self-limited reactivity with molecular hydrogen, depositing pure metals, or water vapor, deposging metal oxides.
Abstract: A series of homoleptic metal amidinates of the general type [M(R-R'AMD)(n)](x) (R = (i)Pr, (t)Bu, R' = Me, (t)Bu) has been prepared and structurally characterized for the transition metals Ti, V, Mn, Fe, Co, Ni, Cu, Ag, and La. In oxidation state 3, monomeric structures were found for the metals Ti(III), V(III), and La(III). Bridging structures were observed for the metals in oxidation state 1. Cu(I) and Ag(I) are held in bridged dimers, and Ag(I) also formed a trimer that cocrystallized with the dimer. Metals in oxidation state 2 occurred in either monomeric or dimeric form. Metals with smaller ionic radii (Co, Ni) were monomeric. Larger metals (Fe, Mn) gave monomeric structures only with the bulkier tert-butyl-substituted amidinates, while the less bulky isopropyl-substituted amidinates formed dimers. The new compounds were found to have properties well-suited for use as precursors for atomic layer deposition (ALD) of thin films. They have high volatility, high thermal stability, and high and properly self-limited reactivity with molecular hydrogen, depositing pure metals, or water vapor, depositing metal oxides.
349 citations
TL;DR: In this paper, the role of the adsorbed oxygen has been studied by examining the variations of the electrical conductivity of the catalysts during the processes of oxygen adsorption-desorption.
Abstract: The catalytic combustion of some volatile organic compounds (VOCs) has been investigated over LaMnO3 and LaCoO3 perovskite-type oxides. Redox titration has shown that cobalt is present in LaCoO3 exclusively in the 3+ oxidation state whereas LaMnO3 contains considerable amount of Mn4+ (35%) in addition to Mn3+. VOCs reactivity towards total oxidation follows the trend: acetone > isopropanol > benzene. The oxidation of isopropanol occurs through the formation of acetone in the homogeneous reaction. The increase of the oxygen partial pressure is beneficial for total oxidation of acetone. The adsorptive properties of the catalysts towards the VOCs and H2 have been examined by means of temperature programmed desorption. The LaMnO3 surface is the most reactive to the adsorption of VOCs and H2. The role of the adsorbed oxygen has been studied by examining the variations of the electrical conductivity of the catalysts during the processes of oxygen adsorption–desorption.
197 citations
TL;DR: In this article, a mix-valenced cobalt oxide, CoOx, was prepared from cobalt nitrate aqueous solution through a precipitation with sodium hydroxide and an oxidation by hydrogen peroxide.
Abstract: A mix-valenced cobalt oxide, CoOx, was prepared from cobalt nitrate aqueous solution through a precipitation with sodium hydroxide and an oxidation by hydrogen peroxide. Further, other pure cobalt oxide species were refined from the CoOx by temperature-programmed reduction (TPR) at 170, 230 and 300 °C (labeled as R-170, R-230 and R-300, respectively). They were characterized by X-ray (XRD), infrared (IR), thermogravimetry (TG) and TPR. The major composition of CoOx is CoO(OH), with a small amount of Co4+ species; R-170 is CoO(OH) with a hexagonal structure; R-230 is Co3O4 with a spinel structure and R-300 is CoO with a cubic structure. Their catalytic activities toward the CO oxidation were further studied in a continuous flow microreactor. The results indicated that the relative activity decreased significantly with the oxidation state of cobalt, i.e., CoO(+2)≳Co3O4(+8/3)≫CoO(OH)( +3)≳CoOx(>+3).
190 citations
TL;DR: The one-electron oxidized species of a Ni(II)-phenolate complex has been shown to be in the Ni( II)-phenoxyl radical state at room temperature and the Ni-phenolate state at < -120 degrees C, indicating that the oxidation state is temperature dependent.
Abstract: The one-electron oxidized species of a Ni(II)-phenolate complex has been shown to be in the Ni(II)-phenoxyl radical state at room temperature and the Ni(III)-phenolate state at < -120 degrees C, indicating that the oxidation state is temperature dependent.
171 citations
TL;DR: The use of XANES spectroscopy, both in classical and in dispersive geometries, is illustrated for the study of copper-based catalysts under in situ or in operando conditions as mentioned in this paper.
Abstract: The use of XANES spectroscopy, both in classical and in dispersive geometries, is illustrated for the study of copper-based catalysts under in situ or in operando conditions. As case studies, copper-exchanged MFI zeolites and CuCl2/γ-Al2O3 systems are considered. In the former case, in situ XANES spectroscopy was used to characterise well defined complexes (Cu+N2, Cu+(CO)3, Cu+(NH3)(CO) and Cu+(NO)2) formed on copper ions inside the zeolite cavities under controlled conditions. From these results, useful information concerning the symmetry of the formed complexes can readily be gained. The latter case shows how the use of dispersive XANES spectroscopy allows to follow, in real time, the evolution of a system in working conditions. The simultaneous determination of the catalyst activity and of the average oxidation state of copper in the catalyst allows the evolution of a system in working conditions to be followed in real time. The criteria used for the quantification of the Cu(I) and Cu(II) fraction from XANES spectra are discussed in detail.
160 citations
TL;DR: In this article, the effects of support and additive on the oxidation state and catalytic activity of Pt catalyst in the low temperature propane combustion were systematically investigated on Pt/MgO, Pt/Al2O3 and Pt/SiO2-Al 2O3.
140 citations
TL;DR: The results showed that the uranium sorption and reduction processes on the magnetite surface have very fast kinetics (hours), the reduction process being triggered by sorption, and the speciation of uranium at the surface does not show significant changes with time.
139 citations
TL;DR: In this article, the As sorption capacity of a natural Mn and Fe mineral-containing sample from the Iron Quadrangle province, Brazil, was investigated by combining X-ray diffraction analyses (with Rietveld refinement), Xray fluorescence spectroscopy, optical microscopy, and scanning electron microscopy coupled with Xray energy dispersive spectrometry-EDS.
Abstract: The As sorption capacity of a natural Mn and Fe mineral-containing sample from the Iron Quadrangle province, Brazil, was investigated. A detailed mineralogical identification was obtained by combining X-ray diffraction analyses (with Rietveld refinement), X-ray fluorescence spectroscopy, optical microscopy, and scanning electron microscopy coupled with X-ray energy dispersive spectrometry-EDS. The oxidation state of the adsorbed As species was determined by X-ray absorption near edge structure spectroscopy. The results demonstrate that the presence of naturally occurring Mn oxides promotes the effective oxidation of As (III) to As(V). Also, the Mn minerals show a significant uptake of both the trivalent and pentavalent As species. This study demonstrates that the combined influences of As(III) depletion by oxidation and adsorption on a natural oxide sample consisting of Mn minerals and Fe oxides may effectively contribute to the reduction the As concentration in waters.
116 citations
TL;DR: In this article, partial oxidation of methane to syngas and CH4/CO2 reforming have been investigated over a Ni/TiO2 catalyst in a fixed-bed reactor.
Abstract: Partial oxidation of methane (POM) to syngas and CH4/CO2 reforming have been investigated over a Ni/TiO2 catalyst in a fixed-bed reactor. The Ni/TiO2 catalyst has high initial activity but undergoes significant deactivation during the partial oxidation of methane reaction. Deactivation is due largely to the oxidation of Ni(0) to NiTiO3. After the partial oxidation of methane at 700 °C the catalyst was pale yellow. XRD confirmed that Ni(0) had been converted to NiTiO3 and oxygen pulse reactions found only traces of carbon were present after the POM reaction. The Ni/TiO2 catalyst has a high activity and a long term stability in the CO2 reforming reaction. XRD found Ni(0) was present after the reforming reaction but NiO and NiTiO3 were absent. Activation of methane over Ni/TiO2 was also investigated using pulse reaction techniques in the absence of gas phase oxygen. Methane pulse reactions demonstrated that the mechanism of methane oxidation changes as the oxidation state of nickel changes. CH4 may have been oxidized by oxygen from solid NiO or by active oxygen within the TiO2 support via the non-selective Rideal–Eley mechanism over the oxidized Ni/TiO2 catalyst surface. In contrast, CH4 is efficiently converted to CO and H2 via a direct oxidation mechanism when Ni/TiO2 is reduced. Pulse reaction studies provide evidence that the oxidation state of nickel controls the methane activation mechanism and the product distribution.
106 citations
TL;DR: In situ XAFS spectroscopy was applied in order to determine the catalytically active sites in Fe/ZSM5, prepared by FeCl3 sublimation as discussed by the authors.
TL;DR: In this paper, a 12% Ru/Al2O3 catalyst was prepared by deposition of relatively monodispersed colloidal Ru nanoparticles of about 5.8 nm on alumina.
TL;DR: The fact that complexes with coordination numbers of 10-12 are in agreement is significant since this study is the first example which indicates that high coordination numbers also follow BVS rules, and also reflects the requirement that the BVS must equal the oxidation state.
Abstract: A total of 119 CeO(n)fragments with n = 3-12 were analyzed by using the bond valence sum, or BVS, method to yield new R(0) values for Ce(III)-O of 2.121(13) A and for Ce(IV)-O of 2.068(12) A. These R(0) values can be used to calculate the oxidation state of Ce in complexes where Ce is bonded only to O ligands. Furthermore, the average R(0) value of 2.094 A gives a good indication of whether the oxidation state of the Ce ion is +3 or +4 from the observed distances without any assumptions. The fact that complexes with coordination numbers of 10-12 are in agreement is significant since this study is the first example which indicates that high coordination numbers also follow BVS rules. The Ce-O distances used in deriving the R(0) values for the +3 and +4 complexes are tabulated as a function of coordination number and have a wide range of values, but the average Ce-O distance reflects the requirement that the BVS must equal the oxidation state. Several examples are given where the oxidation state of the Ce ion is apparently incorrectly assigned, as well as cases where problems with the X-ray structure determinations are indicated by a disagreement between the postulated and calculated oxidation state.
TL;DR: In this article, the effects of 3 vol.% of CO2 added in the gas feed are investigated in the oxidative dehydrogenation of propane (ODP) to propene on NiMoO4 catalysts.
Abstract: The effects of 3 vol.% of CO2 added in the gas feed are investigated in the oxidative dehydrogenation of propane (ODP) to propene on NiMoO4 catalysts. In spite of the low reaction temperature range (400-480degreesC), it turns out that CO2 is not inert during the reaction. CO2 behaves as a strong oxidant with respect to the catalyst. CO2 helps to maintain the catalytic surface in a high oxidation state under conditions for which NiMoO4 undergoes a reduction. CO2 clearly promotes the non-selectivity of the catalyst and can inhibit deactivation. Under particular conditions it can improve propene formation. CO2 is able to oxidize propane to propene. We suggest that CO2 dissociates during the reaction to CO and an active oxygen species, which is responsible for the oxidizing effect of carbon dioxide. This work opens promising perspectives in using CO2 to tune dynamically the oxidation state of "working" oxide surfaces in their most active and selective configurations for oxidation processes. (C) 2002 Elsevier Science B.V. All rights reserved.
TL;DR: The first example of homogeneous catalysis by the reaction described in Equation (1) is reported, which occurs in the gas phase with atomic transition-metal cations serving as catalysts and occurs in two steps in which NO is first reduced to N2O.
Abstract: important reactions occurring in automotive catalytic converters where both reactants are undesirable pollutants. Base-metal oxides, mixed metal-oxide compounds such as perovskites, supported metal catalysts, metal zeolites, and alloys have all been investigated as heterogeneous catalysts for this reaction, which does not occur directly in the gas phase at room temperature to any measurable extent. For example, copper in the + 2 oxidation state has been found to be active both as a base-metal-oxide catalyst and in a metalsupported or perovskite form. We report here the first example of homogeneous catalysis by the reaction described in Equation (1), which occurs in the gas phase with atomic transition-metal cations serving as catalysts. The catalysis occurs in two steps in which NO is first reduced to N2O. An analogous three-step catalytic reduction of NO2, in which NO2 is first reduced to NO, was also discovered. The overall catalytic scheme that was established in the study reported here consists of the three catalytic cycles shown in Figure 1. These three cycles were characterized with laboratory measurements of reactions of each of the three nitrogen oxides NO2, NO, and N2O with up to 29 different transition-metal cations M [Eqs. (2)–(4)]:
TL;DR: In this paper, the layered structure of the materials is stabilized by a small amount of Mg substitution for Ni, and the structural stability and cycling behavior are improved by an increase in the Mg content.
Abstract: The Li[Li0.15Ni0.275−xMgxMn0.575]O2
(x
= 0, 0.02, and 0.04) powders have been synthesized using a sol–gel method. The layered structure of the materials is stabilized by a small amount of Mg substitution for Ni. The structural stability and cycling behavior are improved by an increase in the Mg content. The XAS measurements show that charge compensation by delithiation could be achieved by the oxidation of the oxygen ion as well as by the oxidation of Ni2+ to Ni3+, while maintaining the Mn atoms in the 4+ oxidation state.
TL;DR: In this article, the crystal structure of the Mn(II)-aqua complex of 1, shows it to be dimeric via (μ-κO)-bridging through one carboxylate oxygen atom of each of the two ligands.
Abstract: Manganese(II) complexes of mononegative pentadentate N4O ligands [Mn2(mgbpen)2(H2O)2](ClO4)2
(1), (mgbpen−
=
N-methyl-N′-glycyl-N,N′-bis(2-pyridylmethyl)ethane-1,2-diamine) and [Mn2(bzgbpen)2(H2O)2](ClO4)2
(2), (bzgbpen−
=
N-benzyl-N′-glycyl-N,N′-bis(2-pyridylmethyl)ethane-1,2-diamine) have been prepared. The crystal structure of the Mn(II)–aqua complex of 1, shows it to be dimeric via (μ-κO)-bridging through one carboxylate oxygen atom of each of the two ligands. The non-coordinated carboxylate oxygen atoms are H-bonded to the water ligands on the adjacent Mn ion. The magnetic coupling interaction is weak and antiferromagnetic, J
=
−1.3(1) cm−1. The dimeric structures of 1 and 2 are retained in solution and can exist in the gas phase. Complexes 1 and 2 are air stable but can be oxidised by tBuOOH to give unstable mononuclear Mn(III) complexes, or oxo-bridged dimanganese(III) and di-μ-oxo-dimanganese(IV) complexes, depending on solvent. The [Mn(III)–OR]+, R = H or CH3 complexes are generated in water or methanol, respectively, and are potentially useful spectroscopic models for active Mn–lipoxygenases. In acetonitrile, di-μ-oxo-dimanganese(IV) complexes are the highest oxidation state products detected, and these are formed via shorter-lived intermediate μ-oxo-dimanganese(III) compounds. The rate of formation of the various oxidized products is slower in the case of the bzgbpen− systems which contains a bulkier non-coordinating arm. The oxidised complexes were characterised by UV-visible spectroscopy, ESI mass spectrometry and cyclic voltammetry. In addition, III–IV and II–III species were electrochemically generated. Thus the new mononegative pentadentate ligand systems display significant flexibility in the range of Mn oxidation states and species of biological relevance that are accessible: A series of dinuclear compounds with different structures in the five oxidation levels between II–II and IV–IV has been identified. No solid state structures were obtained for high oxidation state species, however it is assumed that in the oxo-bridged compounds the carboxylate groups are terminally ligated in contrast to the starting Mn(II) complexes. Thus the system represents examples of limiting structures in the “carboxylate shift” mechanism proposed to be important in non-heme H2O and O2 activation processes.
TL;DR: In this article, the authors studied the iron local environment in an LDG sample by means of Fe K-edge high-resolution X-ray absorption near edge structure (XANES) spectroscopy to obtain quantitative data on the Fe oxidation state and coordination number in both the Fe-poor matrix and Fe-rich layers.
Abstract: Libyan Desert Glass (LDG) is an enigmatic type of glass that occurs in western Egypt in the Libyan Desert Fairly convincing evidence exists to show that it formed by impact, although the source crater is currently unknown Some rare samples present dark-colored streaks with variable amounts of Fe, and they are supposed to contain a meteoritic component We have studied the iron local environment in an LDG sample by means of Fe K-edge high- resolution X-ray absorption near edge structure (XANES) spectroscopy to obtain quantitative data on the Fe oxidation state and coordination number in both the Fe-poor matrix and Fe-rich layers The pre-edge peak of the high-resolution XANES spectra of the sample studied displays small but reproducible variations between Fe-poor matrix and Fe-rich layers, which is indicative of significant changes in the Fe oxidation state and coordination number Comparison with previously obtained data for a very low-Fe sample shows that, while iron is virtually all trivalent and in tetrahedral coordination ( (4) Fe 3+ ) in the low-Fe sample, the sample containing the Fe-rich layers display a mixture of tetra-coordinated trivalent iron ( (4) Fe 3+ ) and penta-coordinated divalent iron ( (5) Fe 2+ ), with the Fe in the Fe-rich layer being more reduced than the matrix From these data, we conclude the following: a) the significant differences in the Fe oxidation state between LDG and tektites, together with the wide intra-sample variations in the Fe-oxidation state, confirm that LDG is an impact glass and not a tektite-like glass; b) the higher Fe content, coupled with the more reduced state of the Fe, in the Fe-rich layers suggests that some or most of the Fe in these layers may be directly derived from the meteoritic projectile and that it is not of terrestrial origin
TL;DR: In this article, the authors applied Scanning Transmission Soft X-ray Microscopy (STXM) to investigate the charge state distribution of Mn in two kinds of Mn-biominerals, Mn nodules collected from Lake Michigan sediments and Mn precipitates formed by spores of a marine bacillus SG-1 under transport limited reaction conditions.
TL;DR: This is the first time the Cr(2+)/Cr(3+) ratio has been identified directly in an Fe-bearing melt, illustrating the importance of the in situ determination of metal oxidation states in melts.
Abstract: A controlled-atmosphere furnace has been constructed for X-ray absorption spectroscopy experiments under imposed oxygen fugacities at temperatures up to 1773 K. The use of the furnace is demonstrated in a study of the oxidation state of Cr in a basaltic silicate melt (mid-ocean ridge basalt) by K-edge XANES spectroscopy. This is the first time the Cr2+/Cr3+ ratio has been identified directly in an Fe-bearing melt. At typical terrestrial oxygen fugacities around half the Cr is present as Cr2+, even though this oxidation state has never been identified in a terrestrial material and only Cr3+ is observed after quenching to a glass. Cr2+ oxidizes to Cr3+ on cooling in the presence of Fe3+ according to the electron exchange reaction Cr2+ + Fe3+ → Cr3+ + Fe2+. This illustrates the importance of the in situ determination of metal oxidation states in melts.
TL;DR: From the analysis of the experimental data under varying experimental conditions, it is concluded that the metal ion in the complex is at least tetracoordinate and at most hexacoordinated with O/N ligands of the polymer or monomer and thus corroborates the bonding scheme proposed earlier.
TL;DR: In this article, the growth and reactivity of monolayer V 2 O 5 films supported on TiO 2 (1.1) were studied using X-ray photoelectron spectroscopy and temperature programmed desorption (TPD).
TL;DR: DFT calculations support fomulation of the reduced species as a mixed oxidation state of ScII.
Abstract: ScII or mixed oxidation state ScIII/ScI? Reduction of the homoleptic ScIII complex [Sc(P3C2tBu2)3] allows access to the subvalent [{Sc(P3C2tBu2])2}2] complex (see picture), in which the metal centers are formally bivalent. DFT calculations support fomulation of the reduced species as a mixed oxidation state.
TL;DR: In this paper, the authors used a sulfide complex of Ti(III) chloride and 1,2-bis(hexylthio)ethane for atom transfer radical polymerization (ATRP) of styrene.
Abstract: Ti(III) compounds (halides and n-butoxide) along with several mono-, bi-, and tridentate ligands have been studied for the first time in the atom transfer radical polymerization (ATRP) of styrene. The important advantage of titanium compounds is the white color of the Ti(IV) ions (Ti in the highest and air stable oxidation state) which ensures the absence of coloring in the final polymer. The better control over polymerization was realized when conditions increasing the reactivity of the intermediate Ti(IV) species and decreasing their steady state concentration were maintained. This occurred when chlorides were replaced with bromides (which decreased the bond strength), and when ligands with low donor ability were employed. Using a sulfide complex of Ti(III) chloride and 1,2-bis(hexylthio)ethane allowed styrene polymerization with kinetic and molecular weight characteristics inherent to ATRP.
TL;DR: In this paper, the authors investigated the mutual interaction between sulfur and iron in silicate melts to constrain the equilibrium between sulfide and sulfate species, and showed that the role of bulk melt chemistry, affecting through polymerization, and hence the transfer of electrons among the three polarization states of oxygens, the oxidation state of altervalent elements such as Fe and S and the limits of the Temkin approach implicit in chemical equations that consider sulfide as free anions.
Abstract: In silicate melts, the speciation state of altervalent elements depends on the extension and distribution of polymeric units in the system Since polymerization of silicate melts is driven by acid–base properties of constituting oxides depending on their Lux–Flood reactivity, the bulk optical basicity of molten silicates and glasses allows us to compute the distribution of oxygen among three distinct polarization states (O2−, O−, O0) in conjugation with the polymeric model of Toop and Samis Data available in literature are employed to investigate the mutual interaction between sulfur and iron in silicate melts to constrain the equilibrium between sulfide and sulfate species Results put in evidence (i) the role of bulk melt chemistry, affecting through polymerization, and hence the transfer of electrons among the three polarization states of oxygens, the oxidation state of altervalent elements such as Fe and S and (ii) the limits of the Temkin approach implicit in chemical equations that consider sulfide and sulfate in melts as free anions Improvements of the model’s accuracy for sulfur speciation may be attained by accounting for the various dissociation equilibria of molten sulfide M2/νS, oxide M2/ν and sulfate M2/νSO4 species in their standard state of pure component in the melt phase at temperature and pressure of interest instead of that of complete dissociation required by the Temkin model
TL;DR: XPS analysis on 1 and 2 confirms that manganese exists in the +2 oxidation state, and a complete investigation of the magnetic properties of 2 revealed its true nature to be a glassy magnet.
Abstract: Phosphoric acid forms two distinct coordination compounds with manganese salts in aqueous media, a two-dimensional layered structure, [Mn(HPO4).(H2O)3], 1, under ambient conditions, and a three-dimensional synthetic mineral, [Mn5(mu-OH2)2(HPO4)2(PO4)2(H2O)2], 2, under hydrothermal procedures, at 120 degrees C. In compound 1, the oxygen atom of the doubly deprotonated phosphoric acid interconnects the metal centers to form a layered structure. The neutral hydrophilic layers of 1 are separated by 5.5 A and may potentially intercalate hydrophilic organic guest molecules. The metal centers in 2 are octahedral and bridged by PO4(3-), HPO4(2-), and OH2 groups to form a complex three-dimensional network. XPS analysis on 1 and 2 confirms that manganese exists in the +2 oxidation state. Compound 2 is a poor ion exchanger, but some improvement is observed on partial dehydration. The magnetic properties of both 1 and 2 were studied in detail to examine the amplitude of the magnetic interactions through phosphate ligand bridges. While 1 reveals dominant antiferromagnetic interactions between the spin carriers, a complete investigation of the magnetic properties of 2 revealed its true nature to be a glassy magnet.
TL;DR: In this article, the acid site on the monolayer was characterized by temperature-programmed desorption (TPD) of ammonia, together with various physico-chemical techniques, and its role for catalytic reactions was studied.
TL;DR: In situ X-ray absorption fine structure (EXAFS) spectroscopy combined with on-line gas analysis was used to get insight into the oxidation state of the constituents and of the structure of a Pd/ZrO2 catalyst during activation and catalytic combustion of methane as mentioned in this paper.
Abstract: In situ X-ray absorption fine structure (EXAFS) spectroscopy combined with on-line gas analysis was used to get insight into the oxidation state of the constituents and of the structure of a Pd/ZrO2 catalyst during activation and catalytic combustion of methane. The sample was prepared from an amorphous Pd33Zr67-alloy by oxidation at 400 °C. In situ XANES/EXAFS together with thermal analysis showed that the Pd and Zr constituents were oxidized at the same time. Catalytic combustion activity was higher if the catalyst was previously reduced by hydrogen than if the fully oxidized sample was used. According to EXAFS complete reduction of PdO/ZrO2 to Pd/ZrO2 was achieved by hydrogen exposure at room temperature. In situ EXAFS studies during temperature programmed reaction in methane/oxygen and under reaction conditions uncovered that palladium is mainly in an oxidized state. However, during methane combustion in 1% CH4/4% O2/He at 500–550 °C the active catalyst contains some metallic Pd, as evidenced by in situ EXAFS, which seems to be beneficial for the activity. The catalyst can be fully reduced by methane and re-oxidized by oxygen in separate steps at this temperature.
TL;DR: In this article, the effect of small amounts of CO2 and N2O in the reaction feed during the oxidative dehydrogenation of propane to propene on alpha-NiMoO4 catalysts is reported.