A process has been developed to oxidise methane at low temperatures in an excess oxygen environment using ozone as the oxidant. Ozone being more reactive than oxygen allows low temperature methane ...control. A range of catalysts have been screened and a commercially available current production Fe-BEA catalyst, from an automotive application has shown excellent potential for methane control with ozone in the feed, leading to a peak conversion efficiency of 81% at 168 °C in the absence of H
2
O and 60% conversion at 220 °C in the presence of H
2
O.
An essential property of combustion catalysts is long-term (>8000 h) stability at high temperatures in an environment (∼1 atm of both oxygen and water vapor) that aggressively promotes sintering of ...the supporting oxide and coarsening of the active component. Extrapolation of accelerated coarsening rate measurements, determined from shorter exposures at higher temperatures, can be made with more confidence if the physical processes of the coarsening and sintering processes were well understood. The current work examines in detail the coarsening of a high-weight-loaded palladium catalyst supported by silica-stabilized alumina at 900 °C in such an aggressive environment. The results of this investigation showed that the Pd particle size distribution was consistently log-normal for time periods from 100 to 4000 h, the mean particle growth rate was roughly inverse second-order in mean particle diameter, and the support not only sintered but also underwent phase transformation. The results implicate both coalescence and Ostwald ripening as important coarsening processes.
An unusual luminescent inorganic oxide, Sr$_2$CeO$_4$, was identified by parallel screening techniques from within a combinatorial library of more than 25,000 members prepared by automated thin-film ...synthesis. A bulk sample of single-phase Sr$_2$CeO$_4$ was prepared, and its structure, determined from powder x-ray diffraction data, reveals one-dimensional chains of edge-sharing CeO$_6$ octahedra, with two terminal oxygen atoms per cerium center, that are isolated from one another by Sr$^{2+}$ cations. The emission maximum at 485 nanometers appears blue-white and has a quantum yield of 0.48 ± 0.02. The excited-state lifetime, electron spin resonance, magnetic susceptibility, and structural data all suggest that luminescence originates from a ligand-to-metal Ce$^{4+}$ charge transfer.
The spinel structure and the valence states of the Mn ions both at the surface and the bulk were characterized for the Li+extracted and inserted manganese oxide spinels. The Li+extraction from the ...orthorhombic LiMn2O4spinel results in the formation of the cubic spinel, the crystal structure of which is the same asλ-MnO2. The LiMn2O4spinel prepared from an electrolytically prepared manganese dioxide is converted to HMn2O4on dilute acid treatment. X-ray photoelectron spectroscopic analysis revealed that the valence state of the surface Mn ions remains unchanged during the Li+extraction and insertion, which indicates an occurrence of the Li+–H+ion exchange reaction at the surface irrespective of the solution pH. The Fourier transform infrared photoacoustic spectra of the Li+extracted spinel demonstrated the existence of the surface hydroxyl groups, which is considered to be associated with the vacant 8atetrahedral sites in the spinel structure. Based on the thermal stability of the surface hydroxyl groups and the bulk hydroxyl groups, the Li+extracted spinel structure is discussed in relation to its lithium-ion sieve property.
The crystal structures of two new zinc compounds of propylenebis(phosphonic acid) were determined ab initio from their powder diffraction data. These compounds were prepared by the reaction of zinc ...chloride with the phosphonic acid at different pH conditions. The compound, Zn(HO3PC3H6PO3H) (1), crystallizes in the monoclinic space group P21/n with a = 18.167(3) Å, b = 5.083(1) Å, c = 8.658(1) Å, β = 93.630(2)° and Z = 4. The other compound, Zn3(HO3PC3H6PO3)2·2H2O (2), also crystallizes in the monoclinic symmetry but with space group C2/c. Crystal data: a = 20.5853(4) Å, b = 5.0472(1) Å, c = 18.0140(4) Å, b = 97.226(1)°, Z = 4. The intensities of the structure factors were extracted from the powder patterns using the Le Bail method and were used for structure solution by direct methods. The structures were then completed by Fourier methods and refined by Rietveld methods. In structure 1, the metal atoms are tetrahedrally coordinated by four oxygen atoms, two each from two independent phosphonates. The remaining oxygen atom of both phosphonate groups is protonated and is involved only in hydrogen bonding. The metal phosphonate interactions lead to double chains that are linked to each other through the organic linkages, leading to two-dimensional slabs or sheets. These slabs are connected through hydrogen bonds, thus forming a loosely held three-dimensional metal phosphonate network. In the case of compound 2, only one of the phosphonate groups is protonated, while the other is completely deprotonated. In this structure, there are two independent metal atoms that are tetrahedrally coordinated. One is coordinated completely by phosphonate oxygen atoms, while the coordination of the other zinc atom is by two phosphonate oxygens and two water oxygen atoms. The structure is interesting in that it consists of large one-dimensional pores whose dimensions are determined by the length of the organic moiety. Thus, this structure provides a starting point for a broad exploration of a new class of metal phosphonate porous materials with varied pore sizes.
The synthesis of N,N‘-bis(phosphonomethyl)-1,10-diaza-18-crown-6 tetrahydrate (6) from the corresponding diazacrown ether is described and the crystal structure of this diphosphonic acid determined. ...The crystals are triclinic, P1̄ with a = 8.1829(8), b = 8.3092(10), c = 9.1429(10) Å, α = 85.286(9)°, β = 84.736(9)°, γ = 73.158(7)°, and Z = 1. The center of the azacrown ether ring coincides with the center of symmetry, requiring that the CH2PO3H groups lie trans to each other. One of the acid protons of each phosphonic acid group resides on the aza nitrogens, resulting in a zwitterion arrangement. There are four water molecules per unit cell that participate in an extensive system of hydrogen bonding. An important feature of the H-bonding is that between adjacent phosphonic acid groups to form linear chains along the unit cell diagonal. Reaction of 6 with Zr(IV) in the presence of H3PO4 yields zirconium phosphate-type layers cross-linked by the crown ether groups. The types of layers formed were deduced by a combination of 31P NMR and X-ray data. Affixing phosphonic acid groups onto the aza crown ether results in a more rectangular shape to the ring, which is further distorted by the cross-linking of the layers.
New types of zirconium layered compounds containing the N-(phosphonomethyl)iminodiacetic acid group (PMIDAH2) have been synthesized and characterized. A mixed phosphate/phosphonate compound, ...Zr2(PO4)(O3PCH2N{CH2COOH}2)(O3PCH2N{CH2COOHCH2COO-})(H2O)2 (I) was obtained when a mixture of phosphoric acid and diacetatoiminophosphonic acid (H2PMIDAH2) solution in the ratio of 1:1 was heated with the zirconyl chloride in the presence of HF. The layer structure of this compound is different from that of any known layered zirconium phosphonate compounds. The bridging of metal atoms by the phosphate groups within the layer is similar to that found in γ-ZrP, while the mode of phosphonate binding is similar to that found for α-ZrP. When the above reaction was carried out with additional phosphoric acid, a similar layered structure but with composition Zr2(PO4)(O3PC5H7O4N)(O3PC5H8O4N) x (HPO4)1 - x (H2O)2 (II) was obtained. In this compound some of the phosphonate groups are replaced by the HPO4 2- groups. When the ratio of phosphoric acid to H2PMIDAH2 was 4, the compound obtained has the maximum replacement. The value of x for this compound in the above formula is 0.5. Further addition of phosphonic acid yields a new phase with composition Zr(O3PC5H8O4N) x (HPO4)1 - x (III). 31P solid-state MAS NMR and XRD patterns suggest that this new phase is structurally similar to α-ZrP. Intercalation reactions with primary alkylamines, C n H2 n +1NH2 (n = 3−8), were carried out with all these phases. The results show that 2 mol of amines were taken up by compound I to form Zr2(PO4)(PMIDAH2)(PMIDAH)(H2O)2·2RNH2, while 1.5 mol of amine was intercalated into compound III, forming Zr(PMIDAH2) x (HPO4)1 - x ·1.5RNH2. In both compounds the amines appear to pack as double layers. The ion-exchange behavior of these compounds is also discussed.
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