- Isotope effects in the kinetics of simultaneous H and D thermal desorption from Pd
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The kinetics of simultaneous hydrogen and deuterium thermal desorption from PdHxDy has been investigated. A novel experimental approach for the study of the transition state (TS) characteristics of the surface recombination reaction is proposed based on the analysis of the H and D partitioning into H2, HD and D2 molecules. It has been found that the hydrogen molecular isotopes distribution is determined by the energy differences of the corresponding TS of the atom-atom recombination reactions. On the other hand, the mechanisms and activation energies of the desorption process have been obtained. At 420 K, the desorption reaction changes from a surface recombination limiting mechanism during desorption from β-PdHxDy to a reaction limited by the rate of β to α phase transformation during the two phase coexistence. Surface recombination reaction becomes again rate limiting above 480 K, due to a change in the catalytic properties of the Pd surface. TS energies obtained from the kinetic analysis of the thermal desorption spectra are in good accordance with those obtained from the analysis of the H2, HD and D2 distributions. Anomalous TS energies have been observed for the H-D recombination reaction, which may be related to the heteronuclear character of this molecule.
- Leardini,Fernández,Bodega,Sánchez
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- Solid state NMR investigation of hydrous ruthenium oxide
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Amorphous hydrous ruthenium oxide (RuO2·xH2O) with different composition x has been studied using solid-state nuclear magnetic resonance (NMR) spectroscopy. The 2DNMR spectra at different temperatures illustrate that the water molecules undergo fast molecular motion even if the temperature is as low as 213 K. The static 1HNMR spectra indicate the composition dependent proton-proton dipolar interaction. It is demonstrated that the mobility of the water molecules and their interaction with ruthenium oxides play an important role in the proton charge density. In conclusion, the competition between these two antithetical effects provides a mechanism for the proton charge storage of the RuO2·xH2O materials.
- Ma, Zhiru,Zheng, Jim P.,Fu, Riqiang
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- Low temperature investigation of hydrogen bridge bonds in lithium tetrahydroxoborate by Raman spectroscopy, X-ray and neutron diffraction (Li 11B(OD)4)
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Low temperature Raman spectroscopic measurements on isotopically diluted Li11B(OH)4 with 8% D and Li11B(OD)4 with 8% H reveal four crystallographically different hydrogen bridge bonds. With decreasing temperatures beginning at ～50 K measured down to ～10 K the stretching modes of the hydroxide ions shift to higher wave numbers. For the strongest bond O-D...O the frequency shift is 16 cm-1 and for the weakest 7 cm-1. For O-H...O the maximum in the frequency shift is 22 cm-1. X-ray single crystal (LiB(OH)4) and neutron powder diffraction (Li11B(OD)4) data result in bond lengths for the four hydroxide ions in the range of 0.943 (3) A ≤ d(O-D) ≤ 0.974 (3) A. The value of the effect of inversion of the stretching mode frequencies seems to correlate with the strength of the hydrogen bridge bonds and is found to be different for the two isotopes H and D in this compound.
- Jacobs, Herbert,Niemann, Anke,Kockelmann, Winfried
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- Inhibition of Thermal Decomposition of Lithium Chlorate and Formation of the Compound LiOH · LiClO3 in the Lithium Chlorate-Lithium Hydroxide System
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The binary compound LiOH · LiClO3 and its deuterated analogue were prepared and characterized. The incongruent melting point of the adduct is 195-200°C; the eutectic of LiOH · LiClO3 with LiClO3 contains about 30 mol % LiOH with an mp of 90-95°C. The character of the IR spectrum of the adduct suggests the possibility of the ionic structure [Li2OH]+[ClO3]-. The kinetics of chlorate decomposition were studied in mixtures of compositions 1 : 1, 1 : 2, and 1 : 3 (LiClO3 : LiOH) over the range 355-383°C. The decomposition proceeds in one step into chloride and oxygen and the rate of reaction does not depend on the amount of LiOH for these ratios. The process is described by two first-order equations with a transition at α = 0.3-0.4.
- Nikitina,Nikitina,Rosolovskii
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p. 927 - 931
(2008/10/08)
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- Complexing Lithium Salts and Lithium Oxide or Hydroxide: Synthesis and Characterization of a New Cation - Lithiumhydroxonium Li2OH(+)
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An atempt is made to prepare salts of Li2OH(+) and Li3O(+) belonging to the series of simplest oxonium cations H3O(+), LiOH2(+), Li2OH(+) and Li3O(+), whwre the proton and lithium replace each other. Double compoundsof lithium hydroxide with lithium chloride and perchlorate have been ob tained: LiOH * LiClO4, LiOD * LiClO4, LiOH * LiCl, LiOD * LiCl, and LiClO4 * 2LiCl. IR absorption spetra suggest that the perchlorate adduct canbe built of ClO4(-) anions and [Li2OH](+) complex cations. In the chlor ide adduct, OH(-) and Cl(-) regularly alternate in the crystal lattice, and, thus, two types of anion polyhedra surrounding lithium cations overlap. No interaction of Li2O with LiClO4 or LiCl occurs under the conditions of our experiments.
- Nikitina, Z. K.,Nikitina, N. I.,Rosolovskii, V. Ya.
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p. 1295 - 1298
(2008/10/08)
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