RESUMEN
In this investigation, we set out first to characterize the thermodynamics of Mg(AlH4 )2 and secondly to use the determined data to reevaluate and update existing estimation procedures for heat capacity functions, enthalpies of formation and absolute entropies of alanates. Within this study, we report the heat capacity function of Mg(AlH4 )2 in the temperature range from 2â K to 370â K and its enthalpy of formation and absolute entropy at 298.15â K, being - 70 . 6 ± 3 . 6 ${ - 70.6 \pm 3.6}$ â kJ mol-1 and 133.06â J (K mol)-1 , respectively. Using these values, we updated and expanded methods for the estimation of thermodynamic data of alanates.
RESUMEN
The presented work sets out to investigate the influence of aluminium on the hydrogenation of vanadium by first studying the hydrogenation properties of the V-H system in detail followed by the study of the V-Al-H system. Aluminium was found to have a stabilising effect on vanadium hydride phases. Presumably by functioning as an oxygen getter, aluminium lowers equilibrium pressures and increases hydrogen capacities in respect to the V/H ratio compared to the V-H system. Attempts of the synthesis of the hypothetical V(AlH4)x by metathesis and direct hydrogenation were not successful, suggesting its instability below room temperature at ambient pressure as well as up to 180 bar of hydrogen pressure in the temperature range of 30 to 100 °C.
RESUMEN
Arbuscular mycorrhizal fungi (AMF) may affect competitive plant interactions, which are considered a prevalent force in shaping plant communities. Aiming at understanding the role of AMF in the competition between two pasture species and its dependence on soil nutritional status, a pot experiment with mycorrhizal and non-mycorrhizal Lolium multiflorum and Trifolium subterraneum was conducted, with manipulation of species composition (five levels), and nitrogen (N)- and phosphorus (P)- fertilization (three levels). In the non-mycorrhizal state, interspecific competition did not play a major role. However, in the presence of AMF, Lolium was the strongest competitor, with this species being facilitated by Trifolium. While N-fertilization did not change the competitive balance, P-fertilization gave Lolium, a competitive advantage over Trifolium. The effect of AMF on the competitive outcome may be driven by differential C-P trade benefits, with Lolium modulating carbon investment in the mycorrhizal network and the arbuscule/vesicle ratio at the cost of Trifolium.
RESUMEN
The reversible hydrogenation of aminoalanes employing activated aluminium and piperidine has been explored. A selection of transition metal (TM) compounds have been investigated as additives for producing TM-activated aluminium (TM = Ti, Zr, Hf and Y). The effect of these additives on the activation of aluminium with respect to hydrogenation of an aluminium/piperidinoalane system has been studied. It has been shown that Ti, Zr and Hf can efficiently promote the activation of aluminium for its hydrogenation. The experiments performed showed that the TM activity for the piperidinoalane formation decreases in the order Zr > Hf > Ti > Y. Using multinuclear NMR spectroscopy, the reversibility of this piperidinoalane-based hydrogenation system has been evidenced, demonstrating a potential pathway for hydrogen storage in aminoalanes. The syntheses of piperidinoalanes as well as their structural and spectroscopic characterisation are described. Single-crystal X-ray diffraction analyses of [pip2AlH]2 and [pip3Al]2 (pip = 1-piperidinyl, C5H10N) revealed dimers containing a central [AlN]2 unit.