992 resultados para Ni^2
Resumo:
Le biomasse sono attualmente la pi promettente alternativa ai combustibili fossili per la produzione di sostanze chimiche e fuels. A causa di problematiche di natura etica la ricerca oggi si sta muovendo verso l'uso delle biomasse che sfruttano terreni non coltivabili e materie prime non commestibili, quali la lignocellulosa. Attualmente sono state identificate diverse molecole piattaforma derivanti da biomasse lignocellulosiche. Tra queste ha suscitato grande interesse la 2-furaldeide o furfurale (FU). Tale molecola pu essere ottenuta mediante disidratazione di monosaccaridi pentosi e possiede elevate potenzialit; infatti considerata un intermedio chiave per la sintesi di unampia variet di combustibili alternativi come il metilfurano (MFU) e prodotti ad elevato valore aggiunto per lindustria polimerica e la chimica fine come lalcol furfurilico (FAL). In letteratura tali prodotti vengono principalmente ottenuti in processi condotti in fase liquida mediante lutilizzo di catalizzatori eterogenei a base di metalli nobili come: Ni-Co-Ru-Pd, Pt/C o Pt/Al2O3, NiMoB/-Al2O3, in presenza di idrogeno molecolare come agente riducente. La riduzione del gruppo carbonilico mediante lutilizzo di alcoli come fonti di idrogeno e catalizzatori a base di metalli non nobili tramite la reazione di MeerweinPonndorfVerley (MPV), rappresenta un approccio alternativo che limita il consumo di H2 e permette di utilizzare bio-alcoli come donatori di idrogeno. Lo scopo di questo lavoro di tesi stato quello di mettere a punto un processo continuo, in fase gas, di riduzione della FU a FAL e MFU, utilizzando metanolo come fonte di idrogeno tramite un meccanismo di H-transfer. In dettaglio il lavoro svolto pu essere cos riassunto: Sintesi dei sistemi catalitici MgO e Mg/Fe/O e loro caratterizzazione mediante analisi XRD, BET, TGA/DTA, spettroscopia RAMAN. Studio dellattivit catalitica dei catalizzatori preparati nella reazione di riduzione in fase gas di FU a FAL e MFU utilizzando metanolo come fonte di idrogeno.
Resumo:
A family of LiMO2 materials (M=Ni0.25Mn0.75) was prepared from Na1.2-xLixMO precursors (0x0.6) via ion exchange. The resulting IE products were examined via XRD and compared to simulated XRD patterns produced using DIFFax to determine the defect structures resulting from the IE process. For the 0.1x0.6 materials, it is observed that there are 3 LiMO2 sub-phases with different Li contents present. As the amount of Li in the precursor increases, the amount of each phase changes resulting in a net shift to higher 2-theta; corresponding to an overall decrease in lattice parameter, approaching the theoretical values for LiMO2. Additionally, as x increases, the probability of O3-type shifting increases, most likely due to an increase in the amount O3-Li2MO3 minority phase which acts to weaken bonds in the TM layer, allowing the O3 shift to occur more easily. For the x=0 IE product, it was seen that the product had an ~O2-type structure, but with lattice parameters closer to those expected for a NaMO2 material.
Resumo:
The new ligand 4,5-bis (2-pyridylmethylsulfanyl)-4',5'-bis(cyanoethylthio)tetrathiafulvalene (BPM-BCET-TTF) and its nickel(II) complex have been prepared and crystallographically characterized. The Ni(II) complex shows octahedral geometry around the metal ion with the coordination site occupied by the pyridyl nitrogen atoms, the thioether sulfur atoms of the ligand and cis coordination of the halide ions.
Resumo:
Three divalent transition metal complexes of 4,5-bis(2-pyridylmethylsulfanyl)-4,5-ethylenedithiotetrathiafulvalene have been prepared and crystallographically characterized. The isostructural Co(II) and the Ni(II) complexes show octahedral geometries around the metal ions with the coordination sites occupied by the pyridyl nitrogen atoms and the thioether sulfur atoms of the ligand and cis coordination of the halide ions. Cyclic voltammetry reveals that the complexation leads to a small anodic shift in the first oxidation potential of the TTF system.
Resumo:
The preparations, X-ray structures, and magnetic characterizations are presented for two new pentadecanuclear cluster compounds: [NiII{NiII(MeOH)3}8(-CN)30{MV(CN)3}6]xMeOHyH2O (MV = MoV (1) with x = 17, y = 1; MV = WV (2) with x = 15, y = 0). Both compounds crystallize in the monoclinic space group C2/c, with cell dimensions of a = 28.4957(18) , b = 19.2583(10) , c = 32.4279(17) , = 113.155(6), and Z = 4 for 1 and a = 28.5278(16) , b = 19.2008(18) , c = 32.4072(17) , = 113.727(6), and Z = 4 for 2. The structures of 1 and 2 consist of neutral cluster complexes comprising 15 metal ions, 9 NiII and 6 MV, all linked by -cyano ligands. Magnetic susceptibilities and magnetization measurements of compounds 1 and 2 in the crystalline and dissolved state indicate that these clusters have a S = 12 ground state, originating from intracluster ferromagnetic exchange interactions between the -cyano-bridged metal ions of the type NiIINCMV. Indeed, these data show clearly that the cluster molecules stay intact in solution. Ac magnetic susceptibility measurements reveal that the cluster compounds exhibit magnetic susceptibility relaxation phenomena at low temperatures since, with nonzero dc fields, M has a nonzero value that is frequency dependent. However, there appears no out-of-phase (M) signal in zero dc field down to 1.8 K, which excludes the expected signature for a single molecule magnet. This finding is confirmed with the small uniaxial magnetic anisotropy value for D of 0.015 cm-1, deduced from the high-field, high-frequency EPR measurement, which distinctly reveals a positive sign in D. Obviously, the overall magnetic anisotropy of the compounds is too low, and this may be a consequence of a small single ion magnetic anisotropy combined with the highly symmetric arrangement of the metal ions in the cluster molecule.
Resumo:
Digitalisat der Ausg. [S.l.], 1718/19
Resumo:
[Aharon Ben-Samuel aus Hegershausen]
Resumo:
Digitalisat der Ausg. Lemberg, 1865
Resumo:
Zalmn Zev m-Ufhoizn
Resumo:
Digitalisat der Ausg. London, 1819
Resumo:
[elm Ibn-Wirg]
Resumo:
Zalman Rubaow
Resumo:
Digitalisat der Ausg. Amrdm, [1760/61]
