Novel molecular catalyst candidates for H2 evolution from hydrogen storage materials
|Wojciech I. Dzik 1, Wojciech Grochala 1,2|
1. Warsaw University, Faculty of Chemistry, Pasteura 1, Warszawa 02-093, Poland
Thermal stability in a strongly reducing environment of Ni(II) and Cu(II) sulphate complexes with cyclam (1,4,8,11-tetraazacyclotetradecane), or its N-methylated derivatives, was examined using TGA and DSC techniques. Samples were prepared by mechanochemical doping of NaH or LiAlH4 with ca. 2-4 mol % (20-30 wt. %) of a complex. Samples of NaH doped with Ni(II) complexes decompose in two steps. The I-st step corresponds to one-electron reduction of Ni(II) with an evolution of small amounts of hydrogen. During the II-nd step a progressive degradation of the organic ligand takes place. Cyclam complex of CuSO4 - very stable thermodynamically - is very resistant to reduction by NaH (slow degradation is only above 120 oC), while its addition to LiAlH4 results in a decrease of the temperature of the first step of alanate's decomposition (by ca. 30 oC). These results suggest that a range of catalysts for H2 evolution from hydrides might now be expanded, and include cations of electropositive metals (provided the presence of strongly chelating ligands). Complexes studied here form molecular crystals which are much easier to disperse (at a molecular level) wihin a hydrogen storage material, as compared with commonly used extended solid catalysts (TiO2, SiO2, FeCl3). This allows to reduce time for the high-energy milling from days to less than a minute, and to make use of every single metal center as a catalytically active species. The drawback of molecular catalysts is in their large molecular mass; this decreases the active hydrogen content of a H2 storage material.
I thank for financial support of my participation in E-MRS Fall 2006 from a Nationwide Polish Catalytic Network "Nanomaterials as Catalysts for New, Environmentally Friendly Processes" (WD).
Presentation: Poster at E-MRS Fall Meeting 2006, Symposium B, by Wojciech I. Dzik
See On-line Journal of E-MRS Fall Meeting 2006
Submitted: 2006-05-12 11:27 Revised: 2009-06-07 00:44
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