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Isotopic Exchange in Porous and Dense Magnesium Borohydride
Author(s) -
Zavorotynska Olena,
Deledda Stefano,
Li Guanqiao,
Matsuo Motoaki,
Orimo Shinichi,
Hauback Bjørn C.
Publication year - 2015
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201502699
Subject(s) - borohydride , desorption , chemistry , magnesium , hydride , hydrogen , ion exchange , diffusion , porosity , phase (matter) , inorganic chemistry , analytical chemistry (journal) , ion , adsorption , thermodynamics , catalysis , organic chemistry , biochemistry , physics , chromatography
Magnesium borohydride (Mg(BH 4 ) 2 ) is one of the most promising complex hydrides presently studied for energy‐related applications. Many of its properties depend on the stability of the BH 4 − anion. The BH 4 − stability was investigated with respect to H→D exchange. In situ Raman measurements on high‐surface‐area porous Mg(BH 4 ) 2 in 0.3 MPa D 2 have shown that the isotopic exchange at appreciable rates occurs already at 373 K. This is the lowest exchange temperature observed in stable borohydrides. Gas–solid isotopic exchange follows the BH 4 − +D . →BH 3 D − +H . mechanism at least at the initial reaction steps. Ex situ deuteration of porous Mg(BH 4 ) 2 and its dense‐phase polymorph indicates that the intrinsic porosity of the hydride is the key behind the high isotopic exchange rates. It implies that the solid‐state H(D) diffusion is considerably slower than the gas–solid H→D exchange reaction at the surface and it is a rate‐limiting steps for hydrogen desorption and absorption in Mg(BH 4 ) 2.