A Novel Li–Ca–B–H Complex Borohydride: Its Synthesis and Hydrogen Storage Properties

Abstract

The synthesis and hydrogen-storage properties of the mixed alkali metal and alkaline-earth metal borohydride are systematically investigated. It is found that mechanical milling a mixture of LiBH4 and CaCl2 with molar ratio of 3:1 in tetrahydrofuran (THF) forms a new LiBH4·Ca(BH4)2·2THF compound. Thermal analysis indicates that the decomposition process of the new compound involves four steps: (1) LiBH4·Ca(BH4)2·2THF decomposes first into high temperature phase of LiBH4, CaB6, and an intermediate phase Ca–B–H–Cl hydride and synchronously releases a large number of H2 and THF gas together with less B2H6; (2) the eutectic melting of LiBH4 and Ca–B–H–Cl hydride; (3) Ca–B–H–Cl hydride decomposes into CaHCl, CaB6, and a little H2; (4) LiBH4 reacts with CaHCl, generating H2, CaH2, CaB6, LiH, and LiCl. The first dehydrogenation step starts at ca. 70 °C, which is much lower than that of the pristine LiBH4 and Ca(BH4)2. According to Kissenger’s equation, the activation energies of the different dehydrogenation steps are respectively 291.95, 132.06, and 117.13 kJ/mol, except the second decomposition step. Moreover, this new compound LiBH4·Ca(BH4)2·2THF is proved to be partially reversible, which can release 5.63 wt % hydrogen in the second rehydrogenation/dehydrogenation cycle.

New global potential energy surface of the MgH2 system and dynamics studies of the reaction H + MgH → Mg + H2

“…The permutation invariant polynomial neural network (PIP-NN) method [24] is used to fit the PES; PIP-NN is widely used in PES construction, and has been used for reactions such as H + LiH, [25] and O + + H 2 . [26] First, we transform the bond length to Q 1 = 1/r 1 , Q 2 = 1/r 2 + 1/r 3 , and Q 3 = 1/(r 1 *r 3 ), where r 1 is the bond length of the H 2 molecule, and r 2 and r 3 are correspond to the two MgH bond lengths.…”

Improvement on Hydrogen Storage Properties of Complex Metal Hydride

“…It was found that LiCa(BH4)3 exhibits improved (de)hydrogenation properties relative to the component phases. In 2011, Jiang et al studied synthesis and hydrogen storage properties of Li-Ca-B-H hydride [123]. They found that the first dehydrogenation temperature is about 70 o C, much lower than the pristine LiBH4 and Ca(BH4)2.…”

Intelligent Optimization of Na−Mn−W/SiO2 Catalysts for the Oxidative Coupling of Methane

“…In the first report of NaÀMnÀW/SiO 2 , Li et al assumed that a surface cluster of tetrahedral WO 4 species (one W=O bond and three WÀOÀSi bonds) formed by surface reconstruction was the active site. [9] Further study by DFT calculations suggested that tetrahedral WO 4 species with a single bridging oxygen was the active site. [10] Later, they refined this proposal to a two metal oxide model, where gas phase O 2 and CH 4 were activated on Mn 3 + sites and W 6 + sites, respectively.…”

“…[13] In addition, a few research groups reported that the formation of MnWO 4 was reasonable for high performance of this catalyst. [14] It is important to note that traditional mechanism studies are generally based on the limited regulation of composition (approximate 5 wt%Na 2 WO 4 -2 wt%Mn-SiO 2 or 2 wt%Na 2 WO 4 -2 wt%Mn-SiO 2 , [15] ) and structure of NaÀMnÀW/ SiO 2 , [9,16] which might occasionally lead to biased conclusion. In addition, most researchers felt satisfied to find one of the optimized compositions with variable-controlling approach and easily overlooked other optimized compositions.…”