Studies on synthesis and dehydrogenation behavior of magnesium alanate and magnesium–sodium alanate mixture

Magnesium alanate ( Mg ( AlH 4 ) 2 ) has been synthesized by mechanochemically activated metathesis reaction involving MgCl 2 and NaAlH 4 . Its dehydrogenation kinetics and storage capacity has been studied by using Sievertʹs type apparatus. We have obtained dehydrogenation capacity of 2.7 wt% H 2 from Mg ( AlH 4 ) 2 + 2 NaCl during the first decomposition step at 140 ∘ C and 1.1 wt% H 2 during second step decomposition at 280 ∘ C . Efforts were carried out to reduce NaCl content from the product using Soxhlet extraction technique. The Soxhlet extracted product gives the total dehydrogenation capacity of 4.7 wt% H 2 . To enhance the storage capacity, we have synthesized a complex hydride consisting of mixture: x Mg ( AlH 4 ) 2 + y NaAlH 4 ( 0 < x < 1 , y ⩾ 1 ) . In the alanate mixture 0.5 Mg ( AlH 4 ) 2 + NaAlH 4 , the dehydriding temperature of NaAlH 4 gets lowered by ∼ 50 ∘ C (from 190 ∘ C to 140 ∘ C ) with 4 times faster desorption kinetics. The total hydrogen liberated in 180 min from NaAlH 4 + 0.5 Mg ( AlH 4 ) 2 ( + NaCl ) mixture at 140 ∘ C has been observed to be 3.7 wt% H 2 .