Direct synthesis of sodium alanate using mischmetal nanocatalyst

Abstract

This study reports the synthesis of NaAlH 4 by ball milling of NaH and Al mixture along with 3 mol % Mischmetal (Mm) nanocatalyst under hydrogen atmosphere. It is observed that synthesis of the intermediate phase Na 3AlH 6 can be achieved by ball milling even under 1 atm hydrogen at room temperature. Ball milling of the NaH + Al with 3 mol % Mm with 3 atm hydrogen in excess of 40 h time did not lead to the formation of NaAlH 4 but charging of the milled material at 100 atm hydrogen pressure at 120 °C lead to formation of NaAlH 4 phase. Direct synthesis of NaAlH 4 was achieved by milling of NaH + Al with 3 mol % Mm under 100 atm hydrogen pressure. Direct synthesis is possible even without any catalyst by high pressure milling. However catalyst is required to improve the hydrogen sorption characteristics of the synthesized material. The as-prepared Mm catalyzed NaAlH 4 is also found to reversibly store hydrogen up to 4.2 wt% hydrogen. Catalytic activity is attributed to defects promoted by ball milling and catalysts. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.