Light metal amides and imides are promising catalysts for the decomposition of ammonia. They show high catalytic activity comparable to ruthenium-based catalysts, and thus present a low cost method of producing hydrogen from ammonia for utilization in energy storage applications. In an extension of recent work on sodium and lithium amide, an investigation of the performance of lithium-calcium imide (Li2Ca(NH)2) is presented here. It shows comparable ammonia decomposition activity to lithium amide-imide, but has vastly improved containment within the reactor geometry, with almost full recovery of the catalyst mass post-reaction. Despite these improved characteristics, in situ diffraction data show that the material is not stable under ammonia flow in the temperature range of 200-460oC, separating into lithium amide and calcium imide (and small amount of calcium amide) before reforming lithium-calcium imide at higher temperatures. Evidence for non-stoichiometry is reported for lithium-calcium imide and calcium imide, along with the well-documented non-stoichiometry present in lithium amide-imide. Hydrogen-deuterium isotope exchange experiments conducted during the in situ neutron powder diffraction experiment indicate that there is a bulk interaction of ammonia with lithium-calcium imide consistent with that reported in other light metal amide/imide materials. The change in the ammonia conversion rate under deuterated ammonia compared with natural abundance ammonia may be indicative of a kinetic isotope effect consistent with a rate-determining step which involves hydrogen or hydrogen-containing bonds.

Hydrogen production from ammonia using lithium-calcium imide

254th National Meeting (2017)

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