Thermodynamic Properties of Ammonia Production from Hydrogenation of Alkali and Alkaline Earth Metal Amides.

Abstract

Thermodynamic properties of alkali and alkaline earth metal amides are critical for their performance in hydrogen storage as well as catalytic ammonia synthesis. In this work, the ammonia equilibrium concentrations of LiNH2 , KNH2 and Ba(NH2 )2 at ca.10 bar of hydrogen pressure and different temperatures were measured by using a high-pressure gas-solid reaction system equipped with a conductivity meter. Hydrogenation of KNH2 gives the highest ammonia equilibrium concentration, followed by Ba(NH2 )2 and LiNH2 . Based on these data, the entropy and enthalpy changes of the reaction of ANH2 +H2 →AH+NH3 (A=Li, K, and Ba) were obtained from the van't Hoff equation. These thermodynamic parameters provide important information on the understanding of metal amides in catalytic ammonia synthesis reaction.