Nitrogen storage properties based on nitrogenation and hydrogenation of rare earth–iron intermetallic compounds R2Fe17 (R=Y, Ce, Sm)

Abstract

Abstract The nitrogen storage properties for the rare earth–iron intermetallic compounds, R 2 Fe 17 (R=Y, Ce, and Sm), were investigated. These intermetallic compounds formed the corresponding metal nitrides by heating in a mixed gas of NH 3 –H 2 at 350–450°C and the nitrogen was incorporated into interstitial sites of the crystal lattices. The nitrogen stored as the metal nitrides was reversibly released as NH 3 by the following heating in H 2 at 450°C. An amount of the nitrogen released per unit volume of these intermetallic compounds is larger than that of a conventional nitrogen container charged at 15 MPa. The nitrogen storage capacity of Sm 2 Fe 17 N x was increased by repeating the nitrogenation–hydrogenation cycle owing to the formation of FeN x /RN y composites with large surface areas derived from the starting intermetallic compound through the cycle. Furthermore, the nitrogen storage characteristics of Sm 2 Fe 17 powders were effectively improved by surface loading with Ru metal that is active for ammonia generation.