Evaluation of catalysts for decomposition of ammonia in hydrogen isotope purification systems

Abstract

Four catalyst materials were evaluated for suitability for use as ammonia decomposition catalysts in hydrogen isotope impurity removal systems for tritium processing in fusion systems. Suitability was tested both in terms of a comparison of the selected catalysts in ≥80% hydrogen environments, and in terms of compatibility in tritium service. Four different catalysts were characterized and tested, including ruthenium on alumina (Ru/Al), ruthenium on carbon (Ru/C), nickel on alumina (Ni/Al), and iron (Fe). Nickel on alumina may be the most compatible for use in tritiated environments, while still showing comparable performance to the ruthenium on alumina. In higher concentrations of hydrogen, the Ru/C catalyst was unstable and degraded its carbon support by catalytic hydrogenation of the carbon. The catalytic performance of the iron catalyst was shown to be less than the Ni/Al and Ru/Al, and other considerations on the nitridation of iron in the studied conditions are discussed. The catalytic performance of the nickel on alumina was shown to increase with increasing temperature, decreasing flow rate, decreasing pressure, and increasing ammonia concentration.