We request 3 days beam time on POLARIS for the in-situ study of the crystalline phase composition of iron, manganese and ruthenium catalysts for ammonia decomposition. These materials are the most important transition metal catalysts for the decomposition of ammonia. The collection of the first in-situ structural data on these systems will enhance our understanding of the mechanism of catalytic action by identifying the active composition of the catalyst and correlating this composition with observed ammonia decomposition activity.