Among light metal amide-imide catalysts for ammonia decomposition, lithium-calcium imide is the most promising candidate for practical application. Ex situ diffraction data indicate that there are changes in the catalyst composition during the reaction, and thus the precise reaction mechanism remains unclear. Here, we propose to conduct two days of neutron powder diffraction measurements on the POLARIS diffractometer to probe these changes, giving insight to the ammonia decomposition reaction by monitoring the structure of the catalyst during the reaction and examining the data for potential variations in stoichiometry and the extent of isotope exchange in the sample.