Using temperature programmed desorption and high-resolution electron energy loss spectroscopy, we have studied the (partial) decomposition of multilayer NH3 on the hexagonally close packed surface of ruthenium, Ru(001), at 100 K using gas phase atomic hydrogen. Thermal desorption spectra have been collected at various hydrogen atom fluences in order to characterize the evolution of the surface overlayer. At steady-state, the formation of a stable surface overlayer, consisting primarily of NH3, NH, and K, as well as a small concentration of N adatoms, is observed. Thermal desorption spectra, of the steady-state overlayer, show two separate hydrogen desorption peaks. One peak can be assigned to recombinative desorption of hydrogen from the surface while the ether is assigned to the reaction-limited decomposition of surface NH groups. Annealing this overlayer to 450 K leaves a relatively high nitrogen adatom surface coverage of theta(N)=0.30.