The present study highlights the dynamic nature of the [RuH6] catalytic center in enabling mild condition ammonia synthesis. The presence of [RuH7] complex facilitates the hydrogenation of the activated nitrogen from the surplus lattice hydrides. On the contrary, a too high concentration of [RuH7] complex on the surface can deactivate the catalyst from dinitrogen adsorption. The high activation energy for lattice H transfer of the chemisorbed H2 observed in this unique class of material maintains a delicate balance between the availability of lattice hydrogen and active sites. The preferential N2 chemisorption over H2 and kinetic blockage of hydrogen over-saturation are key elements to the success of ternary Ru complex hydride systems for catalyzing NH3 synthesis at low temperatures. Furthermore, a unique temperature-dependent tuning of the reaction kinetics is observed for [RuH6] catalytic center, resulting from a shift in the TDI and TDTS along the reaction pathway.