NH3 is one of the most important chemical products and is responsible for fertilizer production. NH3 synthesis from N2 is the current commercial process but suffers from the high activation barrier of N2, requiring 400-500 C and 150-300 bar operation conditions. Towards low temperature and pressure NH3 synthesis, we have developed LaN-based catalysts, in which the N vacancy (VN) activates N2 whereas metal particles split H2. Our previous energy dispersive RIXS at the N K edge discovered the surface N2 species via its vibrational modes. Here we will monitor the activation of the N2 among different LaN-supported catalysts by determining precise energy spacing between those vibrational modes. So far there is no method to directly probe the N2 activation process and we are the first. The success of this proposal will 1) provide insight into how N2 is activated at VN; and 2) establish a general method to probe surface N2 in NH3 synthesis.