The barrier height and exothermicity for the HN2 --> H+N-2 reaction are predicted by high level ab initio quantum mechanical methods. The classical barrier is predicted to be 10.0 +/- 1.0 kcal/mol, and the reaction exothermicity is predicted to be 3.8 +/- 0.5 kcal/mol. The importance of these parameters to the thermal De-NOx process is discussed. The apparent conflict between the theoretical potential energy surface for HN2 and recent kinetic modelling studies is seen to persist.