A dynamic reactor with mass spectroscopy online product analysis has been used to study the thermal and catalytic decompositions of ionic liquid HAN-based monopropellants. The activity of different catalysts has been evaluated by determining qualitatively and quantitatively the reaction products. A careful calibration of the expected products detected by the mass spectrometer (MS) (N-2, O-2, N2O, NO and NO2) has been performed. The analytical results have been supplemented by Raman spectroscopy of the aqueous solutions trapped after the reactor. The thermal and catalytic decomposition of water-HAN (80 wt.%, hydroxylammonium nitrate NH3OH+NO3-) mixture gave primary products (major N-2, medium NO) and secondary products (medium NO and traces NO2). From the data, a reaction mass balance could be proposed, based on the combination of two parallel competitive reactions: 6NH(3)OHNO(3)(aq) = 3N(2)(g) + 2NO(g) + 10H(2)O(g) + 4HNO(3)(g), Delta H-r degrees = -117.8 kJ HAN mol(-1) 6NH(3)OHNO(3)(aq) = 2N(2)(g) + 2N(2)O(g) + 10H(2)O(g) + 4HNO(3)(g), Delta H-r degrees = -121.0 kJ HAN mol(-1) The influence of the catalyst shape (powder or spheres) has been followed. The isothermal tests at 50 degrees C display the best activity for the powder catalyst with a complete decomposition of the HAN solution, due to a good contact between catalyst bed and monopropellant. On the other hand, the sphere-shaped catalyst leads only to a partial HAN decomposition, due to preferential paths through the catalyst bed. The thermal decomposition at 200 degrees C, leads also to a partial reaction. (c) 2006 Elsevier B.V. All rights reserved.