The regeneration of Lean NOx Trap catalyst (Pt-Rh/BaO-Al2O3) using H-2 + CO was followed with operando IR spectroscopy methodology. The role of H-2 was investigated from 2 to 20 vol.% H-2. The increase of H-2 partial pressure allowed a subsequent decrease of the regeneration duration. The quantity of NH3 formed during the regeneration was related to H-2 quantity which suggests that NH3 formation is governed by the supply of H-2. The reactivity of nitrate was found slower than that of nitrite species towards hydrogen at 250 degrees C. CO addition strongly inhibited ammonia production at 150 degrees C due to accumulation of carbonate species at the surface of the catalyst. Above 250 degrees C, two processes coexisted for the reduction of NOx into ammonia in the presence of H-2 + CO mixture: the successive hydrogenation of N atoms from NO dissociation and the hydrolysis of isocyanate species evidenced by IR. (C) 2012 Elsevier B.V. All rights reserved.