Advantages of syngas for the regeneration of NOx trap system investigated with operando IR measurements

The regeneration of Lean NOx Trap catalyst (Pt–Rh/BaO–Al2O3) using H2 + CO was followed with operando IR spectroscopy methodology. The role of H2 was investigated from 2 to 20 vol.% H2. The increase of H2 partial pressure allowed a subsequent decrease of the regeneration duration. The quantity of NH3 formed during the regeneration was related to H2 quantity which suggests that NH3 formation is governed by the supply of H2. The reactivity of nitrate was found slower than that of nitrite species towards hydrogen at 250 °C. CO addition strongly inhibited ammonia production at 150 °C due to accumulation of carbonate species at the surface of the catalyst. Above 250 °C, two processes coexisted for the reduction of NOx into ammonia in the presence of H2 + CO mixture: the successive hydrogenation of N atoms from NO dissociation and the hydrolysis of isocyanate species evidenced by IR.