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Steady State Isotopic Transient Kinetic Analysis (SSITKA) coupled with Temperature-Programmed Surface Reaction (TPSR) experiments, using on line Mass Spectroscopy (MS) and in situ DRIFTS have been performed to study essential mechanistic aspects of the selective catalytic reduction of NO by H 2 under strongly oxidizing conditions (H 2 -SCR) at 140 °C over a novel 0.1 wt % Pt/MgO-CeO 2 catalyst for which patents have been recently obtained. The nitrogen paths of reaction from NO to N 2 and N 2 O gas products were probed by following the 14 NO/H 2 /O 2 f 15 NO/H 2 /O 2 switch (SSITKA-MS and SSITKA-DRIFTS) at 1 bar total pressure. It was found that the N-pathways of reaction involve two different in structure active chemisorbed NO x species, one present on the MgO and the other one on the CeO 2 support surface. The amount of these actiVe NO x intermediate species formed was found to be 14.4 µmol/g, corresponding to a surface coverage of θ ) 3.1 (based on Pt metal surface) in agreement with the SSITKA-DRIFTS results. A large fraction of it (87.5%) was found to participate in the reaction path for N 2 formation, in harmony with the high N 2 selectivity (82%) exhibited by this catalyst. Inactive adsorbed NO x species were also found to accumulate on both Pt and support (MgO and CeO 2 ). The mechanism of reaction must involve a H-spillover from the Pt metal to the support surface (location of active NO x species). It was proven via the NO/H 2 / 16 O 2 f NO/H 2 / 18 O 2 (SSITKA-MS) experiment that gaseous O 2 does not participate in the reaction path of N 2 O formation.

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