N ₂ O Formation Mechanism and Suppression Strategy on Pt Catalysts for NO _<i>x</i> Removal from Hydrogen-Internal Combustion Engines

Pt-based catalysts exhibit excellent low-temperature activity in the selective catalytic reduction of NO _<i>x</i> with H₂ (H₂-SCR), but their tendency to form N₂O poses a significant challenge for practical use. This issue is further complicated by unclear formation mechanisms, hindering the development of more efficient catalysts. This study explored the N₂O generation mechanisms on Pt catalysts supported by MgO, Al₂O₃, SiO₂, and TiO₂, aiming to achieve a deep understanding that could advance the Pt catalysts with high NO _<i>x</i> conversion and minimized N₂O emissions. Through systematic kinetics and characterization analyses, the direct influence of the support acidity and reactant dynamics (O₂ and NO) on N₂O formation was clearly revealed. Notably, the Pt catalysts with strong NO adsorption capacity showed reduced N₂O generation, highlighting the critical role of NO adsorption sites in the H₂-SCR process. By incorporation of NO adsorption sites (<i>i.e.</i>, MgO, BaO, CeO₂) onto Pt/SiO₂, both the H₂-SCR efficiency and N₂ selectivity (reduced N₂O selectivity) were significantly enhanced, effectively reducing the N₂O emissions through optimized surface NO adsorption. These findings provide a design framework for more selective Pt-based catalysts, advancing H₂-SCR systems for effective NO _<i>x</i> abatement from hydrogen-internal combustion engines, which is a promising carbon-free transportation technology.