Surface property descriptors governing high N2 selectivity over CuO in NH3/H2 co-combustion and its implementation in structured catalysts

The transition toward carbon-free energy has highlighted ammonia (NH 3 ) as a promising fuel candidate. However, its practical utilization is limited by low reactivity and undesired NO x formation during combustion. In this study, catalytic NH 3 /H 2 co-combustion over transition metal oxides (Mn 2 O 3 , Co 3 O 4 , and CuO) was systematically investigated to elucidate the governing property-activity relationships. Among the catalysts, CuO achieved complete NH 3 and H 2 conversion with > 99% N 2 selectivity at 500 °C, significantly outperforming Mn 2 O 3 and Co 3 O 4 . Characterization and density functional theory (DFT) calculations show that catalytic performance is governed by surface acidity, the electronic nature of lattice oxygen (O lat ), and oxygen mobility. Co 3 O 4 , characterized by abundant oxygen vacancies and high oxygen mobility, promotes rapid NH 3 activation but leads to excessive NO formation. Mn 2 O 3 , possessing strong acid sites and nucleophilic O lat , favors overoxidation pathways resulting in N 2 O formation. In contrast, CuO exhibits weak surface acidity, electrophilic O lat , and moderate oxygen mobility, which suppress overoxidation and drive the selective reduction of NO to N 2 . Furthermore, CuO was successfully implemented into structured catalysts using cordierite monoliths and copper foams, retaining high activity and N 2 selectivity. These findings provide mechanistic insights and practical design guidelines for developing efficient catalysts for carbon-free combustion systems.