The escalating demand for ammonia (NH 3 ) as a promising energy vector and essential chemical raw material in both industrial and agricultural applications, coupled with its noxious and caustic properties, has led to significant atmospheric emissions that pose environmental and health risks. Photocatalytic NH 3 oxidation over TiO 2 is a promising strategy for air purification but is hindered by poor selectivity, often leading to the formation of toxic NO x byproducts due to the complex reaction network involving multiple competing pathways and intermediates. This study addresses this selectivity issue by designing a modified TiO 2 photocatalyst through a synergistic defect-dopant engineering approach. Through controlled doping and defect engineering, we demonstrate that N doping and O Vs distinctly modulate the reaction mechanism and products’ selectivity. Nitrogen doping thermodynamically promotes N 2 formation by stabilizing NH 2 intermediates and facilitating their selective coupling with NO, whereas O Vs kinetically facilitate NH 3 and O 2 dissociation, promoting superoxide-mediated oxidation, leading to overoxidized products such as NO x and nitrate/nitrite HNO x – species. An optimal N-doped TiO 2 catalyst achieves 87% NH 3 conversion with 80% N 2 selectivity and minimal NO x emission (∼5 ppm), while exhibiting excellent stability over multiple cycles. This work elucidates a defect-dopant strategy that optimizes kinetic and thermodynamic aspects of NH 3 oxidation, providing a design principle for selective photocatalytic nitrogen management toward sustainable air purification.
Zhu et al. (Thu,) studied this question.