Continuous low-temperature NOx abatement over structured FeTiO₃ catalysts with stable surface performance

• FeTiO ₃ was immobilized on 3D-printed structured supports to enhance photocatalytic performance. • The photocatalytic system achieved efficient NO x removal under low-temperature and high-humidity conditions. • Continuous-flow operation was evaluated and optimized using Response Surface Methodology (RSM). • Ilmenite-based photocatalysis offers a sustainable and low-cost alternative to conventional NO x abatement technologies. Mitigating nitrogen oxides (NO x ) at low temperature remains a major challenge for decentralized combustion systems, where conventional Selective Catalytic Reduction (SCR) and Selective Non-Catalytic Reduction (SNCR) units lose efficiency. Here we introduce a compact structured photocatalytic reactor that enables continuous NO x oxidation under humid, low-temperature conditions using unmodified ilmenite (FeTiO ₃ ) as a natural semiconductor catalyst. FeTiO ₃ was immobilized on 3D-printed polylactic-acid lattices coated with a thin epoxy layer, producing mechanically robust and photochemically active surfaces. Under UV-C irradiation, the reactor sustained stable operation across 10–50 ppmv NO at gas hourly space velocities of 4–12 h⁻¹. Response-surface modelling identified an optimal NO x conversion of 92 % at 20 ppmv and 450 mL/min, which was experimentally validated with excellent agreement. Experiments and DFT calculations jointly show that FeTiO ₃ maintains its photo-oxidative activity in moisture-rich streams due to weak nitrate binding and the preservation of surface electronic states, enabling a self-cleaning response during operation. The simplicity of the mineral, together with the scalability of additive-manufactured supports, highlights the potential of ilmenite-based photocatalytic units for decentralized NO x control in small-scale combustion sources.