Boosting NO Oxidation in the Catalytic Peroxone Process over TiO₂: The Key Role of Surface Sulfate

Developing facile TiO₂ preparation methods is crucial for advancing the industrial implementation of a catalytic peroxone process for NO oxidation. In this study, three types of precursors, including titanium butoxide (Ti-BO), metatitanic acid (Ti-MTA), and titanyl sulfate (Ti-TOS), were used to synthesize TiO₂. Remarkably, Ti-TOS and Ti-MTA exhibited enhanced activity compared to that of Ti-BO, with 93 and 87% NO oxidation efficiency (373 K, O₃/NO = 0.4, H₂O₂/NO = 1.2, GHSV = 1.2 × 10⁵ h^-1), which is higher than that of Ti-BO (78%). Further investigations revealed that residual sulfate groups (SO₄ ^2-) from precursors enhance Lewis acidity by withdrawing electrons from the Ti⁴⁺ sites, thereby facilitating H₂O₂ deprotonation and Ti-OOH formation. This accelerates radical generation for NO oxidation while inhibiting nitrate accumulation and weakening NO adsorption to optimize reaction kinetics. In addition, sulfates also inhibit the accumulation of oxidation product nitrates on the catalyst surface, thereby improving catalytic stability. This work reveals the promotion mechanism of SO₄ ^2- on the catalytic peroxone process from multiple perspectives.