Formic Acid-Mediated Regeneration Strategy for As-Poisoned VO-WO/TiO Catalysts with Lossless Catalytic Activity and Simultaneous As Recycling.

Regeneration of spent VO-WO/TiO catalysts is highly desirable, especially for those containing hypertoxic As, which is categorized as hazardous waste. However, common solution-leaching methods suffer from the trade-off between As removal and VO retention, and it would be necessary to introduce extra proceedings like ingredients reimplantation and As-bearing waste treatment after regeneration. Herein, a formic acid-mediated regeneration strategy has been developed to achieve superior catalytic activity, short timescale regeneration, and nontoxic metallic As recycling with controllable and safe conduction. The specific activity of the optimal regenerated catalyst reaches 98.3% of the fresh catalyst with 99.1% As removal and less than 1.8% V loss within 15 min. Structure characterizations reveal that the distorted VO molecular structure, surface acidity, and redox property recover to the fresh level after regeneration. In situ investigation of the regeneration process indicates that As-OH removal together with V-OH generation occurs at the first regeneration stage, followed by the active center V═O sites over-reduction at the second stage. The retained V═O species by suitable regeneration temperature and time are essential for NH-selective catalytic reduction (SCR) since As existence and VO over-reduction will separately cause unstable and excessive NH adsorption to further suppress the reaction cycle. The developed strategy and improved understanding of active site protection would exert benefits on the development of efficient and time-saving regeneration methods for spent catalysts.