Regeneration of spent V2O5-WO3/TiO2 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 V2O5 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 x 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 NH3-selective catalytic reduction (SCR) since As existence and VO x over-reduction will separately cause unstable and excessive NH3 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.

Secondary problems, such as the occurrence of side reactions and the accumulation of by-products, are a major challenge in the application of wet denitrification technology through urea solution. We revealed the formation mechanism of urea nitrate and clarified the main and side reaction paths and key intermediates of denitrification. Urea nitrate would be separated from urea absorption solution only when the concentration product of [urea], [H+] and [NO3−] was greater than 0.87~1.22 mol3/L3. The effects of the urea concentration (5–20%) and reaction temperature (30–70 °C) on the denitrification efficiency could be ignored. Improving the oxidation degree of the flue gas promoted the removal of nitrogen oxides. The alkaline condition was beneficial to the dissolution process, while the acidic condition was beneficial to the reaction process. As a whole, the alkaline condition was the preferred process parameter. The research results could guide the optimization of process conditions in theory, improve the operation efficiency of the denitrification reactor and avoid the occurrence of side reactions.

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Perovskite is of burgeoning interest in catalysis, principally due to such material having high thermal stability, modifiable variability, ferromagnetism, and excellent catalytic performance in peroxomonosulfate (PMS) activation. In this study, the SrCoxMn1−xO3 perovskites with different Mn doping were synthesized by a facile sol-gel method for peroxymonosulfate (PMS) activation to degrade Rhodamine B. The obtained SrCo0.5Mn0.5O3 perovskite exhibited the best catalytic efficiency, as Rhodamine B (40 mg/L) was removed completely within 30 min. In the system of SrCo0.5Mn0.5O3–PMS, several reactive species were produced, among which sulfate radicals and the singlet oxygen mainly contributed to Rhodamine B degradation. The relatively high catalytic performance could be attributed to the coupled redox cycle between Mn and Co, and the abundant oxygen vacancies. Moreover, the SrCo0.5Mn0.5O3 catalyst showed excellent stability and reusability, maintaining a high catalytic activity after several cycling tests. This study demonstrated that the Mn doping of SrCoO3 could not only enhance the B-site activation in SrCo0.5Mn0.5O3 but also enrich the oxygen vacancies, thus improving the efficiency of PMS activation.