Sustainable Approach for Spent V<sub>2</sub>O<sub>5</sub>–WO<sub>3</sub>/TiO<sub>2</sub> Catalysts Management: Selective Recovery of Heavy Metal Vanadium and Production of Value-Added WO<sub>3</sub>–TiO<sub>2</sub> Photocatalysts

In order to control nitrogen oxides emissions, V<sub>2</sub>O<sub>5</sub>–WO<sub>3</sub>/TiO<sub>2</sub> catalysts are widely applied in coal-fired power plants. Consequently, a large number of V<sub>2</sub>O<sub>5</sub>–WO<sub>3</sub>/TiO<sub>2</sub> catalysts are spent annually because of their short operating life. Although these spent catalysts contain amounts of heavy metals, they have also been regarded as a potential secondary resource for the recovery of valuable elements titanium, tungsten, and vanadium. Therefore, this study developed an efficient method for selective leaching of heavy metal vanadium with an “H<sub>2</sub>SO<sub>4</sub> + Na<sub>2</sub>SO<sub>3</sub>” acid reduction system. The use of this leaching solution achieved nearly 100% efficiency in vanadium removal, and the effects of the leaching parameters on the vanadium leaching efficiencies were investigated. Subsequently, the titanium-enriched residue obtained from the leaching process was used to produce high-performance WO<sub>3</sub>–TiO<sub>2</sub> photocatalysts with dominant {001} facets via a hydrothermal treatment. The influence of the amount of hydrogen fluoride on the morphology and percentage exposure of the {001} facets of the photocatalysts was studied systematically. The method proposed in this study constitutes a novel and sustainable approach for the disposal of spent V<sub>2</sub>O<sub>5</sub>–WO<sub>3</sub>/TiO<sub>2</sub> catalysts.