Green Recovery of Titanium and Effective Regeneration of TiO2 Photocatalysts from Spent Selective Catalytic Reduction Catalysts

The extensive use of selective catalytic reduction (SCR) catalysts will afford many spent SCR catalysts. The mass fraction of the titanium component is over 80% in spent SCR catalysts, but currently, it is usually thrown away without proper recycling. This work aims to develop a clean, green, and economical approach to recovering titanium and regenerating TiO2 photocatalysts from spent SCR catalysts based on the conversion of the titanium component. This titanium component is converted into metastable α-Na2TiO3 with high efficiency (>98%) using a NaOH molten salt method, and the optimal conditions were found to be a roasting temperature of 550 °C, a NaOH-to-spent-SCR-catalysts mass ratio of 1.8:1, a roasting time of 10 min, and a NaOH concentration of 60–80 wt %. And a possible chemical reaction mechanism is proposed. A subsequent hydrothermal treatment of α-Na2TiO3 regenerates TiO2 photocatalysts with high purity (>99.0%) that can satisfy commercial requirements. In addition, the present iron element contained in spent SCR catalysts is doped into regenerated TiO2 photocatalysts, resulting in providing visible-light-driven photocatalytic activities. The regenerated TiO2 photocatalysts possess superior photocatalytic degradation capacities for dye pollutants and can be used to efficiently treat wastewater. This work introduces a promising technology for the cyclical regeneration of titanium from spent SCR catalysts.