Hydrogen-rich reduction coupled with wet leaching for the conversion of spent SCR catalysts into carbide solid solutions

Spent SCR catalysts, classified as high-risk solid waste, are produced in large quantities and are rich in critical metals such as Ti, V, W, and Mo, making them highly valuable for recycling. This study proposes a novel process combining hydrogen-rich reduction with hydrometallurgical leaching for the recycling of spent SCR catalysts. Thermodynamic calculations and experimental validation showed that the proposed process converts high-value oxides (TiO 2 , V 2 O 5 , WO 3 and MoO 3 ) into multicomponent carbides under a CH 4 –H 2 atmosphere. The effects of temperature, reaction time, and Fe 2 O 3 additives on phase transformation were systematically investigated. To remove residual impurities that were not reduced in the high-temperature reaction, selective acid and alkaline leaching were employed. Owing to their chemical stability, the formed multicomponent carbides remained inert during leaching. The optimized recycling process involved the addition of 8 wt% Fe 2 O 3 to the catalyst, followed by thermal treatment at 1400 °C for 3 h. Impurities were removed using 0.5 mol·L⁻¹ HCl and 1 mol·L⁻¹ NaOH solutions. The final product exhibited a face-centered cubic structure with a uniform distribution of Ti, V, W, and Mo and an average lattice parameter of 4.3012 Å, as revealed through Rietveld refinement. Impurities such as Fe, Al, Si, Ca, and S were effectively removed. The product can be used in fields such as conductive materials and hard alloys. This study provides a promising route for the high-value utilization of spent SCR catalysts.