High-efficiency recovery of precious metals from spent automotive three-way catalysts by diatomite-supported ternary BiOCl-TiO2 composite

As a crucial secondary resource, spent automotive three-way catalysts (TWCs) possess significant recycling value due to their content of precious metal components like Pd, Pt, and Rh. Recently, photocatalytic technology has been explored for PGM recovery, existing studies predominantly use new TWCs or metallic elements as research objects, which differ significantly from the complex composition of actual waste TWCs (carrier materials, oil and carbon deposits, and oxidized precious metals). This study employed the sol-gel method to load TiO2 onto the surface of diatomite, followed by a solvothermal process to combine BiOCl with TiO2/diatomite, successfully preparing a ternary BiOCl-TiO2/diatomite composite photocatalytic material. It was found that the material demonstrated superior PGMs leaching efficiency compared to commercial P25 catalyst under UV irradiation, the leaching rates were 98.58% for Pd, 97.30% for Pt, and 65.37% for Rh, respectively. Experimental results demonstrate that diatomite incorporation preferentially exposes BiOCl (001) facets, thereby enhancing photocatalytic activity. Further systematic analysis of the changes in liquid composition and free radicals elucidated the key mechanism behind PGMs leaching in actual spent TWCs.