Ionic Couple-Driven Palladium Leaching by Organic Triiodide Solutions

Pd dissolution capabilities of a variety of organic triiodides (OrgI3) in organic solvent, where Org+ = 3,5-bis(phenylamino)-1,2-dithiolylium [(PhHN)2DTL+], 3,5-bis(morpholino)-1,2-dithiolylium (Mo2DTL+); tetrabuthylammonium (TBA+); and tetraphenylphosphonium (Ph4P+), toward the crude metal and model-spent three-way catalyst (TWC), are described here. Enhanced Pd-leaching yields from TWC were obtained using OrgI3 solutions (up to 98%) in spite of the fully inorganic KI3 one (38%) in the same mild conditions. The reaction products were isolated and characterized as Org2[Pd2I6]. Crystallographic and DFT studies highlighted the presence of several ion-pair secondary interactions in the products, which can explain the improved effectiveness of the Pd etching by OrgI3. For comparison purposes, the gold leaching by using R2DTLI3 and the obtained Au complexes were investigated. Preliminary results addressed to recover the metal and the reagents from the etching product showed that (PhHN)2DTLI3 is the most promising reagent to improve sustainability in the whole process.