Ionic Couple-Driven Palladium Leaching by Organic Triiodide Solutions

Abstract

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

Catalytic Oxidation of Methane: Pd and Beyond

“…Efficient and cost‐effective recycling strategies are needed in order to increase the sustainability of the catalysts manufacturing process. We recently demonstrated novel environmental friendly routes to recycle Pd from spent catalysts using highly effective and Pd‐selective organic ligands , . Rare earth recycling is also an existing challenge, due to the similar physicochemical properties of lanthanides, whose recovery is very relevant for electric cars and wind power motors fabrication …”

Oxidative Dissolution of Metals in Organic Solvents

“…The organic molecules dithiomalonamides (PhHN) 2 DTM and Mo 2 DTM (see Scheme 3 ) can react with iodine in organic solvent to form organic triiodides (OrgI 3 ), namely 3,5-bis(phenylamino)-1,2-dithiolylium triiodide ([(PhHN) 2 DTL]I 3 ) and 3,5-bis(morpholino)-1,2-dithiolylium triiodide [Mo 2 DTL]I 3 . 55 These were applied for leaching of palladium from metal powders and model spent car exhaust catalysts at room temperature. Two more triiodides with tetrabutylammonium (N 4444 ) and tetraphenylphosphonium (Ph 4 P) cations were formed directly from the corresponding iodide salt with iodine, and they were studied for leaching of palladium as well.…”

“… Leaching of palladium from spent catalyst by organic triiodides in methylethylketone (MEK) under reflux for 7 days. Reprinted with permission from ref ( 55 ). Copyright 2017 American Chemical Society.…”

“…Moreover, the organic lixiviants are sometimes more efficient than the aqueous lixiviant for oxidative dissolution of metals. 55 Dihalogen adducts are claimed to be safe, cheap, easy to handle, and noncytotoxic. However, most of the organic compounds are destroyed in order to recover the metals after dissolution, so that these organic compounds cannot be reused.…”

Characterization and Structural Insights of the Reaction Products by Direct Leaching of the Noble Metals Au, Pd and Cu with N,N′-Dimethyl-piperazine-2,3-dithione/I2 Mixtures

“…[Cu(Me 2 dazdt) 2 ]I 3 ( 5 ), the corresponding salt of 3 where the ligand consists in a hepta-atomic cyclic DTO, is similarly obtained by using as leaching mixture N , N ′-dimethyl-perhydrodiazepine-2,3-dithione (Me 2 dazdt, Scheme 1 )/I 2 . Detailed inspection of structural features of 1 – 5 , including the packing mode at the solid state, will be presented here with the view to provide information on bonding inside the cations and anions and interactions at supramolecular level, which may affect the formation of the different complexes and the effectiveness of noble metal dissolution [ 29 ]. Density functional theory (DFT) calculations, combined with experimental results, will help in elucidating the structure/bonding relationship.…”