Platinum group metals (PGMs) are critical raw materials, and their sustainable recovery from secondary sources supports supply security and a circular economy. End-of-life ammonia oxidation catalysts are considered attractive feedstocks due to their high PGM content. A systematic evaluation of oxidising agents was conducted to assess the dissolution of palladium, platinum and rhodium in chloride media under identical conditions (80°C, 8 h). Near-complete and non-selective dissolution (~100% for palladium, platinum and rhodium) was achieved with aqua regia. Selective palladium dissolution was observed with hydrochloric acid (HCl) combined with oxidants: 92.9% (hydrogen peroxide (H 2 O 2 )), 95.4% (sodium chlorate (NaClO 3 )) and 87.9% (sodium hypochlorite (NaClO)), while platinum and rhodium remained <70% in single-stage runs. The HCl–NaClO system exhibited the highest palladium selectivity (S Pd:Pt 1.8; S Pd:Rh 2.0). A combined HCl–H 2 O 2 –NaClO system increased overall recoveries to palladium 93.3%, platinum 81.4%, rhodium 75.5%, but reduced selectivity. A two-stage dissolution strategy reconciled selectivity and recovery, achieving >99.5% overall dissolution while concentrating 85–92% of palladium in the first stage (S Pd:Rh up to 8.9). Thermodynamic analysis (Eh-pH (Pourbaix) diagrams, standard ΔG°, ΔS° and ΔH°) confirmed that redox control governs selectivity. This work provides a quantitative, mechanistically grounded framework for designing selective hydrometallurgical routes to recover PGM from high-grade catalysts.
Johnson Matthey Emission Control Technologies, Orchard Road, Royston, Hertfordshire SG8 5HE, UK Email: robert.hanley@matthey.com “Palladium-Catalyzed Coupling Reactions”, published by Wiley in 2013, is a comprehensive handbook and guide to modern aspects of this reaction type. The book focuses on state of the art techniques. The use of different reaction media, catalyst recycling, supported catalysts, microwave assisted synthesis and continuous fl ow reaction systems are all examined, making this book an excellent resource. The book avoids delving into the specifi cs of each type of coupling reaction and instead presents a variety of topics, discussing recent progress and potential future work in each given area. It was edited by Arpad Molnar, a Professor of Chemistry in the University of Szeged, Hungary, who has no less than 200 publications to his name. Numerous research papers in the fi eld of catalyst development, coupled with review papers on many of the subjects covered in this book, qualify Professor Molnar for his position of editor. The content of this book covers fi ve general topics: an introduction and background to Pd-catalysed coupling reactions, Pd catalysts on various support materials, coupling reactions in different reaction media, reaction conditions for coupling reactions and industrial applications of Pd catalysed coupling reactions.
