Abstract
The production of new automotive catalytic converters requires the increase of the quantity of Platinum Group Metals in order to deal with the strict emission standards that are imposed for vehicles. The use of PGMs coming from the recycling of spent autocatalysts could greatly reduce the cost of catalyst production for the automotive industry. This paper presents the synthesis of novel automotive Three-Way Catalysts (PLTWC, Pd/Rh = 55/5, 60 gPGMs/ft3) and diesel oxidation catalysts (PLDOC, Pt/Pd = 3/1, 110 gPGMs/ft3) from recovered PGMs, without further refinement steps. The catalysts were characterized and evaluated in terms of activity in comparison with benchmark catalysts produced using commercial metal precursors. The small-scale catalytic monoliths were successfully synthesized as evidenced by the characterization of the samples with XRF analysis, optical microscopy, and N2 physisorption. Hydrothermal ageing of the catalysts was performed and led to a significant decrease of the specific surface area of all catalysts (recycled and benchmarks) due to sintering of the support material and metal particles. The TWCs were studied for their activity in CO and unburned hydrocarbon oxidation reactions under a slightly lean environment of the gas mixture (λ > 1) as well as for their ability to reduce NOx under a slightly rich gas mixture (λ < 1). Recycled TWC fresh catalyst presented the best performance amongst the catalysts studied for the abatement of all pollutant gases, and they also showed the highest Oxygen Storage Capacity value. Moreover, comparing the aged samples, the catalyst produced from recycled PGMs presented higher activity than the one synthesized with the use of commercial PGM metal precursors. The results obtained for the DOC catalysts showed that the aged PLDOC catalyst outperformed both the fresh catalyst and the aged DOC catalyst prepared with the use of commercial metal precursors for the oxidation of CO, hydrocarbons, and NO. The latter reveals the effect of the presence of several impurities in the recovered PGMs solutions.
Highlights
Every modern vehicle equipped with an internal combustion engine possesses a catalytic system (Three-Way Catalytic converters (TWCs) for petrol engines or Diesel Oxidation Catalysts (DOCs) for diesel engines) to reduce efficiently the emissions of harmful compounds such as carbon monoxide (CO), unburned hydrocarbons (HC), and nitrogen oxides (NOx)
This paper presents the synthesis of novel automotive Three-Way Catalysts (PLTWC, Pd/Rh = 55/5, 60 gPGMs/ft3) and diesel oxidation catalysts (PLDOC, Pt/Pd = 3/1, 110 gPGMs/ft3) from recovered Platinum Group Metals (PGMs), without further refinement steps
The present paper has reported the synthesis of new, small-scale catalytic monoliths with the direct use of PGMs containing nitrate solutions coming from the recovery of spent autocatalysts
Summary
Every modern vehicle equipped with an internal combustion engine possesses a catalytic system (Three-Way Catalytic converters (TWCs) for petrol engines or Diesel Oxidation Catalysts (DOCs) for diesel engines) to reduce efficiently the emissions of harmful compounds such as carbon monoxide (CO), unburned hydrocarbons (HC), and nitrogen oxides (NOx). Platinum Group Metals comprise six similar elements: iridium, osmium, palladium, platinum, rhodium, and ruthenium. These elements are included by the European Commission in the list of critical raw materials, based on their economic importance and supply risk [1]. Due to the high value of PGMs and the fact that autocatalysts comprise a rich source of PGMs, the attractiveness to recover those metals from end-of-life products, such as spent autocatalysts, is extremely high In this respect, the very restrictive legal regulations regarding the obligation to obtain specific recovery rates for end-of-life (ELV) vehicles and the mandatory removal of catalysts have improved the situation of the European Union in the area of PGM recovery [5]
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