Characterization of virgin and used automobile catalysts aiming at precious metals recycling

Platinum and platinum group metals (PGM) have important applications in catalysis. Automotive catalysts usually present platinum, palladium and rhodium. These metals play an important role in the conversion of toxic gases from fuel burn in gases less hazardous to the environment. The need for platinum and PGM allied to their scarcity in earth crust and elevated prices turn their recycling paramount. The automotive characterization is an important step for the selection of the proper recycling route, once there is no standard formulation for the manufacture of such catalysts. The virgin monolithic catalysts used by the automotive industry usually present around 1.89 g/kg of platinum, 0.29 g/kg of palladium besides 0.10 g/kg of rhodium, all high valued precious metals. In this paper two automobile catalyst samples were characterized: a virgin one, provided by Umicore - Brazil and an used one, bought in the market. Optical microscopy, scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction and fluorescence and termogravimetry coupled with differential thermal analysis (TG-DTA) were analytical techniques employed throughout this work. It was observed that the catalysts present a cordierite (Mg2Al4Si5O18) honeycomb structure covered with a PGM impregnated alumina layer. In the virgin catalyst around 0.99 g/kg of platinum was detected, while in the used one the platinum grade was 0.44 g/kg. In the used catalyst sample the presence of cracks and the deposition of carbonaceous matter onto the alumina layer were observed, which can lead to lose of activity of the catalyst.