NO and C Oxidation with Pt Recovered From Spent Catalytic Converters

Abstract

Several powder samples obtained from a spent catalytic converter, which contained approximately 1.1% w/w of platinum (Pt), were subjected to a leaching process to assess the relationships between the amount of recovered Pt, the time, and the temperature of the leaching process. The leached powder samples were characterized by X-ray fluorescence (XRF), which showed that the amount of recovered Pt increased linearly with increasing temperature. Our best recovery results (nearly 85% recovery) were reached at a temperature of 100°C, that was applied for 1 h. In the second step of the process, the leached solution was exposed to 100°C for 1 h and then run through ion exchange column with two basic resins: Amberlite-IRA 400 and 900. The aim of this second stage was to eliminate the impurities that originated from the first stage. The purity of the recovered Pt was higher when the process was carried out with the macroreticular matrix resin. Two 2-wt% Pt/Al2O3 catalyst powder samples were synthesized via incipient wetness impregnation, either using recovered platinum or an aqueous hydrogen hexachloroplatinate solution. The activity of these catalysts toward carbon and NO oxidation was assessed using a temperature-programmed combustion (TPC) plant. Results showed that the Tp values (peak combustion temperatures) of carbon oxidation were 555 and 560°C for the commercial Pt and the recovered Pt catalysts, respectively. When the catalysis of NO to NO2 is considered, both catalysts showed similar performances. They both reached their highest conversion (~61%) at 310°C without the production of nitrous oxide.