Alternative Recovery and Valorization of Metals from Exhausted Catalytic Converters in a New Smart Polymetallic Catalyst

Graphical Abstract

A polymetals solution, recovered from exhausted catalytic converters, was transformed in the catalyst Met_x-EPS by the use of a culture broth of Klebsiella oxytoca DSM 29614. Indeed, this microorganism produces the exopolysaccharide EPS, able to embed these metals. This new metals-polymeric composite showed a good catalytic activity and recyclability in the aqueous biphasic hydrogenation of different substrates.

Abstract

A new metals-polymeric composite, Met_x-EPS (I), was prepared to be used as catalyst in water or in two-phase aqueous conditions. The metals source was an exhausted catalytic converter that was grinded and treated with an acidic solution at room temperature. After filtration, the solution was concentrated, neutralized and added to a broth of Klebsiella oxytoca DSM 29614 to produce (I) where metals are embedded in a peculiar polysaccharide structure (EPS). The composite was easily recovered from the fermentation broth and purified. The process protocol was verified many times and was shown to be reproducible satisfactorily. The % recovery of metals, originally present in the converter, was good as determined by atomic absorption. The morphology and the chemical state of main metals in (I) were investigated by X-ray absorption spectroscopy methods (XANES and EXAFS). No metallic alloy seems to be evident. The catalytic activity and a possible synergic effect due to the presence of the different metals was valuated in the hydrogenation of some substrates, valuable precursors for the production of fine chemicals.