Abstract
Electronic scrap represents an attractive alternative to natural ores for the supply of precious metals for our economy. Nevertheless, their exploitation remains limited, mainly for reasons of scale, due to their high variability. At the same time, demand for precious metals for chemical applications is growing, due to their performance in many catalytic processes. In our laboratory, we have recently proposed efficient cycles for producing homogeneous catalysts directly from electronic scrap, by- passing all final isolation and purification steps needed for the refining of precious metals. Given that the majority of industrial processes make use of industrial catalysts, the aim of this thesis project is to directly prepare heterogeneous catalysts for the total oxidation of methane from recycled Pd, avoiding the ultimate purification and isolation steps of this metal. In this work, leaching solutions from a batch of used electronic components containing Pd were used to prepare catalysts Pd based catalysts supported on y-Al2O3. Preparing catalysts from leaching solutions presents two main problems: acidity impacts the stability of the support, and the presence in solution of other elements (Ag, Cu, Fe, Ni, Pb, Sn, etc.) leads to very poor catalytic performance compared with pure Pd catalysts (1%Pd/ y-Al2O3). Different catalysts preparation strategies have been developed to overcome these two issues. In particular, a deposition-precipitation method has been employed and allows to overcome the issue of acidity. To understand the impact of impurities on the catalytic performance, model Pd and multi-metallic (Pd, Ag, Ba, Ti, Bi) based catalysts supported on y-Al2O3 have been prepared, characterized (ICP/OES, XRD, phys-N2, TEM-EDS/HAADF-STEM-EDS) and evaluated for the total oxidation of methane. After targeting the impact of major impurities, we have shown that the precise control of the pH during the impregnation allows to limit the precipitation of impurities having a negative impact on the catalytic performance, leading to a significant increase in the catalytic performance of the prepared catalysts. An alternative preparation strategy has been investigated, involving the selective extraction of Pd(II) from the leach solution using different extractants (dioctyl sulfide, N,N,N',N'- tetrahexylmalonamide) and the preparation of a catalyst directly from the extraction phase. This approach has enabled us to prepare catalysts with catalytic performances very close to those of reference catalysts, thus overcoming the problems associated with both acidity and the presence of impurities.