Investigation of PdZn nanoparticle formation upon the thermal decomposition of acetate precursors by in situ XRD and XAFS

The formation of metal or metal-oxide nanoparticles from four different precursor systems, including palladium(II) acetate, zinc(II) acetate, their 1: 1 mechanical mixture and the palladium-zinc bimetallic acetate complex PdZn(OCOMe)4(H2O), upon heating in a He + 5% H2 atmosphere is studied using the X-ray diffraction and EXAFS (Extended X-ray absorption fine structure) techniques in the in situ mode. X-ray diffraction is primarily used to monitor changes in the phase composition of the samples. At specific moments when qualitative changes in the composition occur, EXAFS spectra at the K-edges of Pd and Zn are also measured. Using a combination of these two techniques, a detailed sequence of the phase transformations in each of the four precursor systems is revealed. It is found that the bimetallic acetate complex and the mixture of two monometallic acetates undergo chemical reduction to form zerovalent palladium under milder conditions than zinc acetate. However, the formation of a PdZn alloy from the mixture of metal acetates proceeds with a significant diffusion barrier.