Metal(II) formates (M = Fe, Co, Ni and Cu) stabilized by tetramethylethylenediamine (tmeda): Convenient Molecular Precursors for the Synthesis of Supported Nanoparticles

gamma-Alumina supported 3d transition-metal nanoparticles are commonly used catalysts for several industrial reactions, such as Fischer-Tropsch, reforming, methanation, and hydrogenation reactions. However, the activity of such catalyst is often limited by the low metal dispersion and a high content of irreducible metal, inherent to the conventional preparation methods in aqueous phase. In this context, we have recently shown that [{Ni(mu(2)-OCHO)(OCHO)(tmeda)}(2)(mu(2)-OH2)] (tmeda=tetramethylethylenediamine) is a suitable molecular precursor for the formation of 1-2 nm large nanoparticles onto alumina. Here, we explore the synthesis of the corresponding Fe, Co, and Cu molecular precursors, namely [{Fe(mu(2)-OCHO)(OCHO)(tmeda)}(4)], [{Co(mu(2)-OCHO)(OCHO)(tmeda)}(2)(mu(2)-OH2 )], [Cu(kappa(2)-OCHO)(2)(tmeda)], which are, like the Ni precursor, soluble in a range of solvents, rendering them convenient metal precursors for the preparation of supported metallic nanoparticles on gamma-alumina. Using a specific adsorption of the molecular precursor on gamma-alumina in a suitable organic solvent, treatment under H-2 provides small and narrowly distributed Fe (2.5 +/- 0.9 nm), Co (3.0 +/- 1.2 nm), Ni (1.7 +/- 0.5 nm), and Cu (2.1 +/- 1.5 nm) nanoparticles. XAS shows that the proportion of MAl2O4 (M = Co, Ni, Cu) is small, thus illustrating the advantage of using these tailor-made molecular precursors.