Synthesis and catalytic application of palladium nanoparticles supported on kaolinite-based nanohybrid materials.

Palladium nanoparticles (PdNPs) were deposited on the surface of the modified clay mineral, kaolinite. To improve compatibility, abundance and control of the size of the nanoparticles, kaolinite was modified by the grafting of an amino alcohol (triethanolamine (TEA)) and an ionic liquid (1-(2-hydroxyethyl)-3-methylimidazolium (ImIL)). Characterization techniques (XRD, TGA, solid state (13)C NMR and FTIR spectroscopy) confirmed the effective grafting of these compounds on the internal surface of kaolinite. After the synthesis of PdNPs onto clay particles, TEM allowed the visualization of abundant PdNPs with sizes ranging from 4 to 6 nm, uniformly distributed onto the platelets of modified kaolinite. Unmodified clay showed low abundance and random distribution of the nanoparticles. The catalysts obtained were effective for the catalytic reduction of 4-nitrophenol (4-NP), the material with TEA being the most effective. These materials have exhibited excellent performance during the Heck and particularly the Suzuki-Miyaura coupling reactions, with reaction yields up to 100%. These catalysts showed a very slight loss in activity for three consecutive catalytic cycles (less than 10% decrease of the activity compared to the first cycle). This was an evidence that the prior grafting modification of kaolinite helps in significantly improving the quality of the synthesized NPs and also promotes their strong attachment onto the clay mineral surface.