Cobalt and Nickel\nNanocatalysts Confined inside Halloysite\nNanotubes for Selective Hydrogenations

Innovative cobalt and nickel catalytic materials containing\nmetal\nnanoparticles immobilized into the inner tubes of pristine halloysite,\na naturally occurring nanoclay, and their application in hydrogenation\nreactions of a large variety of substrates from biomass and industrial\nwastes are described herein. The catalytic materials with a high metal\nloading (>24 wt %) were prepared by a one-pot two-step procedure\nin\nthe absence of additional stabilizers, leading to metal nanoparticles\nessentially confined into the support lumen (constituted of aggregates\nof small nanoparticles) as a result of the privileged electrostatic\ninteractions between aluminols and metal acetate salts [Ni(OAc)<sub>2</sub> and Co(OAc)<sub>2</sub>]. Both catalytic materials, <b>Ni/Hal</b> and <b>Co/Hal</b>, gave different chemoselectivities\ntoward the reduction of unsaturated functional groups (carbonyl, CC,\nand nitrile) under solvent-free conditions, thus affording selectively\nvalue-added compounds depending on the nature of the metal. In particular,\nthe squalene hydrogenation monitoring permitted identification of\nthe partial hydrogenated products and estimation of the partial turnover\nnumbers and frequencies, achieving a cumulative TON of 110 and TOF\nof 151 h<sup>–1</sup> using the most active catalytic system,\ni.e., <b>Ni/Hal</b>.