Mesoporous Metal Catalysts Templated on Clay Nanotubes

Halloysite is a natural tubular aluminosilicate clay of ca. 50 nm diameter and 0.5-1.5 micrometers in length. The nano-architectural modification of halloysite inner/outer surfaces can be achieved through supramolecular and covalent interactions exploiting its different inside/outside chemistry (Al2O3/SiO2). The tubular morphology makes halloysite a prospective nano-template for core-shell structured mesoporous catalysts. Catalytic metals can be incorporated on the nanotubes' outer surface or in the inner lumens with selective metal binding. 2-5nm diameter Au, Ag, Pt, Pd, Co, Ru, Cu-Ni, Fe2O3, CoxBy, CdS, and CdxZn1-xS particles were templated on halloysite. In this work, CdS and Ru-containing halloysite based nanocatalysts were synthesized via modification with organic ligands and microwave-assisted wetness ion impregnation. The catalytic hydrogenation of benzene and its homologues as well as phenol was performed. The impacts of the core-shell architecture, the metal particle size and seeding density were optimized for high reaction efficiency. An efficient Co-halloysite catalyst was formed using azines as ligands, and it contained 16 wt.% of cobalt with hydrogen evolution rate of 3.0 L/min x g(cat). The mesocatalysts produced are based on a safe and cheap natural clay nanomaterial and may be scaled-up for industrial applications.