Formation of metal clusters in halloysite clay nanotubes

<p>We developed ceramic core-shell materials based on abundant halloysite clay nanotubes with enhanced heavy metal ions loading through Schiff base binding. These clay tubes are formed by rolling alumosilicate sheets and have diameter of <i>c</i>.50 nm, a lumen of 15 nm and length ~1 μm. This allowed for synthesis of metal nanoparticles at the selected position: (1) on the outer surface seeding 3–5 nm metal particles on the tubes; (2) inside the tube’s central lumen resulting in 10–12 nm diameter metal cores shelled with ceramic wall; and (3) smaller metal nanoparticles intercalated in the tube’s wall allowing up to 9 wt% of Ru, and Ag loading. These composite materials have high surface area providing a good support for catalytic nanoparticles, and can also be used for sorption of metal ions from aqueous solutions.</p

Core/Shell Ruthenium–Halloysite Nanocatalysts for Hydrogenation of Phenol

Halloysite tubular nanoclay was applied as a template for synthesis of ruthenium core–shell composite catalysts for the first time; 50 nm diameter ceramic tubular systems with metal seeded interiors were produced. The procedure for the metal deposition and prior halloysite modification had a significant influence on properties of the catalyst and, as a consequence, on its activity in hydrogenation of phenol. Cyclohexanol was the main reaction product, but its yield depended on the substrate conversion and nanoarchitectural composition of the catalysts used. The maximum catalytic activity (turnover frequency, TOF) achieved was 17 282 h^–1 in terms of hydrogen uptake per surface Ru atoms. The substrate selectivity of halloysite-based catalysts was also demonstrated at the comparative hydrogenation of phenol and various cresols