Novel supported catalytic materials based on multiwalls carbon nanotubes

In this work is presented a method that allows proper control of the nanoscale curvature of the external surface in multiwall carbon nanotubes (MWCNT), and shown its effect on the properties of Ni/MWCNT catalyst. After removal of residual nickel by treatment with HNO₃ the external surface of parent CNT's was decorated with 15-17 nm nanoparticles of CaCO ₃ (25 wt.%) by carbonization of deposited Ca-nitrate. The followed partial catalytic air-combustion of CNT's at conversions 30-50% modified the morphology of their walls. After removal of CaCO₃ catalyst by treatment of the CNT's surface with HNO₃ the modified nanotubes were decorated with metallic nickel by sonochemical deposition. The partial combustion of carbon constituting the CNT walls catalyzed by CaCO₃ nanoparticles converts their structure from parallel grapheme layers to aggregates formed by grapheme onions with diameter of 5-12 nm. The nickel nanoparticles were located exclusively at the onions tops due to increasing the energetic barrier for metal adatoms (clusters) surface diffusion. It decreased the Ni crystal size from 8 to 2 nm at similar loadings of 50-60 wt.% and increased the catalytic activity in hydrogenation of chloroacetophenone more than twice.