Resettable Heterogeneous Catalyst: (Re)Generation and (Re)Adsorption of Ni Nanoparticles for Repeated Synthesis of Carbon Nanotubes on Ni-Al-O Thin Films

Liquid-feed flame spray pyrolysis (LF-FSP) of selected metalloorganics provides [NiO]_0.25[Al₂O₃]_0.75 and [NiO]_0.5[Al₂O₃]_0.5 spinel nanopowders (NPs) without aggregation and with good stoichiometric control. Both compositions were processed to thin films as a first step in preparing Ni:Al₂O₃ nanocomposite films for catalytic synthesis of CNTs. NPs dispersed in polymer were cast giving 30 ± 10 μm green films that were debindered (370 °C), sintered at 1000-1500 °C/air, and then heated at 1000-1100 °C in H₂/N₂ 5:95 to generate Ni particles as catalyst sites. These Ni particles promote the growth of CNTs. The CNTs were then oxidatively removed coincident with regeneration of the [NiO]_1-x[Al₂O₃]_x surfaces. Thereafter, reduction, CNT syntheses, and catalyst regeneration were repeated two times more. The quality and quantity of CNTs were the same after each cycle. This represents what we believe is a new, general approach to catalyst recycling/regeneration.