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

Abstract

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.

Challenging thermodynamics: combining immiscible elements in a single-phase nano-ceramic

“…The “encapsulated exsolution” yielded small Ni nanoparticles of 8.7 nm (Fig. 5e ), dramatically smaller than the Ni nanoparticles generated by conventional exsolution from various spinel and perovskite materials (>30 nm) 40 – 43 . III.…”