Fixed- and fluidised-bed synthesis of coiled carbon fibres on an in situ generated H2S-modified Ni/Al2O3 catalyst from a NiSO4/Al2O3 precursor

NiSO4/Al2O3 and NiO/Al2O3 catalyst precursors were formed by calcination of NiSO4·6H2O/Al2O3 at 500 and 800 °C, respectively. The catalyst precursor was reduced under H2 and N2 and then reacted under C2H2, H2 and N2 at 650 °C. Coiled carbon fibres were formed in fixed- and fluidised-bed reactors using the NiSO4/Al2O3 catalyst precursor. Thermodynamic modelling using an infinite equilibrium stage construction predicted complete reduction of NiSO4 to Ni and simultaneous H2S formation occurs in both fixed- and fluidised-bed systems. XRD measurements confirmed that Ni was the only catalytically active crystalline species present at concentrations >0.5 wt.% (XRD detection limit) post-reduction, however XRF and XPS measurements additionally detected the presence of small quantities (<0.9 wt.% S) of S species. S is adsorbed onto the Ni surfaces during reduction when H2S is released and dissociates on the Ni surface. Non-coiled carbon fibres produced on the Ni/Al2O3 catalyst formed from the NiO/Al2O3 precursor demonstrated that modification of Ni/Al2O3 with S is required for coiled carbon fibre synthesis.