Effect of acid treatment on the surface of multiwalled carbon nanotubes prepared from Fe–Co supported on CaCO3: Correlation with Fischer–Tropsch catalyst activity

Abstract Carbon nanotubes (CNTs) were obtained through the catalytic decomposition of C 2 H 2 at 700 °C over Fe–Co supported on CaCO 3 and confirmed by TEM to be composed of multiwalled carbon nanotubes. The CNTs were refluxed in 30% and 55% HNO 3 for 2 and 6 h in order to remove impurities and introduce oxygen surface groups. This rendered the CNTs less hydrophobic. The morphology, microstructure, surface area, pore volume and surface chemical properties of the acid treated CNTs were analysed by TEM, N 2 physisorption, TGA, FTIR, Raman spectroscopy and zeta potential measurements. The surface roughness, together with the degree of surface functionalization correlated with the harshness (time and concentration) of the acid treatment. Fischer–Tropsch synthesis studies (275 °C, 8 bar) were performed on all the Fe loaded (10%)/CNT catalysts and activity studies revealed that the more severe the acid treatment the higher the activity of the catalysts.