Effect of Fe/Fe2O3 loading on the catalytic activity of sulfonated single-walled carbon nanohorns for the esterification of palmitic acid

Abstract

The effect of dispersion of Fe/Fe₂O₃ nanoparticles in sulfonated single-walled carbon nanohorns (SO₃H/SWCNHs) on their catalytic activity for the esterification of palmitic acid was investigated. A gas-injected arc-in-water (GI-AIW) method was employed to initially synthesize SWCNHs dispersed with iron nanoparticles (Fe-SWCNHs). The Fe-loading amount in the Fe-SWCNHs was varied by changing the number of Fe wires inserted in an anode. The results showed that Fe-loading amount proportionally increased from 6 to 13 wt% with an increase in the number of Fe wires. The surfaces of the Fe-SWCNHs were functionalized with acid functional groups by two sequential steps: impregnation of sulphuric acid and calcination in air. From the characterization results, their acid site concentrations were estimated to be 5.6–8.5 mmol g⁻¹, suggesting that the catalyst was a solid superacid catalyst. XRD analyses indicated that most of the Fe was transformed to α-Fe₂O₃. The catalytic activity of the SO₃H/Fe-SWCNHs for the esterification of palmitic acid was evaluated to investigate the influence of the Fe-loading on their catalytic activity. The results showed that the yield of methyl palmitate was significantly enhanced by an increase in the Fe-loading amount. It was discovered that the catalytic activity and the magnetic susceptibility of SO₃H/Fe-SWCNHs can be preserved during repeated use, if the Fe-loading amount is large enough.