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

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 alpha-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 Feloading amount. It was discovered that the catalytic activity and the magnetic susceptibility of SO3H/FeSWCNHs can be preserved during repeated use, if the Fe-loading amount is large enough.