Catalytic activity enhancement of sulfated metal oxide by doping Co on MIL-100(Fe) for esterification

Sulfated metal oxides are widely used in catalyzing esterification for biodiesel production due to their low corrosivity and easy separation. While, the catalytic stability is still a challenge on account of active site leaching during successive batch experiments. To this end, the typical metal organic frameworks, MIL-100(Fe) doped with Co was adopted to load ammonium sulfate ((NH 4 ) 2 SO 4 ) for stable heterogeneous acid preparation, which was employed to catalyze the esterification of methanol and oleic acid. Influence of preparation factors of (NH 4 ) 2 SO 4 loading amount and activation temperature on catalytic activity were initially evaluated. Furthermore, to elucidate the effect of Co doping, catalysts were characterized by TG, XRD, FTIR, nitrogen adsorption–desorption, Py-FTIR, XPS, SEM and NH 3 -TPD. Results indicated that the maximum esterification conversion of 92.56 % was achieved by MS(Fe/Co) with molar ratio of methanol to oleic acid of 8:1 and catalyst amount of 8 wt% at 70 °C in 2 h. In comparison to MS(Fe), Co doping significantly improved the stability, where the catalytic activity of MS(Fe/Co) was increased by 20 % at the fifth cycle. The activation energy and pre-exponential factor of esterification catalyzed by MS(Fe/Co) were also calculated as 42.06 kJ/mol and 5.24 × 10 5 min −1 . This study provides a feasible way to enhance the catalytic stability of heterogeneous acid for biodiesel production.