The effect of support material on the transesterification activity of CaO–La2O3 and CaO–CeO2 supported catalysts

Abstract

The effects of support materials—lanthanum oxide, cerium oxide, zirconium oxide, titanium oxide, γ-alumina, and ZSM-5—on the transesterification activity of CaO–La₂O₃ and CaO–CeO₂ catalysts were investigated. The metal composition and surface acidity (or basicity) of the supported catalysts played a significant role in determining the activity of the catalyst. Results showed that both catalytic activity and basicity of the supported catalysts decreased in the following order: CaO–La₂O₃/La₂O₃ ≥ CaO–La₂O₃/CeO₂ > CaO–La₂O₃/ZrO₂ > CaO–La₂O₃/γ-Al₂O₃ > CaO–La₂O₃/ZSM-5 > CaO–La₂O₃/TiO₂. In addition, leaching of Ca species from the catalyst was more pronounced with basic supports. However, Ca leaching could be minimized by coupling with La₂O₃ or CeO₂ on an appropriate support. This was verified in a flow reactor study of the CaO–CeO₂/La₂O₃ catalyst, where, over 200 h of continuous operation, the transesterification yield held constant at 88∼90% while the initial Ca concentration in the product decreased from 194 ppm to below 5.0 ppm after 144 h. This further suggests that Ca leaching had little long-term effect on the overall FAME activity of the catalyst.