Chemical simulation of high-performance CaO/La2O3 catalysts and their CO2/H2O resistance during biodiesel production

Abstract

Biodiesel, a renewable liquid fuel, is undergoing eco-transition in catalyst research and development. Calcium oxide (CaO) is a widely studied heterogeneous catalyst due to its considerable activity. However, the poor stability of CaO during storage in air, especially by CO₂ and H₂O poisoning, presents a challenge. This research successfully developed a high-activity CaO/La₂O₃ catalyst for biodiesel production with CaO nanoparticles well-dispersed on the La oxide support (Ca/La = 0.12). Under mild reaction conditions, a fatty acid methyl ester (FAME) yield of 96.9% was achieved. After exposure to air for two weeks, the CaO/La₂O₃ (Ca/La = 0.12) catalyst absorbed 49% less CO₂ and 91% less water than pure CaO and retained 71.4% of the original activity. Thermogravimetric and in situ Fourier transform infrared spectroscopy analyses reveal that CO₂ and H₂O will preferentially be captured by La oxides and keep the supported CaO active sites safe. DFT calculations confirmed that CO₂ and H₂O adsorption on CaO terrace sites became an unfavoured process due to the lattice compression of CaO nanoparticles on La₂O₃, which imparts the CO₂/H₂O-proof property to the CaO/La₂O₃ catalyst. Methanol adsorption, dissociation, and migration pathways on CaO/La₂O₃ that produce active methoxy anions at Ca–La interfaces were identified as key steps in achieving efficient catalytic reactions.