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

Biodiesel, a renewable liquid fuel, is undergoing eco-transition in catalyst research and development. Calcium oxide (CaO) was 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 esters (FAMEs) 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 keeps 71.4% of the original activity. Thermogravimetric and in-situ Fourier Transform Infrared Spectroscopy analysis 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 lattice compression of CaO nanoparticles on La2O3, which imparts the CO2/H2O-proof property to 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.