Enhanced hydroxyl bridge-mediated microalgal lipid conversion via mixed-valence Zr/Ce-MOF-808 catalysts at reduced temperatures

Abstract

Considering the rapid growth and high oil content of microalgae, biodiesel production from microalgal oil is a key technology to address declining crude oil resources and environmental pollution. To enhance the low-temperature activity of Zr based metal–organic framework (Zr-MOFs), we employed a simple and versatile one-pot synthesis approach to fabricate mixed-valence Ce-doped MOF-808 with enhanced bridging hydroxyl groups, for the conversion of microalgal lipids at significantly reduced temperatures. Density functional theory calculations revealed that successful doping of Ce(III) ions facilitated electronic delocalization of neighboring atoms in Zr/Ce-MOF-808, lowering the activation temperature of methanol and forming a unique electron-rich bridging hydroxyl structure, thereby greatly enhancing low-temperature activity. Compared to pristine MOF-808, Zr/Ce (1 : 1)-MOF-808 exhibited a catalytic conversion efficiency increase from 8.34% to 89.51% at 100 °C, significantly reducing reactor pressure from 4036 kPa at 200 °C to 352 kPa at 100 °C. With indirect contact established between the catalyst's metal centers and reactants, the catalyst demonstrated only a 3% decrease in conversion efficiency after five cycles of use.