Coupling ZnO nanoparticles and Zn single atoms anchored on N-doped carbon nanocomposite for microalgal lipids conversion

A bifunctional ZnO/Zn-NC catalyst coupling ZnO nanoparticles and Zn single atoms anchored on N-doped carbon nanocomposite was synthesized through breaking saturated Zn-N4 structures of zeolitic imidazolate frameworks (ZIF-8) to facilitate microalgal lipids conversion. DFT calculations showed that ZnO nanoparticles and Zn (single atoms)-N2 sites in ZA-400 catalyst, which was derived from calcination of ZIF-8 at 400 °C, reduced energy barrier of esterification by 0.50 eV and 0.38 eV compared with Zn-N4 site, respectively. Methanol reactant exhibited stronger activation and deprotonation ability on pyridinic nitrogen and lattice oxygen. The ZA-400 catalyst with an increased Lewis acidity (3.209 mmol/g) and basicity (0.592 mmol/g) exhibited a high conversion efficiency of 98.1% in microalgal biodiesel production.