Orthovanadate intercalated CuFe-LDO catalyzed hydrothermal liquefaction of microalgae for low nitrogen bio-oil production

Hydrothermal liquefaction (HTL) of microalgae for bio-oil production is a promising strategy to avoid extensive fossil fuel utilization, while tandem amidation and Maillard reactions during hydrolysis of cellular compounds unavoidably result in formation of nitrogen containing (N-containing) compounds, reducing quality of bio-oil. Accordingly, VO43− intercalated Cu–Fe layered double oxides named as Cu2Fe-VO4-LDO is firstly synthesized to both catalyze hydrolysis of cellular compounds and block N-containing compounds formation. The results indicate Cu2Fe-VO4-LDO can improve bio-oil yield from 19.32 to 20.32 wt%, with decrease of N/C ratio from 0.70 of control to 0.67 of experimental group, and increase of H/C ratio from 0.129 to 0.132. The insert of VO43− provides more strong-acid sites, which are beneficial to hydrolysis of cellular compounds. Meanwhile, more strong-base sites of Cu2Fe-VO4-LDO promote decarboxylation of fatty acids and removing amino-group of amino acids, subsequently improve production of alkanes. Furthermore, the reversible oxidation of VO43− promotes oxidation of reducing sugars, blocking tandem amidation and Maillard reaction between intermedia of hydrolyzed lipids, carbohydrates, and proteins. This work reports a methodology for synthesis of Cu2Fe-VO4-LDO with strong acid-base sites and reversible oxidize interlayer sites, providing a strategy to simultaneously improve bio-oil yield and reduce its N/C ratio.