MgAl-LDH/LDO-Catalyzed Hydrothermal Deoxygenation of Microalgae for Low-Oxygen Biofuel Production

High oxygen content of microalgae-derived bio-oil limits their direct use in modern motors. In this study, instead of noble metal-catalyzed two-step hydrodeoxygenation, MgAl layered double hydroxides/oxides (MgAl-LDH/LDO) with tunable acidic and basic properties are developed for catalyzing the hydrothermal liquefaction (HTL) of microalgae to obtain bio-oil with a low oxygen content. The results show that both MgAl-LDH3 and MgAl-LDO3 enhance low O/C bio-oil production through catalyzing both the hydrolysis of cellular compounds and decarboxylation and decarbonylation of biocrude during HTL of microalgae. MgAl-LDH3 with more acidic sites is more effective at catalyzing the hydrolysis of cellular compounds than MgAl-LDO3 according to the relative increases of 12.98% and 9.72% of biocrude yields, respectively. However, MgAl-LDO3 with more basic sites is more efficient in catalyzing the decarboxylation and decarbonylation and amidation of fatty acids to form hydrocarbons, esters, alcohols, and amides, which contributes to a 22.6% decrease of O/C and 28.4% increase of N/C in the bio-oil product, respectively. This work reveals that MgAl-LDHx and MgAl-LDOx are efficient at catalyzing not only the hydrolysis of cellular compounds but also the deoxidation of the reaction intermediates to produce low O-containing bio-oil, which might pave the way for its direct use in modern motors.

Automated summary

The study found that MgAl-LDH3 and MgAl-LDO3 are effective catalysts in reducing the oxygen content in bio-oil during hydrothermal liquefaction, with MgAl-LDH3 more efficient in catalyzing the hydrolysis of cellular compounds and MgAl-LDO3 more efficient in catalyzing decarboxylation and decarbonylation reactions to produce hydrocarbons, esters, alcohols, and amides.