Catalytic hydrothermal liquefaction of spirulina to bio-oil in the presence of formic acid over palladium-based catalysts

This paper reports our investigation of the catalytic hydrothermal liquefaction (HTL) of microalgae spirulina to bio-oil. Palladium-based catalysts Pd/HZSM-5@meso-SiO₂ (Pd/HZSM-5@MS) and Pd/HZSM-5 were synthesized. X-ray diffraction analysis, scanning electron microscopy, and transmission electron microscopy were used to characterize the catalysts that were applied to the HTL of algae in the presence of formic acid. Elemental analysis and gas chromatography–mass spectrometry were used to analyze the resulting bio-oil. The characterizations indicated that the Pd/HZSM-5@MS-catalyzed HTL had a high bio-oil yield of 37.30% and a low coke yield of 8.56%, and that the obtained bio-oil contained no acids. Furthermore, this study suggests that Pd/HZSM-5 promoted hydrodenitrogenation of the bio-oil and that Pd/HZMS-5@MS promoted hydrodeoxygenation of the bio-oil. Catalyst recycling and the performance of the recycled catalyst were also investigated and discussed.