Synthesis of Acid–Base Bifunctional Catalysts by In Situ Growth of Co-LDH Nanosheets on HY Zeolite To Enhance Co(OH)x Utilization for Microalgal Lipid Conversion

To improve Co-LDH nanosheet utilization in catalytic conversion of microalgal lipids to biodiesel, an efficient bifunctional catalyst with synergetic acid and base sites was synthesized by in situ growth of Co-LDH nanosheets on HY zeolite. The bifunctional catalyst with a molar ratio of Co-LDH nanosheets to HY zeolite at 4 exhibited synergistic catalysis of acid sites in the HY zeolite and base sites Co(OH)x (x = 2, 3) in the Co-LDH nanosheets, which promoted esterification of free fatty acids and transesterification of triglycerides in microalgal lipids. Co-LDH nanosheets were dispersed on the HY zeolite surface through generated Si–O–Co bonds to enhance Co(OH)x (x = 2, 3) utilization, while the specific surface area of the catalyst increased from 107.9 m2/g (Co-LDH) to 272.5 m2/g. Therefore, the optimal catalyst promoted conversion efficiency from 87.8 to 96.1%, and the conversion efficiency remained at 87.6% after six reusability cycles.