Microwave-assisted catalytic pyrolysis of microalgae over a composite catalyst of HZSM-5/BC for nitrogen-containing chemicals

Microalgae with high nitrogen content are conducive to preparing nitrogen-containing chemicals. The robust methods for enhancing the yield and selectivity of the target product are crucial. In this study, microwave-responsive composite catalysts were synthesized via hydrothermal growth using HZSM-5 as the active components and SiC or biochar (BC) as microwave absorbers. The product distribution and selectivity under various catalytic conditions were investigated, and a temperature sensitivity analysis was conducted. Results showed that the composite catalyst HZSM-5/BC exhibited the richest pore structure, highest specific surface area, and strongest microwave absorption ability, achieving the highest bio-oil yield of 54.65 % at 550 °C. Compared with HZSM-5 and BC separately in nitrogen-containing compound yields, HZSM-5/BC composite catalyst boosted the yield by 13.83 % and 16.12 %, respectively, to 58.73 %. Its nitrile selectivity was 25.07 %, 3.5 and 4.5 times higher than HZSM-5 and BC. The HZSM-5/BC catalyst, with its well-developed porous structure and high microwave-absorbing capacity, couples effectively with the in-situ microwave-catalytic system to collectively enhance energy absorption and catalytic efficiency. This integrated system efficiently converts biomacromolecules into valuable nitrogenous chemicals, including N-heterocycles and nitriles, through reactions such as Maillard and ring-opening. These advantages collectively lay a solid foundation for the continuous industrial production of high-value nitrogen-containing chemicals from microalgae.