Elucidating and Controlling Reaction Pathways for 2-Methylfuran Aromatization Using Bifunctional Zeolite Catalysts

Understanding and controlling the reaction pathways is pivotal in achieving heightened selectivity for aromatics from catalytic pyrolysis of biofurans. Herein, liquid nitrogen quenching-dissolution-extraction and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) techniques were employed to elucidate the mechanistic pathways for converting 2-methylfuran (MF) into aromatics. Bifunctional HZSM-5 catalysts were developed to regulate aromatic selectivity. Key intermediates identified in the conversion of MF to aromatics over HZSM-5 include olefins, dimethylbenzofuran (DBF), and 2-cyclopenten-1-ones (CPOs). Three possible pathways for MF aromatization were discovered: (1) MF cracks into olefins that polymerize into aromatics; (2) MF oligomerizes into DBF, then decarbonizes to form alkylbenzenes, dominant at low temperatures; (3) MF forms CPOs, which deoxygenate to benzene and alkylbenzenes─the most significant pathway. Introducing metal oxides (Fe, Mo, and Zn) into zeolites alters the Brønsted to Lewis acid ratios, positively correlating with CPO content, resulting in increased aromatic selectivity and decreased coke formation. These findings can provide new insights into the reaction pathways of biofuran aromatization and the critical issues of catalytic pyrolysis of biomass, such as rational design of improved zeolite catalysts.