FeCl3·6 H2O/CF3COOH deep eutectic solvent-modified USY zeolite for catalytic upgrading of coal pyrolysis volatiles

To achieve efficient upgrading and clean utilization of lignite-derived tar, an integrated zeolite modification strategy based on deep eutectic solvents (DESs) was developed, in which a Fe-based DES system was constructed with FeCl 3 ·6 H 2 O and CF 3 COOH. This DES realized the simultaneous acid modification and metal incorporation of ultrastable Y (USY) zeolite, thereby simplifying the catalyst preparation process. Characterization results revealed that DES treatment at an optimal molar ratio of 1:9 preserved the structural integrity of the Faujasite framework while inducing a hierarchical “micropore-sacrifice/mesopore-compensation” architecture. Meanwhile, Fe species were introduced uniformly, leading to the reduction of Brønsted acid sites and the enhancement of Lewis acid sites, thereby constructing multifunctional catalytic centers with synergistic acidity and redox activity. Mechanistic analysis demonstrated that DES-induced mesoporosity enhanced mass transfer and diffusion, while the cooperation between Fe redox sites and Lewis acid sites facilitated C-C and C-O bond cleavage as well as aromatization reactions. In the fixed-bed pyrolysis of NMH lignite, the optimized catalyst exhibited superior catalytic performance: the light oil fraction in tar increased from 16.86 % to 27.94 %, the relative content of light tar reached 75.61 %, gas yield reached 21.53 %, and PAHs content dropped sharply. Furthermore, the catalyst was confirmed to possess superior reusability in successive runs. This study highlights DES as tunable functional media, serving as an efficient platform for the integrated regulation of zeolite structure, acidity, and activity. Consequently, it provides a novel strategy for fabricating high-performance modified molecular sieve catalysts, which are applicable to the clean and value-added conversion of coal pyrolysis tar.