Acidity-controlled hollow HZSM-5 for lignite pyrolysis volatiles valorization to light aromatics

Abstract

The hollow HZSM-5 (HZ5) was evaluated for catalyzing reforming of lignite volatiles into light aromatics (LAs), with special emphasis on the effect of catalyst acidity. Hierarchical HZ5 variants with diverse cavity volumes and mesopores in the shell were synthesized using varying concentrations of TPAOH and TPABr. The results revealed that the desilication-recrystallization induced a reconfiguration of catalyst acidity by TPA+ and OH–, leading to increased Brønsted acid sites (BAS) and accessibility to outer surface acids. The resulting hollow zeolites, featuring elevated BAS, notably enhanced LAs yield, particularly benzene among monocyclic aromatic hydrocarbons, while decreasing oxygenates in the liquid product. Notably, correlation coefficients between LAs yields and catalyst physical properties underscored the dominance of catalyst acidity, especially BAS, as the key driver for increased LAs formation compared to mesoporous volume.