Is hydrolysis a bad news for p-xylene production from 2,5-dimethylfuran and ethylene? Mechanism investigation into the role of acid strength during 2,5-hexanedione conversion

DMF hydrolysis is not scaring, but further condensation of HDO over strong acid sites is the intrinsic cause for loss in PX selectivity and carbon balance. [Display omitted] •Acid strength exhibits a significant influence on PX selectivity.•DMF hydrolysis to HDO is not the intrinsic cause for decrease in PX selectivity.•Condensation of HDO over strong acid sites results in loss of PX selectivity.•The process starting with HDO and ethylene for PX production is investigated.•Reducing strong acid site amount helps to improve PX selectivity. Although a precise understanding of acid strength would be essential to elucidate the reaction mechanism and boost the catalytic activity, it is still severely deficient during p-xylene (PX) production from 2,5-dimethylfuran (DMF). Herein, a series of metal phosphate catalysts featuring varied acid strength are prepared and afford an ideal platform. A combination study including kinetic analysis, converting pathway investigation and isotopic labelling experiments reveal the reversible reaction between DMF and 2,5-hexanedione (HDO) and the vital role of strong acid sites during the further conversion of HDO. DMF hydrolysis to HDO is not the intrinsic cause for decrease in PX selectivity, but further condensation of HDO over the strong acid sites is to blame. It destroys the equilibrium state of the reversible reaction and leads to loss in PX selectivity and carbon balance. Besides, the process starting with HDO and ethylene for PX production and strategies to improve PX selectivity have also been proposed. This work provides a much deeper insight into the crucial role of acid strength, which would be constructive for rational design of new catalysts and the corresponding mechanistic understanding.