Phosphorus modified hierarchically structured ZSM-5 zeolites for enhanced hydrothermal stability and intensified propylene production from 1-butene cracking

Abstract

Hierarchically structured ZSM-5 zeolites (HSZ) were synthesized by a mesoporogen-free procedure and subsequently modified with varied amounts of phosphorus (1–3 wt%) through impregnation of phosphoric acid solution. Materials characterization using various techniques showed that the hierarchical structures of HSZ were well preserved after phosphorus modification, and more interestingly, their hydrothermal stability were improved significantly and the main textural properties kept almost unchanged even after hydrothermally treated at 750 °C for 4 h in 100% steam. The strong acid sites of HSZ were found to be gradually eliminated by the phosphorus induced dealumination of tetrahedral framework aluminum (TFAL), however, weak acid sites remained almost intact. In the 1-butene cracking reactions, benefitting from the auxiliary mesopores and phosphorus modification, P-modified HSZ showed remarkably improved selectivity (∼52%) and yield (∼43%) of propylene as well as superior anti-deactivation ability. All these properties of P-modified HSZ made it a promising catalyst for industrial application.