Phosphorus promotion on hydrothermal stability of ZSM-5 by P precursors with different molecular sizes

Abstract

The promotional effects of phosphorous modification on ZSM-5 zeolites by phosphorus oxyacids (H4P2O7, H3PO4, H3PO3, and H3PO2) with different molecular sizes were investigated with catalytic cracking of n-tetradecane as the probe reaction. It was verified that the diffusion of P precursor molecules into ZSM-5 channels was important to prevent aggregation of P species for better stabilization on tetra-coordinated framework aluminum. Meanwhile, the P–Al interaction was proposed based on results of 27Al, 31P, and 29Si MAS NMR. With H3PO2 as the P precursor, easy diffusion into ZSM-5 channels contributed to less formation of polyphosphates, homogeneous distribution of P species, better reserved crystallinity, microporous area and acidic sites for improving cracking performance of n-tetradecane.