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

The promotional effects of phosphorous modification on ZSM-5 zeolites by phosphorus oxyacids (H 4 P 2 O 7 , H 3 PO 4 , H 3 PO 3 , and H 3 PO 2 ) 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 27 Al, 31 P, and 29 Si MAS NMR. With H 3 PO 2 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.