Pressured hydrothermal activation on phosphorus to stabilize framework Al for better ZSM-5-based cracking catalysts

Abstract

A novel method, the pressured hydrothermal treatment was proposed to activate phosphorus species to stabilize framework Al of ZSM-5 based upon the nature of the endothermic equilibrium reaction between H2O and phosphorus species. As well as low temperature, the introduction of steam or pressured steam could effectively shift the reaction from larger condensed polyphosphate species toward smaller monomer or oligomeric phosphorus species, which were small enough to penetrate channels of ZSM-5 for consecutive stabilization on framework Al. The interaction between phosphorus species and Al was favored at elevated temperature, however too high hydrothermal treatment temperature could lead to further dealumination. It was found that the innovative pressured hydrothermal treatment could improve the distribution of phosphorus species and enhances the interaction between P and Al to enhance hydrothermal stability of ZSM-5 with more acid sites preserved, which showed higher conversion than the conventional phosphorus-impregnated samples, as well as higher yields of propylene and butenes.