Modification of H-ZSM-5 zeolites with phosphorus. 1. Identification of aluminum species by 27Al solid-state NMR and characterization of their catalytic properties

Aluminum species in P-ZSM-5 zeolites were identified and quantified using 27Al MAS and MQMAS NMR methods. Samples containing between 0% and 15% P2O5 were studied after calcination or calcination followed by steaming. In addition to the tetrahedral framework aluminum, Altet-f, and the octahedral aluminum, Aloct, we also observed significant quantities of highly distorted aluminum with tetrahedral coordination, Altet-dis, and octahedrally coordinated aluminum in aluminum phosphate, Aloct-O-P. Furthermore, small quantities of the pentahedrally coordinated species Alpent-O-P were seen in samples with high phosphorus content. There was a good correlation between the amount of framework aluminum and acidity measured by TPD of n-propylamine. In contrast, the aluminum phosphate was shown to be catalytically inactive both by acidity measurements and catalytic tests.