Modification of H-ZSM-5 zeolites with phosphorus. 2. Interaction between phosphorus and aluminum studied by solid-state NMR spectroscopy

A suite of one- and two-dimensional solid-state NMR methods was used to follow the complex structural changes in different types of phosphorus species in P-ZSM-5 zeolites that were generated upon treatment of H-ZSM5 zeolites with 0–15% P2O5, followed by calcination or calcination and steaming. Through space and through bond 27Al–31P correlations were used for the first time to study the interaction of phosphorus with the aluminum species. Homogeneous impregnation of phosphorus inside the zeolite channels was observed even at low concentrations. In the calcined samples, the 31P resonances were assigned mainly to orthophosphates, short chain polyphosphates and condensed phosphates. These species were converted into various types of aluminum phosphates with steaming and with the increase in P content. The mechanisms of formation of phosphates and aluminum phosphates are proposed.