Investigations on the aqueous solution and solid-state cation exchanged MAPO-ATS type molecular sieve

Abstract

MAPO-36 (magnesium substituted aluminophosphate of ATS type) have been prepared and modified by the liquid mediated cation exchange and contact induced cation exchange methods. Modified samples prepared by the liquid cation exchange (sodium/caesium/calcium-MAPO-36) and solid-state ion exchange at different temperatures (sodium-MAPO-36) were studied by XRD, SEM, FTIR, TG, BET, 27Al and 31P MAS NMR. The XRD, SEM and FTIR results indicate that the crystal structure and crystal morphology of Na/Cs/Ca exchanged MAPO-36 samples prepared by liquid cation exchange method are similar to the parent calcined MAPO-36 material. However, the crystal phase morphology and surface area are drastically affected when the sodium exchanged MAPO-36 samples are prepared by the solid-state reaction. Above 723 K and in the presence of sodium chloride, a dense tridymite phase formation from the ATS phase was observed. 27Al MAS NMR spectra of the Na/Cs/Ca MAPO-36 samples prepared by liquid cation exchange are similar to that of MAPO-36 and show characteristic peaks for tetrahedral and pentahedral coordinated Al. In the contact induced cation exchanged samples, symmetric and narrow 27Al NMR peak related to tetrahedrally coordinated Al was observed. The 31P MAS NMR of the MAPO-36 and the samples prepared by liquid cation exchange are similar but differ significantly from those samples prepared by solid-state cation exchange. The catalytic activity of the MAPO-36 and the sodium exchanged samples prepared by liquid and solid-state cation exchanges in the o-xylene conversion reaction was studied.