Solid-State Nuclear Magnetic Resonance Study of the Microporous Aluminophosphate AlPO4-41

Highly crystalline aluminophosphate molecular sieve AlPO4-41 has been synthesized using dipropylamine as the templating molecule. Materials in the as-made, calcined never rehydrated, and calcined rehydrated forms have been characterized by solid-state NMR spectroscopy using 27Al and 31P magic angle spinning (MAS), two-dimensional 27Al 5Q-MAS, and 27Al → 31P CP/MAS techniques. Both 31P MAS and 27Al 5Q-MAS spectra of the as-synthesized AlPO4-41 exhibit several resonances, all of them being assigned to framework atoms. Spectra are drastically modified after calcination. While the 31P MAS spectrum of the calcined never rehydrated solid is composed of a single broad resonance at ca. −30.5 ppm, five signals can be observed after rehydration. Rehydration slightly modifies the unit cell parameters, particularly the b axis and γ angle, but it is a completely reversible process. 27Al NMR spectroscopy shows that water preferentially coordinates one of the five nonequivalent aluminum sites of the structure and transf...