Solvothermal synthesis and structural relations among three anionic aluminophosphates; catalytic behaviour

Abstract

Three microporous aluminophospates with Al/P ratios of 1 ∶ 1, 2 ∶ 3, and 1 ∶ 2 have been solvothermally synthesized. (NH₄)_{2 − x}(H₃O)_xAl₂(PO₄)₂(OH)₂ (I) and (NH₄)₃Al₂(PO₄)₃ (II) have 3D structures and exhibit nets of three-dimensional intersecting channels: (NH₄)₃Al(PO₄)₂ (III) is a very open layered material with 12R windows. Ammonium cations compensate for the negative charges of the three frameworks. Compounds I and II are very active and selective heterogeneous solid catalysts for the Friedel-Crafts acylation and acetalization reactions, the latter showing an effective protection of aldehydes by formation of the corresponding dimethyl acetals. Both catalysts are stable in water and organic solvents and can be recovered and reused at least four times without loss of reactivity. They maintain their respective structures after being recovered.