Role of the Al source in the synthesis of aluminum magadiite

The role of the aluminum source on the insertion of Al in the silicate layers during the hydrothermal crystallization of magadiite (NaSi7O13(OH),4H2O), a lamellar silicate, was investigated. Three aluminum sources were compared: aluminum isopropoxide, aluminum sulfate and aluminum hydroxide We observed that aluminum isopropoxide leads to the presence of mordenite impurities, aluminum sulfate to an only partial insertion of aluminum, whereas aluminum hydroxide allows preparing at 150°C in 3days, well crystallized Al–magadiite samples with Si/Al ratios of 20 or 40. Characterization by 29Si and 27Al NMR of the Al–magadiite samples obtained with aluminum hydroxide as Al source indicates that the samples retain the main characteristics of magadiite and all the aluminum atoms are in tetrahedral substitution in the silicate framework. The presence of acid sites is evidenced by the activities of these samples in cumene cracking, a model reaction for strong Brønsted acidity. Well crystallized rosette-shaped Al–Magadiite particles (SEM), with all Al atoms in Td substitution in the silicate layers (27Al NMR) up to Si/Al=20 can be obtained within 3days of hydrothermal treatment at 150°C, provided that the appropriate aluminium source (Al(OH)3) is used. This lamellar aluminosilicate shows Brønsted acid properties which is promising for its use as starting material for the preparation high surface area acidic supports. [Display omitted] ► Effect of the nature of the Al precursor on the crystallization of Al–magadiite. ► Well crystallized Al–Magadiite (Si/Al=40 and 20) in 3days at 150C using Al(OH)3. ► Brønsted acid sites evidenced by cumene cracking.