Microporous and Mesoporous Materials 22 ( 1998) 211–224 Stability of mesoporous aluminosilicate MCM-41 under vapor treatment, acidic and basic conditions1 D. Trong On, S.M.J. Zaidi, S. Kaliaguine * Department of Chemical Engineering, Laval University, Ste-Foy, Que ´bec G1K 7P4, Canada Received 24 November 1997; received in revised form 12 February 1998; accepted 16 February 1998 Abstract The coordination state of aluminum in relation to the stability of mesoporous aluminosilicate MCM-41 following various treatments (vapor treatment and treatment in solution at different pH ) is characterized using XRD, MAS NMR and BET techniques. As a result of the treatment with water vapor at 723 K, five-coordinated aluminum is observed in unusually large proportion in mesoporous Al-MCM-41. This coordination is stable under dehydration conditions. The amount of five-coordinated aluminum species can be controlled by varying the vapor treatment time without essentially damaging the MCM-41 structure. In contrast, upon treatment in solution, the state of aluminum coordination as well as the stability depend strongly on pH and treatment time. Moreover, amorphous aluminosilicate containing simultaneously four- and five-coordinated aluminum species can also be prepared from Al-MCM-41 without the formation of octahedral aluminum species. © 1998 Elsevier Science B.V. All rights reserved. Keywords: Mesoporous molecular sieves, stability of; MCM-41; Aluminosilicates; Penta-coordinated aluminum 1. Introduction array of uniform mesopores with pore diameter ranging between 15 and 100 A ˚ , depending on the template and synthesis conditions. The presence Aluminosilicates, such as zeolites, are widely used catalysts in acid-catalysed reactions for the of these very large uniform pores combined with acidic properties opens new possibilities in the production of petrochemicals and fine chemicals. Recently, the new family of mesoporous alumino- catalytic conversion of large molecules [3]. The properties of aluminosilicates have been the silicate molecular sieves, designated as M41S [1,2] has been reported. This attracted considerable subject of many investigations, since aluminum is the origin of the Bro ¨nsted acidity in aluminosilicate interest because of the potential of these materials for use as solid-acid catalysts. The member of this molecular sieves. The nature of acidity remains one of the key questions in mechanistic studies of the family designated as MCM-41 shows a hexagonal acid–base reactions. In mordenites, an enhanced activity observed after hydrothermal treatment was * Corresponding author. Fax: +1 418 656 5993; explained by an interaction of bridging hydroxyl E-mail: kaliagui@gch.ulaval.ca groups with non-framework aluminum species [4]. 1Dedicated to Professor Lovat V.C. Rees in recognition and Similarly, Lago et al. [5] observed an enhanced appreciation of his lifelong devotion to zeolite science and his outstanding achievements in this field. activity of H-ZSM-5 after mild steaming at 813 K 1387-1811/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved. PII: S1387-1811(98)00073-0