EFFECT OF STRUCTURAL ALUMINUM ON THE MESOPOROUS STRUCTURE OF MCM-41

X-Ray diffraction (XRD), Al-27 magic-angle-spinning (MAS) NMR, N-2 adsorption measurements and transmission electron microscopy (TEM) show that the one-dimensional channels of the mesoporous aluminosilicate MCM-41 containing only structural (four-coordinate) aluminium are much shorter in the sample with an Si/Al ratio of 34.1 (ca. 160 Angstrom) than in purely siliceous MCM-41 (ca. 400 Angstrom). The quality of the XRD patterns rapidly deteriorates as the aluminium content of the solid increases. However, aluminosilicate MCM-41 still preserves a perfect mesoporous structure with an average pore diameter of ca. 30 Angstrom, a surface area of 990 m(2) g(-1) and a pore volume of 0.74 cm(3) g(-1). When the Na+ form of aluminosilicate MCM-41 is transformed into the Bronsted acidic H+ form, and some of the aluminium is removed from the structure, the uniform hexagonal mesopores partially collapse and macropores 20-2000 Angstrom in diameter are formed.