The nature and concentration of the acid sites of MCM-41 material as a func
tion of Si/Al ratio have been monitored by in situ IR using pyridine as a p
robe molecule. The thermal stability of aluminium in the framework of these
materials is studied using Al-27 MAS NMR spectroscopy. The tetrahedral to
octahedral aluminium ratio is found to increase with higher aluminium incor
poration. The sample with the lowest Si/Al ratio is found to exhibit higher
acidity compared to the other samples. However, the acidity of these mesop
orous aluminosilicates is less compared to the conventional H-Y zeolite. (C
) 1999 Elsevier Science B.V. All rights reserved.