Methanol interaction with mesoporous silica-aluminas

Amorphous mesoporous silica-aluminas with different textural properties are prepared by the sol-gel procedure and compared in the "in situ" reaction o f methanol by infrared (FT-IR) spectroscopy. Depending on the gelling agent , silica-aluminas with porosity centred in micro and/or mesopores region ha ve been obtained. Acid site characterisation, by IR adsorption/desorption of pyridine and vol umetric adsorption of ammonia, shows the low capacity of these materials to interact with probes. Few strong and medium strength acid sites are presen t. The density of the OH groups and the Al content influence the acidity (d ensity and strength). The nature and distribution of hydroxyls are evaluated by IR spectroscopy i n the OH region after treatments at increasing temperature. After treatment at 100 degreesC, these samples show a large amount of silanols (involved o r not in H-bonding), decreasing sharply as the temperature of treatment is increased. All materials bond methanol (600-700 mu mol/g) and the formed CHO-Si groups are stable during evacuation up to 400 degreesC. The strength of these gro ups is determined from the shift of the hydroxyls IR signals after methanol interaction. Though no direct bonding between methanol and AlOH groups is monitored, the presence of Al increases the strength of some hydroxyls. (C) 2001 Elsevier Science B.V. All rights reserved.