Evaluation of surface enthalpy of porous aluminosilicates of the MCM-41 type using immersional calorimetry: Effect of the pore size and framework Si : Al ratio

Citation
Mj. Meziani et al., Evaluation of surface enthalpy of porous aluminosilicates of the MCM-41 type using immersional calorimetry: Effect of the pore size and framework Si : Al ratio, J COLL I SC, 233(2), 2001, pp. 219-226
Citations number
38
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF COLLOID AND INTERFACE SCIENCE
ISSN journal
00219797 → ACNP
Volume
233
Issue
2
Year of publication
2001
Pages
219 - 226
Database
ISI
SICI code
0021-9797(20010115)233:2<219:EOSEOP>2.0.ZU;2-W
Abstract
Surface properties of porous aluminosilicates of the MCM-41 type have been tested by immersional calorimetry. Two series of materials, referred to as SiAL chi Cn, where chi is the Si:Al mole ratio and n the chain length of th e surfactant template, having (1)chi = 32 and n = 8, 12, 14, 16, 18 and (2) n = 14 and chi = 8, 32, oo, were used. The results of thermogravimetric ana lysis on these samples served to evaluate the surface density of hydroxyl g roups. This parameter is rather sensitive to the pore size than to the alum inium content in the solid matrix. Based on the experimentally measured ent halpies of immersion in n-heptane, water, and formamide per unit BET specif ic surface area, estimates could be made of the apolar, Lewis acid, and Lew is base contributions to the total surface enthalpy of MCR-41 materials. Th e samples studied have a predominant surface acidic character, which is mar kedly enhanced by incorporating aluminium into the silica matrix. Surface a cidity is also modified by changes in the porous structure, although the tr ends are less noticeable here. Nevertheless, the total surface enthalpy of MCM-41 aluminosilicates appears to be small in comparison with typical inor ganic oxides, such as silica or alumina. (C) 2001 Academic Press.