Number and strength of surface acidic sites on porous aluminosilicates of the MCM-41 type inferred from a combined microcalorimetric and adsorption study
A combined microcalorimetry and adsorption study has been used to characterize the surface acidity of two series of MCM-41 aluminosilicates (referred to as SiAlxCn, where x is the mole Si:Al ration and n the chain length of the surfactant template). {sup 29}Si magic angle spinning NMR spectra of a selected sample (SiAl32C16) indicates the presence of siloxane groups, Si(OSi){sub 4}, and three types of silanol groups, that is, single (SiO){sub 3}-Si-OH, hydrogen-bonded (SiO){sub 3}-SiOH{hor{underscore}ellipsis}HO-Si-(SiO){sub 3}, and germinal (SiO){sub 2}-Si(OH){sub 2}. It is also possible to detect the contributions from Si(3Si, 1Al) and Si(2Si,2Al) sites. The volumetric and calorimetric measurements of gas ammonia adsorption at 353 K were used to determine the number and strength of surface acidic sites. With the exception of H{sup +}-SiAl32C14 and SiAl8C14, all samples have low surface acidity. Following the pyridine-TPD study on SiAl9C14 sample, Lewis acid sites producing surface pyridine complexes constitute the strongest acidic site.
- Research Organization:
- Univ. Montpellier (FR)
- OSTI ID:
- 20017511
- Journal Information:
- Langmuir, Vol. 16, Issue 5; Other Information: PBD: 7 Mar 2000; ISSN 0743-7463
- Country of Publication:
- United States
- Language:
- English
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