The Presence of OH group can be determined by FTIR spectroscopy. The OH group stretching band appears between 3200 t0 3600 cm-1. The wavelength position depends on whether the hydroxyl group is free or hydrogen bonded to nearby OH groups. Make KBr pellets and scan sample from 400 cm-1 to 4000 cm-1. If you want to quantify the OH groups, you should have a standard sample that contains OH groups in the same environment as in the sample.

At one point, I had used a wet-chemistry + UV/VIS spectroscopy method to titrate OH groups on the surface of titania powders. A literature search on titration of surface hydroxyl groups using wet chemistry may give you some insights.

Thanks for your answers. I have already performed proton NMR and IR in the OH zone...The point now is how to diferenciate between Si-OH and Al-OH.

Hi Izabel,

Zeolitic structures are composed by SiO4 and AlO4 tetrahedral units, and because Al is a trivalent atom it will hold a negative charge that must be counterbalanced by a positively charged atom, in your case a proton. Therefore the OH group will be located in Si-OH-Al. If your material have separated Si-OH and Al-OH groups, it means that these groups are extra-framework. An extra-framework Al-OH or Si-OH is a group that is not tetrahedrally bound into the zeolitic framework. Their existence are expected and concentration depends on the degree of crystallinity of your material. Strength of this acid site will depend on structural (e.g. type of zeolite) and chemical factors (e.g. Si/Al ratio).

The broadening of the absorption band of the -OH groups in FTIR analysis may not facilitate the analysis you are looking for. Perhaps FTIR analysis of adsorbed pyridine may be more helpful. Proton NMR is a good way to go. Compare your results with literature. For instance, the steam activation o zeolite Y (to form USY) generates extra-framework Al-OH groups. Thus proton NMR of USY materials will display signals for both in-framework and out-framework Al-OH groups. By analogy, the desilication process of zeolites will generate extra-framework Si-OH groups.

I hope this information will be useful for your studies. I found some references to assist you (links are posted).

Best Regards,

Alexandre.

http://pubs.acs.org/doi/abs/10.1021/jp001620p

https://link.springer.com/article/10.1007%2FBF00808330

http://pubs.acs.org/doi/abs/10.1021/la00034a003

I invite you to consult the following bibliography. I hope it's useful

Please see:

1-Simultaneous optimization of methane conversion and aromatic yields by catalytic activation with ethane over Zn-ZSM-11 zeolite: The influence of the Zn-loading factor

Catalysis Today, Volume 171, Issue 1, 10 August 2011, Pages 36-42

2. Fe-containing ZSM-11 zeolites as active catalyst for SCR of NOx: Part I. Synthesis, characterization by XRD, BET and FTIR and catalytic properties

Applied Catalysis A: General, Volume 264, Issue 1, 18 June 2004, Pages 93-101

Oscar A Anunziata, Andrea R Beltramone, Zoran Juric, Liliana B Pierella, Felix G Requejo

3. Expanded regional rate analysis: A novel method to determine regional formation rates in catalyzed reactions

Applied Catalysis A: General, Volume 165, Issues 1–2, 31 December 1997, Pages 35-49

Oscar A. Anunziata, Liliana B. Pierella, Raúl G. Marino

Hi Izabel,

A just accepted manuscript in The Journal of Physical Chemistry C come out yesterday and may be of interest to you. Entitled as "Characterization of Catalytic Materials Through a Facile Approach to Probe OH Groups by Solid State NMR".

Best Regards, Alexandre.

http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.7b02283

sorry late......it become right if you choice Solid State NMR, but you use deconvulution and you can calculate how mach Si-OH and Al-OH.

Article The use of the combination of ftir, Pyridine adsorption, 27A...