CO2 is a titre gas often used to measure the number of bassic sites.  If the structure of the adsorbent suggests that both acid and base sites are present, then it makes sense to titrate for both types of sites.  Ammonia is often used to titrate acid sites, but, one finds that it counts not only strong but also weak sites.  Another titre for acid sites is pyridine.  When it chemisorbs to Bronsted acid sites, the IR spectrum of protonated pyridine is quite evident and different from pyridine adsorbed to Lewis acid sites.  Thus, one can imagine a series of experiments where isotherms are developed using CO2 and pyridine in separate experiments to determine the number of strongly adsorbed sites.  The same gas adsorption apparatus can be sued for both titres.  For the acid site sitre; one can measure the ratio of Lewis and Bronsted sites measured using IR spectroscopy and by ratioing the area's of the peaks characteristic to Lewis and Bronsted acid sites.  See older literature on acid site titrations with pyridine to learn the details.

Mark suggestions are absolutely correct.

Sorry for bad english.

The most correct is infrared spectroscopy during adsorption deuterochloroform.

See .book "Infrared spectroscopy in heterogeneous acid-base catalysis" E.A.Paukshtis, 1992 (Russian) and

http://www.mathnet.ru/php/archive.phtml?wshow=paper&jrnid=rcr&paperid=3452&option_lang=eng

Bes and the most effective way is to combine electrochemical methods with in situ XAS, particularly our relatively new technique referred to as Delta Mu.  Check out our papers by typing Sanjeev Mukerjee in google scholar.

Thanks everyone for your input!

I think one of the best and simple methods for correct measuring the strength and concentration of basic sites is titration  by benzoic acid with different indicators.

Tanabe " Solid acids and basics" 

Probably by NaCl ion exchange.

Obviously CO2 and SO2 as probe molecules are fine. Microcalorimetry of such probe molecules and TPD are also very useful methods. Some catalytic reactions are also used for that. See the book "solid base catalysis by Y.Ono &  H Hattori (Springer, 2011) and Chem Rev 95 (1995) 537 or Catal Rev Sci Eng. 48 (2006) 315,...

Thank above all greatly for the kind suggestions and comments!

In my humble opinion, I think that Temperature-programmed desorption (TPD) with CO2 or NH3 is the most appropriate characterization method for determination of strength and concentration (amount) of basic sites. In literature review, you can find papers that use this technique (using one or both molecules probes), and the results correlate correctly with catalysts activity.

TPD by katharometer using, instead of the mass spectrometer can be not correctlyюIn the recorded signal contributes dehydroxylation and conversion of residual catalyst phase by thermolysis..

CO2 is acidic molecule. basic sites can be calculated from CO2 TPD. Temperature programmed desorption of CO2. In CO2 TPD the basic sites of catalysts can be adsorbed on the CO2 surface, Weak basic sites at lower desorption temperature and moderate basic sites at 300 to 450 oC. Higher desorption temperature 500 to 650 oC are strong basic are are observed.

 TPD-CO2 is the best Technics for determining basic site of your materials, please see the following references:

Thermochimica Acta 496 (2009) 45–49

Applied Clay Science 48 (2010) 133–137

International Journal of Greenhouse Gas Control 17 (2013) 140–147

Journal of Colloid and Interface Science 402 (2013) 215–222

u can also try with benzoic acid titration method.

Direct titration by acid-base indicators for determination of strength and concentration of basic sites

Tanabe '' Solid acids and bases"

Hi

you can use TPD- CO2 by heating the sample to 200 oC and then exposure the sample to CO2 flow till it will be saturated with CO2 and them you can compare the weight loss in TGA analysis before and after CO2 exposure and finally from the weight of CO2 you can calculate the no of moles of CO2 adsorbed on you catalyst which represent the basicity

have a very good day