How is the material and where are these sites ? for examples is it liquid, solid or something on a substrate like that .

its solid heterogeneous catalyst like WO3 supported on alumina

You could try temperature-programmed desorption (TPD) of specific probe molecules. It is a quite simple technique that will allow you to characterize the acidity of surface sites. You can have a look here as starting point: http://www.azonano.com/article.aspx?ArticleID=1475#_Molecular_Probes_For_Characterizing. Regards, Aitor.

The book "Solid Acids and Bases" by Tanabe is a very good reference on this topic. It's old, but still relevant.

I agree with Aitor Hornes, that NH3-TPD allows us to calculate the acidic strength of catalyst. we cannot calculate the exact amount of lewis or bronsted acidic sites. but from some research articles, we can observe that determination of weak, strong acidic sites from desorption amount of NH3 in diffrent temperature zones.

Thank you very much for your answers but i am not satisified with the answer  that is answered for that question . I know NH3 TPD and Py FTIR are the techiniques :) i want to find the Lewis and bronsted acidity other than these techinique.

Model reactions have been used to a great degree. Model compounds I recall be used include 2-methyl-2-pentene and isobutane.  It was a long time ago but I think Exxon did some work chracterizing tungsten oxide via the 2M2P reaction. Search the name Gary Mcvicker.  Search this topic more generally and you will reviews on the subject like this: Acc. Chem. Res, 1990, 23, 392.

There were also a large number of other indicators used other than pyridine, collectively called Hammett indicators.  Again, I would refer you back to texts written on this topic such as that by Tanabe or search for more recent papers that reference these eariler works.

Also, be aware that all of these techniques have pitfalls: you might not be measuring what you think you are.  Ideally, one would apply multiple techniques to the material at hand to develop the most complete picture of the surface acidity/basicity. 

IRMS-TPD system which is combined technology of NH3 TPD and FTIR. We developed with Prof. NIWA and Katada of Tottori Univ.

Microporous and Mesoporous Materials

Volume 82, Issues 1–2, 5 July 2005, Pages 105–112

What methodology did you finally choose?

Dear Colleague Marakatti,

1- The total number of acidic sites (sites. m-2) over each catalyst can be measured using the temperature programmed desorption of pyridine (TPD-pyridine) as the probe molecule. The details have been described in previous publication (attached).

The acidity populations over the surface of catalysts, under investigation, were measured thermogravimetrically using the adsorption of pyridine as probe molecule. Small portions (50mg) of each sample were pre-heated at 250°C for 2 h in air before the exposure to the probe molecule. 15-20 mg of pyridine–covered samples were subjected to TG analysis on heating up to 600°C (at 20°C/min heating rate) in dry N2 (flow rate = 40 ml/min). The mass loss due to desorption of pyridine from the acidic sites, was determined as a function of total surface acidity as sites.g-1cat.

2- To detect the Bronsted acidic sites, you can use 2,6-dimethylpyridine as a probe of the strength of Brønsted acid sites.

Finally if substracted the number of acidic sites from step 2 (Lewis +Bronsted) from step 1 (Bronsted only, you can get the number of lewis acidic sites

However, FTIR- Pyridine is only used to distinguish between the Lewis and Brønsted

Hope this helping

Have a very good day

Hello Ahmed,

Thank you very much for your Input on this.

I totally agree with the TG-DTA analysis for determining the both acidic Sites.

Regards

Dear Vijaykumar Marakatti

You are very welcome

Have a very good day

Ahmed

 Dr. Kazuyuki Nakai , you talked about IRMS-TPD. I read two papers. I just need to know that at present your company presents this instrument to clients or it is merely for some research?

Thank you.