Duan Weng et al. performed in 2010 a NH3-TPD analysis on cerium/zirconium catalysts, modified with nickel and sulfate groups. Their TPD curve shows the presence of two peaks, of which the low-temperature peak they ascribed to Lewis acid sites, while the high-temperature peak was ascribed to Bronsted acid sites.

Weng, D. Catalysis Communications 11 (2010) 1045-1048

I am not sure about conclusions from TPD analysis, but IR should help you. Check paper from I. Wachs Catalysis Today 27 (1996) 437-455

Hi Gobinda

Firstly NH3 is very small molecule and can over estimate your acidity measurement. what you need is to do N-Propylamine TPD which will tell you more about your Bronsted acid sides and pyridine TPD for your lewis acid sides.

one of the possibility is to run XPS experiments. I use to run it here in my institute in France after a NH3 chimisorption over catalyst surface. The XPS is a fine tool to probe the nature of surface sites (Lewis and Bronsted sites) which present different interaction with NH3 (binding energy for nitrogen 1s orbital ionization is clearly different on XPS spectrum). Do not hesitate to ask me more details

No its Not possible to distinguish the Lewis or bronsted acidity by TPD ,only pyridine FT-IR study will help to distinguish the two,The peak at 1450 cm-1 is due t lewis acidity and at 1550 cm-1 is due to bronsted acidity,.The TPD will give total acidity including the Lewis and bronsted.

but you can correlate the area of Pyridin FTIR and TPD if both are coming same then you can do that i think,but take caution in doing that

mean you caluclate area under bronsted peak and lewis peak by both the methods and then find B/L ratio if they are same for both then you can say,

but this should have reproducibility and other thing is their

"The bonding between NH3 and Bronsted acid sites is weaker and can easily be broken down at lower temperature where as in case of lewis acid sites it is reverse"

i dont no much of the above statement. you mentioned in ur question.

You right Vijaykumar Marakatti, but besides Pyridin, its possible to use CO too, isnt it?

The TPD allows to distinguish only acid site strength. Their nature normally can be found by FTIR of adsorbed CD3CN (see [SolStateChem2007_180(3)_1130] or pyridine (see [Journal of Catalysis 254 (2008) 84–90]). A lot of other literature sources is known. Only solution by TPD of NH3 can be realized, if you surely know from other literature sources, that other methods confirms for WO3 "Bronsted sites are weak and Lewis sites are strong". If it is true, use the TPD for quantification

CO is used to determine the basicity of catalyst and not the acidity.

for more infromation please find the following review article

http://www.ijvs.com/volume6/edition1/review.pdf

Thank you all dear colleagues. I know that its not possible to distinguish BAS and LAS by NH3-TPD. It can be distinguished by pyridine TPD and Pyridine IR. But I just assumed that statement what I have written in my question. I just asked your suggestion whether we can write that statement in case of NH3-TPD. So from above discussion its clear that my assumption is wrong and I have to perform pyridine-TPD and pyridine IR.

Dear Dupin, Its very interesting to know about the determination of BAS and LAS from XPS analysis. Could you kindly say me the detail procedure you follow for this analysis?

Me also interested to know how XPS will distinguish the B and L acid sites

i leave you some refs from my lab with close up explanations about the XPS/chimisorption gas coupling:

1- Recent Res. Devel. Catalysis, 2 (2003) 99-120

2- Microporous Materials 11 (1997) 275-291

You could get a first approach of the way to discriminate the Bronsted and Lewis acid sites (same for basic site with adsorption of SO2 gas).

Keep in touch if you have other questions but we do that kind of experiments in the lab every week!

Its Ok dear Dupin. Don't mind. I will go through these papers and will ask if face any problem. Thanking You

Duan Weng et al. performed in 2010 a NH3-TPD analysis on cerium/zirconium catalysts, modified with nickel and sulfate groups. Their TPD curve shows the presence of two peaks, of which the low-temperature peak they ascribed to Lewis acid sites, while the high-temperature peak was ascribed to Bronsted acid sites.

Weng, D. Catalysis Communications 11 (2010) 1045-1048

Dear Ladislao

Many thanks for this article. I have gone through the paper and found the same. Although they have reported this but the most appropriate technique is pyridine-TPD and pyridine-FTIR. Lets see how other RG colleagues give remarks on this discussion.

Thank you Dupin for your information about a new technique of determination of BA and LA sites.

Dear Gobinda, what is the chemical composition of your support material? have you got a good dispersion of WO3 active phase and what is content (percentage weight) of W?. The Lewis acid sites are mainly located near WO3 sites. Effectively , we assume that at low temperature, the interaction of support-W (electrostatic or Van der Waal bonds) contribute to the reaction, however, at high temperature, only the Lewis sites (WO3) reacts with ammonia gaseous.

The solid may be a mixture of acid sites L/B : acid sites L>>B or acid sites B>>L (more strong), all depends of your final solid.

Hi

I think you can differentiate between Bronsted and Lewis acidic sites by DRIFTS-Pyridine

With Ammonia TPD we can measure only acidic strength. Lower temperature desorption corresponds to weak acid sites and higher temp to storng acid sites. Lewis and Bronsted acidity can be diffentied by Pyridine absorption -FITR.

Dear Sharad V Lande

In our country nobody works on Pyridine. can you mention me another ways to estemitate Bronsted and Lewis sites ?@