I have obtained the proton form of LTA by ion-exchange treatments with NH4NO3. TPD profiles didn't give any significant peaks analogous to other high silica topologies. However, the molecular dimensions of NH3 are smaller than LTA pore channels. Hence I request someone to assist with the topic.
Thanks in advance
Did you not put the NH3 in/on the zeolite? So, it must be able to come off. What is the temperature range? Have you tried a slower rate of TPD?
Yes, NH3 has been adsorbed prior to analysis. and then the desorption was carried out at the rate of 10C/min and range is 100-600C.
How about trying this probe molecule: Di-tert-Butylpyridine (DTBPy), which as kinetic diameter of 10.5 angstrom. This following paper use NH3-TPD to measure total acid density and then DTBPy to measure external acid density. The internal acid density is calculated by difference. The catalyst they used was proton-exchanged ZSM-5. However, since there are only very limited external acid sites for DTBPy adsorption, you should consider sample size. Low sample size won't give you good resolution.
J. Phys. Chem. B 106 (2002) 9552
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