I observed a sharp peak at high temperature in ammonia TPD profile of metal impregnated zeolite.
Could you give more information on your experiment ? What detector did you use to follow the desorption of NH3 (TCD vs mass spectrometer), at what temperature do you observe this extra peak and what metal did you deposit ?
I deposited nickel. The temperature at which new desorption peak appeared was 753 K. TCD detector was used.
If you are using a TCD detector you cannot be sure that what desorbs at 753 K is ammonia, and hence that you indeed have an increase in the number of acid sites. You probably should try to perform the measurement using a mass spectrometer for detection. I have another question, during you NH3 TPD experiment, at what temperature did you pretreat your sample prior to expose it to ammonia ?
Did you performed reduction, prior to NH3-TPD ?
If not, the peak might be due to the oxide of Nickel, which gives the desorption peak at higher temperatures.
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