Hello dear scientists,
I carried out an adsorption-desorption isotherm of a catalyst as show in the attached file. Nevertheless, when I was analyzing the desorption I observed that this way is so strange since this isotherm present a mix between H2 and H3 loop.
I don't know why is the reason?
I repeated the experiment but I obtained the same isotherm.
Could some one explain me why could be the reason of the desorption way?
Thanks a lot,
Julián.
Hi!
This is most likely due to adsorption hysteresis (shortly, partially irreversible adsorption in the conditions of your system). Some molecules of adsorbate will become permanently trapped in the pores of the adsorbent. You can find lots of info about this in published literature as well as a classification for the different isotherms somehow showing the phenomena.
Cheers!
Can you let us know the surface area of your sample, when you have lower surface area of your sample, you should consider the dead volume of your sample holder, rectify if that is the case ! regards
VIJAY
Julián E. Sánchez-Velandia What material is this ? Pl. perform TGA of the solid sample. Then degas it properly for longer period of time, I am feeling sample is not degassed properly.
Julián E. Sánchez-Velandia The isotherm is a beautiful example of pore blocking and a desorption step referred to as "cavitation". The isotherm has blended hysteresis characteristics of H2(a), H2(b) and H3/H4 !!
https://www.degruyter.com/downloadpdf/j/pac.2015.87.issue-9-10/pac-2014-1117/pac-2014-1117.pdf
The large cavitation step is due to a significant volume of mesopores (given by the step height) which are blocked by micropores. These papers will explain in more detail exactly what is cavitation:
http://coewww.rutgers.edu/~aneimark/PDFs/Cavitation_Langmuir_2010.Pdf.pdf
https://rua.ua.es/dspace/bitstream/10045/22586/1/Silvestre_Well_defined_mesoporosity_Carbon.pdf
What is the explanation when an adsorption isotherm of N2 does not close?
Juan CARLOS Moreno-Piraján Their can be a number of reasons: (i) analysis time too short (i.e. done too quickly) which means true equilibrium has not been achieved, (ii) incomplete sample preparation (degassing), (iii) adsorbed volumes very small so not closing is within experimental "noise", (iv) some instrument issue such as a leak or contamination within the measurement zone itself.