Throughout the literature for adsorption of carbon monoxide on Cu(I) modified surfaces, the adsorption capacity decreases with an increase in temperature. The material I am using is a mixture of Cu(I), Cu(II), and Cu(0). What I expect is the formation of Pi-Complexation between Cu(I) and CO, and a physisorption of CO on Cu(II) and Cu(0). Therefore, with an increase in temperature, the adsorption capacity should decrease. However, I observed the increase of adsorption capacity by increasing temperature.
What could be a possible reason for this increase?
Perhaps the dominant phenomenon is the chemical reaction between Cu(0) and CO in which carbonyls are formed.
If the adsorption capacity increases with temperature, that means the adsorption is an activated process. Therefore, you have a chemisorption rather than only physisorption. in this case the thermal energy is used to overcome the activation energy of the chemisorption process (energy barrier).
Also, a less likely scenario, you may have an internal diffusion limitations and increasing the temperature facilitates the diffusion.
Thank you Dr. Mirosław Grzesik and Mohammad Alqahtani
I have taken the XRD of my samples but no new phases were formed confirming the chemical reaction happening in the bulk. I believe a surface characterization is necessary to confirm the chemical reaction. What technique would you suggest to use for this investigation?
Hi, I think it would be helpful to compare the FT-IR spectra before and after the adsorption process to find any alterations in the functional groups.
For a surface characterization, I would suggest XPS.
Performing Temperature programmed desorption (TPD) could be very helpful in determining the possible desorbed CO species and their relative adsorption strength. In-situ FTIR analysis could be very revealing as well.