Adsorption: Screencasts
Explains the concept of adsorption and derives the Langmuir isotherm.
We suggest you list the important points in this screencast as a way to increase retention.
An introduction to Langmuir Isotherms.
We suggest you list the important points in this screencast as a way to increase retention.
Optional screencast: Langmuir Isotherm: Dissociative Adsorption
Important Equations:
Langmuir isotherm for species A adsorbed on a surface:
\[\theta _A = \frac{K_AP_A}{1 + K_AP_A}\]
where \(K_A\) = adsorption equilibrium constant for species A,
\(P_A\) = pressure of species A, and
\(\theta _A\) = fraction of the surface covered by species A.
The Lanmuir isotherm for molecules A and B co-adsorbed has the form:
\[Molecules \,\, of \,\, A\,\, adsorbed/site\,\,= \frac{K_AP_A}{1+K_AP_A + K_BP_B}\]
\[Molecules \,\, of \,\, B\,\, adsorbed/site\,\,= \frac{K_BP_B}{\alpha (1+K_AP_A +K_BP_B)}\]
where \(K_B\) = adsorption equilibrium constant for species B,
\(P_B\) = pressure of species B, and
\[\alpha = \frac{sites\,\,needed\,\,for\,\,B}{sites\,\,needed\,\,for\,\,A}\]
\[K_A = K_{A0}exp \left( \frac{-\Delta H}{RT} \right)\]
where \(\Delta H\) = enthalpy change on adsorption, which is negative because adsorption is exothermic.
\(K_{A0}\) is a temperature-independent term.
Lanmuir adsorption isotherm for dissociative adsorption of H2:
\[\theta _H = \frac{K^{0.5} _{\alpha} P^{0.5} _{H_2}}{1+K^{0.5} _{\alpha} P^{0.5} _{H_2}}\]
where \(\theta _H\) = fraction of sites covered by H atoms
\(K_{\alpha}\) = adsorption equilibrium constant, and
\(P_{H_2}\) = H2 pressure.