Micromeritics TriStar II 3020 - Freundlich Isotherm; Temkin Isotherm

TriStar II 3020 Appendix C
302-42828-01 - Dec 2012 C-35
Freundlich Isotherm
Q
Q
m
-------
CP
1/m
=
QQ
m
CP
1/m
=
Qlog Q
m
C
1
m
----
Plog+log=
The Freundlich isotherm has the form:
where
Q
= quantity of gas adsorbed
Q
m
= quantity of gas in a monolayer
C = temperature-dependent constant
m = temperature-dependent constant
The pressure is absolute; typically, m > 1. In terms of quantity adsorbed,
Taking the log of both sides yields:
Temkin Isotherm
Q
Q
m
-------
RT
q
0

---------
A
0
Pln=
Q
RTQ
S
q
0

--------------
A
0
P
Po
-------


ln+ln=
The Temkin isotherm has the form,
where
Q
= quantity of gas adsorbed
Q
m
= quantity of gas in a monolayer
q
0
= the differential heat of adsorption at zero surface coverage
A=a
0
exp {-q
0
/RT}, where 
0
and a
0
are adjustable constants
In terms of quantity adsorbed,
Thus, the plot of the natural log of absolute pressure
vs. quantity adsorbed yields a straight line with
slope RTQ
m
/q
0
and intercept (ln A) RTQ
m
/q
0
.