Typical Hysteresis of Adsorption-Desorption Cycle

  • Typical hysteresis of adsorption-desorption cycle

  • Langmuir isotherm :

    influence of the coefficient ‘b’

  • Variations on Langmuir and Henry

  • Variations of Langmuir and Henry

  • Théorie de Brunauer Emmett et Teller (BET)

  • Hypothèses

–Starting from the second layer E1»EL energy of molecules in liquid state

  • Basic hypothesis of the BET theory

E1 = Energy of adsorption for the first layer

El  = Energy of liquid state

  • Basic hypothesis of the BET theory

surface so covered with 0 adsorbed layers

…     s1          …           1

…                  …           …

…     si           …            i

Accessible surface A = so + s1 + … + si + …

  • Derivation of the BET formula

  • Derivation of the BET formula

  • Derivation of the BET formula

  • Theory of Brunauer Emmett and Teller (BET)

  • Equations

– N= number of layers

x = p/p0 = relative equilibrium

pressure

––if N ® ¥
–Transformed  equation BET

  • Influence of number of layers N on the shape of isotherms of adsorption (BET)

  • Influence of the constant ‘C’ on the shape of isotherms of adsorption (BET)

  • Application for calculation of the adsorption surface

    example : alumin NPL / N2 / 77 K

  • Verifications of BET results

    example : alumin NPL / N2 / 77 K

  • Approach thermodynamic – energie of adsorption

  • Example:

    mesoporous system: MCM-41 et 77K

CO & CH4

Typical for heterogeneous surface

Dadsh (»2 kJ.mol-1) during the capillary condensation

Kr

Dadsh (»5 kJ.mol-1) during the capillary condensationÜ solidification ?

  • Milestone properties

  • Milestone properties

  • Milestone properties

  • Nitrogen / black of de carbon (Carbopack)

  • Adsorption on precipitated silica

    Isotherms : N2 & Ar à 77K

  • The conditions of the sample preparation are very important!!!!


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