reaction engineering pt 1

general steps in catalytic reaction mechanisms

adsorption

surface reaction

desorption

difficulties of finding rate of catalytic reactions

rarely follow power rate law

need to develop mechanism and derrive rate law for steps

active site

a point on the surface that can form strong chemical bonds with an adsorbed atom or molecule

where do catalystic reactions happen

at active sites where there are unsatirated atoms

Heterogeneous Catalytic Reaction steps

Mass transfer of A to surface

Diffusion of A from pore mouth to internal catalytic surface

Adsorption of A onto catalytic surface

Reaction on surface

Desorption of product B from surface

Diffusion of B from pellet interior to pore mouth

Diffusion of B from external surface to the bulk fluid (external diffusion)

adsorption mechanisms

dissociation of molecules

Langmuir

molecular adsorption

surface reaction mechanisms

single site

dual site

Eley-Rideal

Eley-Rideal

1 reactant adsorbst to active site and the other stays in the gas phase

dual site

some reactants or products are larger and need 2 sites or need a vacant site adjacent to react.

some catalysts can have different types of sites with preferences for different molecules