10-04-2017, 08:29 PM
Nanotechnology of Catalysis
[attachment=640]
Catalysts are perhaps the first industrial nanotechnology
2-10 nm particles (sometimes larger) on high surface area support (Al2O2, SiO2)
Catalyst Particles
Catalytic reactions occur on catalyst surfaces
Small particles maximize surface area
-reduce catalyst volume (smaller reactors)
-optimize use of catalysts
(more metal atoms at surface)
Catalyst dispersion
fraction of catalyst atoms
at surface (10-40%)
What is Catalysis?
Berzelius, 1836 (as formulated by Ostwald):
A catalyst is a substance that promotes a chemical reaction with no net participation in it; it is neither consumed nor replenished.
Catalyst turnover : one complete reaction cycle
Turnover rate [=] s 1: number of reaction cycles completed at a catalyst site per second
Though the idea of a turnover is inherent in the definition of a catalyst, the concept did not come into common use until after 1965.
Catalysis Fundamentals
Steps in catalytic reactions
1.Adsorption of reactants
2.Surface diffusion of reactants
3.Surface reaction
4.Surface diffusion of products
5.Desorption of products
Catalysis requires balance of adsorption, reaction, and desorption
Catalyst strongly adsorbing > no rxn.
Catalyst weakly adsorbing > no rxn.