08-06-2012, 05:17 PM
Nanotechnology of Catalysis
Nanotechnology of Catalysis.ppt (Size: 881 KB / Downloads: 7)
•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.