Colloidal catalysis. Transport versus surface control
Abstract
It has been shown that the flux of material diffusing to the surface of a colloidal particle is greater than to a plane surface of the same area and diffusion layer thickness (δ). Around a small sphere of radius R the effective Nernst layer thickness δeff is given by
These findings were applied to redox reactions heterogeneously catalysed at a colloidal metal surface, and equations were derived for surface control, transport control, and mixed surface and transport control. These suggest that plots of 1/RVcat against R should generally be linear, where Vcat is the catalytic rate. This was confirmed by literature data for the reaction between hydrogen ions and methyl viologen radical cations catalysed by platinum and gold sols.