Elimination of internal diffusion in nanocatalysts
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What is the minimum particle size in nanometers for a nanocatalyst, so that the effect of internal diffusion can be eliminated? (Or has any literature mentioned that when the catalyst particle size is less than 80 nm, the effect of internal diffusion can be eliminated?)
There is no clear specification for this; catalysts with different pore sizes, as well as different reaction media, result in different particle sizes for eliminating internal diffusion in the catalyst.
Generally, only catalysts with particle sizes on the millimeter scale require consideration of the effects of internal diffusion; catalysts with particle sizes at the micron and nanoscale do not need to take these effects into account.
It depends on what kind of catalyst you have: a metal-supported catalyst or a molecular sieve catalyst? Typically, for metal-supported catalyst pellets (where the metal nanoparticles are also only a few nm to several dozen nm in size), the effect of internal diffusion is eliminated at a mesh size of 80 or higher. The particle size that eliminates the effect of internal diffusion is not fixed; it depends on the relative magnitude of the reaction rate and the internal diffusion rate, and is closely related to factors such as the active phase, pore structure parameters, and the diffusion system of the substances involved. It can be determined through experiments or estimated using models. For molecular sieve catalysts, it is indeed necessary to consider diffusion within the nanocrystals.