Theory 24/Competing Rates/Catalysis
Catalyst Efficiency Is Diffusion Against Reaction
The claim
The apparent activity of a porous catalyst is set by the ratio of diffusion rate to intrinsic reaction rate, so a faster intrinsic catalyst can appear slower.
01Mechanism
When reaction outpaces diffusion, only the outer shell of the pellet is used; the effectiveness factor falls with the ratio.
02Prediction
Activity should peak at an intermediate intrinsic rate.
03Refutation
Activity tracking intrinsic rate monotonically would remove transport.