A spherical porous catalyst particle of radius R promotes zero-order surface reaction A → B. With negligible film mass transfer resistance and pore diffusion controlling, the effectiveness factor is 7/8. Which statement holds true?
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Answer: A. Inner catalyst core of radius R/8 does not participate in reaction
Explanation
An effectiveness factor of 7/8 means that 7/8 of the catalyst volume participates in the reaction. The remaining 1/8 volume represents an inner catalyst core where reactants cannot penetrate. For this zero-order geometry, the unreacted inner core corresponds exactly to radius R/8. Pore diffusion resistance can restrict reactant penetration deep into porous catalyst pellets. The effectiveness factor quantifies the actual reaction rate relative to a diffusion-free rate. Zero-order reaction kinetics produce distinct penetration profiles inside porous catalyst spheres.
Catalyst pellet design balances particle size to minimize internal pore diffusion limitations. Chemical engineers optimize catalyst porosity to maximize active surface utilization in reactors. Ineffective catalyst cores represent wasted expensive precious metal catalytic materials. An inner core of radius R/2 would result in a different effectiveness factor calculation. A core of radius 7R/8 would mean almost the entire pellet is dead, yielding a low factor. Effectiveness factors can certainly be less than one when pore diffusion limits the reaction.
- Subject
- Engineering
- Category
- Chemical Engineering
- Topic
- —
- Difficulty
- medium
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