Question

In a heterogeneous catalytic reaction, the effectiveness factor is:

• A. Ratio of actual rate to rate if no diffusion limitations
• B. Ratio of surface area to catalyst weight
• C. Mass transfer coefficient
• D. Catalyst deactivation factor

Hint:

Effectiveness factor helps identify if internal diffusion resistance limits catalytic performance. Values much less than 1 indicate poor utilization of catalyst interior.

Answer 1

The Correct Option is A

In heterogeneous catalysis, reactions occur at the surface of solid catalysts and may be limited by the rate at which reactants diffuse into the catalyst pores.
The effectiveness factor ($\eta$) quantifies how effectively a catalyst particle is being utilized.
It is defined as:
\[ \eta = \frac{\text{Actual observed reaction rate}}{\text{Reaction rate if entire catalyst volume were at surface concentration}} \]
This means it is the ratio of the actual reaction rate inside the porous catalyst to the rate if there were no internal diffusion resistance.
Key characteristics:
- $\eta = 1$ implies no internal mass transfer limitations (ideal case).
- $\eta < 1$ implies that diffusion resistance exists and the catalyst is not fully utilized.
Incorrect options explained:
- (2) Ratio of surface area to weight: This relates to catalyst design, not performance under diffusion.
- (3) Mass transfer coefficient: This is a property of external film transport, not a measure of catalytic effectiveness.
- (4) Catalyst deactivation factor: Related to aging or fouling, not diffusion-related performance.
Therefore, the effectiveness factor specifically represents the ratio of actual rate to the ideal rate without diffusion limitations.