Question

With increase in pressure, the bulk diffusion in catalyst pore:

• A. Decreases
• B. Increases
• C. Increases exponentially
• D. Remains unchanged

Hint:

For gases, bulk diffusion \( D \propto \frac{1}{P} \). In catalyst pores, higher pressure means more collisions and slower diffusion.

Answer 1

The Correct Option is A

Step 1: Understanding Bulk Diffusion
Bulk diffusion refers to the movement of gas molecules through a medium under a concentration gradient, typically governed by Fick's Law. In porous solids like catalysts, this diffusion can be significantly influenced by pressure. Step 2: Effect of Pressure on Diffusivity
According to the kinetic theory of gases, diffusivity \( D \) is inversely proportional to pressure \( P \): \[ D \propto \frac{1}{P} \] This occurs because as pressure increases, gas molecules become more densely packed, leading to more frequent collisions and hence reduced mobility. Step 3: Implications for Catalyst Pores
Inside catalyst pores, bulk diffusion becomes slower at higher pressures because of restricted movement and increased molecular interactions. Thus, increasing pressure leads to a decrease in diffusion rates. Conclusion: As pressure increases, bulk diffusion in catalyst pores decreases.