AdvancedTopic 86 of 100Materials & Chemical
Heterogeneous catalysis
Reactions on solid catalyst surfaces with diffusion limitations.
In depth
Steps: external diffusion, pore diffusion, adsorption, surface reaction, desorption, diffusion out. Langmuir-Hinshelwood kinetics; effectiveness factor η and Thiele modulus indicate pore diffusion limitations. Catalyst pellet shape and size are optimised.
Key points
- Mass-transfer limited vs kinetically controlled
- Surface area and porosity
- Packed-bed design
ExampleZeolite catalysts crack large hydrocarbon molecules in refineries.
What is Heterogeneous catalysis?
Reactions on solid catalyst surfaces with diffusion limitations.
Why is it important to understand heterogeneous catalysis?
Heterogeneous catalysis happens on solid surfaces, where diffusion to and from the surface can limit the overall rate.
What are the main steps in heterogeneous catalysis?
Diffusion to the surface, adsorption, reaction on the surface, desorption and diffusion away from the surface.
What is effectiveness factor?
The ratio of the actual reaction rate in a pellet to the rate that would occur if the whole pellet were at the external concentration.
How is Heterogeneous catalysis used in practice?
Typical applications include designing a packed bed of catalyst pellets for a reformer, assessing whether pore diffusion limits a catalyst pellet and choosing a pellet size that balances pressure drop and effectiveness.
What should I learn before Heterogeneous catalysis?
Study "Catalysis" first (topic 85 of 100 in Materials & Chemical). It covers the groundwork this topic builds on.
What are the key points of Heterogeneous catalysis?
Mass-transfer limited vs kinetically controlled. Surface area and porosity. Packed-bed design.
Can you give an example of Heterogeneous catalysis?
Zeolite catalysts crack large hydrocarbon molecules in refineries.
What comes after Heterogeneous catalysis?
The next topic is "Residence time distribution", which builds directly on this one.
How difficult is Heterogeneous catalysis?
It is classed as Advanced in Materials & Chemical (topic 86 of 100). It is an advanced topic. It assumes you are comfortable with the intermediate topics in Materials & Chemical.