Advanced Topic 501 of 1102 Kinetics & Equilibrium
Surface Catalysis Steps
Reactants adsorb, react on the surface, and products desorb in heterogeneous catalysis.
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In-depth explanation of Surface Catalysis Steps
Heterogeneous catalysis proceeds through a sequence of steps: diffusion of reactants to the surface, adsorption onto active sites, reaction on the surface, desorption of the products and diffusion of products away from the surface. Any one of these steps can be rate limiting, depending on the conditions. The Langmuir-Hinshelwood mechanism describes reactions in which both reactants adsorb on the surface and react with each other, while the Eley-Rideal mechanism describes reactions in which only one reactant is adsorbed and it reacts with a second reactant from the gas phase. Understanding these steps helps engineers design catalysts with the right balance of adsorption strength.
Going deeper: Surface Catalysis Steps
Key ideas: Langmuir-Hinshelwood: rate = k K_A P_A K_B P_B / (1 + K_A P_A + K_B P_B)^2, which has a maximum with respect to pressure. Eley-Rideal: rate = k theta_A P_B. At low pressure the rate is first order in pressure, at high pressure of a strongly adsorbed species it becomes zero or even negative order. Langmuir isotherm: theta = KP/(1 + KP).
Common mistakes and connections: Students think rate always increases with pressure, but a strongly adsorbed reactant can block sites and slow the reaction, giving negative order. Another error is confusing physisorption with chemisorption: only chemisorption provides the activation, with enthalpies of about 40 to 400 kJ per mol. Related to heterogeneous catalysis, zero order kinetics and surface area effects.
Visualization of Surface Catalysis Steps
Reactants adsorb onto the surface, react over a barrier there, and products desorb; any of these steps may limit the rate. The interactive lesson shows this as a live animation or chart.
Worked example and use case
The oxidation of carbon monoxide on platinum follows a Langmuir-Hinshelwood mechanism, with both CO and O adsorbed on neighbouring sites.
Frequently asked questions about Surface Catalysis Steps
What is Surface Catalysis Steps?
Reactants adsorb, react on the surface, and products desorb in heterogeneous catalysis.
Is Surface Catalysis Steps a beginner, intermediate or advanced topic?
Surface Catalysis Steps is a advanced topic in Kinetics & Equilibrium. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before Surface Catalysis Steps?
Study these earlier topics in Kinetics & Equilibrium first: Rate vs Time Graphs, Catalytic Converters, Inhibitors and Poisons.
What comes after Surface Catalysis Steps?
The next topics in Kinetics & Equilibrium are Zeolites and Reaction Coordinate Diagram.
Can I practise Surface Catalysis Steps with quizzes?
Yes. The interactive lesson includes a self-check question on Surface Catalysis Steps, and the Kinetics & Equilibrium quiz draws on every topic in this area.
Where Surface Catalysis Steps fits in Kinetics & Equilibrium
Surface Catalysis Steps is topic 82 of 91 in Kinetics & Equilibrium.