Heterogeneous & Homogeneous Catalysts

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  • 0:04 Types of Catalysts
  • 0:37 Heterogeneous Catalysts
  • 2:55 Homogeneous Catalysts
  • 4:16 Poisoned Catalysts
  • 5:23 Lesson Summary
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Lesson Transcript
Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

Expert Contributor
Maria Airth

Maria has a Doctorate of Education and over 20 years of experience teaching psychology and math related courses at the university level.

There are two main groups of catalysts, heterogeneous and homogeneous. In this lesson, we'll learn how they are different, how each type reacts, and look at examples of each.

Types of Catalysts

In order to help change toxic gases that cars produce into nontoxic gases, a catalytic converter is used. This catalytic converter gets its name because it uses a catalyst to help in the reaction to convert the toxic gas into a nontoxic form.

A catalyst is a compound used to help a reaction occur faster by lowering the activation energy. There are two types of catalysts, homogeneous and heterogeneous. A homogeneous catalyst is a catalyst that is in the same phase as the reactants, while a heterogeneous catalyst is in a different phase than the reactants.

Heterogeneous Catalysts

As we just covered, a heterogeneous catalyst is in a different phase than the reactants. Because of this, it can't mix in with the reactants. The most common way these catalysts work is that the reactants adsorb onto the surface of the active site of the catalyst. With the reactants connected to the catalyst, the reaction occurs faster. There are several different mechanisms by which this occurs. Sometimes the reactants are brought into close proximity with each other. Sometimes the connection between one of the reactants and the catalyst helps make the reactant more reactive. After the reaction occurs, the catalyst releases the product. A good catalyst needs to bind tightly enough to the reactant to allow the reaction to occur, but weak enough to release the product. Let's take a closer look at some examples of heterogeneous cataysts.


There are several processes which use heterogeneous catalysts to help speed up the reaction. The contact process is one of the most widely used methods for sulfuric acid, H2 SO4, production. By adding excess oxygen to sulfur dioxide, sulfuric acid can be formed. But this is a very slow reaction. Vanadium oxide (V2 O5) is a brown/yellow solid on which the oxygen and sulfur dioxide can adsorb in order to react with each other to form sulfuric acid. This reaction is interesting because the vanadium oxide is reduced during the process of this reaction. Simply adding extra oxygen reforms the catalyst so that it can still be used.

Methanol, CH3 OH, can be produced by many different methods. But, by using carbon monoxide and hydrogen, a lot of energy (in the form of heat) is also produced, which can be used as power. The carbon monoxide and hydrogen method isn't as fast as other methods, such as keeping a stream of carbon dioxide, water, carbon monoxide, and hydrogen gases mixed together to form methanol. So, a catalyst such as Cr2 O3 can be used to make this an energy efficient method.

Ammonia, NH3, is an important product used in commercial farming. One way it can be made is through the Haber process, which uses nitrogen and hydrogen to form ammonia. In this process, nitrogen from the air can be used, a plentiful reactant. Iron is used as the catalyst, but it isn't pure iron. Instead, iron and potassium hydroxide work together to help the nitrogen and hydrogen come together to combine into ammonia.

Homogeneous Catalysts

As we mentioned earlier, with a homogeneous catalyst, the catalyst and the reactants are in the same phase. The allows the catalyst to directly interact with the reactants. Sometimes the catalyst can be positively charged and bring two negative charges together.

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Additional Activities

Real World Examples

In this activity, you will be finding examples of heterogeneous and homogeneous catalysts or catalytic reactions in the real world.


Step 1: To successfully complete this activity, you will need to find two examples of each type of catalyst:

  • Heterogeneous
  • Homogeneous
  • Autocatalyst
  • Poisoned catalyst

Step 2: For each catalyst (or catalytic reaction) you identify, you will need to:

  • Identify where in the real world the reaction can be found. For example
    • The poisoned catalyst of lead in gasoline can be found at the fuel station or at least identified at the fuel station.
  • Label the reaction with its correct catalyst type (hetero-, homo-, auto- or poisoned catalyst).
  • Explain how you know which type of catalyst or catalytic reaction it is. For example:
    • The reaction of manganese with oxalic acid is an autocatalyst because the manganese is part of the reactant but also speeds up the reaction above and beyond the normal slow reaction.
  • Write a brief summary of how the reaction takes place; what chemical changes occur due to the catalyst and why.

Step 3: Finally, write a summary of your findings. Answer these questions:

  • What do all homogeneous catalysts have in common?
    • You may notice that when these happen in nature they are slow reactions that occur over time.
  • What do all the heterogeneous catalysts have in common?
    • As an example, you may notice these are explosive.
  • What about the autocatalysts? What characteristics do they all share?
  • Do all the poisoned catalysts share any commonalities?
  • Is it possible to tell what type of catalyst is reacting with substances without being able to see things on a molecular level?
    • Why or why not?

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