Catalysts: All You Have to Know

A catalyst is a substance that increases the rate of a chemical reaction by providing an alternative reaction pathway with a lower activation energy, without being consumed or undergoing any permanent chemical change itself. Essentially, a catalyst facilitates a chemical reaction without being consumed in the process, allowing it to participate in multiple reaction cycles. They are important because they accelerate chemical reactions by lowering the activation energy, making processes more efficient. They enable cost-effective and environmentally friendly production, reduce energy requirements, and enhance the selectivity of reactions.

Types of Catalysts

There are mainly 3 types of catalysts. Let’s take a look at the differences among them:

Homogeneous Catalysts

Homogeneous catalysts are catalysts that exist in the same phase (e.g., liquid or gas) as the reactants in a chemical reaction. These catalysts dissolve in the reaction medium, and their active species directly participate in the reaction. And they often form intermediate complexes with reactants during the reaction. For example the reaction “2H₂O₂ (aq) → 2H₂O (l) + O₂ (g)” reaction proceeds extremely slowly, however, it can be catalyzed by I^– ions. Here is how the reaction occurs:
H₂O₂ (aq) + I^– (aq) → H₂O (l) + IO^– (aq) then
H₂O₂ (aq) + IO^– (aq) → H₂O (l) + O₂ (g) + I^– (aq)
As you see above, I^– (aq) ions are regenerated, not used up. Although it seems to be practical, recovery and separation of homogeneous catalysts from the reaction mixture can be challenging.

Heterogeneous Catalysts

Heterogeneous catalysts are catalysts that exist in a different phase (e.g., solid) from the reactants in a chemical reaction. These catalysts are typically solids with a large surface area. Reactants adsorb onto the catalyst surface, where the reaction takes place. Let’s look at the example:
2SO₂ + O₂ ^{[Pt catalyst (solid)]} → 2SO₃
These types of catalysts are generally used in technological devices such as cars in order to facilitate the conversion of harmful gases into less harmful gases.

Enzymatic Catalysts

Enzymatic catalysts are biological catalysts that accelerate chemical reactions within living organisms. Such enzymes are usually proteins with specific three-dimensional structures. They are highly selective, often catalyzing specific reactions. Here comes an example:
Starch (C₆H₁₀O₅)_n + (n-1)H₂O ^{(amylase enzyme)} → Sugar molecules (C₆H₁₂O₆)
These enzymes are operating under mild conditions with extreme conditions (pH, temperature etc.) such as our stomachs. However, these enzymes are sensitive to change as they’re made of proteins, therefore they may stop functioning under different circumstances.

How Do They Work?

Activation Energy

Activation energy is the minimum energy required for a reaction to occur. It represents the energy barrier that reactant molecules must overcome for the reaction to proceed. In simple words, some reactions need energy to take place. If this energy is provided, the reaction starts and continues until the end. A catalyst works by providing an alternative reaction pathway with a lower activation energy. This lower energy barrier makes it easier for reactant molecules to transition to the product state.

Catalysts’ Role

Catalysts work by providing an alternative reaction pathway for a chemical reaction, lowering the activation energy required for the reaction to proceed. The primary mechanisms by which catalysts operate depend on their types (homogeneous, heterogeneous, or enzymatic), but the underlying principles involve interactions with reactant molecules to facilitate the formation of products.

Conclusion

There are countless catalysts all around us. We owe the unique properties of our bodies to this. Of course, we know a lot about catalysts, but there is still much more to learn. Catalysts will play a crucial role in a world where speed matters.