Chemical Reaction Catalysis

What is Catalysis?

All starting materials must surpass a specific energy threshold, commonly referred to as activation energy, to transition into products. This activation energy represents the variance between the energy levels of the transition state and the initial reactant molecules. While some reactant molecules possess adequate kinetic energy to surpass this barrier, others lack the necessary energy.
Consequently, reactions do not uniformly occur at identical rates under standard conditions. To facilitate the conversion of reactants into products, certain substances are introduced that decrease the requisite activation energy. These substances, termed catalysts, expedite the process by reducing the activation energy, a phenomenon known as catalysis.

Catalysis accelerates chemical reactions by employing a catalyst. Catalysts expedite reaction rates without experiencing any chemical or physical alterations themselves. As previously mentioned, catalysts merely diminish the energy barrier necessary for the transformation of reactants into products.

Categories of Catalysis

Catalysis of chemical reactions is commonly categorized into two types:

• Homogeneous Catalysis: In homogeneous catalysis, both the reactants and the catalyst exist in the same phase during the reaction. For instance, the hydrolysis of sugar in the presence of sulfuric acid.
• Heterogeneous Catalysis: Heterogeneous catalysis involves reactants and catalysts existing in different phases during the reaction. For example, the reaction of hydrogen and nitrogen in the presence of finely divided iron to produce ammonia.

Mechanism of Heterogeneous Catalysis

The contemporary theory of adsorption delineates a five-step mechanism for the catalysis of chemical reactions. These steps encompass:

• Introduction and diffusion of reactant molecules onto the catalytic surface.
• Adsorption of reactant molecules onto the catalytic surface.
• Formation of intermediates on the catalytic surface through chemical reactions among reactant molecules.
• Desorption of product molecules from the catalytic surface.
• Diffusion of product molecules away from the catalytic surface to yield final products.