(a) Most commercial heterogeneous catalysts are extremely finely divided solid materials. Why is particle size important? (b) What role does adsorption play in the action of a heterogeneous catalyst?

Heterogeneous catalysts are catalysts that are in a different phase than the reactants. They are typically solid materials that help speed up chemical reactions without being consumed in the process. Heterogeneous catalysts generally work by providing a surface for the reactants to interact with, reducing the energy barrier required for a successful reaction to take place. ### Step 2: The importance of particle size in heterogeneous catalysts ###

Particle size is crucial in commercial heterogeneous catalysts because it directly affects the surface area of the catalyst exposed to the reactants. When a solid catalyst is finely divided into smaller particles, the surface area per unit mass increases, which implies that more reaction sites are available for the reactants to interact. This increased surface area consequently leads to higher reaction rates and improved efficiency. ### Step 3: Understanding adsorption ###

Adsorption is a process where a substance (like a reactant molecule) accumulates on the surface of a solid or liquid material, such as a catalyst particle. In the context of heterogeneous catalysis, adsorption indicates the binding of reactant molecules onto the catalyst's surface, which typically involves chemical or physical forces. Adsorption can be classified into two categories: physisorption, which involves weak van der Waals forces, and chemisorption, which involves stronger covalent or ionic bonds between the reactant and the catalyst. ### Step 4: The role of adsorption in heterogeneous catalysis ###

Adsorption plays a vital role in the action of a heterogeneous catalyst by facilitating the chemical reaction in the following ways: 1. Bringing reactant molecules close together on the catalyst surface, thereby increasing the probability of a successful collision and reaction. 2. Weakening the bonds within the reactant molecules, which lowers the activation energy required for the reaction to proceed. 3. Providing an alternative reaction pathway that may involve intermediates formed during the adsorption process. 4. Enabling better control over reaction conditions, such as temperature and pressure, which can affect the rate of adsorption and determine the selectivity of specific reactions. By adsorbing reactants on its surface, a heterogeneous catalyst can enhance and control the rate of chemical reactions, reduce energy costs, and ultimately improve process efficiency.