Heterogeneous catalyst

Definition

A heterogeneous catalyst is a substance that increases the rate of a chemical reaction without being consumed, and exists in a different phase than the reactants, typically as a solid while the reactants are gases or liquids. This phase difference allows for easier separation of the catalyst from the products after the reaction, and plays a crucial role in influencing the activation energy and the pathway of the reaction.

5 Must Know Facts For Your Next Test

1. Heterogeneous catalysts typically provide active sites on their surface where reactions occur, allowing for multiple reaction pathways.
2. The effectiveness of a heterogeneous catalyst can depend on its surface area; increased surface area generally leads to higher catalytic activity.
3. Common examples of heterogeneous catalysts include metals like platinum and palladium used in catalytic converters to reduce vehicle emissions.
4. The adsorption process is critical in heterogeneous catalysis, as reactant molecules must adhere to the catalyst's surface for the reaction to proceed.
5. Regeneration of a heterogeneous catalyst can be achieved by removing impurities that accumulate on its surface, restoring its catalytic activity.

Review Questions

• How does a heterogeneous catalyst influence the activation energy and overall reaction pathway in a chemical reaction?
  • A heterogeneous catalyst influences activation energy by providing an alternative pathway for the reaction that requires lower energy compared to an uncatalyzed process. By offering active sites on its surface, it enables reactant molecules to adsorb and interact more effectively. This interaction can change the mechanism of the reaction, leading to faster product formation and potentially different products compared to reactions without a catalyst.
• Discuss how surface area affects the efficiency of heterogeneous catalysts and provide examples of materials that are commonly used.
  • The efficiency of heterogeneous catalysts is significantly impacted by their surface area because a larger surface area allows for more active sites where reactions can occur. For example, finely divided platinum and palladium are often used as catalysts in automotive catalytic converters due to their high surface area relative to volume. This increased exposure enhances their ability to facilitate reactions like the oxidation of carbon monoxide and hydrocarbons into less harmful substances.
• Evaluate the importance of adsorption in heterogeneous catalysis and how it relates to reaction mechanisms.
  • Adsorption is essential in heterogeneous catalysis because it is the first step where reactants attach to the catalyst's surface. This interaction can influence the rate-determining steps within a reaction mechanism by stabilizing intermediates or altering transition states. A better understanding of adsorption helps chemists design more effective catalysts tailored for specific reactions, ultimately improving efficiency and selectivity in various chemical processes.

Related terms

homogeneous catalyst: A catalyst that is in the same phase as the reactants, usually in solution, and participates in the reaction to form an intermediate.

activation energy: The minimum energy required for a chemical reaction to occur, which can be lowered by the presence of a catalyst.

reaction mechanism: The step-by-step sequence of elementary reactions by which overall chemical change occurs, detailing how catalysts affect each step.