Catalysts age due to several mechanisms: 1. Thermal Degradation: High temperatures can cause sintering, where catalyst particles agglomerate, reducing the active surface area. 2. Poisoning: Certain substances, called _poisons_, can adsorb onto the active sites of the catalyst, rendering them inactive. 3. Fouling: The accumulation of unwanted materials on the catalyst surface hinders access to active sites. 4. Chemical Leaching: Active components can be dissolved and removed by the reaction medium. 5. Structural Changes: Prolonged exposure to reaction conditions can alter the crystalline structure of the catalyst.
