What are the main causes of catalyst deactivation?

Main causes include: Poisoning - strong chemisorption of impurities on active sites (sulfur on metal catalysts), Fouling/Coking - physical blocking by deposits (carbon on cracking catalysts), Sintering - loss of surface area at high temperatures (metal particle growth), Attrition - physical breakdown of catalyst particles (fluidized beds), and Leaching - loss of active component in liquid phase. Deactivation can be reversible (regeneration possible) or permanent, and affects catalyst life and reactor performance.