Heterogeneous catalysis is a fundamental process where catalysts and reactants exist in different phases. Unlike homogeneous catalysis, this involves surface reactions at interfaces between solid catalysts and gas or liquid reactants. The catalyst surface contains active sites where molecules adsorb, react, and desorb as products. This process is crucial in major industrial applications like ammonia synthesis, petroleum refining, and automotive emission control.
Catalyst surface structure determines reactivity through different types of active sites. The surface contains terrace sites with low activity, step sites with medium activity, and highly reactive kink sites. Surface atoms have lower coordination numbers compared to bulk atoms, creating electron-deficient sites that readily interact with reactant molecules. The varying electron density across these sites leads to different binding strengths and reaction pathways.