Gerhard Ertl's contributions to catalysis are vast, but he is particularly noted for his groundbreaking studies on the mechanisms of chemical reactions at solid surfaces. His work has elucidated the fundamental steps of heterogeneous catalysis, especially in the context of the Haber-Bosch process, which is crucial for ammonia synthesis. By employing sophisticated surface science techniques, Ertl was able to provide detailed insights into the adsorption, dissociation, and reaction of molecules on catalytic surfaces.