Several aspects contribute to the complexity of catalytic systems:
1. Nature of the Catalyst: Catalysts can be homogeneous, heterogeneous, or enzymatic. Each type has unique properties and mechanisms. For example, homogeneous catalysts are in the same phase as the reactants, leading to different kinetic and thermodynamic behaviors compared to heterogeneous catalysts.
2. Reaction Conditions: Temperature, pressure, and the presence of other chemicals can profoundly affect the catalyst's performance. Catalysts often require stringent conditions to remain active and effective, and slight deviations can lead to significant changes in reaction rates and selectivity.
3. Surface Interactions: In heterogeneous catalysis, the interaction between reactants and the catalytic surface is a key factor. The surface structure, electronic properties, and the presence of surface defects can all influence the activity and selectivity of the catalyst.
