Publisher Summary The frequency response technique for studying catalytic adsorption phenomena is an important experimental method. The method is illustrated by actual data from a hydrogen-on-nickel system. The amount of adsorbed gas on a catalyst that is part of an isothermal system varies with time when the pressure changes. This variation depends on the adsorption kinetics and the heterogeneity of the surface. During chemical adsorption on a catalyst surface, several processes occur simultaneously. This may result from the heterogeneous nature of the surface or to the existence of different adsorbed states. The tools of process control theory can be used to separate the phenomena and yield information on their nature. To determine the dynamic characteristics of an unknown system, the control engineer uses or induces certain forms of disturbances or “inputs” and observes or interprets their effects or “outputs.” Two of the most useful types of inputs for the study of process dynamics are the step function and the sine wave.