5. Influence of adsorbed phase transfer on internal efficiency

Since the chemical transformation of a catalytic reaction takes place in the adsorbed phase, even when the adsorption and desorption stages correspond to conditions close to thermodynamic equilibrium, the existence of a concentration gradient for reactants and products in the gas phase will necessarily generate a concentration gradient for reactants and products in the adsorbed phase. Within the adsorbed phase, this gradient will give rise to a diffusional transfer which may, in some cases, be superimposed on the diffusional transfer in the gas phase. Under these conditions, for fixed external operating conditions, the reagent flow rate consumed within the particle may be different from that evaluated by limiting diffusional transfer within the gas phase. These differences can occur both for a reaction with a single stoichiometry, and for a chemical transformation with multiple stoichiometries...