Abstract
Adsorption kinetics on energetically heterogeneous surfaces under isothermal conditions is analyzed using the uniform energy distribution model. Considering the quasi-equilibrium of surface diffusion between the adsorption sites with different energy, the kinetic equations d Θ / d t = ( k a p − A d K diff ) ( 1 − Θ ) for first-order adsorption and d Θ / d t = k a p ( 1 − Θ ) 2 − A d K diff Θ ( 1 − Θ ) for dissociative adsorption are obtained, where K diff is a coefficient describing the surface diffusion equilibrium, which depends on the coverage and the energy distribution. Under isochoric conditions with p decreasing due to adsorption, surface diffusion accelerates the rate towards equilibrium significantly, as observed in static calorimetric adsorption experiments. An approximate solution in Lagergren form is derived for this condition.
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