Modeling and simulation of transient adsorption and reaction in vacuum using the temporal analysis of products reactor

For determining rate constants of catalytic processes (adsorption, desorption, and reaction) from the evaluation of transient experiments in vacuum applying the temporal-analysis-of-products (TAP) reactor, suitable models were developed taking into account the gas-phase transport of the molecules and the surface processes. On the basis of simulation results, it is shown that by applying the TAP technique absolute values for rate constants of adsorption and desorption can be derived within a ''window'' of their order of magnitudes. It is shown that different types of adsorption (Langmuir, Temkin, Freundlich, and dissociative) result in different simulated response signals. Models were developed accounting for reactions including the simulation of experiments with sequential pulsing of two gases in order to study the reaction of adsorbed and gaseous species. The specific position of the catalyst-between two inert layers in the TAP reactor has to be considered because it-influences the response in the case of adsorption/desorption processes and results in a partial back-diffusion of a reaction product to the reactor inlet thus enhancing consecutive reactions.