Multiscale modelling of total pressure effects on complete methane oxidation over Pd/Al2O3

Licentiate thesis, 2018

The models used in heterogeneous catalysis are becoming more advanced and the literature shows an increased interest in incorporating the atomistic scale into microkinetics. Coupling kinetics based on first-principles calculations to macroscopic effects can pave the way towards more comprehensive modelling methods and to tailored catalyst designs. The theme of this thesis is to coupling a reaction model based on first-principles to mass and heat transport and develop a multiscale reactor model for complete methane oxidation. The multiscale model is used to determine if the activity of an alumina supported palladium catalyst can be enhanced by increasing the reaction total pressure. First, a 1D porous catalyst model is developed where the kinetics and mass and heat transport is discussed for complete methane oxidation over Pd/Al2O3 for a simulated exhaust gas. It is shown that the catalyst performance can be enhanced by increasing the total pressure. However, the positive effect is constrained by a high coverage of the hindering surface species bicarbonates, adsorbed water and hydroxyl groups originating from the water and carbon dioxide in the bulk gas. The reaction controlling phenomena are identified for a range of temperatures and total pressures. Next, a 2D multiscale reactor model is developed to predict methane conversions. The conversion can be in- creased if the temperature is sufficiently high to overcome the desorption barriers of surface species hindering dissociative methane adsorption. The effects of total pressure on surface kinetics and mass and heat transport are discussed.