(709d) Microkinetic Modeling with Blowers-Masel Approximation to Scale Activation Energy Based on Enthalpy Change

Mean-field microkinetic modeling is used to design catalysts and to explore possible reaction mechanisms in heterogeneous catalysis. While screening for catalysts, considering coverage effects, or fitting to experimental data, the enthalpy of species needs to be adjusted, so the reaction enthalpies should be modified accordingly. The Blowers-Masel (BM) approximation scales the activation energy based on enthalpy change, like an Evans-Polanyi expression. The advantage of the BM approximation is that it only needs one parameter, called intrinsic activation energy, to estimate the activation energy in three different enthalpy ranges.

We implemented this new rate expression in Cantera, a software for reactor simulation, and applied it to model the catalytic partial oxidation of methane (CPOM) over a set of hypothetical metal surfaces. 81 CPOM mechanisms on unique metal catalysts are generated with Reaction Mechanism Generator (RMG) based on the linear scaling relationship and merged into one to incorporate all reaction pathways. Cantera is used to simulate the CPOM process on 81 metals using the BM approximation in a plug flow reactor (PFR). Density functional theory data are calculated or taken from literature to discuss the validity of the BM approximation. The energy diagram of the main reaction path is investigated with BM-adjusted activation barriers. Species' concentration profiles through the PFR and reaction kinetic sensitivity analyses do not substantially change after adding the BM approximation. However, the BM approximation significantly influences the species thermo-sensitivity, and the “volcano surface” plots illustrate different active areas, thus leading to conflicting conclusions when screening catalysts. Future work includes coupling the BM approximation with coverage-dependent thermodynamics to capture coverage effects.

The contribution made through this work is implementing a reaction kinetics expression in Cantera to estimate the reaction barrier based on the reaction enthalpy, to further provide flexibility in diverse applications of microkinetic modeling.