First-Principles-Based Microkinetic Modeling of Methane Steam Reforming with Improved Description of Product Desorption

Abstract

The method combining density functional theory (DFT) calculations with microkinetic modeling has attracted increasing attention in obtaining a deeper understanding of catalytic reactions. While product desorption is conventionally regarded as an equilibrated process in the microkinetic modeling, it might be influential to product selectivity when competing reactions should be considered. In this work, a complex reaction network is established first for the methane steam reforming reaction using the equilibrium and immobile models over Ni, Pd, and Pt surfaces. This provides a basis to further investigate the reaction mechanism and kinetic modeling results. The results show that when different desorption models are considered, the total activity regarding methane conversion and the coverage and DRC value of the main species at the steady state are the same on each surface. In contrast, the mechanism of CO2 formation is varied based on different desorption models. Consequently, the rate and selectivity of CO2 generation on each metal catalyst are significantly improved when the barrier of CO desorption is considered in the microkinetic modeling compared with the modeling only with barrierless CO desorption.

Top‐down kinetic modeling from power law to elementary steps using KASTER: A methane steam reforming case study

“…This could be expected as water does not have a negative effect on any of the individual reaction steps in the considered reaction mechanisms. The potential negative reaction order of water is sometimes attributed to competitive adsorption, 7,55 but the molecular/ dissociative adsorption equilibrium coefficients obtained from first principles calculations indicate that the gas phase species are highly favored thermodynamically compared to their adsorbed counterparts, 32,33 at the very high temperatures (900-1300 K) which are usually employed for methane steam reforming. 7 However, the first principles calculations only consider the interaction between the catalyst surface and the adsorbed component, while in reality adsorbed molecules will possibly affect the adsorption of subsequent molecules, especially for polar components such as water.…”

“…For more complex (microkinetic) models, it is not always easy to obtain reliable thermodynamic data in the field of heterogeneous catalysis, as it requires reliable estimations of the enthalpy and entropy of the surface species on the catalyst. However, several methods are commonly used to calculate such thermodynamic properties, for example, DFT methods, [32][33][34] which can include corrections by considering experimental data, 35 or methods which estimate the adsorption enthalpy and entropy on a certain catalyst, such as the UBI-QEP method. 36 To obtain reliable thermodynamic data for methane steam reforming on a Ni catalyst, the tool RMG-cat was considered in this work.…”

A microkinetic study of CO2 hydrogenation to methanol on Pd1–Cu(111) and Pd1–Ag(111) catalysts: a DFT analysis

“…Density functional theory (DFT) stands out as a viable computational method that assists in unravelling the predominant reaction pathways, providing valuable microkinetic insights for the development of functional catalysts that enhance CH 3 OH production. 14 For instance, Tezsevin et al 15 observed that the Cu(211) surface doped with Ho is highly effective in activating CO 2 than the Cu(111) surface. The presence of the Ho-doped Cu(211) surface enhances the formate reaction mechanism, favouring the development of the H 2 COO* intermediate over the HCOOH* intermediate.…”

Kinetic Monte Carlo Simulations Coupling the Isomerization and Diffusion of Xylenes in HZSM-5

“…Consequently, the qualitative prediction of changes in product distribution based solely on free energy data from elementary processes becomes limited. While microkinetic modeling based on the mean-field approximation is commonly applied to predict the rates of surface catalytic reactions, − its primary application lies in describing steady-state kinetics.…”