From atomic scale reactant ordering to mesoscale reaction front propagation: CO oxidation on Pd(100)

CO Oxidation on Rh(100): Multisite Atomistic Lattice-Gas Modeling

“…Our analysis in the following sections utilizes a general multisite lattice-gas (LG) model for surface reaction on unreconstructed metal(100) surfaces, selecting parameters to describe Rh(100). This model refines one presented previously for CO+O/Pd(100). , It provides a realistic and flexible description of adlayer structure and dynamics, allowing population of not just the low-coverage adsorption sites for each adspecies, but also other sites that might be occupied at higher coverages or under mixed adlayer reaction conditions. As indicated above, we consider bridge (br), fourfold hollow (4fh), and on-top (top) sites assigning appropriate binding energies for different sites for CO and O (so that those sites with the lowest binding energy will have the smallest, often negligible, population).…”

Kinetic Monte Carlo Simulation of Statistical Mechanical Models and Coarse-Grained Mesoscale Descriptions of Catalytic Reaction–Diffusion Processes: 1D Nanoporous and 2D Surface Systems

“…For fcc(100) surfaces, the first realistic modeling for CO oxidation was attempted in 2004 for an unreconstructed Pd(100) surface. 45 This modeling was subsequently extended to model experimental TPR studies, 71 and refined to include a more realistic description of adsorption dynamics. 7 Below we describe the current, more generic version of the model that has been applied to Rh(100) 169 and more recently to unreconstructed Pt(100) and Ir(100) surfaces.…”

“…METAL (100) SURFACES The recently developed realistic multisite lattice-gas reaction models for CO oxidation described in section 6 have been fairly successful in capturing experimental behavior. 7,45,57,71,72,169 However, the complexity of these models can inhibit understanding of the relationship between various model ingredients and observed behavior, for example, of the bifurcation diagram for bistable reactions. Thus, we describe three alternative approaches intended to facilitate enhanced understanding.…”

“…67,68 A version of HMM termed heterogeneous coupled lattice-gas (HCLG) simulation was developed in the mid-1990s specifically for application to surface reaction systems, 69,70 and has been more recently applied to realistic reaction models. 45,71,72 For accurate description of basic behavior in 1D nanoporous systems and of spatiotemporal behavior in 2D surface systems, an appropriate description of chemical diffusion in mixed multicomponent systems is key. This should be based on an appropriate Onsager formulation of transport theory that recognizes the coupling between concentration gradients and diffusion fluxes of different species and thus involves a diffusion tensor.…”

“…To this end, one can implement spatially discrete stochastic (Markovian) reaction–diffusion models. For reactions in 1D nanoporous systems , as described in section , one can divide the pore into cells comparable to reactant size and treat continuous diffusion by hopping and exchange between adjacent cells. − ,− For reactions on 2D crystalline surfaces , we shall assume that reactants are localized on well-defined adsorption sites possibly of multiple types, and then implement appropriate detailed and realistic single-site or more generally multisite lattice-gas (msLG) models. ,,− Extensive input is required for these models for both system thermodynamics (adsorption energies, adspecies interactions) and kinetics (adsorption and desorption dynamics, reaction pathways and barriers), which is obtained from or by comparing with experiment and increasingly from density functional theory (DFT) analysis . The behavior of these models is in principle described exactly by master equations. , However, given the difficulty of reliable analysis of the master equations, model behavior is usually instead determined precisely by kinetic Monte Carlo (KMC) simulation, − as described extensively in recent reviews. ,, More details are provided in section .…”