A realistic kinetic Monte Carlo simulation of the faceting of a Pt(110) surface under reaction conditions

Multi-scale Simulation of Equilibrium Step Fluctuations on Cu(111) Surfaces

Understanding the nature of active sites is a non-trivial task, especially when the catalyst is sensitively affected by chemical reactions and environmental conditions. The challenge lies on capturing explicitly the dynamics of catalyst evolution during reactions. Despite the complexity of catalyst reconstruction, we can untangle them into several elementary processes, of which surface diffusion is of prime importance. By applying density functional theory-kinetic Monte Carlo (DFT-KMC) simulation employed with cluster expansion (CE), we investigated the microscopic mechanism of surface diffusion of Cu with defects such as steps and kinks. Based on the result, the energetics obtained from CE have shown good agreement with DFT calculations. Various diffusion events during the step fluctuations are discussed as well. Aside from the adatom attachment, the diffusion along the step edge is found to be the dominant mass transport mechanism, indicated by the lowest activation energy. We also calculated time correlation functions at 300, 400, and 500 K. However, the time exponent in the correlation function does not strictly follow the power law behavior due to the limited step length, which inhibits variation in the kink density.

Kinetic modelling of heterogeneous catalytic systems

The importance of heterogeneous catalysis in modern life is evidenced by the fact that numerous products and technologies routinely used nowadays involve catalysts in their synthesis or function. The discovery of catalytic materials is, however, a non-trivial procedure, requiring tedious trial-and-error experimentation. First-principles-based kinetic modelling methods have recently emerged as a promising way to understand catalytic function and aid in materials discovery. In particular, kinetic Monte Carlo (KMC) simulation is increasingly becoming more popular, as it can integrate several sources of complexity encountered in catalytic systems, and has already been used to successfully unravel the underlying physics of several systems of interest. After a short discussion of the different scales involved in catalysis, we summarize the theory behind KMC simulation, and present the latest KMC computational implementations in the field. Early achievements that transformed the way we think about catalysts are subsequently reviewed in connection to latest studies of realistic systems, in an attempt to highlight how the field has evolved over the last few decades. Present challenges and future directions and opportunities in computational catalysis are finally discussed.

In situ tracing of atom migration in Pt/NiPt hollow spheres during catalysis of CO oxidation

NiPt hollow spheres decorated by Pt nanoparticles were synthesized by a facile wet chemical route through galvanic replacement. In situ STEM imaging and 3D reconstruction were performed to evidence the migration of Pt atoms during catalysis of CO oxidation, providing a practical insight into the structural stability of bimetallic catalysts.

CO-activator model for reconstructing Pt(100) surfaces: local microstructures and chemical turbulence

We present the results of the modeling of CO adsorption and catalytic CO oxidation on inhomogeneous Pt(100) surfaces which contain structurally different areas. These areas are formed during the CO-induced transition from a reconstructed phase with hexagonal geometry of the overlayer to a bulklike (1 x 1) phase with square atomic arrangement. In the present approach, the surface transition is explained in terms of nonequilibrium bistable behavior. The bistable region is characterized by a coexistence of the hexagonal and (1 x 1) phases and is terminated in a critical bifurcation point which is located at (T(c) approximately 680 K, p(CO)(c) approximately 10 Torr). Due to increasing fluctuations, the behavior at high temperatures and pressures in the vicinity of this cusp point should be qualitatively different from the hysteresis-type behavior which is typically observed in the experiments under ultrahigh vacuum conditions. On the inhomogeneous surface, we find a regime of nonuniform oscillations characterized by random standing waves of adsorbate concentrations. The resulting spatial deformations of wave fronts allow us to gain deeper insight into the nature of irregular oscillations on Pt(100) surface.

Nucleation of chemical waves at defects: A mirror electron microscopy study of catalytic CO oxidation on Pt(110)

Using mirror electron microscopy (MEM) as spatially resolving method the nucleation of chemical waves in catalytic CO oxidation on a Pt(110) surface was investigated in the 10(-5) mbar range. The waves nucleated at an electrically insulating impurity of approximately 15 microm diameter (the "defect") which most likely represents a diamond particle left over from the polishing process. Nucleation events are initiated by a dynamic process in a boundary layer of approximately 1 microm width between the defect and the surrounding Pt(110) surface. Depending on the parameter choice the fronts/pulses do not escape from the vicinity of the defect and later on die out or, in a supercritical nucleation, propagate across the surface. Asymmetric nucleation leads to spiral waves which remain pinned to the defect. The defect has a kind of steering effect causing chemical waves to collide exactly at the defect. This steering effect is evidently due to a distortion of the substrate lattice in the vicinity of the defect.