Automated Detection and Characterization of Surface Restructuring Events in Bimetallic Catalysts

<div>Surface restructuring in bimetallic systems has recently been shown to play a crucial role in heterogeneous catalysis. In particular, the segregation in binary alloys can be reversed in the presence of strongly bound adsorbates. Mechanistic characterization of such restructuring phenomena at the atomic level remains scarce and challenging due to the large configurational space that must be explored. To this end, we propose an automated method to discover elementary surface restructuring processes in an unbiased fashion, using Pd/Ag as an example. We employ high-temperature classical molecular dynamics (MD) to rapidly detect restructuring events, isolate them, and optimize using density functional theory (DFT). In addition to confirming the known exchange descent mechanism, our systematic approach has revealed three new predominant classes of events at step edges of close-packed surfaces that have not been considered before: (1) vacancy insertion; (2) direct exchange; (3) interlayer exchange. The discovered events enable us to construct the complete set of mechanistic pathways by which Pd is incorporated into the Ag host in vacuum. These atomistic insights provide a step toward systematic understanding and engineering of surface segregation dynamics in bimetallic catalysts.</div>

Automated Detection and Characterization of Surface Restructuring Events in Bimetallic Catalysts

<div>Surface restructuring in bimetallic systems has recently been shown to play a crucial role in heterogeneous catalysis. In particular, the segregation in binary alloys can be reversed in the presence of strongly bound adsorbates. Mechanistic characterization of such restructuring phenomena at the atomic level remains scarce and challenging due to the large configurational space that must be explored. To this end, we propose an automated method to discover elementary surface restructuring processes in an unbiased fashion, using Pd/Ag as an example. We employ high-temperature classical molecular dynamics (MD) to rapidly detect restructuring events, isolate them, and optimize using density functional theory (DFT). In addition to confirming the known exchange descent mechanism, our systematic approach has revealed three new predominant classes of events at step edges of close-packed surfaces that have not been considered before: (1) vacancy insertion; (2) direct exchange; (3) interlayer exchange. The discovered events enable us to construct the complete set of mechanistic pathways by which Pd is incorporated into the Ag host in vacuum. These atomistic insights provide a step toward systematic understanding and engineering of surface segregation dynamics in bimetallic catalysts.</div>

Generalizedα-Attractor Models from Elementary Hyperbolic Surfaces

We consider generalizedα-attractor models whose scalar potentials are globally well-behaved and whose scalar manifolds are elementary hyperbolic surfaces. Beyond the Poincaré diskD, such surfaces include the hyperbolic punctured diskD⁎and the hyperbolic annuliA(R)of modulusμ=2log⁡R>0. For each elementary surface, we discuss its decomposition into canonical end regions and give an explicit construction of the embedding into the Kerekjarto-Stoilow compactification (which in all three cases is the unit sphere), showing how this embedding allows for a universal treatment of globally well-behaved scalar potentials upon expanding their extension in real spherical harmonics. For certain simple but natural choices of extended potentials, we compute scalar field trajectories by projecting numerical solutions of the lifted equations of motion from the Poincaré half plane through the uniformization map, thus illustrating the rich cosmological dynamics of such models.

Geographic envelope of the Moon and the identification of Moon landscapes with the use of the axiomatic method

Three consequent concepts that build up the algorithm of the identification of modern landscapes on the Moon surface are suggested. They are anaglyphonosphere axiomatic and landscape concepts obtained with the use of the axiomatic method. The first concept depicts the geographic envelope of the Moon as an anaglyphonosphere layer (relief) that is a continuum (total environment). The latter becomes the research subject for both a geomorphologist and a landscape researcher. Continuity, dynamics, range (amplitude), and erosion potential determine anaglyphonosphere. Axiomatic concept means constructing the sole scheme (mathematically determined) of the search for the elementary surface units using the geometric interpretation of surface patterns of the Moon and its landscape interpretation. The landscape concept is based on the classical principles of the landscape theory and the axiomatic principles of the previous concept. The synthesis of concepts is implemented in the models of Moon landscapes of four scales: zero, linear, two- and three-dimensional. The paper offers the last two models of Davy Catena. Proposed concepts with appropriate correction can be used in parallel studies of the natural environment: geological, geomorphological, climatic, etc. The advantages of the axiomatic method consist in the objective approach to the division of the surface into specific units (the landscapes in our case). The proposed method of identifying and displaying the landscape complexes on the lunar surface can be a significant complement for the study and mapping of terrestrial planets, satellites of planet-giants, etc.

Nanocatalysis

This article discusses nanocatalysis and especially the interrelation between the structure, composition and properties of catalysts. It begins with a review of techniques that have been developed and employed for surface characterization, which can be divided intothree main areas: spectroscopy, diffraction, and microscopy. After describing the nanocharacterization tools, the article considers the theoretical underpinnings of catalysts and catalytic processes. It also examines how detailed atomic-scale insight into elementary surface processes relevant to catalysis can be obtained mainly by means of high-resolution scanning tunnelling microscope studies on single-crystal surfaces. More specifically, it explores the surface structure, adsorption, dissociation and diffusion, and surface chemical reactions of catalysts. The article also looks at the design of new catalysts from first principles and concludes with an assessment of nanocatalysts and transmission electron microscope studies of nanoclusters on high surface area supports.