Effect of Force and Confinement on Chemical Reaction Kinetics

This work studies model systems that are relevant to understanding the fundamentals of surface chemical processes. A Cu(100) single crystal surface modified by methyl thiolate species, formed from the adsorption of dimethyl disulfide, is used for modeling the effect of an external force in a chemical reaction. Furthermore, 2D-Zeolite is synthesized, characterized and postulated as a model system for studying chemistry in confined space. Furfural adsorption on Pd(111) is studied under different experimental conditions by means of infrared reflection-absorption spectroscopy. Furfural uptake experiments from sub-monolayer to multilayer coverages and sequential heating lead to an analysis of conformational changes and tilting angles as a function of coverage and temperature. Finally, surface self-assembly processes are explored by means of Monte Carlo simulations that produce results with potential use as a general computational model for studying the interconnection of distributed particles on surfaces

Exploring Zeolite Chemistry with the Tools of Surface Science: Challenges, Opportunities, and Limitations

The complexity of catalysts that the surface science community has been able to address has increased substantially in a systematic manner, starting with metal and oxide single crystal surfaces and evolving to an atomistic description of clusters and nanoparticles on well-defined, planar supports. The next step in adding complexity is now to address surfaces of porous oxide materials, in particular of zeolites, which are the most extensively used catalysts in the industry. The recently reported successful fabrication of well-ordered thin films, consisting of planar arrangement of aluminosilicate polygonal prisms on a metal substrate counting with highly acidic bridging hydroxyl groups on the surface, represents the limiting case of infinitely large pore and cages in zeolites. This model system allows one to study reactions catalyzed by zeolites using the toolkit of surface science. In this Perspective, we describe the zeolitic model system, with its virtues and limitations, as well as the challenges, opportunities and expectations for the future in modelling porous catalysts by a surface science approach

Sonósferas : Experiencias sobre la enseñanza de la composición musical mediante grafías

El siguiente trabajo se realiza en el marco de una experiencia de vinculación propuesta desde la cátedra de Metodología y Práctica de la Enseñanza (Plan '86). Trata de una experiencia que busca generar una aproximación a la creación y puesta en marcha de actividades en unidades curriculares (UC) de diversas instituciones. Estas experiencias son realizadas en grupos, en nuestro caso, en pareja pedagógica. Nuestro grupo desarrolló sus actividades en “Collegium”, institución privada radicada en la ciudad de Córdoba, Argentina, en la UC composición II. Vale la pena señalar que la institución se originó (en 1982) como una idea alternativa a la educación musical que en ese momento tenía el conservatorio Provincial Félix T. Garzón, una de las pocas ofertas en educación musical en la cuidad. (Gentile y Carricaburu, 2018) Composición II es una unidad de definición institucional 2 en la carrera de Profesorado en Música de dicha institución se trata de una unidad curricular que se destina a la enseñanza a futuros docentes de música, quienes no necesariamente se desempeñarán como compositores.Fil: Boscoboinik, Iván. Universidad Nacional de Córdoba. Facultad de Artes. Departamento Académico de Música; Argentina

Support effects on the atomic structure of ultrathin silica films on metals

We studied the atomic structure of ultrathin silica films on Pt(111) in comparison with the previously studied films on Mo(112) and Ru(0001). The results obtained by scanning tunneling microscopy, photoelectron spectroscopy, and infrared reflection absorption spectroscopy suggest that the metal-oxygen bond strength plays the decisive role in the atomic structure of the silica overlayers on metal substrates. Metals with high oxygen adsorption energy favor the formation of the crystalline monolayer SiO2.5 films, whereas noble metals form primarily vitreous SiO2 bilayer films. The metals with intermediate energies may form either of the structures or both coexisting. In the systems studied, the lattice mismatch plays only a minor role

Stabilization of Ultrathin Zinc Oxide Films on Metals: Reconstruction versus Hydroxylation

Thin (0001)-oriented films of ZnO on metals may exhibit interlayer relaxations, resulting in the hexagonal boron nitride-like crystal structure. The driving force for such reconstruction is the polar instability of either Zn- or O- terminated surfaces of ZnO(0001). Here, we examined surface hydroxylation as another possible stabilization mechanism. Zinc oxide films grown on Pt(111) were studied by infrared reflection–absorption spectroscopy (IRAS) as a function of film thickness and morphology as imaged by scanning tunneling microscopy. Despite prepared in pure oxygen ambient, the “as grown” films on Pt(111) expose hydroxyl groups. In contrast, the bilayer films on Ag(111) do not exhibit OH species, not even upon dosing of hydrogen or water. The results show that hydrogen may efficiently be provided by a Pt support, even for the multilayer films, via hydrogen dissociation and subsequent diffusion of H atoms through the film. Thermal stability of the OH-terminated surfaces depends on the film thickness, with a monolayer film being the least stable. Removal of OH species from a monolayer film proceeds through water desorption and may be accompanied by hydrogen spillover onto more stable multilayer structures. Stabilization of the polar ZnO surface in the metal-supported films seems to be a delicate balance between interlayer relaxation and hydroxylation and depends on the metal support

Mechanistic insights into carbon–carbon coupling on NiAu and PdAu single-atom alloys

Carbon–carbon coupling is an important step in many catalytic reactions, and performing sp³–sp³ carbon–carbon coupling heterogeneously is particularly challenging. It has been reported that PdAu single-atom alloy (SAA) model catalytic surfaces are able to selectively couple methyl groups, producing ethane from methyl iodide. Herein, we extend this study to NiAu SAAs and find that Ni atoms in Au are active for C–I cleavage and selective sp³–sp³ carbon–carbon coupling to produce ethane. Furthermore, we perform ab initio kinetic Monte Carlo simulations that include the effect of the iodine atom, which was previously considered a bystander species. We find that model NiAu surfaces exhibit a similar chemistry to PdAu, but the reason for the similarity is due to the role the iodine atoms play in terms of blocking the Ni atom active sites. Specifically, on NiAu SAAs, the iodine atoms outcompete the methyl groups for occupancy of the Ni sites leaving the Me groups on Au, while on PdAu SAAs, the binding strengths of methyl groups and iodine atoms at the Pd atom active site are more similar. These simulations shed light on the mechanism of this important sp3–sp3 carbon–carbon coupling chemistry on SAAs. Furthermore, we discuss the effect of the iodine atoms on the reaction energetics and make an analogy between the effect of iodine as an active site blocker on this model heterogeneous catalyst and homogeneous catalysts in which ligands must detach in order for the active site to be accessed by the reactants

Thin silica films on Ru(0001): monolayer, bilayer and three-dimensional networks of [SiO₄] tetrahedra

The atomic structure of thin silica films grown over a Ru(0001) substrate was studied by X-ray photoelectron spectroscopy, infrared reflection absorption spectroscopy, low energy electron diffraction, helium ion scattering spectroscopy, CO temperature programmed desorption, and scanning tunneling microscopy in combination with density functional theory calculations. The films were prepared by Si vapor deposition and subsequent oxidation at high temperatures. The silica film first grows as a monolayer of corner-sharing [SiO4] tetrahedra strongly bonded to the Ru(0001) surface through the Si–O–Ru linkages. At increasing amounts of Si, the film forms a bilayer of corner-sharing [SiO4] tetrahedra which is weakly bonded to Ru(0001). The bilayer film can be grown in either the crystalline or vitreous state, or both coexisting. Further increasing the film thickness leads to the formation of vitreous silica exhibiting a three-dimensional network of [SiO4]. The principal structure of the films can be monitored by infrared spectroscopy, as each structure shows a characteristic vibrational band, i.e., [similar]1135 cm-1 for a monolayer film, [similar]1300 cm⁻-1 for the bilayer structures, and [similar]1250 cm⁻-1 for the bulk-like vitreous silica