Konstantin M. Neyman

Bio: Konstantin M. Neyman is an academic researcher from University of Barcelona. The author has contributed to research in topics: Adsorption & Cluster (physics). The author has an hindex of 56, co-authored 196 publications receiving 9724 citations. Previous affiliations of Konstantin M. Neyman include University of Erlangen-Nuremberg & Universidad Nacional del Sur.

Support nanostructure boosts oxygen transfer to catalytically active platinum nanoparticles

Abstract: Interactions of metal particles with oxide supports can radically enhance the performance of supported catalysts. At the microscopic level, the details of such metal-oxide interactions usually remain obscure. This study identifies two types of oxidative metal-oxide interaction on well-defined models of technologically important Pt-ceria catalysts: (1) electron transfer from the Pt nanoparticle to the support, and (2) oxygen transfer from ceria to Pt. The electron transfer is favourable on ceria supports, irrespective of their morphology. Remarkably, the oxygen transfer is shown to require the presence of nanostructured ceria in close contact with Pt and, thus, is inherently a nanoscale effect. Our findings enable us to detail the formation mechanism of the catalytically indispensable Pt-O species on ceria and to elucidate the extraordinary structure-activity dependence of ceria-based catalysts in general.

First-principles LDA + U and GGA + U study of cerium oxides: Dependence on the effective U parameter

Abstract: The electronic structure and properties of cerium oxides ($\mathrm{Ce}{\mathrm{O}}_{2}$ and ${\mathrm{Ce}}_{2}{\mathrm{O}}_{3}$) have been studied in the framework of the $\mathrm{LDA}+\mathrm{U}$ and $\mathrm{GGA}(\mathrm{PW}91)+\mathrm{U}$ implementations of density functional theory. The dependence of selected observables of these materials on the effective U parameter has been investigated in detail. The examined properties include lattice constants, bulk moduli, density of states, and formation energies of $\mathrm{Ce}{\mathrm{O}}_{2}$ and ${\mathrm{Ce}}_{2}{\mathrm{O}}_{3}$. For $\mathrm{Ce}{\mathrm{O}}_{2}$, the $\mathrm{LDA}+\mathrm{U}$ results are in better agreement with experiment than the $\mathrm{GGA}+\mathrm{U}$ results whereas for the computationally more demanding ${\mathrm{Ce}}_{2}{\mathrm{O}}_{3}$ both approaches give comparable accuracy. Furthermore, as expected, ${\mathrm{Ce}}_{2}{\mathrm{O}}_{3}$ is much more sensitive to the choice of the U value. Generally, the PW91 functional provides an optimal agreement with experiment at lower U energies than LDA does. In order to achieve a balanced description of both kinds of materials, and also of nonstoichiometric $\mathrm{Ce}{\mathrm{O}}_{2\ensuremath{-}x}$ phases, an appropriate choice of U is suggested for $\mathrm{LDA}+\mathrm{U}$ and $\mathrm{GGA}+\mathrm{U}$ schemes. Nevertheless, an optimum value appears to be property dependent, especially for ${\mathrm{Ce}}_{2}{\mathrm{O}}_{3}$. Optimum U values are found to be, in general, larger than values determined previously in a self-consistent way.

Counting electrons on supported nanoparticles

Abstract: Electronic interactions between metal nanoparticles and oxide supports control the functionality of nanomaterials, for example, the stability, the activity and the selectivity of catalysts. Such interactions involve electron transfer across the metal/support interface. In this work we quantify this charge transfer on a well-defined platinum/ceria catalyst at particle sizes relevant for heterogeneous catalysis. Combining synchrotron-radiation photoelectron spectroscopy, scanning tunnelling microscopy and density functional calculations we show that the charge transfer per Pt atom is largest for Pt particles of around 50 atoms. Here, approximately one electron is transferred per ten Pt atoms from the nanoparticle to the support. For larger particles, the charge transfer reaches its intrinsic limit set by the support. For smaller particles, charge transfer is partially suppressed by nucleation at defects. These mechanistic and quantitative insights into charge transfer will help to make better use of particle size effects and electronic metal-support interactions in metal/oxide nanomaterials.

Maximum noble-metal efficiency in catalytic materials: atomically dispersed surface platinum.

Abstract: Platinum is the most versatile element in catalysis, but it is rare and its high price limits large-scale applications, for example in fuel-cell technology. Still, conventional catalysts use only a small fraction of the Pt content, that is, those atoms located at the catalyst's surface. To maximize the noble-metal efficiency, the precious metal should be atomically dispersed and exclusively located within the outermost surface layer of the material. Such atomically dispersed Pt surface species can indeed be prepared with exceptionally high stability. Using DFT calculations we identify a specific structural element, a ceria "nanopocket", which binds Pt(2+) so strongly that it withstands sintering and bulk diffusion. On model catalysts we experimentally confirm the theoretically predicted stability, and on real Pt-CeO2 nanocomposites showing high Pt efficiency in fuel-cell catalysis we also identify these anchoring sites.

Reassignment of the Vibrational Spectra of Carbonates, Formates, and Related Surface Species on Ceria: A Combined Density Functional and Infrared Spectroscopy Investigation

Abstract: Using a combination of state-of-the-art computational modeling and Fourier transform infrared (FTIR) spectroscopy study of the surface species formed during interaction of CO2 or CO with activated (stoichiometric), reduced, and hydroxylated ceria, CeO2, we assigned various experimentally observed vibrational modes to individual types of surface species. We considered carbonates CO32–, formates HCO2–, and hydrogen carbonates CO2(OH)− bound in various ways to the surface of a ceria nanoparticle. Since the structure of the surface carbonate species is particularly versatile, we introduced a notation of different types of such species and computationally determined the regions where the characteristic vibrational frequencies of each type of species can be found. The complementary FTIR measurements of the surface species produced under different conditions revealed the actual experimental vibrational peaks and allowed estimation of the accuracy of the computational method to reproduce the frequencies of differ...

Metal Catalysts for Heterogeneous Catalysis: From Single Atoms to Nanoclusters and Nanoparticles.

Abstract: Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal–support interaction, and metal–reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results o...

Heterogeneous single-atom catalysis

Abstract: Single-atom catalysis has arguably become the most active new frontier in heterogeneous catalysis. Aided by recent advances in practical synthetic methodologies, characterization techniques and computational modelling, we now have a large number of single-atom catalysts (SACs) that exhibit distinctive performances for a wide variety of chemical reactions. This Perspective summarizes recent experimental and computational efforts aimed at understanding the bonding in SACs and how this relates to catalytic performance. The examples described here illustrate the utility of SACs in a broad scope of industrially important reactions and highlight the advantages these catalysts have over those presently used. SACs have well-defined active centres, such that unique opportunities exist for the rational design of new catalysts with high activities, selectivities and stabilities. Indeed, given a certain practical application, we can often design a suitable SAC; thus, the field has developed very rapidly and afforded promising catalyst leads. Moreover, the control we have over certain SAC structures paves the way for designing base metal catalysts with the activities of noble metal catalysts. It appears that we are entering a new era of heterogeneous catalysis in which we have control over well-dispersed single-atom active sites whose properties we can readily tune. Single-atom catalysts are heterogeneous materials featuring active metals sites atomically dispersed on a surface. This Review describes methods by which we prepare and characterize these materials, as well as how we can tune their catalytic performance in a variety of important reactions.

Cu and Cu-Based Nanoparticles: Synthesis and Applications in Catalysis.

Abstract: The applications of copper (Cu) and Cu-based nanoparticles, which are based on the earth-abundant and inexpensive copper metal, have generated a great deal of interest in recent years, especially in the field of catalysis. The possible modification of the chemical and physical properties of these nanoparticles using different synthetic strategies and conditions and/or via postsynthetic chemical treatments has been largely responsible for the rapid growth of interest in these nanomaterials and their applications in catalysis. In addition, the design and development of novel support and/or multimetallic systems (e.g., alloys, etc.) has also made significant contributions to the field. In this comprehensive review, we report different synthetic approaches to Cu and Cu-based nanoparticles (metallic copper, copper oxides, and hybrid copper nanostructures) and copper nanoparticles immobilized into or supported on various support materials (SiO2, magnetic support materials, etc.), along with their applications i...

Fundamentals and Catalytic Applications of CeO2-Based Materials

Abstract: Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40th anniversary since ceria was first employed by Ford Motor Company as an oxygen storage component in car converters, to become in the years since its inception an irreplaceable component in three-way catalysts (TWCs). Apart from this well-established use, ceria is looming as a catalyst component for a wide range of catalytic applications. For some of these, such as fuel cells, CeO2-based materials have almost reached the market stage, while for some other catalytic reactions, such as reforming processes, photocatalysis, water-gas shift reaction, thermochemical water splitting, and organic reactions, ceria is emerging as a unique material, holding great promise for future market breakthroughs. While much knowledge about the fundamental characteristics of CeO2-based materials has already been acquired, new characterization techniques and powerful theoretical methods are dee...