scispace - formally typeset
Search or ask a question
Author

Manuel Corral-Valero

Bio: Manuel Corral-Valero is an academic researcher. The author has contributed to research in topics: Ab initio & Dissociation (chemistry). The author has an hindex of 1, co-authored 1 publications receiving 124 citations.

Papers
More filters
Journal ArticleDOI
TL;DR: In this paper, an atomic picture of highly dispersed palladium and platinum catalysts supported on gamma-alumina is provided, where the interaction energies and the structures of Pd13 and Pt13 clusters are systematically investigated by density functional theory calculations.

134 citations

Journal ArticleDOI
TL;DR: In this article , an adaptive multilevel splitting (AMS) method is proposed to compute the rate constants for catalytic events occurring at the surface of a given material, which is based on a combination of the rare event sampling method and ab initio molecular dynamics.
Abstract: Computing accurate rate constants for catalytic events occurring at the surface of a given material represents a challenging task with multiple potential applications in chemistry. To address this question, we propose an approach based on a combination of the rare event sampling method called adaptive multilevel splitting (AMS) and ab initio molecular dynamics. The AMS method requires a one-dimensional reaction coordinate to index the progress of the transition. Identifying a good reaction coordinate is difficult, especially for high dimensional problems such as those encountered in catalysis. We probe various approaches to build reaction coordinates such as support vector machine and path collective variables. The AMS is implemented so as to communicate with a density functional theory-plane wave code. A relevant case study in catalysis, the change of conformation and the dissociation of a water molecule chemisorbed on the (100) γ-alumina surface, is used to evaluate our approach. The calculated rate constants and transition mechanisms are discussed and compared to those obtained by a conventional static approach based on the Eyring-Polanyi equation with harmonic approximation. It is revealed that the AMS method may provide rate constants that are smaller than those provided by the static approach by up to 2 orders of magnitude due to entropic effects involved in the chemisorbed water molecule.

Cited by
More filters
Journal ArticleDOI
TL;DR: The correlation between the catalytic properties and the exposed facets verifies the chemical nature of the morphology effect and provides an overview of the interactions between the rod-shaped oxides and the metal nanoparticles in metal-oxide catalyst systems, involving crystal-facet-selective deposition of metal particles onto different crystal facets in the oxide supports.
Abstract: Nanocatalysts are characterised by the unique nanoscale properties that originate from their highly reduced dimensions. Extensive studies over the past few decades have demonstrated that the size and shape of a catalyst particle on the nanometre scale profoundly affect its reaction performance. In particular, controlling the catalyst particle morphology allows a selective exposure of a larger fraction of the reactive facets on which the active sites can be enriched and tuned. This desirable surface coordination of catalytically active atoms or domains substantially improves catalytic activity, selectivity, and stability. This phenomenon is called morphology-dependent nanocatalysts: catalyst particles with anisotropic morphologies on the nanometre scale greatly affect the reaction performance by selectively exposing the desired facets. In this review, we highlight important progress in morphology-dependent nanocatalysts based on the use of rod-shaped metal oxides with characteristic redox and acid-base features. The correlation between the catalytic properties and the exposed facets verifies the chemical nature of the morphology effect. Moreover, we provide an overview of the interactions between the rod-shaped oxides and the metal nanoparticles in metal-oxide catalyst systems, involving crystal-facet-selective deposition of metal particles onto different crystal facets in the oxide supports. A fundamental understanding of active sites in morphologically tuneable oxides enclosed by the desired reactive facets is expected to direct the development of highly efficient nanocatalysts.

414 citations

Journal ArticleDOI
TL;DR: In this paper, the projection of the eigenfunctions obtained in standard plane-wave first-principle electronic-structure calculations into atomic-orbital basis sets is proposed as a formal and practical link between the methods based on plane waves and the ones based on atomic orbitals.
Abstract: The projection of the eigenfunctions obtained in standard plane-wave first-principle electronic-structure calculations into atomic-orbital basis sets is proposed as a formal and practical link between the methods based on plane waves and the ones based on atomic orbitals. Given a candidate atomic basis, ({\it i}) its quality is evaluated by its projection into the plane-wave eigenfunctions, ({\it ii}) it is optimized by maximizing that projection, ({\it iii}) the associated tight-binding Hamiltonian and energy bands are obtained, and ({\it iv}) population analysis is performed in a natural way. The proposed method replaces the traditional trial-and-error procedures of finding appropriate atomic bases and the fitting of bands to obtain tight-binding Hamiltonians. Test calculations of some zincblende semiconductors are presented.

349 citations

Journal ArticleDOI
TL;DR: In this paper, the authors highlight the key mechanisms behind support-induced enhancement in the catalytic properties of metal NPs, such as supportinduced changes in the NP morphology, stability, electronic structure, and chemical state.
Abstract: The development of new catalysts for energy technology and environmental remediation requires a thorough knowledge of how the physical and chemical properties of a catalyst affect its reactivity. For supported metal nanoparticles (NPs), such properties can include the particle size, shape, composition, and chemical state, but a critical parameter which must not be overlooked is the role of the NP support. Here, we highlight the key mechanisms behind support-induced enhancement in the catalytic properties of metal NPs. These include support-induced changes in the NP morphology, stability, electronic structure, and chemical state, as well as changes in the support due to the NPs. Utilizing the support-dependent phenomena described in this Perspective may allow significant breakthroughs in the design and tailoring of the catalytic activity and selectivity of metal nanoparticles.

204 citations

Journal ArticleDOI
01 Jan 2019
TL;DR: In this article, the authors reveal the opposite process as a novel deactivation mechanism: nanoparticles rapidly lose activity by high-temperature nanoparticle decomposition into inactive single atoms, leading to severe loss of activity in as little as ten minutes.
Abstract: In the high-temperature environments needed to perform catalytic processes, supported precious metal catalysts severely lose their activity over time. Even brief exposure to high temperatures can lead to significant losses in activity, which forces manufacturers to use large amounts of noble metals to ensure effective catalyst function for a required lifetime. Generally, loss of catalytic activity is attributed to nanoparticle sintering, or processes by which larger particles grow at the expense of smaller ones. Here, by independently controlling particle size and particle loading using colloidal nanocrystals, we reveal the opposite process as a novel deactivation mechanism: nanoparticles rapidly lose activity by high-temperature nanoparticle decomposition into inactive single atoms. This deactivation route is remarkably fast, leading to severe loss of activity in as little as ten minutes. Importantly, this deactivation pathway is strongly dependent on particle density and concentration of support defect sites. A quantitative statistical model explains how for certain reactions, higher particle densities can lead to more stable catalysts.

146 citations

Journal ArticleDOI
TL;DR: In this article, Huanchen Zhai and Anastassia N. Alexandrova discuss the fluxionality of catalytic clusters and how to identify the most stable structure, the global minimum.
Abstract: Viewpoint pubs.acs.org/acscatalysis Fluxionality of Catalytic Clusters: When It Matters and How to Address It Huanchen Zhai † and Anastassia N. Alexandrova* ,†,‡ Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095, United States California NanoSystems Institute, Los Angeles, California 90095, United States 1. INTRODUCTION Small clusters secured at a given size, for example, via deposition on surfaces of semiconductors, can be remarkable catalysts. In the so-called “non-scalable” regime, where every atom and every electron counts in catalyst tuning, 1−4 the opportunities for design are vast and intellectually attractive. At the same time, these systems are incredibly complex to characterize. In particular, in the nonscalable regime, clusters have shapes that are far from being idealized cuts out of the bulk, especially in the presence of adsorbates (reactants, intermediates, products of the reaction) and the support. Instead, cluster shapes can be highly diverse and hardly ever obey our intuition, which is uncomfortably weak in this case. One problem then is to identify the most stable structure, the global minimum. Many efficient Global Optimization (GO) algorithms, including Generic Algorithm (GA), 5−8 Particle Swarm Optimization (PSO), 9,10 Simulated Annealing (SA), 11 and Basin Hopping (BH) 12,13 have been shown to be successfully applied to small cluster systems, when combined with different level ab initio electronic structure methods. In addition, the GO algorithms can be further accelerated by using potential energy surface fitting techniques 14−16 or empirical potentials, 17,18 where the latter can be particularly useful for significantly larger clusters. 19 However, even if the global minimum is found, just the global minimum may tell only part of the story. Potential energy surfaces of clusters are typically rich in low- energy local minima. Many of these isomers are energetically accessible at the elevated temperatures of catalysis, to the degree that thermodynamic equilibration is kinetically possible. For example, the gas-phase Pt 8 cluster has ca. 30 distinct isomers (local minima) within the vicinity of the global minimum that can be populated at 700 K. 14 Of course, it is possible that some isomers are protected kinetically by high barriers, especially when the supporting surface provides strong and selective interactions with certain isomers. Regardless, several isomers should be suspected to be present in the catalytic system. This calls for a statistical ensemble representation of the catalyst. Furthermore, the most stable isomer may not be the most catalytically active. After all, it is intuitive that less-stable species are more likely to be reactive. For example, consider catalytic Au clusters versus stable and inert bulk Au. Thus, if there exists a relationship between the catalytic efficiency of a cluster isomer and its relative stability, then it is more likely to be inversely proportional than otherwise. In summary, even if the global minimum of a cluster is found, the utility of this isomer alone in describing size- specific catalytic activities is likely limited. A cartoon illustration of this point is shown in Figure 1. © 2017 American Chemical Society Figure 1. Conditions of catalysis (A) do not imply a single rigid cluster isomer facilitating a single catalytic event in vacuum (B), but instead, realistic coverage, temperature T, pressure p, access to many cluster isomers (% in C indicating probabilities for occurrences), and fluxionality all have an influence on catalyst activity. Thus, a statistical ensemble representation of the catalyst isomers under catalytic thermal conditions is necessary. The situation is further complicated by the fact that isomers may interconvert from one to another under the influence of increased temperature and because of the changing amount and chemical nature of adsorbates 20,21 (for example, reactants versus reaction intermediates). This phenomenon is called fluxionality, and it is the topic of the present article. From our point of view, the most difficult question is that of the interdependence and the interaction between the catalyzed reaction and cluster isomer interconversion. Clusters covered with reactants may have a different preferred shape or an ensemble of shapes than those covered with reaction intermediates or products. However, does it mean that the cluster rearranges in the course of the reaction step, that is, part of the reaction coordinate? Alternatively, does it mean that the clusters interconvert from one to another within the given free- energy well (say that of the reactants) and, once a particularly catalytic isomer forms in this process of equilibration, the reaction proceeds with a very small barrier? If the latter is the case, then, once the next reaction intermediate is formed, the clusters may again re-equilibrate in the new free-energy well. The generally longer lifetime in the wells should allow for this. At the moment, there is a controversy and a general lack of clarity on this question. How can we begin thinking about it? Received: November 15, 2016 Published: January 27, 2017 DOI: 10.1021/acscatal.6b03243 ACS Catal. 2017, 7, 1905−1911

145 citations