Química i Ordinadors, una bona simbiosi

El treball següent mostra els diferents camins a través dels quals poden tenir lloc les reaccions de transferència d'hidrogen. Amb l'ajut d'un ordinador, han simulat un cas concret d'aquest tipus de reaccions: la d'un catalitzador de ruteni anomenat "catalitzador de Shvo". D'aquesta manera, es troben més a prop d'esbrinar el mecanisme de la reacció, i establir les bases que el millorin, com ara incrementar la seva eficiència i disminuir la producció de processos secundaris no desitjats.El siguiente trabajo muestra los diferentes caminos a través de los que pueden tener lugar las reacciones de transferencia de hidrógeno. Con la ayuda de un ordenador, han simulado un caso concreto de este tipo de reacciones: la de un catalizador de rutenio conocido como "catalizador de Shvo". De este modo, se encuentran más cerca de averiguar el mecanismo de reacción, y establecer las bases que lo mejoren como, por ejemplo, incrementar su eficiencia y disminuir la producción de procesos secundarios no deseados

Activity Trends in the Propane Dehydrogenation Reaction Catalyzed by MIII Sites on an Amorphous SiO2 Model : A Theoretical Perspective

Altres ajuts: Acord transformatiu CRUE-CSICOne class of particularly active catalysts for the Propane Dehydrogenation (PDH) reaction are well-defined M(III) sites on amorphous SiO. In the present work, we focus on evaluating the catalytic trends of the PDH for four M(III) single-sites (Cr, Mo, Ga and In) on a realistic amorphous model of SiO using density functional theory-based calculations and the energetic span model. We considered a catalytic pathway spanned by three reaction steps taking place on selected M-O pair of the SiO model: σ-bond metathesis of propane on a M-O bond to form M-propyl and O-H group, a β-H transfer step forming M-H and propene, and the H-H coupling step producing H and regenerating the initial M-O bond. With the application of the energetic span model, we found that the calculated catalytic activity for Ga and Cr is comparable to the ones reported at the experimental level, enabling us to benchmark the model and the methodology used. Furthermore, results suggest that both In(III) and Mo(III) on SiO are potential active catalysts for PDH, provided they can be synthesized and are stable under PDH reaction conditions

The Effect of the Electronic Nature of Spectator Ligands in the C–H Bond Activation of Ethylene by Cr(III) Silicates: An ab initio Study

The Phillips catalyst, chromium oxides supported on silica, is one of the most widely used catalysts for the industrial production of polyethylene (PE). We recently synthesized a well-defined mononuclear Cr(III) silicate as active site model of the Phillips catalyst. The catalytic activity of this well-defined catalyst was similar to the industrial Phillips catalyst. We proposed that C–H bond activation of ethylene over a Cr–O bond initiates polymerization in this Cr(III) catalyst. Our results also showed that the presence of a second ethylene olefin in the coordination sphere of Cr decreases the intrinsic energy barrier of the C–H activation of ethylene. In order to understand the effect of this additional ligand in the C–H activation of ethylene by the Cr(III) catalyst, we evaluated the energetics of this step with different spectator ligands (C2H4, C2F4, N2 and CO) coordinated to the Cr center. The Charge Decomposition Analysis (CDA) of the bonding interactions between the Cr(III) catalyst and the ligands showed that the intrinsic energy barrier for the C–H activation of ethylene decreases with the increasing electron-donor properties of the spectator ligand

Catalitzadors bidimensionals per convertir el CO2 en un producte de major valor afegit

Un equip de recerca internacional on ha participat l'investigador Aleix Comas Vives ha aconseguit accelerar la transformació de diòxid de carboni i metà, dos gasos que contribueixen a l'escalfament global, en monòxid de carboni i hidrogen, una barreja amb valor afegit, mitjançant làmines de Mxens, un innovador catalitzador bidimensional.Un equipo internacional de científicos en el que ha participado el investigador Aleix Comas Vives ha conseguido acelerar la transformación de dióxido de carbono y metano, dos gases que contribuyen al calentamiento global, en monóxido de carbono e hidrógeno, una mezcla con valor añadido, mediante láminas de Mxens, un innovador catalizador bidimensional

Theoretical study of the catalytic performance of Fe and Cu single-atom catalysts supported on Mo2C toward the reverse water–gas shift reaction

The reverse water–gas shift (RWGS) is an attractive process using CO2 as a chemical feedstock. Single-atom catalysts (SACs) exhibit high catalytic activity in several reactions, maximizing the metal use and enabling easier tuning by rational design than heterogeneous catalysts based on metal nanoparticles. In this study, we evaluate, using DFT calculations, the RWGS mechanism catalyzed by SACs based on Cu and Fe supported on Mo2C, which is also an active RWGS catalyst on its own. While Cu/Mo2C showed more feasible energy barriers toward CO formation, Fe/Mo2C presented lower energy barriers for H2O formation. Overall, the study showcases the difference in reactivity between both metals, evaluating the impact of oxygen coverage and suggesting Fe/Mo2C as a potentially active RWGS catalyst based on theoretical calculations

Strain in Silica-Supported Ga(III) Sites : Neither Too Much nor Too Little for Propane Dehydrogenation Catalytic Activity

Altres ajuts: Acord transformatiu CRUE-CSICWell-defined Ga(III) sites on SiO are highly active, selective, and stable catalysts in the propane dehydrogenation (PDH) reaction. In this contribution, we evaluate the catalytic activity toward PDH of tricoordinated and tetracoordinated Ga(III) sites on SiO by means of first-principles calculations using realistic amorphous periodic SiO models. We evaluated the three reaction steps in PDH, namely, the C-H activation of propane to form propyl, the β-hydride (β-H) transfer to form propene and a gallium hydride, and the H-H coupling to release H, regenerating the initial Ga-O bond and closing the catalytic cycle. Our work shows how Brønsted-Evans-Polanyi relationships are followed to a certain extent for these three reaction steps on Ga(III) sites on SiO and highlights the role of the strain of the reactive Ga-O pairs on such sites of realistic amorphous SiO models. It also shows how transition-state scaling holds very well for the β-H transfer step. While highly strained sites are very reactive sites for the initial C-H activation, they are more difficult to regenerate. The corresponding less strained sites are not reactive enough, pointing to the need for the right balance in strain to be an effective site for PDH. Overall, our work provides an understanding of the intrinsic activity of acidic Ga single sites toward the PDH reaction and paves the way toward the design and prediction of better single-site catalysts on SiO for the PDH reaction. We performed computational calculations of Ga(III) single sites on realistic amorphous models of SiO to evaluate their catalytic activity toward the propane dehydrogenation reaction. Our results show that a balance in strain is key, in which neither too stiff nor too loose Ga−O bonding is needed to obtain the highest catalytic activity

CO oxidation on stepped-Pt(111) under electrochemical conditions: insights from theory and experiment

The co-adsorption of CO and OH on two Pt stepped surfaces vicinal to the (111) orientation has been evaluated by means of density functional theory (DFT) calculations. Focusing on Pt(533) and Pt(221), which contain (100) and (111)-steps, respectively, we find that (111)-steps should be more reactive towards CO oxidation than surfaces containing (100)-steps. The DFT results are compared with electrochemical experiments on the CO adsorption and oxidation on these vicinal surfaces.This work has been supported by the European Union through the Marie-Curie-ITN ELCAT. Further, J.B., A.C.-V. and T.J. gratefully acknowledge support from the “Deutsche Forschungsgemeinschaft” (DFG) as well as from the bwGRiD for computing resources. Further, support from the European Research Council through the ERC-StG THEOFUN is gratefully acknowledged. E.H. and C. B.-R. also acknowledge the support from MICIN (project no. CTQ2010-16271)

A new genus and new species of hypogeum Molopina from Catalan Pyrenean area (L’Alt Urgell, Lleida) (Coleoptera: Carabidae: Pterostichini)

Es descriu un nou gènere i una i nova espècie hipogea de la subtribu Molopina (Coleoptera: Carabidae: Pterostichini). Speleopidius joanivivesi n. gen. & n. sp., procedent de l’Avenc de la Cabana d’en Garraba, Pont de Bar (L’Alt Urgell, Lleida, Espanya). Es compara la relació del nou gènere i nova espècie amb d’altres Molopina hipogeus de la mediterrània occidental.It is described a new genus and a new hypogean species of the subtribe Molopina, tribe Pterostichini (Coleoptera, Carabidae), namely Speleopidius joanivivesi n. gen. & n. sp., from the Avenc de la Cabana d’en Garraba, Pont de Bar (L’Alt Urgell), Lleida, Spain. The relationships of the new taxa with other hypogean Molopina of the Western Mediterranean are discussed

Hypotyphlus clofentae n. sp. d’Anillina del Pallars Jussà, Catalunya (Coleoptera: Carabidae: Trechinae)

Es dona a conèixer una nova espècie del gènere Hypotyphlus Jeannel, 1937, Hypotyphlus clofentae n. sp., recol·lectada en una mina de la comarca del Pallars Jussà, Catalunya, que forma part del grup de H. pandellei segons la definició donada per Jeannel (1963). Es presenten imatges tant de laspecte com de les diferents estructures morfològiques característiques daquesta novetat.It is described a new species of the genus Hypotyphlus Jeannel, 1937, Hypotyphlus clofentae n. sp., collected in a mine in the region of Pallars Jussà, Catalonia. This species is likely a member of the group of H. pandellei according to the criteria given by Jeannel (1963). Images of both the habitus and the different morphological structures characteristic of this novelty are presented