How the hydrogen sorption properties of palladium are modified through interaction with iridium

International audienceHydrogen sorption (adsorption/absorption) on metals, in the form of thin films or nanoparticles, is a key process in the fields of energy storage and heterogeneous catalysis. Atomic hydrogen dissolved in the subsurface of a metal affects its surface atomic and electronic structures, and thereby its surface reactivity and catalytic properties. In addition, alloy effects modify both catalytic and hydrogen sorption phenomena. In order to rationalize recent experimental results showing the negative impact of hydrogen absorption on catalysis, the present article proposes an insight into structure-reactivity relationships through computational simulations, using density functional theory, of hydrogen sorption in the near-surface region of palladium atomic layers interacting with an iridium substrate. A detailed analysis of the electronic structure using local projected densities of states (PDOS) and crystal orbital overlap population (COOP) curves was carried out. It is found that the Pd/Ir system, with respect to pure Pd surfaces, keeps acceptable adsorption properties for surface reactions while preventing hydrogen penetration. The results of electronic structure calculations show that the most important difference between Pd and Ir is related to the strong anti-bonding character of the 1s-H/5p-Ir interaction, leading to the non-bonding character of the sp-Ir interaction with hydrogen. Thus, increasing the Ir concentration in a Pd-based system increases the anti-bonding contribution, which strongly weakens the overall metal-hydrogen interaction

Ultradispersed Mo/TiO2 catalysts for CO2 hydrogenation to methanol

Mo/TiO2 catalysts with atomic dispersion of molybdenum appear active and stable in the gas-phase hydrogenation of CO2. A comparison between various titania materials shows a crucial effect of the support surface structure on the methanol yield. Molybdenum supported at low coverage on rutile titania nanorods is the most active and methanol-selective system. From catalyst characterization by aberration-corrected scanning transmission electron microscopy, near-ambient pressure X-ray photoelectron spectroscopy, diffuse reflectance UV-vis spectroscopy, and temperature-programmed techniques, we suggest that the most active catalysts for methanol production involve ultradispersed molybdate species with high reducibility and strong interaction with the rutile support.Peer ReviewedPostprint (author's final draft

Modelling Free and Oxide-supported Nanoalloy Catalysts : Comparison of Bulk-immiscible Pd-Ir and Au-Rh system and influence of a TiO2 support

SSCI-VIDE+ECI2D+LPIInternational audience--

A DFT study of molecular adsorption on titania-supported AuRh nanoalloys

SSCI-VIDE+ECI2D+LPIInternational audienceAuRh/TiO2 nanocatalysts have proved their efficiency in several catalytic reactions. In this work, density functional theory calculations are performed to investigate the effect of the TiO2 support on the structures of fcc 38-atom and 79-atom AuRh nanoalloys and their adsorption properties towards the reactant molecules CO and O-2. d-band centre analysis shows that the d-band model captures the trends better for both larger and supported alloy clusters due to reduced mechanical effects. Calculations reveal metal-to-support electron transfer, depending mainly on which metal atoms lie at the interface with the support. The adsorption strengths of CO and O-2 molecules on experimentally-relevant Janus segregated structures are slightly lower than on pure Rh clusters, which may reduce poisoning effects, while maintaining the high reactivity of Rh. In addition, higher adsorption energies are predicted for the less stable AucoreRhshell structure, which may lead to adsorption-induced restructuring under reaction conditions. (C) 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

Understanding and controlling the structure and segregation behaviour of AuRh nanocatalysts

Heterogeneous catalysis, which is widely used in the chemical industry, makes a great use of supported late-transition-metal nanoparticles, and bimetallic catalysts often show superior catalytic performances as compared to their single metal counterparts. In order to optimize catalyst efficiency and discover new active combinations, an atomic-level understanding and control of the catalyst structure is desirable. In this work, the structure of catalytically active AuRh bimetallic nanoparticles prepared by colloidal methods and immobilized on rutile titania nanorods was investigated using aberration-corrected scanning transmission electron microscopy. Depending on the applied post-treatment, different types of segregation behaviours were evidenced, ranging from Rh core-Au shell to Janus via Rh ball-Au cup configuration. The stability of these structures was predicted by performing density-functional-theory calculations on unsupported and titania-supported Au-Rh clusters; it can be rationalized from the lower surface and cohesion energies of Au with respect to Rh, and the preferential binding of Rh with the titania support. The bulk-immiscible AuRh/TiO2 system can serve as a model to understand similar supported nanoalloy systems and their synergistic behaviour in catalysis

Computational study of the adsorption of benzene and hydrogen on palladium–iridium nanoalloys

SSCI-VIDE+ECI2D+LPIInternational audienceThe preferred chemisorption sites on a variety of palladium-iridium nanoalloys are determined for benzene and hydrogen molecules. Available sites on the surface of the nanoalloys are explored using a random-search method, directly at the density functional level of theory. These searches successfully reveal the site preference for benzene and significant nanosize effects in the chemisorption of hydrogen. It is hoped that through the study of the chemisorption properties of Pd-Ir nanoalloys, complex catalytic processes, such as tetralin hydroconversion and the preferential oxidation of CO, can be better understood. (C) 2015 Elsevier B.V. All rights reserved

Influence of Pt particle size and reaction phase on the photocatalytic performances of ultradispersed Pt/TiO2 catalysts for hydrogen evolution

Pt/TiO2 photocatalysts were prepared by incipient wetness impregnation followed by oxidative and/or reductive thermal treatments. By varying the TiO2 form (commercial P25 and P90, and homemade shape-controlled), the Pt loading (0.2-1 wt% Pt) and the treatment temperature (200-600°C), it has been possible to tune the Pt cluster size. An increase in the ethanol dehydrogenation rate under ultraviolet irradiation as the Pt cluster average diameter decreases from 17 to 9 Å is suggested by our data. Whereas pre-reduction in H2 leads to Pt clusters, pre-calcination in air leads to atomically dispersed cationic Pt species. The former are more active and stable than the latter. This conclusion is valid both in gas- and liquid-phase reaction conditions for given TiO2 type and Pt loading. The activity results are consistent with a recent theoretical work showing that 1 nm is an optimal Pt cluster size for favoring both photoelectron transfer from TiO2 to Pt and hydrogen coupling on Pt. The best catalytic performance is obtained in gas phase for pre-reduced 0.2 wt% Pt/TiO2-P90, with an H2 production rate of 170 mmol h-1 gcat-1.Postprint (author's final draft

Penilaian Kinerja Keuangan Koperasi di Kabupaten Pelalawan

This paper describe development and financial performance of cooperative in District Pelalawan among 2007 - 2008. Studies on primary and secondary cooperative in 12 sub-districts. Method in this stady use performance measuring of productivity, efficiency, growth, liquidity, and solvability of cooperative. Productivity of cooperative in Pelalawan was highly but efficiency still low. Profit and income were highly, even liquidity of cooperative very high, and solvability was good

Differential cross section measurements for the production of a W boson in association with jets in proton–proton collisions at √s = 7 TeV

Measurements are reported of differential cross sections for the production of a W boson, which decays into a muon and a neutrino, in association with jets, as a function of several variables, including the transverse momenta (pT) and pseudorapidities of the four leading jets, the scalar sum of jet transverse momenta (HT), and the difference in azimuthal angle between the directions of each jet and the muon. The data sample of pp collisions at a centre-of-mass energy of 7 TeV was collected with the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0 fb[superscript −1]. The measured cross sections are compared to predictions from Monte Carlo generators, MadGraph + pythia and sherpa, and to next-to-leading-order calculations from BlackHat + sherpa. The differential cross sections are found to be in agreement with the predictions, apart from the pT distributions of the leading jets at high pT values, the distributions of the HT at high-HT and low jet multiplicity, and the distribution of the difference in azimuthal angle between the leading jet and the muon at low values.United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio