Improving the activity of gold nanoparticles for the water-gas shift reaction using TiO2–Y2O3: an example of catalyst design

In the last ten years, there has been an acceleration in the pace at which new catalysts for the watergas shift reaction are designed and synthesized. Pt-based catalysts remain the best solution when only activity is considered. However, cost, operation temperature, and deactivation phenomena are important variables when these catalysts are scaled in industry. Here, a new catalyst, Au/TiO2–Y2O3, is presented as an alternative to the less selective Pt/oxide systems. Experimental and theoretical techniques are combined to design, synthesize, characterize and analyze the performance of this system. The mixed oxide demonstrates a synergistic effect, improving the activity of the catalyst not only at large-to-medium temperatures but also at low temperatures. This effect is related to the homogeneous dispersion of the vacancies that act both as nucleation centers for smaller and more active gold nanoparticles and as dissociation sites for water molecules. The calculated reaction path points to carboxyl formation as the rate-limiting step with an activation energy of 6.9 kcal mol 1, which is in quantitative agreement with experimental measurements and, to the best of our knowledge, it is the lowest activation energy reported for the water-gas shift reaction. This discovery demonstrates the importance of combining experimental and theoretical techniques to model and understand catalytic processes and opens the door to new improvements to reduce the operating temperature and the deactivation of the catalyst.Ministerio de Economía y Competitividad (CTQ2015-64669-P and ENE2015-66975- C3-2-R)Junta de Andalucía (FQM-132 and TEP-106)European Union (HT-PHOTO-DB No. 752608

The importance of along-margin terrane transport in northern Gondwana: insights from detrital zircon parentage in Neoproterozoic rocks from Iberia and Brittany

Detrital zircons from late Neoproterozoic rocks of the peri-Gondwanan Cadomian belt of SW Iberia and north Armorican Domain of Brittany record Neoproterozoic (ca. 860-550 Ma), Palaeoproterozoic (ca. 2300-1800) and Archaean (ca 3300-2600 Ma) U-Pb ages. The absence of Mesoproterozoic zircons suggests that these terranes evolved in a peri-W African realm. This is in contrast to other western European terranes that preserve Mesoproterozoic zircons and are likely to have evolved in a peri-Amazonian realm. Such a contrast in detrital zircon populations, coupled with the presence of Mesoproterozoic zircons in the Ordovician Armorican quartzite, deposited in a peri-African platform, is interpreted to record along-margin terrane transport. The change in provenance suggests that subduction was replaced by transform faults that juxtaposed Amazonia-derived terranes against W Africa-derived terranes to form the Avalonia and Armorica microcontinents. Subsequent extension along the margin resulted in the birth of the Rheic Ocean and the outboard drift of Avalonia

Lithogeochemical and Sm-Nd and U-Pb isotope data from the Silurian– Lower Devonian Arisaig Group clastic rocks, Avalon terrane, Nova Scotia: A record of terrane accretion in the Appalachian-Caledonide orogen

The Silurian–Lower Devonian Arisaig Group, in the Avalon terrane of Nova Scotia, consists of a thick (~1900 m) sequence of unmetamorphosed fossiliferous siliciclastic strata deposited during terrane accretionary events in the Appalachian-Caledonide orogen. Geochemistry and Sm-Nd and U-Pb (detrital zircon) isotope data of Arisaig Group rocks contrast with the underlying Avalonian rocks, indicating that they were not derived from Avalonian basement. All sedimentary rocks are characterized by strongly negative εNd(t) values (from –4.8 to –9.3, t = 430 Ma) and TDM ages older than 1.5 Ga; the overall trend from the base to the top of the group is toward increasingly negative εNd values. The fact that some Silurian sedimentary rocks contain detrital zircons of similar age suggests that basin formation was broadly coeval with active volcanism in the orogen. These samples also contain abundant Neoproterozoic–Early Cambrian zircons (ca. 620–520 Ma) and lesser abundances at ca. 1200–900 and 2200–1500 Ma. Archean zircons are very minor. The sample of Lower Devonian strata contains Late Silurian and Early Ordovician zircons and, in comparison to the Silurian samples, less abundant Cambrian (ca. 520–510 Ma) and Neoproterozoic (610–550 Ma; 834 Ma) zircons and subordinate Mesoproterozoic (1000–1200 Ma), Meso proterozoic (1400–1600 Ma), and Paleo proterozoic (2000–2100 Ma) zircons. There are no Archean zircons. A comparison between the U-Pb detrital-zircon data and the age of tectonothermal events in potential source areas, together with regional geologic data, suggests that Silurian strata of the Arisaig Group were primarily derived from Baltica, but that there was increasing input from Laurentia by the time of deposition of the Lower Devonian strata of the group. The Arisaig Group is interpreted to have been deposited adjacent to the trailing edge of Avalonia during Appalachian accretionary events, and the geochemical and isotopic characteristics of its strata clearly record the signatures of these regional tectonic events

Safety assessment of underground vehicles passing over highly resilient straight tracks in the presence of a broken rail

In this paper, vehicle-track interaction for a new slab track design, conceived to reduce noise and vibration levels has been analyzed, assessing the derailment risk for trains running on curved track when encountering a broken rail. Two different types of rail fastening systems with different elasticities have been analysed and compared. Numerical methods were used in order to simulate the dynamic behaviour of the train-track interaction. Multibody system (MBS) modelling techniques were combined with techniques based on the finite element method (FEM). MBS modelling was used for modelling the vehicle and FEM for simulating the elastic track. The simulation model was validated by comparing simulated results to experimental data obtained in field testing. During the simulations various safety indices, characteristic of derailment risk, were analysed. The simulations realised at the maximum running velocity of 110 km/h showed a similar behaviour for several track types. When reducing the running speed, the safety indices worsened for both cases. Although the worst behaviour was observed for the track with a greater elasticity, in none of the simulations did a derailment occur when running over the broken rail

First Principles Study of Nickel Complex with 1,3-dithiole-2-thione-4,5-dithiolate Ligands as Model Photosensitizers

Dye-sensitized solar cells (DSSCs) have become in one important and promising technology in the photovoltaic field. The ability for a sensitizer to harvest light photons and inject the excited electrons into a photoanode, typically a metal oxide, determines the performance and operation range of the solar cell. Metal complexes with 1,3-dithiole-2-thione-4,5-dithiolate (dmit) ligands, which are an important class of functional materials, have received extensive attention due to their intriguing chemical and physical properties. The electronic and molecular properties of isolated and adsorbed nickel complexes with dmit ligands have been investigated using first principles calculations based on the density functional theory (DFT). Adsorption energies of metal complexes supported on the anatase TiO2(101) surface were calculated for three different configurations, linked by sulphur atom of Sthione, Sthiole-Sthiolate, and planar. The most stable adsorption configurations found in this study are the Sthiole-Sthiolate and the planar forms for the nickel complex. TD-DFT molecular calculations reveal that the lowest energy transition in ultraviolet visible near-infrared (UV-Vis-NIR) mainly corresponds to the HOMO-LUMO π–π* excitation for the nickel complex. The effect of the TiO2(101) surface on the absorption spectra of the nickel complex is practically limited to a red shift of about 0.1-0.3 eV. The analysis of the density of states for the dmit/TiO2(101) system shows that the LUMO of the metal complex lies at the edge of the TiO2 conduction band indicating, therefore, that electron injection from the complex excited state into the semiconductor surface is unlikel