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

Effects of the capping ligands, linkers and oxide surface in the electron injection mechanism of copper sulfide Quantum Dots sensitized solar cells

Because of the different components that constitute a quantum dots solar cells, QDSCs, and the difficulty of experimentally isolate the effect of each of them on the adsorption spectra of the system, we have modeled different Cu2S QDSCs models by means of DFT. A bottom-up approach can differentiate the effect of each component in the electronic structure and absorption spectra. First, Cu2S QDs were built including a U parameter to effectively describe the localization of the electrons. The effect of the capping agents was addressed using ligands with different electron- donating/- withdrawing groups. The role of the linkers and their adsorption of the surface of the oxide were also examined. Finally, we proposed a main indirect electron injection mechanism based on the position of the peaks of the spectra.Ministerio de Economía y Competitividad CTQ2015-64669-PJunta de Andalucía P12-FQM-159

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

New ideas on the Proterozoic-Early Palaeozoic evolution of NW Iberia: insights from U–Pb detrital zircon ages

U–Pb ages were obtained on single detrital zircon grains separated from six samples of Neoproterozoic and Lower Palaeozoic sedimentary and volcanosedimentary rocks from NW Iberia using the laser ablation microprobe-inductively coupled plasma mass spectrometry (LAM-ICP-MS) method. Precambrian greywackes yielded abundant zircons with Neoproterozoic (800–640 Ma) and Mesoproterozoic (0.9–1.2 Ga) ages, and a smaller proportion of Palaeoproterozoic (1.8–2 Ga) and Archaean zircons. Palaeozoic samples (Lower Cambrian and Ordovician) yielded abundant zircons with younger Neoproterozoic (ca. 550 and 620 Ma) and Mesoproterozoic (0.9–1.2 Ga) ages. Palaeoproterozoic (1.8–2 Ga) and Archaean zircons were also found. This data set, used in conjuction with previous paleogeographic and isotopic studies sheds new light on the Precambrian-early Palaeozoic evolution of NW Iberia and is consistent with the following sequence of events: (1) Early Cadomian-Avalonian subduction and arc construction (ca. 800–640 Ma). This magmatic episode created the main arc edifice (Avalonia); (2) full development of a back arc basin upon which the Neoproterozoic sediments were deposited (ca. 640–640 Ma). The combined U–Pb ages of detrital zircons and Nd isotopic features of these sedimenary rocks suggest that they were mostly shed from the main magmatic arc. On the basis of the presence of Grenvillian age detrital zircons with short waterborne transport before incorporation in the sediment, we propose that the basin was possibly located in a peri-Amazonian realm close to West Avalonian terranes. These basins were developed upon a cratonic basement that possibly involved both Grenvillian (ca. 0.9–1.2 Ga) and Transamazonian (ca. 1.9–2.1) igneous rocks. The reported zircon ages suggest a long-lived subduction, starting at ca. 800 Ma and terminated by ca. 580–570 Ma with no geological record of a final collision event; (3) the continuation of extension gave rise to the undocking of Avalonia from the back-arc. Detrital zircon ages in Lowermost Cambrian strata suggest that the main arc edifice had drifted away by ca. 550–540 Ma and was no longer shedding detritus into the back-arc basin. (4) During the Lower Ordovician, further extension of an already thinned crust gave rise to the Lower Ordovician ‘Ollo de Sapo’ magmatic event (ca. 480 Ma). Coeval volcanism in neighbouring areas displaying within-plate geochemical signatures is consistent with an extensional setting for the generation of the Lower Ordovician igneous and sedimentary rocks. Detrital zircon ages and Nd isotopic features of the Ordovician greywackes reflect both an increase in the contribution from older crustal components and the addition of newly accreted crust. A progressively thinning crust is a likely scenario that would explain the simultaneous exhumation of lower crustal (Grenvillian+Transamazonian/Icartian) material and the generation of coeval magmatism. This latter scenario is consistent with models proposed for other circum-North Atlantic Avalonian-Cadomian terranes where repeated episodes of melting occurred in response to subduction and subsequent rifting events