Recursos de colección

RiuNet. Repositorio institucional de la Universitat de Valencia (102.815 recursos)

RiuNet es el Repositorio Institucional de la Universitat Politècnica de València, gestionado por la Biblioteca, cuyo objetivo es ofrecer acceso en Internet a la producción científica, académica y corporativa de la comunidad universitaria con la finalidad de aumentar su visibilidad y hacerla accesible y preservable.

Artículos, conferencias, monografías

Mostrando recursos 1 - 20 de 4.115

  1. Another beauty of analytical chemistry: chemical analysis of inorganic pigments of art and archaeological objects

    Domenech Carbo, Mª Teresa; Osete Cortina, Laura
    [EN] This lecture text shows what fascinating tasks analytical chemists face in Art Conservation and Archaeology, and it is hoped that students reading it will realize that passions for science, arts or history are by no means mutually exclusive. This study describes the main analytical techniques used since the eighteenth century, and in particular, the instrumental techniques developed throughout the last century for analyzing pigments and inorganic materials, in general, which are found in cultural artefacts, such as artworks and archaeological remains. The lecture starts with a historical review on the use of analytical methods for the analysis of pigments...

  2. Simple organic structure directing agents for synthesizing nanocrystalline zeolites

    Gallego-Sánchez, Eva María; Paris-Carrizo, Cecilia Gertrudis; Díaz-Rey, Maria Del Rocio; MARTÍNEZ ARMERO, MARTA EVELIA; Martínez-Triguero, Joaquín; Martínez, Cristina; Moliner Marin, Manuel; Corma Canós, Avelino
    [EN] The synthesis of the ZSM-5 and beta zeolites in their nanosized form has been achieved by using simple alkyl-substituted mono-cationic cyclic ammonium cations as OSDA molecules. The particular combination of a cyclic fragment and a short linear alkyl-chain group (preferentially C4) within the monocationic OSDA molecules allows directing the crystallization of nanosized zeolites with excellent solid yields (above 90%). Interestingly, the formation of the nanosized ZSM-5 and beta zeolites mostly depends on the size and nature of the cyclic fragment of the OSDA molecule, resulting in all cases in nanocrystalline solids with homogeneous distributions of particle sizes (similar to...

  3. Identification of Distinct Copper Species in Cu-CHA Samples Using NO as Probe Molecule. A Combined IR Spectroscopic and DFT Study

    Concepción Heydorn, Patricia; Boronat Zaragoza, Mercedes; Millan, Reisel; Moliner Marin, Manuel; Corma Canós, Avelino
    [EN] Combining IR spectroscopy of NO adsorption on copper exchanged molecular sieves with the chabazite structure, i.e. Cu-SAPO-34 and Cu-SSZ-13, and theoretical calculations, different types of copper species have been identified. On one hand, [Cu¿OH]+ species can be accurately distinguished, characterized by a ¿NO frequency at 1788¿ 1798 cm¿1 depending on their location in the chabazite structure (6R vs. 8R) and composition (Cu-SAPO-34 vs. Cu-SSZ-13). On the other hand, dimeric copper oxo [Cu¿O¿ Cu]2+ species have been properly identified by means of DFT modelling, that proposes a ¿NO stretching frequency of 1887 cm¿1, which has been confirmed experimentally in the Cu-SAPO-34 sample. Finally the location of isolated Cu2+ ions either in the 6R units...

  4. Functional Acid and Base Hybrid Catalysts Organized by Associated (Organo)aluminosilicate Layers for C-C Bond Forming Reactions and Tandem Processes

    Gaona Cordero, Aide; DÍAZ MORALES, URBANO MANUEL; Corma Canós, Avelino
    [EN] Novel bifunctional acid base monolayered hybrid catalysts (MLHMs), based on associated individual (organo)aluminosilicate sheets with amino and sulfonic pending groups located in the interlayer space, have been successfully prepared by direct alkaline hydrothermal synthesis and evaluated in consecutive catalytic transformations. Different characterization techniques such as chemical and thermogravimetrical analyses, X-ray diffraction, TEM microscopy, nuclear magnetic resonance (NMR), temperature programmed desorption of CO2 and NH3 (TPD), and textural measurements were used to show the physicochemical and structural nature of the materials, evidencing their effectiveness as functional acid, base, and acid base catalysts for different one pot two-step tandem reactions, which...

  5. Generation of subnanometric platinum with high stability during transformation of a 2D zeolite into 3D

    Liu, Lichen; DÍAZ MORALES, URBANO MANUEL; Arenal, Raul; Agostini, Giovanni; Concepción Heydorn, Patricia; Corma Canós, Avelino
    [EN] Single metal atoms and metal clusters have attracted much attention thanks to their advantageous capabilities as heterogeneous catalysts. However, the generation of stable single atoms and clusters on a solid support is still challenging. Herein, we report a new strategy for the generation of single Pt atoms and Pt clusters with exceptionally high thermal stability, formed within purely siliceous MCM-22 during the growth of a two-dimensional zeolite into three dimensions. These subnanometric Pt species are stabilized by MCM-22, even after treatment in air up to 540 degrees C. Furthermore, these stable Pt species confined within internal framework cavities show...

  6. V- and Nb-containing tungsten bronzes catalysts for the aerobic transformation of ethanol and glycerol. Bulk and supported materials

    La Salvia, N.; Delgado-Muñoz, Daniel; Ruiz-Rodríguez, Lidia; Nadji, L.; Masso Ramírez, Amada; López Nieto, José Manuel
    [EN] This work report the applicability of reflux to the synthesis of supported tungsten bronzes (i.e. W-V-O and W-Nb-O), using mesoporous KIT-6 as inert support. For comparison, the corresponding bulk materials prepared by reflux or by hydrothermal synthesis have been also prepared. The catalysts were characterized by several techniques (X-ray diffraction, N-2 adsorption, temperature programmed desorption (NH3), and Raman and FTIR spectroscopies) and tested in the selective aerobic transformation of ethanol and glycerol. These results demonstrate the formation of V- and Nb-containing tungsten oxide bronzes in all of the heat-treated samples (bulk and supported materials), as well as the effective...

  7. Continuous flow photoassisted CO2 methanation

    Albero-Sancho, Josep; Domínguez Torres, Esther; Corma Canós, Avelino; García Gómez, Hermenegildo
    [EN] Photoassisted CO2 methanation using Ni-Al2O3/SiO2 as a photoresponsive catalyst has been carried out at 225 degrees C under continuous flow conditions achieving up to 3.5% conversion of CO2 with complete selectivity to CH4 under 2327 W m(-2) irradiation for a contact time of 1.3 s. An apparent quantum yield of 0.11 was estimated for the continuous flow process.

  8. Oriented Au nanoplatelets on graphene promote Suzuki-Miyaura coupling with higher efficiency and different reactivity pattern than supported palladium

    Candu, Natalia; Dhakshinamoorthy, Amarajothi; Apostol, Nicoleta; Teodorescu, Cristian; Corma Canós, Avelino; García Gómez, Hermenegildo; Parvulescu, Vasile I.
    [EN] Facet 111 oriented Au nanoplatelets (20-40 nm wide, 3-4 nm height) grafted on graphene ((Au) over bar /fl-G) are about three orders of magnitude more efficient than Pd nanoparticles supported on graphene to promote Suzuki-Miyaura coupling. In contrast to Pd catalysis, it is shown here that the product yields in Suzuki-Miyaura coupling catalyzed by Au nanoparticles follow the order chlorobenzene > bromobenzene > iodobenzene. Kinetic studies show that this reactivity order is the result of the poisoning effect of halides for Au that is much higher for I- than Br- and much higher than for Cl-, due to adsorption....

  9. "Ab initio" synthesis of zeolites for preestablished catalytic reactions

    Gallego-Sánchez, Eva María; Portilla Ovejero, Mª Teresa; Paris-Carrizo, Cecilia Gertrudis; Leon Escamilla, Efigenio Alejandro; Boronat Zaragoza, Mercedes; Moliner Marin, Manuel; Corma Canós, Avelino
    [EN] Unlike homogeneous catalysts that are often designed for particular reactions, zeolites are heterogeneous catalysts that are explored and optimized in a heuristic fashion. We present a methodol. for synthesizing active and selective zeolites by using org. structure-¿directing agents that mimic the transition state (TS) of preestablished reactions to be catalyzed. In these zeolites, the pores and cavities could be generated approaching a mol.-¿recognition pattern. For disproportionation of toluene and isomerization of ethylbenzene into xylenes, the TSs are larger than the reaction products. Zeolite ITQ-¿27 showed high disproportionation activity, and ITQ-¿64 showed high selectivity for the desired para and ortho...

  10. Colloidal Crystal Thins Films Grown into Corrugated Surface Templates

    RAMIRO MANZANO, FERNANDO; Bonet Salom, Elvira; Rodríguez, Marie-Isabelle; MESEGUER RICO, FRANCISCO JAVIER
    [EN] The influence of patterned surfaces on the formation of one- and two-dimensional colloidal crystals is analyzed. We have used the corrugated surface of a digital versatile disc (DVD) for template surface processing. When the sphere diameter is on the order of the groove width of patterned substrates, a rich variety of particle decorations appear. However, if particle size is much larger than template patterns, large domains of particle ordering are formed.

  11. Multi-Criteria Optimization for Fleet Size with Environmental Aspects

    Sawik, Bartosz; Faulin, Javier; Pérez-Bernabeu, Elena
    [EN] This research concerns multi-criteria vehicle routing problems. Mathematical models are formulated with mixed-integer programming. We consider maximization of capacity of truck vs. minimization of utilization of fuel, carbon emission and production of noise. The problems deal with green logistics for routes crossing the Western Pyrenees in Navarre, Basque Country and La Rioja, Spain. We consider heterogeneous fleet of trucks. Different types of trucks have not only different capacities, but also require different amounts of fuel for operations. Consequently, the amount of carbon emission and noise vary as well. Companies planning delivery routes must consider the trade-off between the financial and...

  12. Total Oxidation of Propane Using CeO2 and CuO-CeO2 Catalysts Prepared Using Templates of Different Nature

    Solsona, Benjamin; Sanchis, Rut; Dejoz, Ana M.; Garcia, Tomas; Ruiz-Rodríguez, Lidia; López Nieto, José Manuel; Cecilia, Juan Antonio; Rodriguez-Castellon, Enrique
    [EN] Several CeO2 and CuO-CeO2 catalysts were prepared using different methods, i.e., a homogeneous precipitation with urea, a nanocasting route using CMK-3 carbon as a hard template and a sol¿gel process using Poly(methyl methacrylate) (PMMA) polymer as a soft template, and tested in the total oxidation of propane. The catalysts were characterized by a number of physicochemical techniques (XRD, N2 adsorption, TPR, XPS, Raman spectroscopy) showing distinct characteristics. For each series, Cu-Ce-O catalysts with low Cu-loadings (5 wt % CuO) showed the highest activity, higher than those samples either without copper or with high Cu-loading (13 wt % CuO). The...

  13. Characterizing Landscape Spatial Heterogeneity Using Semivariogram Parameters Derived from NDVI Images

    de Oliveira Silveira, Eduarda Martiniano; de Mello, Jose Marcio; Acerbi Junior, Fausto Weimar; dos Reis, Aliny Aparecida; Withey, Kieran Daniel; Ruiz Fernández, Luis Ángel
    [EN] Assuming a relationship between landscape heterogeneity and measures of spatial dependence by using remotely sensed data, the aim of this work was to evaluate the potential of semivariogram parameters, derived from satellite images with different spatial resolutions, to characterize landscape spatial heterogeneity of forested and human modified areas. The NDVI (Normalized Difference Vegetation Index) was generated in an area of Brazilian amazon tropical forest (1,000 km²). We selected samples (1 x 1 km) from forested and human modified areas distributed throughout the study area, to generate the semivariogram and extract the sill (¿²-overall spatial variability of the surface property) and range (¿-the length scale of the...

  14. Experimental simulation of continuous nanofiltration processes by means of a single module in batch mode

    Santafé Moros, María Asunción; Gozálvez-Zafrilla, José M.; Lora-García, Jaime
    [EN] This work proposes a method of simulating the performance of continuous nanofiltration processes by means of experimental runs performed on a laboratory set-up equipped with a spiral-wound module working in batch recirculation mode. It describes how to implement the proper changes in feed concentration and operating conditions in a batch recirculated system in order to obtain similar conditions to those of a continuous one. The analogy between the concentration process in the continuous and in the batch recirculation system is discussed and the difference in ion concentration of the cumulative permeate between the two systems is estimated numerically. The...

  15. Air radon equilibrium factor measurement in a Waste Water Pre-Treatment Plant

    Martinez-Ferri, Javier Enrique; Juste Vidal, Belen Jeanine; Ortiz Moragón, Josefina; Martorell Alsina, Sebastián Salvador; Verdú Martín, Gumersindo Jesús
    [EN] We analyze in this paper a Waste Water Pre-Treatment Plant (WWTP) located at the Mediterranean coast with air radon concentration above Spanish action level (600 Bq per cubic meter). This paper presents a method for radon equilibrium determination by gamma spectrometry measuring of the radon progeny concentrations in the air, in order to estimate WWTP workers effective dose more exactly. The method is based on simultaneous sampling of air through a filter paper and alpha spectrometry measurement of radon activity concentration in the air. According to the measured radon activity concentration in the air of 368 +/- 45 Bq/m(3)...

  16. Predicting mobile apps spread: An epidemiological random network modeling approach

    Alegre-Sanahuja, Juan; Cortés, J.-C.; Villanueva Micó, Rafael Jacinto; Santonja, Francisco-Jose
    [EN] The mobile applications business is a really big market, growing constantly. In app marketing, a key issue is to predict future app installations. The influence of the peers seems to be very relevant when downloading apps. Therefore, the study of the evolution of mobile apps spread may be approached using a proper network model that considers the influence of peers. Influence of peers and other social contagions have been successfully described using models of epidemiological type. Hence, in this paper we propose an epidemiological random network model with realistic parameters to predict the evolution of downloads of apps. With this model, we are able...

  17. Catalysis at the Heart of Success!

    Bornscheuer, Uwe T.; Hashmi, A. Stephen K.; García Gómez, Hermenegildo; Rowan, Michael A.
    Bornscheuer, UT.; Hashmi, ASK.; García Gómez, H.; Rowan, MA. (2017). Catalysis at the Heart of Success!. ChemCatChem. 9(1):6-9. doi:10.1002/cctc.201601553

  18. Anion transport through ceramic electrodialysis membranes made with hydrated cerium dioxide

    Mora-Gómez, Julia; García Gabaldón, Montserrat; Martí Calatayud, Manuel César; Mestre, Sergio; Pérez-Herranz, Valentín
    [EN] In this research, low-cost ceramic anion-exchange membranes have been developed from porous supports manufactured, using a chamotte as a pore former. An inorganic anion-exchanger (hydrated cerium dioxide) has been deposited into the support and fixed by thermal treatment. The effects of some process variables (such as the temperature of the thermal treatment or the pH of the electrolyte) on the properties of the anion-exchange membranes have been investigated. The electrochemical performance of the resulting membranes has been compared to that exhibited by ceramic anion-exchange membranes based on another anion exchanger (hydrated zirconium dioxide) deposited into alumina-kaolin supports. The temperature...

  19. Extending the deterministic Riemann-Liouville and Caputo operators to the random framework: A mean square approach with applications to solve random fractional differential equations

    Burgos, C.; Cortés, J.-C.; Villafuerte, L.; Villanueva Micó, Rafael Jacinto
    [EN] This paper extends both the deterministic fractional Riemann¿Liouville integral and the Caputo fractional derivative to the random framework using the mean square random calculus. Characterizations and sufficient conditions to guarantee the existence of both fractional random operators are given. Assuming mild conditions on the random input parameters (initial condition, forcing term and diffusion coefficient), the solution of the general random fractional linear differential equation, whose fractional order of the derivative is ¿ ¿ [0, 1], is constructed. The approach is based on a mean square chain rule, recently established, together with the random Fröbenius method. Closed formulae to construct reliable approximations for the mean and the...

  20. TiO2 polymorph dependent SMSI effect in Co-Ru/TiO2 catalysts and its relevance to Fischer-Tropsch synthesis

    Bertella, Francine; Concepción Heydorn, Patricia; MARTINEZ FELIU, AGUSTIN
    [EN] Pure anatase and rutile TiO2 samples were synthesized by thermal treatment of reverse microemulsions and applied as supports for preparing Ru-promoted Co catalysts (0.5 wt% Ru, 10 wt% Co). The catalysts were characterized by ICP-OES,XRD,Raman spectroscopy, N2 physisorption, H2-TPR, electronmicroscopy (FESEM, HAADF-STEM), H2 chemisorption,XPS, and in situ IR-CO after H2 reduction and reaction with syngas, and their catalytic performance for Fischer-Tropsch synthesis (FTS) studied at industrial conditions (220 ¿C, 2.0 MPa, H2/CO = 2). The two catalysts exhibited comparable mean Co particle sizes (5¿6 nm) as well as high and alike degrees of cobalt reduction (ca. 90%). The SMSI decoration effect arising during H2 reduction was...

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