An easy handling formulation of hybrid material, which could approach carbon nanomaterials application to industrial catalysts, of carbon nanofibers (CNF) and carbon nanotubes (CNT) over γ-alumina, C@alumina is described. The study discussed the selection of iron precursor to obtain mechanical stable hybrids by analysis of coverage effect of process preparation of seminal γ-alumina pellets, in order to evaluate the yield of carbon nanomaterials (CNFs/CNTs) coverage on the alumina pellets. Each C@alumina series were synthetized by catalytic vapor decomposition of acetylene at 1023 K, and were studied according to the nature of active phase, the iron precursor, by the light of characterization results obtained by thermogravimetric analysis and Scanning Electron Microscopy. Besides, ethanol reaction is employed as chemical reaction test for acid-base surface distribution analysis. Finally, the hydrophobic behavior of every precursor hybrid sample is discussed attending to contact angle. So, it was discussed from de nature of iron precursors of acetylacetonate, chloride, sulfate, cyanide, pentacarbonyl, phthalocyanine, 1,10-phenanthroline, ferrocene the surface structure of 3d-solids obtained, and it is correlated with the effects of iron precursor loading, pKa, and polar surface area (PSA) and metal-surface interaction. It was evidenced the effect of iron precursor selection over the C@alumina hybrid hydrophobic properties.
Powder metallurgy technique has been extended in automobile industry and other engineering applications. Competitive manufacturing costs have led to important innovations in different fields of powder metallurgy. Recently, research has been focused on reaching higher performance at a lower cost. Carbon nanostructures as carbon nanofibres (CNF) have also entered in the material science as reinforcing composites. In this study, different materials formed by low alloy steel Fe-Ni-Mo powder (Distaloy AQ) with 0.4% of graphite and 0.5% CNFs (carbon nanofibres) synthesised at 723, 773, 823 and 873 K have been studied. All the materials were compacted at 700 MPa and sintered at 1393 K and 90N2–10H2 atmosphere. The influence of CNFs synthesis temperature has been analysed for its application in powder metallurgy. The microstructure, mechanical properties such as tensile strength, elongation, hardness, density and wear behaviour were investigated. The CNFs synthesised at 873 K promoted better mechanical properties.
DOI:10.3762/bjnano.7.18
Guzman, E.; Maestro, A.; Llamas, S.; J. Alvarez-Rodriguez;
Francisco Ortega;
Ángel Maroto-Valiente; Ramón G. Rubio;
This work addresses the formation and the internal morphology of polyelectrolyte layers obtained by the layer-by-layer method. A multimodal characterization showed the absence of stratification of the films formed by the alternate deposition of poly(diallyldimethylammonium chloride) and poly(sodium 4-styrenesulfonate). Indeed the final organization might be regarded as three-dimensional solid-supported inter-polyelectrolyte films. The growth mechanism of the multilayers, followed using a quartz crystal microbalance, evidences two different growth trends, which show a dependency on the ionic strength due to its influence onto the polymer conformation. The hydration state does not modify the multilayer growth, but it contributes to the total adsorbed mass of the film. The water associated with the polyelectrolyte films leads to their swelling and plastification. The use of X-ray photoelectron spectroscopy has allowed for deeper insights on the internal structure and composition of the polyelectrolyte multilayers.
DOI:10.1016/j.apcata.2017.02.007
Almohalla, M.; Gallegos-Suarez, E.; Arcoya, A.; J. Alvarez-Rodriguez;
I. Rodríguez-Ramos;
A. Guerrero-Ruiz;
Four Ru/KL-zeolite catalysts containing 2 wt% of Ru were prepared from Ru3(CO)12, RuNO(NO3)3, Ru(C5H7O2)3 and RuCl3 precursors. The evolution of electronic structure and local chemical environment of ruthenium in the samples named Ru(c)/KL, Ru(n)/KL, Ru(acac)/KL and Ru(Cl)/KL was studied by in-situ XANES during temperature-programmed reduction. Also by CO chemisorption and transmission electron microscopy (TEM) the sizes of the Ru nanoparticles were determined. Activity and selectivity of the catalysts were evaluated in the transformation of ethanol, under kinetic conditions, in a fixed bed flow reactor, at 523 K–573 K. Characterization of the samples shows that metal dispersion values follow the trend Ru(c)/KL ≥ Ru(n)/KL > Ru(Cl)/KL ≥ Ru(acac)/KL. Activity of the catalysts is in the order Ru(acac)/KL ≥ Ru(c)/KL > Ru(n)/KL ≥ Ru(Cl)/KL. The TOF values, however, are in the same order of magnitude for all the samples, nonetheless the Ru(Cl)/KL catalyst has slightly lower TOF at all the reaction temperatures. Selectivity towards the dehydrogenation product, acetaldehyde, follows the trend Ru(c)/KL > Ru(n)/KL = Ru(acac)/KL >> Ru(Cl)/KL, this being 100% for Ru(c)/KL. Selectivity towards acetaldehyde is highly diminished for Ru(Cl)/KL in favor of the dehydration products, diethyl ether and ethylene, the higher the decrease the higher the temperature. The catalytic results are related to the properties of the surface metal species and their location in the zeolite framework, as well as to their surroundings, as evidenced from the results of the characterization measurements, which are in turn influenced by the different nature of the metal precursor.
Catalytic performances of Cr–ZSM-5 catalysts (5 wt.% of Cr, Si/Al = 26), prepared by solid-state reaction and aqueous exchange, from Cr nitrate and Cr acetate precursors, were evaluated in the selective ammoxidation of ethylene into acetonitrile in the temperature range 425–500 °C. Catalysts were characterized by chemical and thermal analysis, XRD, N2 physisorption, 27Al MAS NMR, TEM, UV–vis DRS, Raman, DRIFTS and H2-TPR. Characterization results shown that solid-state exchange was favorable for Cr2O3 formation, while exchanging chromium in aqueous phase led, essentially, to Cr(VI) species. Catalysts were actives and selectives in the studied reaction, and among them, those, prepared from aqueous exchange, exhibited the highest acetonitrile yields (23 ± 0.5%, at 500 °C). Improved catalytic properties can be correlated with the chromium species nature. In fact, mono/di-chromates and/or polychromate species, sited in the charge compensation positions, were definitively shown, as being, the active sites. Furthermore, during solid-state reaction, the agglomeration of Cr2O3 oxide should be avoided since these species inhibit the catalyst activity.
DOI:10.1016/j.cej.2012.01.132
Benjamin Solsona, Mónica Pérez-Cabero, Isabel Vázquez, Ana Dejoz, Tomás García, Jesus Álvarez-Rodríguez, Jamal El-Haskouri, Daniel Beltrán, Pedro Amorós
Catalytic performances of Cr–ZSM-5 catalysts (5 wt.% of Cr, Si/Al = 26), prepared by solid-state reaction and aqueous exchange, from Cr nitrate and Cr acetate precursors, were evaluated in the selective ammoxidation of ethylene into acetonitrile in the temperature range 425–500 °C. Catalysts were characterized by chemical and thermal analysis, XRD, N2 physisorption, 27Al MAS NMR, TEM, UV–vis DRS, Raman, DRIFTS and H2-TPR. Characterization results shown that solid-state exchange was favorable for Cr2O3 formation, while exchanging chromium in aqueous phase led, essentially, to Cr(VI) species. Catalysts were actives and selectives in the studied reaction, and among them, those, prepared from aqueous exchange, exhibited the highest acetonitrile yields (23 ± 0.5%, at 500 °C). Improved catalytic properties can be correlated with the chromium species nature. In fact, mono/di-chromates and/or polychromate species, sited in the charge compensation positions, were definitively shown, as being, the active sites. Furthermore, during solid-state reaction, the agglomeration of Cr2O3 oxide should be avoided since these species inhibit the catalyst activity.
DOI:10.1016/j.apcata.2012.06.037
F. Ayari; M. Mhamdi; T. Hammedi; J. Alvarez-Rodriguez; A. Guerrero-Ruiz; G. Delahay; A. Ghorbel;
Cr-zeolites with MFI, BEA, MOR and FAU structures, prepared by solid-state ion exchange, were characterized and tested in C2H4 ammoxidation to acetonitrile in the temperature range 425–500 °C. Based on characterization results, chromate and/or polychromate species, oxo-cations and small Cr2O3 oxide clusters played a key role in the ammoxidation of ethylene, while agglomerated Cr2O3 and bare Cr cations should be avoided. Cr ions sited in the sodalite and hexagonal cages of NH4+–Y are not accessible to the reactants while available catalytic sites are poorly active. However, the mesopores of the ultra stable Y zeolite (USY) favor the diffusion of reactants to the clustered Cr oxide. The corresponding catalyst is therefore active, but the presence of octahedral Al species is crucial to the ammoxidation. Cr ions in zeolites beta and mordenite led to less active catalysts when compared to ZSM-5. In zeolite beta, the micropores are small; therefore, pronounced interactions between ethylamine intermediate molecules could discourage the acetonitrile formation. In mordenite, agglomerates of Cr2O3 oxide inhibited the accessibility of active sites to the reactants and enhanced the hydrocarbon oxidation. The catalytic performance of Cr ions in ZSM-5 provided from a synergy of different parameters: structural, textural and the acid strength (Si/Al ratio).
DOI:/10.1016/j.cej.2012.07.099
J. Alvarez-Rodriguez; I. Rodríguez-Ramos; A. Guerrero-Ruiz; E. Gallegos-Suarez; A. Arcoya;
Ruthenium catalysts supported on KL zeolite, ZrO2 and graphite, prepared by incipient wetness impregnation, were characterized by N2 adsorption, H2 chemisorption, TEM and CO adsorption microcalorimetry and tested in the selective hydrogenation of citral in the liquid phase, at 5 MPa and 323 K. Characterization studies reveal that graphite promotes formation of electron-rich metal species (Run−) that difficult hydrogenation of the conjugated CC double bond of citral and indirectly favor the production of geraniol and nerol. For Ru/ZrO2 catalyst, the Ru ↔ ZrO2 interaction at the interface, with formation of Ru0Zrn+ species as evidenced by the TEM and CO adsorption microcalorimetry measurements, activates the carbonyl group of citral and enhances the selectivity towards unsaturated alcohols. Characterization measurements of Ru/KL evidence that metal nanoparticles placed inside of the zeolite channels block part of ruthenium loading and hinder the free transit of citral through the channels, thus reducing the overall hydrogenation activity of the catalyst. Furthermore, this steric hindrance impedes adsorption the conjugated CC double bond of citral and forces hydrogenation of the carbonyl group in terminal position. On the other hand, the fact that active sites on occluded particles are more resistant to poisoning than those easily accessible to citral enhances the selectivity towards geraniol and nerol, as the reaction time increases. The comparative analysis of the results indicates that, in order to increase the selectivity towards unsaturated alcohols, geometrical effects derived from the size, shape and location of ruthenium particles in the KL structure are more effective than the electronic modifications induced by graphite or zirconia on the ruthenium particles.
