Examinando por Autor "Arroyo, Marta"

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Conversion of Stearic Acid into Bio-Gasoline over Pd/ZSM-5 Catalysts with Enhanced Accessibility
(MDPI, 2019-06-11) Arroyo, Marta; Briones, Laura; Escola, José María; Serrano, D. P.
Palladium supported on nanocrystalline ZSM-5 (n-ZSM-5, Si/Al = 32) and hierarchical ZSM-5(h-ZSM-5) with different acidity (Si/Al = 33, 51, 122) were tested in the liquid-phase conversion of stearic acid undernitrogenatmosphere(6bar). TheincorporationofPdintoZSM-5zeoliteincreased significantly the share of gasoline in the reaction products due to the promotion by this metal of both decarboxylation and hydrogen transfer reactions. Likewise, the Pd nanoparticles dispersed over the zeolitic support favored the conversion of light olefins formed by end-chain cracking reactions into gasoline-range hydrocarbons according to an oligomerization/cyclization/aromatization pathway. Additionally, Pd/h-ZSM-5 gave rise to higher conversion and selectivity towards gasoline than Pd/n-ZSM-5, due mainly to the enhanced accessibility and improved Pd dispersion achieved when using the hierarchical zeolite. The decrease in the Si/Al atomic ratio in Pd/h-ZSM-5 samples resulted in a rise in the stearic acid conversion, although it was lower than expected. This finding denotes that, for supports with high acid sites concentration, the Pd availability became the limiting factor as the metal was loaded in similar amounts in all catalysts. Finally, the increase of the reaction temperature with the Pd/h-ZSM-5 (122) catalyst augmented both stearic acid conversion and gasoline selectivity, since it enhanced the conversion of the light olefins, formed as primary cracking products, into liquid hydrocarbons. Therefore, it can be concluded that Pd supported on hierarchical ZSM-5 zeolite is a convenient catalyst for obtaining bio-gasoline from oleaginous feedstock.
Faunal evidence of the 1755 Lisbon Tsunami in Gibraltar (S Iberian Peninsula)
(Elsevier, 2022) Abad, Manuel; Clemente, María José; González-Regalado, María Luz; Ruiz, Francisco; Rodríguez Vidal, Joaquín; Cáceres, Luis Miguel; Izquierdo, Tatiana; Pérez Quintero, Juan Carlos; Tosquella, Josep; Pozo, Manuel; Gómez, Paula; Toscano, Antonio; Romero, Verónica; Arroyo, Marta; Gómez, Gabriel
This paper analyzes the first systematic faunal record of the 1755 Lisbon tsunami in the Mediterranean. On the basis of sedimentological and paleontological features, the sedimentary record of a core collected in Gibraltar was divided into six sedimentary facies, with a paleoenvironmental evolution from a shallow marine paleoenviroment to an increasingly restricted lagoon. This record includes a bioclastic layer deposited by the 1755 Lisbon tsunami and characterized by an erosive base, presence of basal rip-up clasts and abundant shell debris composed by marine and brackish molluscs. The paleoenvironmental reconstruction derived from the foraminiferal analysis is congruent with that inferred from the sedimentary and the macrofaunal reconstructions, with the introduction of brackish species into the innermost, intertidal areas of a confined lagoon. This paleontological record is the first faunal evidence of the 1755 Lisbon tsunami in the Mediterranean.
Selective Decarboxylation of Fatty Acids Catalyzed by Pd-Supported Hierarchical ZSM‑5 Zeolite
(ACS, 2021) Arroyo, Marta; Briones, Laura; Hernando, Héctor; Escola, José M.; Serrano, David P.
Decarboxylation of fatty acids is an interesting route for the production of renewable long-chain hydrocarbons that could replace fossil resources in the formulation of diesel and jet range fuels. The results reported in the present work demonstrate that Pd supported on hierarchical ZSM-5 zeolite allows for the decarboxylation of different fatty acids (stearic, oleic, and palmitic acids) to proceed under mild operation conditions (T = 250 °C and PH2 = 6 bar) with over 90% selectivity toward middle distillate hydrocarbons and conversions in the range of 60–85%. This outstanding performance has been attributed to a combination of high accessibility and tailored acidity in the zeolitic support that favors the metal dispersion and promotes the interaction between Pd and acid sites. The presence of a hydrogen atmosphere, under low-pressure conditions, is required for activating the Pd sites. It is also noteworthy that the catalyst could be reused after washing with n-dodecane, retaining 74% of its initial stearic acid conversion with just a minor variation in the yield of C17 hydrocarbons.
Selective hydrocarboxylation of fatty acids into long-chain hydrocarbons catalyzed by Pd/Al-SBA-15
(Elsevier, 2019-01-29) Serrano, David Pedro; Escola, José María; Briones, Laura; Arroyo, Marta
Pd/Al-SBA-15 materials, with different Si/Al atomic ratios, have been investigated as catalysts in the hydrodecarboxylation (HDC) of fatty acids for the production of long-chain paraffinic hydrocarbons. The catalytic tests were performed in a stirred batch reactor under H2 atmosphere using stearic, oleic and palmitic acids as substrates. Characterization of the catalysts indicates that the Pd nanoparticles are well distributed on the support, being partially located within their ordered mesopores. Increasing the Al-SBA-15 acidity enhances the stearic acid conversion but provokes a reduction in the selectivity towards hydrodecarboxylation versus hydrodeoxygenation (HDO). Variation of the reaction temperature within 225 - 300 ºC enhanced the catalytic activity, while the HDC selectivity remained over 90%, being just reduced when working at 300 ºC due to the occurrence of cracking reactions. The H2 pressure also increased the stearic acid conversion, in particular when passing from 3 to 6 bar, confirming the positive role of the hydrogen atmosphere in the decarboxylation process. However, when operating at 25 bar of H2 pressure, the HDC selectivity decreases, as the HDO pathway is favored. Comparing the results obtained with stearic, oleic and palmitic acids shows that the Pd/Al-SBA-15 system is an excellent catalyst for this reaction, providing in all cases a significant catalytic activity and a very high HDC selectivity. These findings can be related to the features of the Al-SBA-15 support (high surface area, uniform mesopores and mild Lewis acidity), which provides a good Pd dispersion, a high substrate accessibility and limit the extension of cracking reactions.