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Castillejos López, Eva

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0000-0003-0913-1560
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Castillejos López
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Eva
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2020 - 20242
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  • Miniatura
    Publicación
    Formic Acid Dehydration Using Mechanochemically Prepared TiO2-Graphite Composites
    (Wiley, 2024-07-27) Yruela Garrido, Marta; Martín Rodríguez, Nuria; Castillejos López, Eva; Campos Castellanos, Eduardo; Conesa, José María; Rodríguez Ramos, Inmaculada; Guerrero Ruiz, Antonio R
    Commercial high surface area graphite (HSAG300) and commercial TiO2 were used to produce composite materials through a simple mechanochemical method involving milling and ultrasonic treatments. The acid and basic sites exposed on the surfaces of these materials were characterized by temperature-programmed desorption (TPD) of ammonia and carbon dioxide. The catalytic materials were tested in the dehydration reaction of formic acid to produce hydrogen-free CO. While HSAG300 is practically inactive under reaction conditions (continuous gas flow at temperatures in the range of 100–250 °C), all samples containing TiO2 are active, exhibiting high selectivity to CO without significant deactivation at moderate reaction temperatures. It is demonstrated that the presence of graphite in the catalysts enhances the specific catalytic activity of TiO2. Assuming that the dehydration reaction is catalyzed by acid sites on the TiO2 surfaces, a comparative evaluation of the surface sites reveals that the graphite-TiO2 interactions not only change the density of surface sites but also modify the strength of the acid centers of TiO2. In summary, the interaction of HSAG300 with TiO2 modulates the surface properties of the prepared composite catalysts, decreasing the total number of basic surface sites and increasing the strength of acidic sites compared to bare TiO2.
  • Miniatura
    Publicación
    Taking advantage of sulfur impurities present in commercial carbon nanofibers to generate selective palladium catalysts
    (ELSEVIER, 2020) Morales, María V.; Guerrero Ruiz, Antonio R; Castillejos López, Eva; Asedegbega Nieto, Esther; Rodríguez Ramos, Inmaculada; https://orcid.org/0000-0003-2834-0296; https://orcid.org/0000-0003-1848-5985; https://orcid.org/0000-0003-3881-0757; https://orcid.org/0000-0003-4622-6008
    Achieving high selectivity is one of the major challenges in heterogeneous catalysis, being carbon materials universally employed as catalysts support due to their so-called “inert” nature. However, due to the complexity of its intrinsic characteristics, there are still several factors to bear in mind when selecting the appropriate carbon support. In this work we demonstrate that the remaining sulfur impurities in one type of commercial carbon nanofibers (CNFs) drastically alter the catalytic properties of palladium by triggering electro-deficient active sites. Two as-received CNFs thermally processed at different severity degrees, namely PS and HHT, were used to support Pd nanoparticles through the wet impregnation technique using palladium nitrate as precursor. The proof of principle is demonstrated through two transformation reactions of biomass platform molecules: the hydrogenation of 5-hydroxymethylfurfural, performed in a batch-type reactor, and the ethanol dehydrogenation/decarbonylation reaction, carried out in a continuous flow fixed-bed reactor. In both reactions, Pd/PS was substantially more selective than its sulfur-free counterpart Pd/HHT, and one of the most selective in comparison with the state-of-the-art Pd catalysts. This finding makes available a simple, easy and green strategy to design carbon-supported Pd catalysts for selective hydrogenation and dehydrogenation reactions.