MOLYBDENUM DOPED CARBON AEROGELS WITH CATALYTIC POTENTIAL

Mo-doped carbon aerogels were obtained in the polycondensation reaction of aqueous resorcinol and formaldehyde by adding Mo-salt at two different stages of the synthesis: i) to the initial sol; ii) by incipient wetting impregnation of the supercritically dried polymer gel. Molybdenum added during the polymerization yielded a more compact gel structure with practically no mesoporosity. With post-impregnation, by contrast, mesopores of diameter 3-15 nm were generated. Carbonization appreciably enhanced the microporous character of both samples, but in the mesopore range their pore size distribution was conserved. The Mocontent of the samples was also different: Mo was lost during the solvent exchange before the supercritical drying (i.e., the Mo failed to bind chemically to the polymer matrix). The residual Mo congregated into 25-60 nm bulk clusters of α-Mo2C. In the other carbon aerogel, finely dispersed α-Mo2C and η-Mo3C2 crystals formed, of size 8-20 nm. On the surface of both carbons the Mo formed oxides. In the model test reaction (acetic acid hydroconversion) the catalytic activity of both carbon aerogels was enhanced by molybdenum. The more open pore structure, higher concentration and finer Mo distribution, as well as its chemical form, may all be responsible for the greater conversion and higher value products obtained with the post-impregnated sample

Aplicaciones de los materiales de carbón en catálisis

págs.: 229-272Capítulo incluido en el libro: Desarrollo y aplicaciones de materiales avanzados de carbón. Miguel Ángel Álvarez Merino, Francisco Carrasco Marín, Francisco José Maldonado Hódar (Editores). Sevilla: Univeridad Internacional de Andalucía, 2014. ISBN: 978-84-7993-247-3. Enlace: http://hdl.handle.net/10334

Green chemistry and environmental processes

Funding Information: Acknowledgments: Portuguese FCT—Fundação para a Ciência e a Tecnologia, I.P., under the Scientific Employment Stimulus—Institutional Call (CEECINST/00102/2018) and Associate Laboratory for Green Chemistry—LAQV, financed by national funds from FCT/MCTES (UIDB/50006/2020 and UIDP/50006/2020) and the Spanish Project ref. RTI 2018-099224-B100 funded by ERDF/Ministry of Science, Innovation and Universities. S.M.-T. also acknowledges the Ramón y Cajal contract (RYC-2019-026634-I/AEI/10.13039/501100011033) from MINECO.publishersversionpublishe

Cobalt oxide-Carbon nanocatalysts with highly enhanced catalytic performance for the green synthesis of nitrogen heterocycles through Friedländer condensation.

A novel series of eco-sustainable catalysts developed by supporting CoO nanoparticles on different carbon supports, highly efficient in the synthesis of quinolines and naphthyridines, through the Friedländer condensation, are reported for the first time. Textural properties, dispersion and location of the Co-phase are influenced by the nature of the carbon support, Co-precursor salt and metal loading, having a significant impact on the catalytic performance. Thus, the presence of the mesopores and macropores in carbon aerogels together with the homogeneous distribution of the active phase favours the formation of product 3a as a function of the metal loading. However, an increase in the metal content when using CNTs indicates the formation of CoO aggregates and an optimal concentration of 3 wt% CoO was observed, providing the highest conversion values. The carbon-based catalysts herein reported can be considered to be a sustainable alternative having advantages such as easy preparation, superior stability and notably enhanced catalytic performance, operating at lower temperature and under solvent-free conditions.pre-print815 K

Desarrollo y aplicaciones de materiales avanzados de carbón

432 páginasObra escructurada en dos partes claramente diferenciasdas pero necesariamente complementarias. La primera parte (capítulos I a V) está dedicada a los métidos de síntesis de los distintos tipos de materiales de carbón, desde los clásicos carbones activados a otros materiales más específicos como lo geles, nanotubos o el grafeno, tan de moda actualmente. Se ha prestado atención a la presentación de las técnicas de caracterizacaión de materiales y análisis de resultados, tanto en cuanto a su textura porosa como a sus propiedades químicas, pues entre ambos pilares descansan las posibles aplicaciones de los materiales previamente preparados. El segundo bloque de capítulos (capítulos VI al X) está dedicado a poner de manifiesto la importancia tecnológica de los materiales de carbón

Carbon aerogel supported platinum catalysts for selective hydrogenation of cinnamaldehyde

This paper describes the preparation and characterization of 1% wt. Pt catalysts supported in carbon aerogels for the application in the liquid-phase selective hydrogenation of cinnamaldehyde. Carbon aerogel supports with different textures were activated with hydrogen peroxide and ammonium peroxydisulfate leading to large amounts of surface groups but keeping unchanged their textural properties. After introducing Pt, the surface chemistry and morphology of the catalysts was characterized by analytical techniques like SEM, TPD, N2 adsorption isotherms, mercury porosimetry and H2 chemisorption. Catalysts prepared with activated aerogels exhibited good selectivity towards the desired product, cinnamyl alcohol. A high temperature post-treatment of the catalysts failed to enhance their selectivity, mainly leading to hydrocinnamaldehyde production

Heterogeneous gold nanoparticle-based catalysts for the synthesis of click-derived triazoles via the azide-alkyne cycloaddition reaction

PD/BD 135555/2018 IST-ID/263/2019A supported gold nanoparticle-catalyzed strategy has been utilized to promote a click chemistry reaction for the synthesis of 1,2,3-triazoles via the azide-alkyne cycloaddition (AAC) reaction. While the advent of effective non-copper catalysts (i.e., Ru, Ag, Ir) has demonstrated the catalysis of the AAC reaction, additional robust catalytic systems complementary to the copper catalyzed AAC remain in high demand. Herein, Au nanoparticles supported on Al2 O3, Fe2 O3, TiO2 and ZnO, along with gold reference catalysts (gold on carbon and gold on titania supplied by the World Gold Council) were used as catalysts for the AAC reaction. The supported Au nanoparticles with metal loadings of 0.7–1.6% (w/w relative to support) were able to selectively obtain 1,4-disubstituted-1,2,3-triazoles in moderate yields up to 79% after 15 min, under microwave irradiation at 150◦ C using a 0.5–1.0 mol% catalyst loading through a one-pot three-component (terminal alkyne, organohalide and sodium azide) procedure according to the “click” rules. Among the supported Au catalysts, Au/TiO2 gave the best results.publishersversionpublishe

Catalysts Supported on Carbon Materials for the Selective Hydrogenation of Citral

The heterogeneously catalyzed selective-hydrogenation of citral is one of the more feasible ways for obtaining its appreciated unsaturated-alcohols, nerol and geraniol, which are present in over 250 essential oils. Thus, citral has very recently come to be produced petro-chemically in very large quantities, and so partial hydrogenation of citral has become a very economical route for the production of these compounds. However, the selective hydrogenation of citral is not easy, because citral is an α,β-unsaturated aldehyde which possesses three double bonds that can be hydrogenated: an isolated C=C bond and the conjugated C=O and C=C bonds. For this reason, in catalyst selection there are several important issues which affect the product selectivity, for example, the active metal and metal particle size which are factors related to the catalyst preparation method, catalyst precursor, or support surface area, as well as other factors such as porosity, the addition of a second catalytic metal, and, of course, the type of catalyst support. About this last one, carbon materials are very interesting supports for this type of hydrogenation reaction due to their unique chemical and textural properties. This review collects and analyzes the results obtained in the selective hydrogenation of citral catalyzed by carbon material supported metals.This work is supported by the MICINN-FEDER, project CTM2010-18889

The late Holocene extinction of Pinus sylvestris in the West of the Cantabrian Range

Aim To reconstruct the historical biogeography of Pinus sylvestris in the Cantabrian Range (Iberian Peninsula) during the Holocene, and to consider the interactions between vegetation dynamics, climate change and the role of man in the present-day distribution of the species. Location The study site is a mire (1300 m a.s.l.) at Vega de Viejos, on a south-facing slope of the western Cantabrian Range, Spain. The region’s present-day landscape is almost treeless, with the exception of some patches of Quercus pyrenaica and a few copses of Salix and Betula along stream banks. Methods Tree macrofossils from Vega de Viejos were studied by transmitted light and dark-field reflection microscopy; strobili were subjected to comparative morphological analyses. Two Pinus macrofossils were dated by conventional 14C methods. Results The taxonomic accuracy achieved in the identification of the macrofossils provided new information regarding the Holocene history of Pinus sylvestris in this territory. Ninety-five cones of this species were identified; in fact, more than 80% of the 36 identified wood remains were of Pinus gr. sylvestris. Radiocarbon dating revealed that the forest to which the fossils belonged was present until at least 2170 ± 50 yr bp – its disappearance was therefore relatively recent. Main conclusions Pinus sylvestris suffered long-term isolation, and after the Wu¨rm glacial period tended to migrate towards the east. In western Iberia, a temperate climate and autogenic succession favoured broadleaved taxa at the expense of Pinus. Late Holocene human disturbances may have further accelerated the decline of P. sylvestris; in the Cantabrian Range, only a few stands on southern slopes have persisted until the present day. The history of the capercaillie (Tetrao urogallus), a bird characteristic of pure or mixed Palaeartic coniferous forests, was almost certainly affected by the demise of these forests in this area. Cantabrian capercaillies are the only members of this species that live in purely deciduous forests, perhaps a recent adaptation to the regional extinction of pines. Today’s P. sylvestris and capercaillie populations are now highly fragmented and their future, given the predictions of global climate change, is uncertain