Elena Taboada

Fast and efficient hydrogen generation catalyzed by cobalt talc nanolayers dispersed in silica aerogel

Cobalt talc nanolayers dispersed in silica aerogel constitute an active nanocomposited material with outstanding catalytic properties for the generation of hydrogen by ethanol steam reforming at low temperature. Delamination of talc particles into individual nanolayers of ca. 1.8 nm thick readily occurs under the reforming conditions, which results in a strong enhancement of the exposed catalytic active area. The presence of aerogel assures the immobilization of the talc nanolayers resulting from the delamination while maintaining an excellent mass transfer of products and reactants to the surface of the talc nanolayers. A fast and reversible surface activation for the steam reforming of ethanol occurs at 580–590 K under the reforming conditions. Magnetic characterization and in situ X-ray photoelectron spectroscopy (XPS) show the non-reversible formation of metal cobalt ensembles during activation, which escape HRTEM detection. This material appears as a good candidate for on-board hydrogen generation from ethanol–water mixtures for mobile and portable fuel cell applications.

Cobalt hydrotalcite for the steam reforming of ethanol with scarce carbon production

Co/Mg/Al hydrotalcite-type catalysts have been loaded onto ceramic honeycombs and tested in the ethanol steam reforming (ESR) reaction for producing hydrogen under practical conditions. In contrast with previously reported cobalt-based systems, the formation of carbon was scarce. This has been ascribed to the unique formation of traces of metallic cobalt particles under reaction conditions, as inferred from HRTEM, magnetic measurements, and in situ X-ray photoelectron spectroscopy (XPS) experiments. The best catalytic performance has been exhibited by the catalyst derived from the hydrotalcite with a Co:Mg:Al molar ratio of 1:2:1, where CoAl spinel and CoO strongly interacting with MgO phases have been identified.

Boosted CO2 reaction with methanol to yield dimethyl carbonate over Mg–Al hydrotalcite-silica lyogels

Nonimmobilized and immobilized Mg-Al hydrotalcite-like materials on silica lyogels were prepared and activated by calcination to be tested as catalysts in the direct carboxylation reaction of methanol. The HTs supported on silica lyogels showed an important improvement and high stability in the direct synthesis reaction of DMC from CO2 and MeOH.

Microwave-assisted synthesis of sulfonic acid-functionalized microporous materials for the catalytic etherification of glycerol with isobutene

Commercial Beta, ZSM-5 and mordenite zeolites and commercial montmorillonite K-10 were successfully sulfonated by a one-step simple method using microwaves. Different amounts of the sulfonating agent were required to maximize the incorporation of sulfonic groups for each structure. This has been related to the different dealumination degree suffered by the starting samples during sulfonation together with the different accessibility of the silanols to the sulfonic groups depending on the arrangement and size of their pores. All optimised sulfonated catalysts showed total conversion and very high selectivity (79–91%) to h-GTBE (glycerol di- and tri-ethers), in spite of their microporosity, due to the incorporation of the sulfonic groups that led to a higher number and strength of Bronsted acid sites. Pore size and arrangement together with the external surface area of the catalysts affected the accessibility of the acid sites to the reactants, explaining the evolution of the catalytic results with time for each structure.

Hydrogen from Bioethanol

Bioethanol, ethanol produced from biomass by fermentation, is the most promising renewable source for hydrogen production. Ethanol is advantageous over other conventional substrates because it is readily available, easy to obtain from biomass and to transport, CO 2 neutral and safe to handle. Ethanol is a well-established source of hydrogen by catalytic steam reforming, oxidative reforming or partial oxidation. An efficient catalyst for hydrogen production from ethanol has to dissociate the C–C bond, maintain a low CO concentration and be stable under catalytic operation. Noble metal-based catalysts perform well; they are stable and exhibit high activity. However, they are expensive and need high temperatures to be active. Nickel- and cobalt-based catalysts are inexpensive but under reaction conditions, they suffer from sintering and deactivation by carbon deposition. Supports with redox properties, based on CeO 2 , can oxidize carbon residues and prevent extensive carbon deposition due to its oxygen storage capacity and high oxygen mobility. The use of catalytic membrane reactors, with simultaneous generation and separation of hydrogen, appears as an attractive approach to simplify on-site/on-demand ethanol reformers and to reduce downstream separation costs. Looking for mobile applications, microreactor technologies have been applied to ethanol reforming processes as well. Recently, photocatalytic generation of hydrogen at room temperature from water–ethanol mixtures has been accomplished over noble metals supported over semiconductors.