Energy from hydrogen. Hydrogen from renewable fuels for portable applications

L'hidrogen molecular és una font d'energia neta per al medi ambient, però no es troba disponible a la Terra. La reformació amb vapor de substàncies derivades de la biomassa constitueix una ruta valuosa per a la producció d'hidrogen molecular, i té l'avantatge que és neutre des del punt de vista del CO2 i que no requereix grans infraestructures per a la seva implementació. En aquests moments s'estan desenvolupant catalitzadors per a la reformació selectiva, entre d'altres, de bioalcohols i dimetil èter a hidrogen i diòxid de carboni, tot i que el seu ús en reactors de parets catalítiques per a aplicacions reals encara no està del tot resolta. D'aquests, els reactors estructurats recoberts d'aerogels són molt prometedors perquè la transferència de massa és excel·lent i són capaços de dispersar nanopartícules de metalls actius per a la reacció. El comportament d'aquests sistemes millora considerablement quan s'empren en microreactors. Els microreactors basats en micromonòlits de silici en què s'integra la reacció de reformació i l'oxidació selectiva del monòxid de carboni generat són una opció prometedora per a la producció d'hidrogen in situ i sota demanda en les aplicacions portàtils de les piles de combustible.Molecular hydrogen is an environmentally clean source of energy, but it is not available on Earth. Steam reforming of bio-derived compounds represents a valuable route for the generation of molecular hydrogen and has the advantage that it is CO2 -neutral and it requires a limited amount of additional infrastructure for implementation. At present, suitable catalysts for selective bio-alcohol and dimethyl ether reforming into hydrogen and carbon dioxide are being developed, but their use on structured wall reactors for practical application is still under way. Among them, aerogel-based coated structures appear very promising due to their very high mass transfer rates and their ability to disperse highly active metal nanoparticles. The performance of these systems improves considerably by using microreaction technologies. Microreactors based on silicon micromonoliths together with integrated downstream carbon monoxide selective oxidation hold a promising future for the effective on-site and on-demand generation of hydrogen from renewable fuels in portable fuel cell applications

Organic matter in meteorites

Some primitive meteorites are carbon-rich objects containing a variety of organic molecules that constitute a valuable record of organic chemical evolution in the universe prior to the appearance of microorganisms. Families of compounds include hydrocarbons, alcohols, aldehydes, ketones, carboxylic acids, amino acids, amines, amides, heterocycles, phosphonic acids, sulfonic acids, sugar-related compounds and poorly defined high-molecular weight macromolecules. A variety of environments are required in order to explain this organic inventory, including interstellar processes, gas-grain reactions operating in the solar nebula, and hydrothermal alteration of parent bodies. Most likely, substantial amounts of such organic materials were delivered to the Earth via a late accretion, thereby providing organic compounds important for the emergence of life itself, or that served as a feedstock for further chemical evolution. This review discusses the organic content of primitive meteorites and their relevance to the build up of biomolecules. [Int Microbiol 2004; 7(4):239-248

Organic matter in comets and cometary dust

Comets are primitive conglomerates of the solar system containing a mixture of frozen gases, refractory grains, and carbonaceous particles rich in biogenic elements. The dramatic display of comets is mostly caused by a cloud of micrometer-sized dust particles that leave the comet nucleus when frozen gases sublimate as they approach the Sun. Analyses of cometary dust captured in the stratosphere together with data obtained from space missions to comets have revealed the presence of a great variety of organic molecules. Since substantial amounts of cometary dust were gently deposited on Earth, their organic content could have played a major role in prebiotic processes prior to the appearance of microorganisms. This review discusses the description and implications for life of the organic content of comets and cometary dust. [Int Microbiol 2005; 8(1):5-12

Ceria Catalysts at Nanoscale: How Do Crystal Shapes Shape Catalysis?

Engineering the shape and size of catalyst particles and the interface between different components of heterogeneous catalysts at the nanometer level can radically alter their performances. This is particularly true with CeO2-based catalysts, where the precise control of surface atomic arrangements can modify the reactivity of Ce4+/Ce3+ ions, changing the oxygen release/uptake characteristics of ceria, which, in turn, strongly affects catalytic performance in several reactions like CO, soot, and VOC oxidation, WGS, hydrogenation, acid base reactions, and so on. Despite the fact that many of these catalysts are polycrystalline with rather ill-defined morphologies, experimental and theoretical studies on well-defined nanocrystals have clearly established that the exposure of specific facets can increase/decrease surface Oxygen reactivity and metal-support interaction (for supported metal nanoparticles), consequently affecting catalytic reactions. Here, we want to address the most recent developments in this area, showing that shape (and size) modification, surface/face reconstruction, and faceting of ceria at the nanoscale level can offer an important tool to govern activity and stability in several reactions and imagine how this could contribute to future developments

Anaerobic co-digestion of acetate-rich with lignin-rich wastewater and the effect of hydrotalcite addition

The methane potential and biodegradability of different ratios of acetate and lignin-rich effluents from a neutral sulfite semi-chemical (NSSC) pulp mill were investigated. Results showed ultimate methane yields up to 333 ± 5 mL CH4/gCOD when only acetate-rich substrate was added and subsequently lower methane potentials of 192 ± 4 mL CH4/gCOD when the lignin fraction was increased. The presence of lignin showed a linear decay in methane production, resulting in a 41% decrease in methane when the lignin-rich feed had a 30% increase. A negative linear correlation between lignin content and biodegradability was also observed. Furthermore, the effect of hydrotalcite (HT) addition was evaluated and showed increase in methane potential of up to 8%, a faster production rate and higher soluble lignin removal (7–12% higher). Chemical oxygen demand (COD) removal efficiencies between 64 and 83% were obtained for all samples.Peer ReviewedPostprint (author's final draft

Purificació catalítica d'hidrogen en microcanals

En aquest treball mostrem el funcionament d'un microdispositiu catalític dissenyat al nostre grup de recerca per purificar de manera catalítica i selectiva monòxid de carboni en presència d'hidrogen. Hem aconseguit desenvolupar un mètode per recobrir amb èxit els seus canals, d'entre 2 i 4 μm de diàmetre, amb una capa homogènia d'òxid de titani de només uns 100 nm de gruix. Sobre aquesta fina capa s'han ancorat unes nanopartícules d'or innovadores embolcallades amb lligands rics en silici que presenten una gran estabilitat i activitat per oxidar selectivament el monòxid de carboni (CO-PrOx) en un rang de temperatures comprès entre els 363 i els 473 K. El microreactor representa una intensificació del procés d'oxidació selectiva de CO i, gràcies a la reducció d'escala obtinguda en aquesta microestructura (en comparació amb reactors de parets catalítiques convencionals), s'han obtingut activitats específiques (quantitat de CO convertit per unitat de volum de reactor) cent vegades majors treballant a la mateixa temperatura i amb les mateixes mescles d'alimentació. Així, doncs, el microreactor desenvolupat resulta molt atractiu per realitzar la reacció de CO-PrOx a microescala i per ser combinat amb una etapa de reformació prèvia. L'acoblament d'ambdós processos per alimentar piles de combustible de baixa temperatura ofereix noves possibilitats dins del món de la tecnologia del vector hidrogen i, en concret, per a aplicacions de petita escala i portàtils.This paper describes the operation of a catalytic microdevice designed by our research group to catalytically and selectively purify carbon monoxide in the presence of hydrogen. We have developed a method of successfully coating channels of only 2-4 μm in diameter with a homogenous 100 nm-thick titanium oxide layer. Novel gold nanoparticles protected with a Si-rich shell have been anchored onto this thin layer. The gold nanoparticles show great stability and activity in preferentially oxidizing carbon monoxide (CO-PrOx) in a temperature range of 363 to 473 K. The microreactor intensifies the CO selective oxidation process. Due to the scale reduction achieved in this structure (compared to conventional catalytic wall reactors), specific activities (amount of converted CO per reactor volume) that are 100 times larger were obtained, operating at the same temperature level and with the same feed mixtures. Consequently, this microreactor is very interesting for performance of the CO-PrOx reaction at microscale and for combination with a preliminary reforming stage. The connection of both processes to feed low-temperature fuel cells offers new possibilities in hydrogen technology and, particularly, in small-scale and portable applications

Nonlinear model predictive control for hydrogen production in an ethanol steam reformer with membrane separation

© 2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other worksThis paper presents a new Nonlinear Model Predictive Control (NMPC) design for an Ethanol Steam Reformer with Pd-Ag membrane separation stage. The reformer is used to produce pure hydrogen able to feed a Proton Exchange Membrane Fuel Cell. Mass and energy balances are used to obtain the nonlinear dynamic model of both the reforming and the separation stages. Constraints, system nonlinearities and flexible cost function are the main reasons to select an NMPC controller, which is tested against the ordinary differential equations as simulation model, and has an internal model based on the sample data technique.Accepted versio

Role of the synthesis route on the properties of hybrid LDH-graphene as basic catalysts

Layered double hydroxides (LDH or HT) or their derived mixed oxides present marked acid-base properties useful in catalysis, but they lead to agglomerate inducing a weak accessibility to the active sites. In this study we report the preparation and characterization of HT/Graphene (HT/rGO) nanocomposites as active and selective basic catalysts for the acetone condensation reaction. The graphene high specific surface area and structural compatibility with the HT allowed increasing the number and accessibility of the active sites and activity of this later. Two series of HT/rGO nanocomposites with 0.5 = HT/rGO = 10 mass ratio were prepared by: i) direct HT coprecipitation in the presence of GO; ii) self-assembly of preformed HT with GO. The prepared HT/rGO nanocomposites were dried either in air at 80 °C or freeze-dried. A series of characterizations showed the great influence of the preparation method and HT/rGO mass ratio on both the nanocomposite structure and catalytic activity. An optimum activity was observed for a HT/rGO = 10 catalyst. Particularly, the highest catalytic activity was found in those nanocomposites obtained by coprecipitation and freeze dried (3 times more active than bulk HT) which can be connected to their structure with a better accessibility to the basic sites.Postprint (author's final draft