Sònia Abelló

Supported choline hydroxide (ionic liquid) as heterogeneous catalyst for aldol condensation reactions

Choline hydroxide was used as a basic catalyst for aldol condensation reactions to produce new C-C bonds between several ketones and aldehydes. Choline supported on MgO exhibits higher TOF values than other well known basic catalysts in these reactions.

Exploring iron-based multifunctional catalysts for Fischer-Tropsch synthesis: a review.

The continuous increase in oil prices together with an increase in carbon dioxide concentration in the atmosphere has prompted an increased interest in the production of liquid fuels from non-petroleum sources to ensure the continuation of our worldwide demands while maximizing CO(2) utilization. In this sense, the Fischer-Tropsch (FT) technology provides a feasible option to render high value-added hydrocarbons. Alternative sources, such as biomass or coal, offer a real possibility to realize these purposes by making use of H(2)-deficient or CO(2)-rich syngas feeds. The management of such feeds ideally relies on the use of iron catalysts, which exhibit the unique ability to adjust the H(2)/CO molar ratio to an optimum value for hydrocarbon synthesis through the water-gas-shift reaction. Taking advantage of the emerging attention to hybrid FT-synthesis catalysts based on cobalt and their associated benefits, an overview of the current state of literature in the field of iron-based multifunctional catalysts is presented. Of particular interest is the use of zeolites in combination with a FT catalyst in a one-stage operation, herein named multifunctional, which offer key opportunities in the modification of desired product distributions and selectivity, to eventually overcome the quality limitations of the fuels prepared under intrinsic FT conditions. This review focuses on promising research activities addressing the conversion of syngas to liquid fuels mediated by iron-based multifunctional materials, highlights their preparation and properties, and discusses their implication and challenges in the area of carbon utilization through H(2)/CO(+CO(2)) mixtures.

Effect of temperature and pressure on characteristics and reactivity of biomass-derived chars

This study evaluates the influence of pyrolysis temperature (350-450°C) and pressure (0.1-2.0MPa) on product yields and char properties. Spruce chars were produced under slow pyrolysis conditions in a fixed bed reactor. Special attention was devoted to the study of the oxidation reactivity of the produced chars, and its relationship with the evaluated char properties. The obtained results showed that the effect of the pyrolysis condition on char production and in particular on the mechanism of secondary char formation strongly influenced the char reactivity. Additionally it has been observed that the interval of temperature between 350 and 450°C may be key in the mechanism of tar repolymerization. The information provided in this study is of great interest for the determination of optimal operation conditions and the design of new gasification concepts or the development of bioenergy carriers via pyrolysis technologies.

Perturbing the properties of layered double hydroxides by continuous coprecipitation with short residence time

A previous work (S. Abello and J. Perez-Ramirez, Adv. Mater., 2006, 18, 2436) revealed an unanticipated variation in the textural properties of Mg–Al hydrotalcite, prepared by continuous coprecipitation with short residence time, τ = 1 s which, at that time, was not fully understood. Herein, we report the generalisation of such variation in physical properties to layered double hydroxides (LDHs) of different composition (Ni–Al, Mg–Al, and Mg–Fe hydrotalcite-like compounds). In particular stable colloidal suspensions and, on drying, impervious LDH particles have been prepared using the in-line dispersion precipitation (ILDP) method with τ = 1 s. This is thought to be a consequence of variation in the mechanism of inter-crystallite interactions with decreasing crystallite size. The resulting materials are characterised using multiple techniques and are compared to analogous materials attained at longer residence times (τ = 12 s). We show that despite the apparent compositional similarity and structural isomorphicity of the precipitates, their textural and morphological properties and their thermal stability differ strongly. Thermal activation of the LDHs, however, resulted in the development of comparable textural properties in the corresponding oxides, independent of the residence time.

Ternary Ni–Al–Fe catalysts for ethanol steam reforming

Ternary mixed oxides prepared from takovite/reevesite Ni3Al1−xFex precursors were tested in ethanol steam reforming for hydrogen production. The influence of the trivalent cation (Al3+ or Fe3+) on phase composition and derived catalytic performance of the resulting oxides was studied. The physico-chemical properties of the hydrotalcite-like precursors and related oxides were characterized by ICP, XRD, TGA-DSC, Raman, H2-TPR, and TEM analyses. Compared to pure binary systems (Ni3Al and Ni3Fe), the ternary systems showed the best performance in ethanol reforming, leading to high and stable hydrogen selectivity of up to ca. 70% in 100 h reaction tests. The increase in activity can be attributed to a cooperative effect between aluminum and iron, favoring ethanol dehydrogenation as the primary step, followed by acetaldehyde reforming and/or cracking, reverse water gas shift, and methanation, and concomitantly limiting the dehydration route to ethylene.

Synthetic natural gas by direct CO2 hydrogenation on activated takovites: effect of Ni/Al molar ratio

Takovite-derived mixed oxides in Ni/Al molar ratios from 1 to 3 have been used as catalysts in hydrogenation of CO2 to CH4. The catalysts were characterized by XRD, BET, TEM, TGA, and H2-TPR, and monitored by in situ DRIFTS under reaction conditions. The catalytic performance for the CO2 methanation has been investigated in a fixed-bed reactor at the temperature range from 225 to 400 °C and pressures of 10.0 and 1.0 bar(g). Takovite decomposition leads to the formation of a NiO phase containing Al ions and a nickel-containing alumina phase (Ni-deficient spinel). The percentage of spinel increases upon decreasing the Ni/Al ratio, and consequently, a lower amount of metallic nickel after subsequent reduction is achieved. All catalysts were partially reduced upon time on stream, leading to the formation of small Ni0 crystallites (ca. 3 nm) dispersed on a NiAl2O4 matrix. The most active and selective catalyst was the one with a Ni/Al ratio of 2, which was also very stable after a 500 h lifetime test at atmospheric pressure and 275 °C.