Transition metal b-site substitutions in laalo3 perovskites reorient bio-ethanol conversion reactions

LaAlO3 perovskites, as such and with 25% molar Al substitution by Cu, Co, or Ga, have been prepared by sol-gel methods and tested as heterogeneous catalysts in the gas-phase conversion of ethanol. LaAlO3 presented a significant acidic character, with high formation of ethylene by ethanol dehydration. B-site substitutions increased the basicity of the catalysts, favoring the dehydrogenation of ethanol to acetaldehyde. The most reducible Cu-and Co-substituted materials, characterized by easier formation of surface oxygen vacancies, promoted the self-condensation of acetaldehyde by the Tishchenko mechanism, with formation of acetone and odd-carbon number products. Aldol coupling of acetaldehyde, favored on pure and Ga-substituted LaAlO3, led to the formation of butadiene and hexadiene. The role of Ga insertion, favoring both dehydrogenation of ethylene and dehydration of higher alcohols, corresponds to an amphoteric character. The formation of olefins and diolefins on all catalysts suggests that LaAl-based materials present the most acidic character among La-perovskites

Design of Multicationic Copper-Bearing Layered Double Hydroxides for Catalytic Application in Biorefinery

Ethanol has been used as a renewable hydrogen-donor in the conversion of a lignin model molecule in subcritical conditions. Noble metal-free porous mixed oxides, obtained by activation of Cu-Ni-Al and Cu-Ni-Fe layered double hydroxide (LDH) precursors, have been used as heterogeneous catalysts for Meerwein-Ponndorf-Verley (MPV) hydrogen transfer and further hydrogenation by ethanol dehydrogenation products. Both the Cu/(Cu+Ni) ratio and the nature of the trivalent cation (Al or Fe) affect the activity of the catalysts, as well as the selectivity towards the different steps of the hydrogenation reactions and the cleavage of lignin-like phenylether bonds. Accounting for the peculiar behaviour of Cu2+ and M(III) cations in the synthesis of LDHs, the coprecipitation of the precursors has been monitored by titration experiments. Structural and textural properties of the catalysts are closely related to the composition of the LDH precursors

Alginate: A Versatile Biopolymer for Functional Advanced Materials for Catalysis

Alginates are natural polysaccharides extracted mainly from brown algae, constituted by sequences of uronic units. These renewable biopolymers, available in virtually unlimited amounts, can be subjected to different manipulations rendering tailored gel materials endowed with excellent properties for catalytic applications. This chapter collects and summarizes emerging catalytic uses of alginate materials, in their different formulations, as: (i) supports for organometallic catalysts, (ii) supports for metal ions, (iii) supports for nanoparticles, and (iv) heterogeneous Brønsted acid promoters. A broad range of chemical transformations can be promoted by these alginate-based catalytic systems, which are tolerant to different reaction media. Some of the reported examples show the importance of morphology and textural properties of the alginate materials on the catalytic activity. Their heterogeneous nature guarantees the easy recovery from the reaction mixtures, and, in some cases, their reuse in several reaction cycles

Alginic acid aerogel: A heterogeneous Br\uf8nsted acid promoter for the direct Mannich reaction

We demonstrate that highly dispersed alginic acid aerogel beads can function as heterogeneous promoters for Br\uf8nsted acid catalyzed reactions. The activity displayed by alginic acid, benchmarked in the three-component direct Mannich reaction, depended on its morphology, with the aerogel formulation providing distinct advantages over other forms

Chitosan Aerogel Beads as a Heterogeneous Organocatalyst for the Asymmetric Aldol Reaction in the Presence of Water: an Assessment of the Effect of Additives

The catalytic properties of chitosan aerogel for the direct asymmetric aldol reaction in water assisted by various surfac- tants and acid co-catalysts have been evaluated by em- ploying a range of donor and acceptor systems. A beneficial effect on both the yields and enantioselectivities was observed, and the combination of surfactants and acid co-catalysts has proven particularly useful in the case of heterocyclic ketone donors

The chemical-loop bio-alcohol reforming for hydrogen production

International audienc

The chemical-loop bio-alcohol reforming for hydrogen production

International audienc

Control of the mechanism of chemical-looping of ethanol in non-stoichiometric ferrites by Cu-Mn substitution

Copper-manganese spinel ferrites have been evaluated as solid oxygen carriers for the production of hydrogen from water by ethanol-steam redox cycles. The materials were characterized by X-ray diffraction, Mo center dot ssbauer spectroscopy, temperature-programmed reduction, oxygen isotope exchange and textural analysis. Surface re-actions were followed by DRIFT spectroscopy. The amount and purity of hydrogen, produced in redox cycles at constant temperature of 450 degrees C, were highly affected by the nature of the oxygen carrier phases in the reduction step of the cycle. Cu-rich ferrites were reduced by ethanol to metallic copper and iron carbides, whereas Mn-rich ferrites were less deeply reduced to manganowustite. Ethanol was mainly oxidized by Cu-ferrites to CO and CO2, while mainly oxydehydrogenation products were formed on Mn-ferrites. In the reoxidation of the oxygen carrier by steam, the production of CO and CO2 by oxidation of carbides negatively affected the purity of the hydrogen formed