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CICECO-Aveiro Institute of Materials
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A review of solar thermochemical CO2 splitting using ceria-based ceramics with designed morphologies and microstructures
Publication . Pullar, Robert C.; Novais, Rui M.; Caetano, Ana P. F.; Barreiros, M. Alexandra; Abanades, Stéphane; Oliveira, Fernando Almeida Costa
ABSTRACT: This review explores the advances in the synthesis of ceria materials with specific morphologies or porous macro- and microstructures for the solar-driven production of carbon monoxide (CO) from carbon dioxide (CO2). As the demand for renewable energy and fuels continues to grow, there is a great deal of interest in solar thermochemical fuel production (STFP), with the use of concentrated solar light to power the splitting of carbon dioxide. This can be achieved in a two-step cycle, involving the reduction of CeO2 at high temperatures, followed by oxidation at lower temperatures with CO2, splitting it to produce CO, driven by concentrated solar radiation obtained with concentrating solar technologies (CST) to provide the high reaction temperatures of typically up to 1,500 degrees C. Since cerium oxide was first explored as a solar-driven redox material in 2006, and to specifically split CO2 in 2010, there has been an increasing interest in this material. The solar-to-fuel conversion efficiency is influenced by the material composition itself, but also by the material morphology that mostly determines the available surface area for solid/gas reactions (the material oxidation mechanism is mainly governed by surface reaction). The diffusion length and specific surface area affect, respectively, the reduction and oxidation steps. They both depend on the reactive material morphology that also substantially affects the reaction kinetics and heat and mass transport in the material. Accordingly, the main relevant options for materials shaping are summarized. We explore the effects of microstructure and porosity, and the exploitation of designed structures such as fibers, 3-DOM (three-dimensionally ordered macroporous) materials, reticulated and replicated foams, and the new area of biomimetic/biomorphous porous ceria redox materials produced from natural and sustainable templates such as wood or cork, also known as ecoceramics.
Cyclopentadienyl vs indenyl control of thermal/photoactivated CO release in cationic molybdenum(II) dicarbonyl-ethylenediamine complexes
Publication . Bruno, Sofia M.; Calhau, Isabel B.; Dias, Tiago M.; Santos, Adriana; Silva, Luis Cunha; Nolasco, Mariela M.; Goncalves, Isabel S.; Pillinger, Martyn
ABSTRACT: Molybdenum half-sandwich carbonyl complexes continue to attract attention as potential anticancer agents and prodrugs for therapeutic use of carbon monoxide. Building on the known bioactivity and hydrolytic stability of cyclopentadienyl-based Mo fragments, we report the synthesis, structural characterization, and solution behavior of two cationic half-sandwich complexes, [(eta 5-Cp)Mo(CO)2(en)][BF4] (3) and [(eta 5-Ind)Mo(CO)2(en)][BF4] (4) (Cp = cyclopentadienyl, Ind = indenyl, en = ethylenediamine). Complex 3 is described here for the first time, while 4 was structurally characterized by single-crystal X-ray diffraction, revealing a distorted square-pyramidal geometry with cis-CO ligands and a chelating en ligand positioned beneath the indenyl ring. Both compounds are air-stable in the solid state and exhibit enhanced solubility in polar media due to their ionic nature. UV-vis stability studies under simulated physiological conditions (PBS, pH 7.4, 37 degrees C) show gradual decomposition of both complexes, accelerated by visible-light irradiation and/or the presence of air. CO-release behavior was quantified using the myoglobin assay: the allyl precursors [(eta 5-Cp')Mo(eta 3-C3H5)(CO)2] were inert, whereas complexes 3 and 4 released CO slowly, with 4 exhibiting significantly faster thermal CO liberation (t1/2 approximate to 129 min; 0.74 equiv. CO after 6 h). Complex 3 showed minimal thermal CO release but underwent enhanced and sustained photodecarbonylation under visible-light irradiation, enabling controlled CO delivery. These results identify 3 and 4 as rare examples of Mo-based CO-releasing molecules capable of slow, tunable CO release under biologically relevant conditions, with 3 displaying light-responsive behavior and 4 functioning as a spontaneous thermal CO donor.
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Fundação para a Ciência e a Tecnologia
Programa de financiamento
6817 - DCRRNI ID
Número da atribuição
UID/CTM/50011/2019