Examinando por Autor "Orfila, María"

Mostrando 1 - 4 de 4

Experimental evaluation and energy analysis of a two-step water splitting thermochemical cycle for solar hydrogen production based on La0.8Sr0.2CoO3-δ perovskite
(Elsevier, 2022) Orfila, María; Linares, María; Pérez, Antonio; Barras García, Inés; Molina Gil, Raúl; Marugán, Javier; Botas, Juan Ángel; Sanz, Raúl
A study of the hydrogen production by thermochemical water splitting with a commercial perovskite La0.8Sr0.2CoO3-d(denoted as LSC) under different temperature conditions is presented. The experiments revealed that high operational temperatures for the thermal reduction step (>1000 C) implied a decrease in the hydrogen production with each consecutive cycle due to the formation of segregated phases of Co3O4. On the other hand, the experiments at lower thermal reduction operational temperatures indicated that the material had a stable behaviour with a hydrogen production of 15.8 cm3 STP/gmaterial$cycle during 20 consecutive cycles at 1000 C, being negligible at 800 C. This results comparable or even higher than the maximum values reported in literature for other perovskites (9.80 e10.50 STP/gmaterial$cycle), but at considerable lower temperatures in the reduction step of the thermochemical cycle for the water splitting (1000 vs 1300e1400 C). The LSC keeps the perovskite type structure after each thermochemical cycle, ensuring a stable and constant H2 production. An energy and exergy evaluation of the cycle led to values of solar to fuel efficiency and exergy efficiency of 0.67 and 0.36 (as a percentage of 1), respectively, which are higher than those reported for other metal oxides redox pairs commonly found in the literature, being the reduction temperature remarkably lower. These facts point out to the LSC perovskite as a promising material for full-scale applications of solar hydrogen production with good cyclability and compatible with current concentrating solar power technology.
Hydrogen production by isothermal thermochemical cycles using La0.8Ca0.2MeO3±δ (Me = Co, Ni, Fe and Cu) perovskites
(Elsevier, 2023) Pérez, Alejandro; Orfila, María; Linares, María; Sanz, Raúl; Marugán, Javier; Molina, Raúl; Botas, Juan A.
Solar-driven thermochemical water splitting has the potential to transform concentrated solar energy into green hydrogen and other solar fuels. In this work, La0.8Ca0.2MeO3±d (Me ¼ Co, Ni, Fe and Cu) perovskites have been synthesised by a modified Pechini method and evaluated as materials for hydrogen production by two step thermochemical water splitting cycles. Performing the thermal reduction at temperatures of 1200 and 1000 C, while the oxidation is done at 800 C, allows a remarkable and stable hydrogen production after 5 consecutive cycles. However, the perovskites suffer changes in the structure after each redox cycle, with potential effects in the long-term cyclic operation. On the contrary, the isothermal thermochemical cycles at 800 C produce a stable amount of hydrogen with each consecutive cycle maintaining the perovskite structure. This hydrogen production ranges from 3.60 cm3 STP/gmaterial$cycle for the material with the lowest productivity (La0.8Ca0.2FeO3±d) to 5.02 cm3 STP/gmaterial$cycle for the one with the highest activity (La0.8Ca0.2NiO3±d). Particularly the Ni-based material shows the highest H2 productivity accompanied by very good material stability after 15 consecutive cycles, being possible to combine with current solar thermal facilities based on concentrated solar power technologies like plants with central receivers.
MgO-based catalysts for selective delignification of lignocellulosic waste and carboxylic acids production under mild hydrothermal conditions
(Elsevier, 2025-08) Vidal, Nora; Ventura, María; Orfila, María; Martínez, Fernando; Melero, Juan Antonio
Lignocellulosic biomass offers a sustainable alternative to traditional raw materials. However, its complex structure, and particularly the presence of lignin, presents a significant challenge for its conversion into valuable products. This study explores the catalytic performance of magnesium oxide (MgO) based materials for the selective delignification of lignocellulosic waste and concomitant carboxylic acids production. Different MgO samples have been synthesized through various synthetical methods with the purpose of promoting the selective delignification of a lignocellulose waste while minimizing the degradation of other polymers (cellulose and hemicellulose). The resultant lignin-free holocellulose solid after selective depolymerization might be used in subsequent fermentation processes. The catalytic results demonstrated that MgO synthesized by a sol-gel method exhibited the highest catalytic activity, achieving ca. 90 % lignin conversion with minimal degradation of cellulose and hemicellulose and outstanding production of carboxylic acids (ca. 30 % of the carbon of the degraded polymers was converted into carboxylic acids). The high concentration of medium-strength base sites combined with significant macroporosity are crucial for enhancing the catalytic performance of MgO-based catalysts. Importantly, these results were achieved under mild conditions (120 ◦ C) using water as a solvent and without addition of external oxidant agents. Furthermore, the study observed a significant production of valuable (di) carboxylic acids, such as fumaric acid during the depolymerization process over optimized MgO catalyst. This research provides valuable insights into the potential of MgO as a sustainable catalyst for the selective conversion of lignin present in lignocellulosic biomass into valuable chemicals and biofuels.
Reticulated porous structures of La0.8Al0.2NiO3-δ perovskite for enhanced green hydrogen production by thermochemical water splitting
(Elsevier, 2024-12) Pérez, Alejandro; Orfila, María; Díaz, Elisa; Linares, María; Sanz, Raúl; Marugán, Javier; Molina, Raúl; Botas, Juan A.
The preparation and optimisation of La0.8Al0.2NiO3-δ (LANi82) perovskite shaped as reticulated porous ceramic (RPC) structures for H2 production by thermochemical water splitting is presented for the first time. The perovskite was first synthesised in powder form following a modified Pechini method. The redox properties of the LANi82 were first tested under N2/air flow in a thermogravimetric analyser. After that, the sponge replica method for preparing RPCs was optimised in terms of slurry composition and final thermal treatment to obtain a LANi82-RPC structure with porosity and strength appropriate to enhance heat and mass transfer in further solar reactors. The optimised LANi82-RPC material showed an outstanding hydrogen production of 8.3 cm3 STP/gmaterial·cycle at isothermal conditions (800 °C). This production was increased up to 11.5 cm3 STP/gmaterial·cycle if the thermal reduction was performed at 1000 °C. Additionally, a stable activity with almost constant H2 production in consecutive cycles was obtained for the optimised LANi82-RPC in both cases. The structure of the reticulated porous materials, with open macroporosity and wide interconnected channels, enhances heat and mass transfer, leading to higher hydrogen productions of the LANi82-RPC as compared to the materials as powder form in the same experimental set-up. These facts reinforce the favourable prospects of LANi82-RPC for large-scale hydrogen production, improving the coupling to current solar thermal concentration technologies developed, such as concentrated solar power tower