Examinando por Autor "Vidal, Nora"

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Beta zeolite as an efficient catalyst for the synthesis of diphenolic acid (DPA) from renewable levulinic acid
(Elsevier, 2022) Morales, Gabriel; Melero, Juan A.; Paniagua, Marta; López-Aguado, Clara; Vidal, Nora
The solvent-free production of diphenolic acid (DPA) from levulinic acid (LA) and phenol is studied using readily accessible commercial acid zeolites like Beta, ZSM-5 and USY. Acid zeolites are cost-effective catalysts, and they are herein benchmarked against the sulfonic acid resins Amberlyst-15 and Nafion®, and sulfonic acidfunctionalized SBA-15 silicas. Beta zeolite with a moderate aluminum content (H-Beta 19, Si/Al=23) presents the best catalytic performance, owing to the right combination of the shape selectivity effect conferred by the BEA structure, and the adequate balance of acidity (Al content and speciation). The optimization of the reaction conditions is tackled by the response surface methodology using as optimization factors the temperature, the PhOH:LA molar ratio, and the catalyst loading. Thus, under the optimized reaction conditions (12 mmol LA, 140 ᵒC, 0.30 g catalyst loading, PhOH:LA = 6:1 mol), over 70% yield to DPA with LA conversion around 77% is obtained after 72 h. Despite the catalyst shows a progressive activity decay in successive uses because of fouling, removal of the formed organic deposits by calcination in air allows restoring the starting catalytic performance.
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.
Understanding the role of Al/Zr ratio in Zr-Al-Beta zeolite: Towards the one-pot production of GVL from glucose
(Elsevier, 2021-04-07) Paniagua, Marta; Morales, Gabriel; Melero, Juan Antonio; Iglesias, Jose; López-Aguado, Clara; Vidal, Nora; Mariscal, Rafael; López-Granados, Manuel; Martínez-Salazar, Irene
The direct one-pot transformation of glucose into γ-valerolactone (GVL) can be accomplished by means of a cascade of reactions in which Brønsted acid-catalyzed transformations are combined with catalytic transfer hydrogenation (CTH) by using 2-propanol as sacrificial alcohol, avoiding the use of high-pressure hydrogen. Catalysts containing Zr Lewis acid sites have been successfully applied in CTH reactions while the acid-driven transformations can be preferentially promoted by Brønsted Al-related acidity. Here, we present the combination of Zr and Al as active sites within a BEA zeolite structure as catalyst, with the possibility of adjusting the Al/ Zr ratio from ∞ (commercial H-Beta) to 0 (aluminium-free Zr-Beta), which show a scale of Brønsted/Lewis acid sites ratios. The Al/Zr ratio has a strong impact on the products distribution. As the Zr content increases, higher amount of GVL is obtained, leading to a maximum over the catalyst with high amount of Zr and low content of Al acid sites (Al/Zr = 0.2). An increase of reaction temperature, as well as reaction time, allows an enhancement of yields towards the desired products, leading to a maximum yield towards GVL of 24 mol% over Zr-Al-Beta (2.0), and a maximum yield towards isopropyl lactate of 26 mol% over Zr-Beta at 190 ◦C.