Examinando por Autor "Botas, J.A."

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Kinetic modeling of the first step of Mn2O3/MnO thermochemical cycle for solar hydrogen production
(Elsevier, 2012-12) Marugán, J.; Botas, J.A.; Molina, R.; Herradón, C.
This work reports the kinetic study of the first step of the Mn2O3/MnO thermochemical cycle for hydrogen production by water splitting. The reaction kinetics of Mn (III) oxide thermal reduction has been evaluated using dynamic thermogravimetric analysis at constant heating rate under nitrogen flow. This way the reaction rate can be described as a function of temperature and different kinetic models were fitted to the experimental data obtained from thermogravimetric experiments. A good fitting can be observed for each experiment, although a significant disparity in the values estimated for the Arrhenius parameters has been found (activation energies and pre-exponential factors). Unique values for the kinetic parameters have been calculated by application of a multivariate non-linear regression method for the simultaneous fitting of data from all the experiments carried out at different heating ramps. However, also in this case the values of the Arrhenius parameters are significantly different depending on the chosen kinetic equation. Optimal kinetic parameters have been finally calculated through the estimation of activation energy values by model-free isoconversional methods and using a rigorous multivariate nonlinear regression for the calculation of the model-dependant pre-exponential factors.
Production of high value-added phenolic compounds through lignin catalytic pyrolysis over ion-exchanged hierarchical ZSM-5 and Beta zeolites
(Elsevier, 2025-08-01) Ávila, M.I.; Alonso-Doncel, M.M.; Cueto, J.; Briones, L.; Gómez-Pozuelo, G.; Escola, J.M.; Serrano, D.P.; Peral, A.; Botas, J.A.
Synthesised H-ZSM-5 and H-Beta zeolites with hierarchical porosity (h-H-ZSM-5 and h-H-Beta) have been ion-exchanged with alkali (Na+ and K+) and alkaline-earth (Mg2+) metals and have been evaluated as catalysts to produce high value-added products through catalytic pyrolysis of lignin. In comparison with the thermal test, hierarchical zeolites in acid form are effective catalysts for lignin pyrolysis, favouring the production of valuable light compounds although reducing bio-oil* yield and increasing gas and coke formation. In this way, h-H-ZSM-5 zeolite promotes the formation of oxygenated aromatics, being guaiacols and syringols the major products. Alkali-exchanged variants of this zeolite enhance demethylation reactions improving the selectivity towards 2-methoxy-phenol and syringol, by modifying acid site properties. On the other hand, h-H-Beta zeolite, with larger pore size and stronger acidity, leads to higher concentration of oxygenated aromatics for both parent and ion-exchanged catalysts. Specifically, h-KH-Beta promotes the production of 2-methoxy-phenol and syringol. Besides, h-MgH-Beta stands out for its greater selectivity towards phenol and alkylphenols, such as dimethylphenol. Overall, the combination of accessibility, provided by the hierarchical porosity, with the different nature and strength of the acid sites, induced by the ion-exchange with alkali and alkaline-earth metals, allows tailoring the lignin catalytic pyrolysis process to selectively produce high value-added compounds.
Tailoring the preparation of USY zeolite with uniform mesoporosity for improved catalytic activity in phenol/isopropanol alkylation
(Elsevier, 2025-06-15) Molina, C.; Abdrassilova, A.; Ávila, M.I.; Alonso-Doncel, M.M.; Cueto, J.; Gómez-Pozuelo, G.; Briones, L.; Botas, J.A.; Serrano, D.P.; Peral, A.; Escola, J.M.
The preparation of hierarchical USY zeolite, exhibiting uniform mesoporosity and high Si/Al atomic ratio (48–52), has been investigated by means of a surfactant/ammonia post-treatment applied to a commercial USY sample. The procedure involved the use of temperatures within 40–135 °C, a low ammonia concentration solution (0.05 N) and hydrothermal synthesis times of 20 h. When working at 40–80 °C, the obtained USY samples exhibit enhanced intraparticular mesoporosity (324–418 m2 g−1), showing increasingly uniform mesopores around 4.0 nm, while holding a remarkable zeolitic microporosity (413–363 m2 g−1). In contrast, higher temperatures resulted in a steady abatement of crystalline zeolitic domains, with a total collapse of the zeolite structure at 135 °C. These hierarchical USY materials were tested in the alkylation of phenol with isopropanol, wherein one of the obtained products, e.g. 2,6-diisopropylphenol (Propofol), is the most important intravenous anaesthetic in the market. Interestingly, the generation of the uniform mesoporosity in USY samples led to an enhancement of both the phenol conversion and the selectivity towards C-alkylation products. Thus, the sample treated at 60 °C (USY-60) gave rise to the highest selectivity towards C-alkylation products (84 %) and poly-alkylphenols formation (72 %), with an encouraging selectivity towards 2,6-diisopropylphenol (43 %).
Treatment of an agrochemical wastewater by integration of heterogeneous catalytic wet hydrogen peroxide oxidation and rotating biological contactors
(Elsevier, 2013-06-15) Melero, J.A.; Pariente, M.I.; Siles, J.A.; Molina, R.; Botas, J.A.; Martinez, F.
The treatment of a non-biodegradable agrochemical wastewater has been studied by coupling of heterogeneous catalytic wet hydrogen peroxide oxidation (CWHPO) and rotating biological contactors (RBCs). The influence of the hydrogen peroxide dosage and the organic content of the wastewater (dilution degree) were studied. The CWHPO of the raw wastewater at 80 ºC and using a moderate amount of oxidant (0.23 gH2O2/gTOC) reduced significantly its total organic carbon content and increased its biodegradability. Likewise, the iron leaching of the heterogeneous catalyst (Fe2O3/SBA- 15) was less than 2 mg/L in the treated effluent. Under the best operating conditions, the resultant CWHPO effluent was successfully co-treated by rotating biological contactors (RBCs) using a simulated municipal wastewater with different percentages of the CWHPO effluent (2.5, 5 and 10 % v/v). The RBCs showed high stability for the treatment of the highest percentage of the CWHPO effluent, achieving total organic carbon (TOC) and total nitrogen (TN) reductions of ca. 78 % and 50 %, respectively. The integration of both processes on a continuous mode has been successfully accomplished for the treatment of the as-received agrochemical wastewater.