Browsing by Author "Escalona Burgos, Néstor Guillermo"
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- ItemAlkali-driven selectivity of products on carbon-supported Ni-based catalysts during the HDO of guaiacol(2024) Matos, Juan; Samudio-González, Diana; Blanco, Elodie; Poon, Po S.; Escalona Burgos, Néstor GuillermoThe catalytic hydrodeoxygenation (HDO) of guaiacol as a representative bio-oil molecule was studied using a series of carbon-supported Ni-based catalysts. The promoter effect of alkali metals (Ca and Mg) on the catalytic activity and selectivity was verified. Catalysts were prepared by wetness incipient method and N2 gas adsorp tion/desorption isotherms, X-ray diffraction, reduction/desorption temperature-programed, and CO chemi sorption analysis were performed to characterize the catalysts. In terms of the initial reaction-rate catalysts with 1 wt% alkali-promotors showed an increase in the activity up to ca. 1.4 and 1.2 times higher on Ni-Ca(1 %)/AC and Ni-Mg(1 %)/AC, respectively, compared to Ni/AC catalyst. The increase to 5 wt% in alkali promotors slightly reduced the initial activity of Ni. However, the turn-over frequencies estimated showed higher values when alkali content is increased from 1 wt% to 5 wt%. These apparent contradictorial results suggest the formation of new actives sites along reaction, probably constituted by a mixture of oxides NiO-CaO and NiO-MgO. The selectivity of products showed remarkable changes due to the presence of alkali-promotors and a mechanism or reaction is proposed based on the kinetics of formation and evolution of products. Mg-promoted led to the formation of cyclohexane. On the contrary, Ca-promoted catalysts led the mechanism to representative benzene yields. This is remarkable result regarding the efficiency of a HDO biorefinery. In general, it can be concluded that Ni-based catalysts promoted with alkali metals are an economical alternative for the catalytic conversion of representa tive target molecules from a bio-oil feed.
- ItemCobalt-based core@shell catalysts for guaiacol hydro conversion: use of salicylic acid as a sacrificial modulator of the interaction between the metal phase and the silica support(2024) Aguirre Abarca, Diego Alejandro; Pazo Carballo, César Alexander; Laurenti, Dorothee; Karelovic, Alejandro; Dongil, Ana B.; Escalona Burgos, Néstor GuillermoIn this work, four cobalt-based catalysts were obtained using two routes of preparation which differed in the expected degree of interaction with the silica matrix, using salicylic acid as a sacrificial modifier during the synthesis to modulate the interaction between the cobalt phase and the silica support due to its complexing properties. The catalysts were tested for the hydroconversion of guaiacol at 300 degrees C and 5 MPa of H2, with clear differences between each procedure. It is found that the synthesis route has a deep impact on the catalytic activity, with the catalysts prepared using a one-pot route being less active and having an increased selectivity to cyclohexane. In contrast, the ones prepared using a two-step process have increased yield towards phenol and cyclohexanol under the conditions used herein. Salicylic acid increases the catalytic activity in comparison to the untreated material for both families of materials, without changing the observed selectivity between samples with the same preparation., Salicylic acid as a cobalt-based catalyst modifier enhances the activity with increased selectivity towards cyclohexanol. This is linked to changes induced by the modifier over the cobalt surface, allowing for tuning of the catalytic activity.
- ItemEffects of two chemical treatments on the optical properties of the rutile crystalline phase.Efectos de dos tratamientos químicos sobre las propiedades ópticas de la fase cristalina de rutilo(2022) Retamoso Llamas Claudia Patricia; Escalona Burgos, Néstor Guillermo; González Hormazábal, Marcelo Andrés; Barrientos Poblete, Lorena Julieta© 2022, Universidad de Los Andes. All rights reserved.The optical properties of the photocata-lysts are related to the band gap since it impacts the results of contaminant removal effectiveness during irradiation. Among the photocatalysts, anatase has been studied more than rutile. In the present work, chemical treatments were carried out on rutile to shift the band gap towards the visible zone of the electromagnetic spectrum. The results suggest that the incipient impregnation with Fe salts effectively shifts the energy gap to the visible area, significantly decreasing the maximum absorbance levels. While the partial reduction of rutile increases the absorbance levels when carried out at a temperature of 250 °C.
- ItemExperimental Analysis of Helix Aspersa Shell as Cementitious Material(Springer, 2024) Campos-Cortes, María José; Brescia-Norambuena, Leonardo; Retamoso, Claudia; Escalona Burgos, Néstor GuillermoThe high environmental impact of the cement industry demands the study of new cementitious materials. Often supplementary cementitious materials such as fly ash or silica fume are used; however, the depletion of raw materials encourages the assessment of new sources. Due to the high calcium content of snail shells, this research explored the use of crushed powder of Helix Aspersa to replace cement, evaluating its use at different percentages of replacement in weight (0, 5, and 10%), calcination temperature (0, 450, and 900 °C) and water-cementitious materials ratios (0.35, 0.40, and 0.45). The results included analysing setting time, compressive and flexural strength, water absorption, and shrinkage. Results indicated that snail shells (i) create an expansion during the first days (~15%), reaching similar values at 28 days, (ii) decrease the water absorption at calcination temperatures ≥450 °C, and (iii) slightly reduce the flexural strength (~16% in average) and compressive strength (~10% in average). As the main decrement of the responses is at a low w/cm ratio, it is expected that calcined snail shells offer the opportunity to save cement and pollution from the construction industry.
- ItemExploration of the initial photocatalytic activity parameters of ?Fe2O3–rutile for methylene blue discoloration in water through the OFAT process(2023) Retamoso Llamas, Claudia Patricia; Escalona Burgos, Néstor Guillermo; González Hormazábal, Marcelo Andrés; Barrientos Poblete, Lorena JulietaThe photocatalyst response is related to experimental conditions that improve effectiveness in removing contaminants. A parameter analysis of ?Fe2O3–rutile and water contaminated with methylene blue (MB) was carried out to obtain initial factors that impact reaction conditions. Moreover, the following factors were tested: the ?Fe2O3–rutile load, the initial MB concentration, and the initial pH solution. These one-factor-at-a-time variations were made to explore the conditions of each variable with the other two fixed. Above all, a significant change was identified in the initial discoloration rate from 5.2 to 35.56 10?9 mol g?1 s?1, with 34 and 91 % removal effectiveness, respectively. These results were achieved with an ?Fe2O3–rutile load of 1.0 g L?1, an initial MB concentration of 8.0 10?6 mol L?1, and a pH of 8.8, after 540 min of irradiation. This high discoloration effectiveness with ?Fe2O3–rutile had not been previously reported. The parameter that most influenced the photocatalytic activity was the initial pH solution due to the interaction of the point of zero charge of ?Fe2O3–rutile and the contaminated water; the pH of the solution exceeds the isoelectric point, it causes electrostatic forces and hydrogen bonds with MB to increase its effectiveness. The combination of ?Fe2O3–rutile and the removal of methylene blue in water improves adsorption on the surface of the ?Fe2O3–rutile, providing the highest discoloration rate.
- ItemSíntesis de productos químicos de alto valor agregado mediante reacciones One-Pot Tándem condensación/hidrogenación sobre catalizadores del tipo MOFS(2024) Pazo Carballo, César Alexander; Escalona Burgos, Néstor Guillermo; Schott Verdugo, Eduardo; Pontificia Universidad Católica de Chile. Escuela de QuímicaLa transformación catalítica de la biomasa se presenta como una ruta eficiente y selectiva para la generación de combustibles no convencionales y de productos químicos con valor agregado. El acoplamiento C-C de moléculas derivadas de la biomasa y posterior hidrogenación se ha planteado hoy día como una reto científico y novedoso. En este trabajo de tesis doctoral se estudió la actividad catalítica de las mallas metal-orgánicas (MOFs por sus siglas en inglés) sobre la condensación aldólica del benzaldehído y acetona sobre catalizadores mono- y bimetálicos-UiO-66 de Zr(IV), Hf(IV) y Ce(IV). Todos los catalizadores fueron sintetizados por el método solvotermal y se caracterizaron utilizando diversas técnicas analíticas. La actividad catalítica de las reacciones de condensación e hidrogenación se llevaron a cabo en un reactor discontinuo. Los resultados mostraron que la mayor actividad se observó sobre el Hf-UiO-66 debido al carácter oxofílico del metal, mostrando una mayor velocidad inicial de reacción para dar benzalacetona sin desactivar sus sitios activos. Efecto contrario se observó al cambiar el enlazador orgánico (ácido-2,5-piridin tereftálico) conllevando a cambios en la actividad catalítica y selectividad. En base a estos resultados, se seleccionó al Hf-UiO-66 como base del MOF con mejor potencial para su uso como soporte de las nanopartículas de ReOx- y ReOx-Pd. La caracterización fisicoquímica puso de manifiesto que las propiedades de estos materiales tras la adición con éxito de estas especies químicas, no alteró la cristalinidad del soporte microporoso. La evaluación catalítica de estos materiales en la hidrogenación de la benzalacetona mostró que todos presentan actividad catalítica con pequeñas variaciones en la selectividad hacia la formación de productos químicos de interés industrial. Finalmente, el ReOx-Pd/UiO-66 se evaluó en la reacción one-pot tándem condensación/hidrogenación mostrando actividad para ambas reacciones partiendo de la mezcla de sustratos benzaldehído/acetona.