Browsing by Author "Escalona Burgos, Nestor Guillermo"

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    Atrazine degradation through a heterogeneous dual-effect process using Fe-TiO2-allophane catalysts under sunlight
    (2024) Castro-Rojas, Jorge; Jofré-Dupre, Pablo; Escalona Burgos, Nestor Guillermo; Blanco, Elodie; Ureta-Zañartu, María Soledad; Mora, Maria Luz; Garrido-Ramírez, Elizabeth
    This study investigated the novel application of Fe-TiO2-allophane catalysts with 6.0% w/w of iron oxide and two TiO2 proportions (10% and 30% w/w) for degrading atrazine (ATZ) using the heterogeneous dual-effect (HDE) process under sunlight. Comparative analyses with Fe-allophane and TiO2-allophane catalysts were conducted in both photocatalysis (PC) and HDE processes. FTIR spectra reveal the unique hydrous feldspathoids structure of allophane, showing evidence of new bond formation between Si-O groups of allophane clays and iron hydroxyl species, as well as Si-O-Ti bonds that intensified with higher TiO2 content. The catalysts exhibited an anatase structure. In Fe-TiO2-allophane catalysts, iron oxide was incorporated through the substitution of Ti4+ by Fe3+ in the anatase crystal lattice and precipitation on the surface of allophane clays, forming small iron oxide particles. Allophane clays reduced the agglomeration and particle size of TiO2, resulting in an enhanced specific surface area and pore volume for all catalysts. Iron oxide incorporation decreased the band gap, broadening the photoresponse to visible light. In the PC process, TiO2-allophane achieves 90% ATZ degradation, attributed to radical species from the UV component of sunlight. In the HDE process, Fe-TiO2-allophane catalysts exhibit synergistic effects, particularly with 30% w/w TiO2, achieving 100% ATZ degradation and 85% COD removal, with shorter reaction time as TiO2 percentage increased. The HDE process was performed under less acidic conditions, achieving complete ATZ degradation after 6 hours without iron leaching. Consequently, Fe-TiO2-allophane catalysts are proposed as a promising alternative for degrading emerging pollutants under environmentally friendly conditions.
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    Catalytic evaluation of MOF-808 with metallic centers of Zr(IV), Hf(IV) and Ce(IV) in the acetalization of benzaldehyde with methanol
    (Royal Society Chemistry, 2024) Arellano Valderrama, Yazmin Anay; Pazo Carballo, César Alexander; Roa, Vanesa; Hidalgo-Rosa, Yoan; Zarate, Ximena; Llanos, Jaime; Escalona Burgos, Nestor Guillermo; Schott, Eduardo
    In the context of climate change, it is of utmost importance to replace the use of fossil fuels as raw material in areas of industrial interest, for example, in the production of chemical inputs. In this context, a viable option is biomass, since by subjecting it to chemical processes such as pyrolysis, it is possible to obtain platform molecules that are the basis for the generation of value-added chemical products. Acetals are molecules obtained from biomass derIVatIVes, which have various applications in cosmetic chemistry, in the pharmaceutical industry as intermediates or final compounds, food additIVes, among others. Different catalysts have been used in the acetalization reaction, including MOFs, which have the advantage of being porous materials with high surface area values. The large surface area translates into a greater number of catalytically actIVe sites available for the reaction. Among the MOFs that have been used for this purpose is MOF-808, which is characterized by having a lower number of ligands attached to its metal cluster, therefore, it has a greater exposure of the metals that make up its structure. In this context, the work carried out studied the catalytic performance of MOF-808 when its Zr(IV) metal centers are replaced by Hf(IV) and Ce(IV) atoms in the acetalization reaction of benzaldehyde with methanol. The MOFs obtained by solvothermal synthesis were characterized by powder X-ray diffraction, N-2 adsorption and desorption, FT-IR spectroscopy, acid-base potentiometric titration, XPS and thermogravimetric analysis. The results of the catalysis indicate that the MOF with the best performance was MOF-808-Ce, which achieved conversions greater than 80% in a period of ten minutes. MOF-808-Ce exhibits a higher number of defects and therefore a higher availability of catalytic sites for the reaction to occur, which explains the better performance. Finally, the performance of MOF-808 in the acetalization of benzaldehyde with methanol was also supported by density functional theory (DFT) calculations.
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    H2 production through aqueous phase reforming of ethanol over molybdenum carbide catalysts supported on zirconium oxide
    (Wiley, 2024) Pavesi Contreras, Camila Andrea; Blanco, Elodie; Pazo Carballo, César Alexander; Dongil, A.B.; Escalona Burgos, Nestor Guillermo
    Molybdenum carbide catalysts supported on monoclinic and tetragonal zirconium oxide were studied for hydrogen production through aqueous phase reforming of ethanol. Catalysts were characterized by N2 physisorption, XRD, TPR and XPS. Results showed that 10%Mo2C/m-ZrO2 was less carburized and had a lower surface area than 10%Mo2C/t-ZrO2 and 10%MoC/t-ZrO2. Mo oxide was identified on the surface as well as two types of Mo oxycarbide and Mo oxynitride. The α crystalline phase of the carbide was more active than β phase and was ascribed to its higher relative superficial distribution. However, the α phase generated less H2 probably because there was less oxycarbide presence. 10%Mo2C/m-ZrO2 produced significantly more H2 and was stable for five consecutive reactions. This catalyst showed higher carburization degree after the reaction, which greatly enhanced the generation of H2, suggesting that carbides species improved H2 production compared to oxycarbides.
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    H2 production through aqueous phase reforming of ethanol over molybdenum carbide catalysts supported on zirconium oxide
    (2024) Pavesi Contreras, Camila Andrea; Blanco, Elodie; Pazo Carballo, César Alexander; Dongil, A.B.; Escalona Burgos, Nestor Guillermo
    Molybdenum carbide catalysts supported on monoclinic and tetragonal zirconium oxide were studied for hydrogen production through aqueous phase reforming of ethanol. Catalysts were characterized by N2 physisorption, XRD, TPR and XPS. Results showed that 10%Mo2C/m-ZrO2 was less carburized and had a lower surface area than 10%Mo2C/t-ZrO2 and 10%MoC/t-ZrO2. Mo oxide was identified on the surface as well as two types of Mo oxycarbide and Mo oxynitride. The α crystalline phase of the carbide was more active than β phase and was ascribed to its higher relative superficial distribution. However, the α phase generated less H2 probably because there was less oxycarbide presence. 10%Mo2C/m-ZrO2 produced significantly more H2 and was stable for five consecutive reactions. This catalyst showed higher carburization degree after the reaction, which greatly enhanced the generation of H2, suggesting that carbides species improved H2 production compared to oxycarbides.
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    Selective benzaldehyde/acetone to benzalacetone cross-aldol condensation catalyzed by UiO-66 MOFs
    (2025) Pazo Carballo, Cesar Alexander; Camu Macaya, Esteban Alonso; Yoan Hidalgo-Rosa; Llanos, Jaime; Zarate, Ximena; Dongil, Ana Belén; Schott Verdugo, Eduardo Enrique; Escalona Burgos, Nestor Guillermo
    Cross-aldol condensation reactions are an important family of reactions that generate added-value chemicals with long chain products. Those products have multiple applications, such as those in the pharmaceutical industry, flavors and fragrances, agricultural chemicals and fine and specialty chemicals, among others. Possible products are long chain aromatic compounds, which could be used to generate fuels. The ability to generate that kind of fuel from biomass has been a challenge over the last few years. In this report the cross-aldol condensation reaction study using a family of UiO-66 MOFs between benzaldehyde and acetone to produce benzalacetone was performed. Thus, a family of UiO-66 MOFs was synthesized and characterized (by means of N2 physisorption, NH3-TPD, CO2-TPD, ATR-FTIR, and powder X-ray diffraction) and its catalytic activity was studied in detail. Good conversion and selectivity were obtained. A thorough study of the kinetics of this reaction was performed for all the used UiO-66 MOFs. In this sense, the Langmuir–Hinshelwood kinetic models fitted the experimental data. The behavior predictions using different metals (Zr, Hf or Zr/Hf) and linkers (BDC or PDC) were fitted from the bimolecular one-site and two-site models. Competitive and non-competitive mechanisms were used to explain the production of the main intermediate compound (β-hydroxy ketone). The catalyst Zr/Hf-UiO-66 showed the best activity, which could be attributed to the greater total interaction energy of benzaldehyde/acetone on the catalyst surface (as shown by DFT calculations). A synergetic effect is observed for the bimetallic UiO-66 catalyst between Zr and Hf, obtaining a higher reaction rate than for the monometallic catalysts. Furthermore, a similar effect was reflected in the TOF for Zr/Hf-UiO-66. The best selectivity towards benzalacetone was obtained for Hf-UiO-66-PDC under iso-conversion conditions. Finally, depending on the metal–linker pair, differences in the benzaldehyde/acetone adsorption modes were observed, indicating the presence of bimolecular kinetic adjustments at one and two sites for the aldol condensation of benzaldehyde. All the results shown herein were supported by means of DFT calculations.