Navegando por Autor "Rojas, Alex"
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Artigo Fluoride-mediated synthesis of TON and MFI zeolites using 1-butyl-3- methylimidazolium as structure-directing agent(Elsevier, 2017-11-01) Pergher, Sibele Berenice Castellã; Lopes, Christian W.; Hortigüela, Luis Gomez; Rojas, AlexIn this work, 1-butyl-3-methylimidazolium (1B3MI) cation has been employed as a structure-directing agent for the synthesis of pure silica and Ti-containing zeolites in fluoride media. The 1B3MI OSDA exhibited distinct phase selectivity depending on the synthesis conditions, and particularly the concentration of the synthesis gel. Thus, under more diluted conditions (H2O/SiO2 ¼ 14), the 1B3MI cation yielded pure silica TON zeolite with high crystallinity. Attempts to obtain Ti-containing zeolites, however, failed at this diluted condition even after 15 days of synthesis. In contrast, highly crystalline Ti-MFI was the only phase obtained upon reducing the H2O/SiO2 molar ratio from 14 to 7. The presence of Ti in the MFI zeolite framework was confirmed by both infrared and DRS UV-vis spectroscopies. The presence of intact OSDA molecules within the micropores was inferred from elemental analysis and 13C CP-MAS NMR spectroscopy. On the other hand, thermogravimetric analyses showed a different packing of the 1B3MI cation in the pure silica TON and Ti-MFI samples. Moreover, the environments for Si and F species in the as-made materials were investigated by means of 29Si and 19F MAS NMR, respectively. Finally, molecular simulations showed that the most stable arrangement of the 1B3MI cations involves the location of the imidazolium rings on the channel intersections and of the butyl chains on the sinusoidal channelsArtigo Introduction of Al into the HPM-1 framework by in situ generated seeds as an alternative methodology(MDPI, 2018-09-13) Pergher, Sibele Berenice Castellã; Vinaches, Paloma; Rojas, Alex; Alencar, Ana Ellen V. de; Castellón, Enrique Rodríguez; Braga, Tiago P.An alternative method for the introduction of aluminum into the STW zeolitic framework is presented. HPM-1, a chiral STW zeolite with helical pores, was synthesized in the pure silica form, and an aluminum source was added by in situ generated seeds. Displacements of the peak positions in the Al samples were found in the X-ray diffractograms, indicating the possible incorporation of the heteroatom into the framework. Using an analysis of the 29Si and 27Al magic-angle spinning nuclear magnetic resonance (MAS NMR) spectra, we concluded that the aluminum was effectively introduced into the framework. The (AlTETRAHEDRAL/AlOCTAHEDRAL) ratio and its textural properties were studied to explain the catalytic ethanol conversion results at medium temperatures. The sample with the lowest Si/Al ratio showed the best results due to its higher surface area and pore volume, in comparison to those observed for the sample with the highest Si/Al ratio, and due to its higher bulk tetrahedral aluminum content, in comparison to the intermediate Si/Al ratio sample. All catalysts were selective to ethylene and diethyl ether, confirming the presence of acidic sitesArtigo Synthesis and characterization of Ti-STF zeolite using 1,2,3-triethyl-4- methylimidazolium as structure-directing agent(Elsevier, 2018-05-15) Pergher, Sibele Berenice Castellã; Variani, Yuri Miguel; Rojas, AlexA new composition of STF zeolite, Ti-STF, was synthesized via the fluoride route using 1,2,3-triethyl-4-methylimidazolium (123TE4MI) as a structure-directing agent (SDA). The Si/Ti ratios used in the synthesis of the TiSTF materials were 50 and 25, and the synthesis of pure silica STF, as a blank, was also carried out. The obtained materials were studied and characterized by different techniques such as X-ray diffraction, 13C and 27Si solidstate NMR, thermogravimetric analysis, among others. Additionally, the Ti incorporated into the STF zeolite framework was studied by diffuse reflectance ultraviolet–visible (UV–vis) spectroscopy. This characterization showed that Ti species are mostly tetrahedrally coordinated in the STF zeolite framework; however, a minority of Ti is octahedrally coordinated, i.e., extra-framework