Navegando por Autor "Díaz, Urbano"

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Dandelion-like microspherical MCM-22 zeolite using BP 2000 as a hard template
(Sociedade Americana de Química, 2018-06-11) Pergher, Sibele Berenice Castellã; Schwanke, Anderson; Rocha, Jhonny Villarroel; Sapag, Karim; Díaz, Urbano; Corma, Avelino
The chemistry between layered MWW zeolite and carbon black pearls (BP 2000) as an inexpensive hard template was investigated to develop a rational one-pot synthesis of MCM-22 microspheres. The characterization results showed that the insertion of BP 2000 in the gel synthesis did not substantially compromise the crystallinity and microporosity, and the microscopic analyses showed that BP 2000 played a key role in controlling the final morphology of the MCM-22 zeolite, creating beautiful dandelion-like microspherical particles. The morphology obtained is due to the tortuous shape of the hard template, the particular MWW particle crystals, the interaction with the external surface of the MWW zeolitic precursor, and the synthesis conditions. The stacking of MWW crystals with edge-to-face orientations generates meso-/macrovoids, allowing access to the interiors of the microspheres. The microspheres were homogeneous with sizes ranging from 6 to 8 μm with an increase of the external surface and a macroporous size distribution centered at 200 nm, which is two times that of the traditional MCM-22 zeolite
Recyclable swelling solutions for friendly preparation of pillared MWW-type zeolites
(Elsevier, 2017-11-15) Pergher, Sibele Berenice Castellã; Schwanke, Anderson Joel; Díaz, Urbano; Corma, Avelino
We studied the recycling of swelling solution of MWW-type lamellar zeolitic precursor with a Si/Al ¼ 25. Swollen materials were obtained up to a third reuse without any compensation of reactants, pH or decrease of lamellar ordering degree. The pillared material showed a surface area of 777 m2 g1 and mesopores sizes of 2e4 nm characteristic of pillared MWW materials obtained by traditional approaches
The influence of ethanol-assisted washes to obtain swollen and pillared MWW-type zeolite with high degree ordering of lamellar structure
(Elsevier, 2019-02) Pergher, Sibele Berenice Castellã; Schwanke, Anderson Joel; Díaz, Urbano; Corma, Avelino
We studied the influence of the ethanol used as a washing solvent for obtaining swollen and pillared MWW topology zeolites with long-range ordering of lamellar structure. The diffractogram results showed that the increased number of washes increases the degree of order of the lamellar structure. Thermogravimetric results showed a considerable removal of the weakly interacting surfactant molecules after the third wash. The washes with ethanol did not remove the surfactant that strongly interacted with the MWW structure. The pillared material after the third wash showed a long-range ordering of the lamellar structure with the surface area of 728 m2 g−1, mesopore sizes of 2–4 nm and morphology characteristic of pillared MWW-type zeolites
The influence of swelling agents molecular dimensions on lamellar morphology of MWW-type zeolites active for fructose conversion
(Elsevier, 2017-12) Pergher, Sibele Berenice Castellã; Schwanke, Anderson Joel; Díaz, Urbano; Corma, Avelino
A new route to obtain pillared, disordered or desilicated MWW-type zeolites was developed assisted by quaternary ammonium surfactants with different hydrocarbon tail size acting as swelling agents (C12TAþ, C16TAþ, C18TAþ) and TPAþ both exchanged to their hydroxide forms instead of only one swelling agent (CnTAþ or TPAþ) in hydroxide form. Effect of surfactant concentration and swelling conditions were determinant to obtain MWW-type zeolites with different lamellar organization and spatial distribution of individual zeolitic layers. Specifically, soft swelling at 25 C with C12TAþ preserved layer structure reaching a final disordered/pillared structure while pillared structures are obtained in the case of materials swollen with C16TAþ and C18TAþ. Aggressive swelling processes at 80 C favored desilication, damaging the layers structure in case of C12TAþ while pillared materials are obtained after swollen with C16TAþ and C18TAþ surfactants. It was proved that both swelling agents in hydroxide forms combining with swelling and pillaring procedure influenced on physico-chemical and morphological nature of MWW-type materials due to the particular conditions used. The obtained derivative MWW zeolites with different morphology, order and accessibility levels were firstly evaluated by catalytic dehydration of fructose to 5-hydroxymethylfurfural (5-HMF) showing superior activity compared to beta zeolites reported in literature

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Navegando por Autor "Díaz, Urbano"