Synthesis and characterization of montmorillonite clays with modulable porosity induced with acids and superacids

Abstract

The structural transformation of natural montmorillonite clay with different acids and superacids (hydrochloric, HCl; sulfuric, H 2 SO 4 ; hydrofluoric, HF; perchloric, HClO 4 ; chlorosulfonic, HSO 3 Cl; and trifluoromethanesulfonic, HSO 3 CF 3 acids) is evaluated by various techniques, allowing its full characterization. The process involves the modulated digestion of the aluminum and silicon atoms from the original clay without the loss of the original mass in the material from a careful drying methodology. The x-ray diffraction technique suggests that the process is disruptive, causing different magnitudes of modification, depending on the acidic source, taking the material with natural lamellar structure as reference. By 27 Al and 29 Si magnetic resonance, it is also shown that all the silicon and aluminum atoms were removed from the chemical structure to be physisorbed or dispersed in the interstices of the clay lattice when HF, HSO 3 Cl, and H 2 SO 4 acid treatments were carried out. However, with treatment of HClO 4 , the results suggest that only was achieved partial digestion and physisorption of the aluminosilicate core. Treatment with HCl led to a mild digestion that increased the laminar distance of the montmorillonite. Finally, HSO 3 CF 3 acid achieved a total disorder of the lamellar structure of the clay. In addition, by infrared spectrometry, the disappearance of the absorption peaks assigned to Al 2 OH, AlMgOH, and Al-O-Si are other evidence of the complete digestion of silicon and aluminum atoms caused by the acidic medium. On the other hand, the Brunauer-Emmett-Teller (BET) surface areas of the acidified clays showed a great enlargement in comparison with the unmodified clay. The porosimetry measurements demonstrate the presence of mesopores and hysteresis as observed in the physisorption isotherms, which indeed exhibited a capillary condensation into the porous structures. The present results are the first full characterization research and structural comparison between the acidic and the not-extensively-studied superacidic modified clays of this type.

Effects of Bentonite on p-Methoxybenzyl Acetate: A Theoretical Model for Oligomerization via an Electrophilic-Substitution Mechanism

“…To investigate the novel catalytic capabilities of TAFF, this work studied the transformation of para -methoxybenzyl acetate ( 1 ). Despite the Lewis and Brønsted-Lowry acid character of the studied clay, its acidity is very low in comparison with sulfuric or triflic acids [19]. Thus, the phenylmethanes 2 - 4 and linear oligomers 5 - 8 were obtained when the reaction was carried out in carbon disulfide at room temperature.…”

Memorias del VII Congreso de la Red Latinoamericana de Ciencias Ambientales

“…Adicionalmente se identificó silicato de aluminio. Después del tratamiento ácido y térmico, los picos característicos de la haloista permanecen prácticamente iguales, sin embargo los correspondientes al silicato de aluminio se ven incrementados, resultado que indica que en las condiciones del experimento, se extrae parte del alumnio y del silicio, pero se mantiene la estructura de la haloista, resultados similares se han obtenido con el tratamiento ácido (clorhídrico) y térmico de montmorillonita (Vargas-Rodríguez, Beltrán, Vázquez-Labastida, Linares-López, & Salmón, 2007).…”

Effect of Acid Treatment of Montmorillonite on “Support-Activator” Performance to Support Metallocene for Propylene Polymerization Catalyst

“…With respect to the first point, Weiss et al proposed that OH groups at the end of silicate layers, which were formed by aluminum extraction from octahedral sheets, are the sites of alkyl‐aluminum fixation on which the metallocene complexes are activated. Acid treatment of MMT induces morphological changes such as increased surface area (SA) and pore volume (PV) . Therefore, the position of the surface species proposed by Weiss et al would closely be related to the morphological changes of MMT.…”

“…Acid treatment of MMT induces morphological changes such as increased surface area (SA) and pore volume (PV). [4][5][6][7][8] Therefore, the position of the surface species proposed by Weiss et al [3] would closely be related to the morphological changes of MMT. In contrast, Kurokawa et al reported that metallocene complexes are intercalated into the layer, where ethylene polymerization proceeds when Mg 2+ cationexchanged mica is used.…”