Abstract
Zeolites are microporous crystalline aluminosilicates with a number of useful properties including acidity, hydrothermal stability, and structural selectivity. However, the exclusive presence of micropores restricts diffusive mass transport and reduces the access of large molecules to active sites. In order to resolve this problem, mesopores can be created in the zeolite, combining the advantages of microporous and mesoporous materials. In this work, mesospores were created in the Ultrastable USY zeolite (silicon/aluminum ratio of 15) using alkaline treatment (NaOH) in the presence of cetyltrimethylammonium bromide surfactant, followed by hydrothermal treatment. The effects of the different concentrations of NaOH and the surfactant on the textural, chemical, and morphological characteristics of the modified zeolites were evaluated. Generating mesoporosity in the USY zeolite was possible through the simultaneous presence of surfactant and alkaline solution. Among the parameters studied, the concentration of the alkaline medium had the greatest influence on the textural properties of the zeolites. The presence of Cetyltrimethylammonium Bromide (CTA+) prevented the amorphization of the structure during the modification and also avoided desilication of the zeolite.
Highlights
Zeolites are a class of natural and synthetic minerals that have several structural characteristics in common based on three-dimensional combinations of tetrahedra (TO4, where T represents atoms of silicon and aluminum) connected by oxygen atoms [1].The microporous zeolite structure is responsible for the acidity, hydrothermal stability, and structural selectivity of these materials [2]
USY zeolite revealed revealed that only the zeolite modified without the addition of a surfactant (YB0.08-S0)
We evaluated the influence of the presence of the concentrations of surfactant (CTA)+ surfactant during modification of the USY zeolite on the generation of mesopores
Summary
Zeolites are a class of natural and synthetic minerals that have several structural characteristics in common based on three-dimensional combinations of tetrahedra (TO4 , where T represents atoms of silicon and aluminum) connected by oxygen atoms [1]. Each of these reactions required a certain volume of mesopores to ensure enhanced performance Another approach reported in the literature is alkaline treatment in the presence of a CTAB surfactant at room temperature, followed by heating of the mixture at 150 ◦ C for several hours to rearrange the structure and create ordered mesopores in the zeolite [8,10,11]. The advantage of this technique, compared to the recrystallization method, is that it avoids complete amorphization of the zeolite by the surfactant, which can occur during more severe alkaline treatments [5]. The main objective was to investigate the effects of different alkaline medium and surfactant concentrations on the structural, textural, and chemical properties of zeolites with mesopores, as well as to evaluate the role of the surfactant during modification
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