Influence of anions on the structural and catalytic properties of CTA-MCM-41
CTA-MCM-41 — Mobil Composition of Matter 41 with cetyltrimethylammonium cations (CTA+) — is a hybrid silica known for its high basic catalytic activity due to anionic silanolate sites ([tbnd]Si−O-) that are bound to CTA+. The synthesis of this material depends on the properties of CTA+ micelles in a...
| Autores: | , , , , |
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| Tipo de recurso: | artículo |
| Estado: | Versión publicada |
| Fecha de publicación: | 2024 |
| País: | Brasil |
| Institución: | Universidade Estadual Paulista (UNESP) |
| Repositorio: | Repositório Institucional da UNESP |
| Idioma: | inglés |
| OAI Identifier: | oai:repositorio.unesp.br:11449/306623 |
| Acceso en línea: | http://dx.doi.org/10.1016/j.colsurfa.2024.134850 https://hdl.handle.net/11449/306623 |
| Access Level: | acceso abierto |
| Palabra clave: | Anions Basic catalysis CTA-MCM-41 Micelles Silicas |
| Sumario: | CTA-MCM-41 — Mobil Composition of Matter 41 with cetyltrimethylammonium cations (CTA+) — is a hybrid silica known for its high basic catalytic activity due to anionic silanolate sites ([tbnd]Si−O-) that are bound to CTA+. The synthesis of this material depends on the properties of CTA+ micelles in aqueous dispersion which, in turn, depend on the surrounding anions. Thus, this study investigated different types and amounts of anions in the synthesis of CTA-MCM-41. Chloride (Cl-), bromide (Br-), iodide (I-), nitrate (NO3-) and hydroxide (OH-) anions in sodium form were added to the synthesis mixture, and the obtained silicas were tested in the transesterification reaction. It is hereby presented a comprehensive study on how micelles-anion interfaces play a key role in the synthesis of this important hybrid silica catalyst, and it was possible to synthesize a more active basic catalyst than the conventional CTA-MCM-41, just by exploring such surface chemistry effects. Three significant features are highlighted: (1) improved catalytic activity of CTA-MCM-41 applied in transesterification; (2) Synthesis of CTA-MCM-41 with higher retention of cations per silica and higher amount of silanolate basic sites; (3) deepening knowledge of the synthesis mechanism of materials from the MCM-41 family. The effects are more pronounced in the order I- > NO3- > Cl-, in accordance with the Hofmeister ion series. Hydroxide anions, however, led to the greatest increase in the number of sites and basic catalytic activity (up to 52.4 %). These results reinforce the validity of the {S+, X-, I-} (S: surfactant; X: anion; I: silica) silica formation mechanism and reveal a synthesis with hydroxide anions that produces a catalyst more active than conventional CTA-MCM-41. |
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