Agradecimentos: This research was funded by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) [grant number 132770/2019–9], Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), [grant number 88887.509044/2020–00], Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), [grant number 001] and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPSP) [grant number 2018/21136–1]. This research was developed in Federal University of São Carlos, São Carlos, SP, Brazil. Special thanks to Embrapa Instrumentações for carrying out the Dynamic Light Scattering measurements, and to Laboratório Nacional de Nanotecnologia for conducting the cryogenic electron microscopy experiments Ver menos

Abstract: 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 (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 Ver menos