Synthesis and properties of hybrid silicas containing alkylammonium surfactants

• Published in: Catalysis today Vol. 344; pp. 41 - 51
• Main Authors: de Campos, Ana Flávia P., Ferreira, Aurélia Retiella O., da Silva, Laura Lorena, Neto, Pedro Paulo Modesto, Cardoso, Dilson
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.03.2020
• Subjects: Base catalysis; Cationic surfactants; Hybrid silicas; Transesterification; Hybrid silicas; Base catalysis; Transesterification; Cationic surfactants
• ISSN: 0920-5861; 1873-4308
• DOI: 10.1016/j.cattod.2018.10.026

[Display omitted] •Increase of cetyltrialkylammonium head group resulted in silicas with larger pore diameters.•Increase of alkyltripropylammonium tail resulted in silicas with larger pore diameters.•Decrease the particle size of the hybrid silicas was the main factor to increase their catalytic activities.•The formation of silicas with the MCM-41 structure using surfactants with larger heads requires longer tails. This work describes the synthesis of silicas containing cetyltrialkylammonium and alkyltripropylammonium (CnPr3Br, n = 14–22) surfactants in their mesopores. The aqueous dispersions of these surfactants were characterized by small-angle X-ray scattering (SAXS). The hybrid silicas synthesized from the dispersions were evaluated by X-ray diffractometry (XRD), thermogravimetric analysis, nitrogen physisorption, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), as well as in terms of their catalytic properties. The mesoporous silicas synthesized using cetyltrialkylammonium surfactants showed increases in pore diameter and decreases in structural order as the head group of the surfactant became larger. An increase of the alkyltripropylammonium tail also resulted in silicas with larger pore diameters, but with better structural order. The mesoporous silica with the largest pore diameter (3.60 nm), which was synthesized with C22Pr3Br surfactant, exhibited a narrower pore diameter distribution and a hexagonal organization characteristic of MCM-41 silica. The catalytic properties of the hybrid silicas synthesized using the cetyltrialkylammonium surfactants were evaluated in the transesterification reaction, in which the silica containing C16Et3+ cations showed the highest catalytic performance.