Micelle Formation inside Zeolites: A Critical Step in Zeolite Surfactant-Templating Observed by Raman Microspectroscopy

Abstract

Micelle formation inside faujasite (FAU) zeolite, a critical step in the introduction of mesoporosity in zeolites by surfactant templating, has been confirmed by both 13 C NMR and Raman spectroscopy. Here we provide unambiguous evidence of the incorporation of surfactant molecules inside zeolites during the first step of the surfactant-templating process followed by their self-assembly into micelles after hydrothermal treatment. The homogeneous presence of these micelles throughout zeolite crystals has been directly observed by Raman microspectroscopy, confirming the uniform incorporation of mesoporosity in zeolites by surfactant templating.

Post‐Synthetic Ensembling Design of Hierarchically Ordered FAU‐type Zeolite Frameworks for Vacuum Gas Oil Hydrocracking

“…It is noteworthy that the development of mesopore ordering is widely reported in FAU-type zeolites using CTAB at low pH conditions. [19,21,22] However, in the current work, the dissolution studies were carried out at higher pH to ensure the complete reorganization of zeolite precursor at different synthesis temperatures using different templates and bases. From the optimization studies, we found that the typical small size or linear PDAs such as…”

“…Figures S1A and S1B depict the X‐ray diffraction (XRD) patterns of zeolites prepared by employing CTAB or organosilane‐dimethyloctadecyl‐(3‐trimethoxy‐silyl‐propyl)‐ammonium chloride as surfactants in the presence of a high concentration of ammonium hydroxide or urea. Small PDAs such as CTAB not only interact at the external surface of the crystal but also readily diffuse inside the zeolitic pores to prevent comprehensive dissolution for a complete reorganization [19] . Therefore, despite the formation of regional micelles, the mesopore ordering could be limited to shorter domains [22] .…”

“…[15] In the past, numerous efforts have been made to introduce mesoporosity in zeolite frameworks by using a variety of PDAs. [16][17][18][19][20] The base-mediated reorganizations were either carried out in a single step [19,[21][22] or two different steps involving separate base treatment and PDA treatment. [23][24] In particular, a high degree of mesoporosity was achieved in the case of FAU-type zeolites by using PDAs such as cetyltrimethylammonium bromide (CTAB) and tetrapropylammonium salts and bases viz., NH 4 OH and NaOH.…”

“…In particular, a high degree of mesoporosity was achieved in the case of FAU‐type zeolites by using PDAs such as cetyltrimethylammonium bromide (CTAB) and tetrapropylammonium salts and bases viz ., NH 4 OH and NaOH [25–26] . Among the PDAs, the influence of surfactant‐templating by CTAB has been extensively studied due to its ability to generate uniform intracrystalline mesoporosity in FAU‐type zeolites by surfactant‐templating [19,21–22] . Importantly, the mesoporous zeolites obtained by the aforementioned strategies have shown excellent catalytic performance both at the lab scale and in large‐scale applications [18,25,27] .…”

“…[25][26] Among the PDAs, the influence of surfactant-templating by CTAB has been extensively studied due to its ability to generate uniform intracrystalline mesoporosity in FAU-type zeolites by surfactanttemplating. [19,[21][22] Importantly, the mesoporous zeolites obtained by the aforementioned strategies have shown excellent catalytic performance both at the lab scale and in large-scale applications. [18,25,27] Nevertheless, if not controlled thoroughly, these strategies can result in composite phases with poor crystallinity or uneven mesopore connectivity, both of which play a key role in catalytic transformations.…”