Synthesis of ZSM-5 zeolite hollow spheres with a core/shell structure

Abstract

Hollow and core/shell ZSM-5 spheres were simply synthesized through in situ transformation of mesoporous silica spheres (MSS) into MFI-type zeolite with the assistant of isopropylamine (IPA) as a structure-directing agent (SDA). IPA, with a mild structure-directing ability for the construction of MFI structure, triggered a stepwise crystallization of MSS after Al addition. First, the sphere surface was crystallized to a shell of ZSM-5 crystals. The silica and alumina species in the core condensed and crystallized to ZSM-5 thereafter, forming zeolite crystal aggregates inside the spheres. The obtained ZSM-5 spheres were highly crystalline materials and maintained the shape of pristine MSS, but exhibited a hollow and core/shell structure. The techniques of XRD, FT-IR, SEM, N 2 adsorptiondesorption, 29 Si and 27 Al MAS NMR were employed to trace the crystallization process, which allowed us to propose a ''templating and surface to core'' crystallization mechanism. This strategy may serve as an alternative way for synthesizing hollow zeolite spheres.

A facile method for the fabrication of IM-5 hollow zeolite sphere in emulsion system

“…6, the 29 Si MAS NMR spectrum of IM-5 HZS (i) and reference IM-5 zeolite. The reference sample exhibited three resonances located at À92, À101 and À112 ppm, which are assigned to the Q 2 , Q 3 and Q 4 species [15,27], respectively. Compared with the reference sample, the Q 2 and Q 3 species were more intensive in the IM-5 HZS (i).…”

“…A series of innovative approaches have been devoted to fabricate HZSs. According to the previous reports, the synthesis system mainly adopted hard sphere-like templates, such as polystyrene spheres [11][12][13][14], mesoporous silica spheres [15,16] and carbon black [17] to prepare HZSs. Recently, there are few reports utilized oil in water (O/W) surfactant emulsion soft template to synthesis silicate-1 HZSs [18].…”

On the reversed crystal growth of BaZrO3 decaoctahedron: shape evolution and mechanism

“…Evidence of such novel crystal growth phenomenon has been found in materials such as zeolites and CaTiO 3 perovskite. [43][44][45][46][47][48] However, this mesoscale transformation process and its mechanism are still challenging because current interests are more focused on the investigation of its role rather than on comprehensive insight into the mechanism. Concomitant mechanisms lead to increased difficulty in understanding this growth process, which is important and must be the focus of detailed studies of the nanocrystal growth mechanism.…”

Early stages of non-classic crystal growth

“…Wu and co-workers demonstrated a "templating and surface to core" crystallization mechanism with hollow zeolite ZSM-5 (MFI) microspheres, which were synthesized through an in situ transformation of mesoporous silica spheres into this MFI-type zeolite in the presence of isopropylamine as a structure-directing agent (Figure 7) [34]. The original spheres were disordered mesoporous silica (Figure 7(a), (b)).…”

“…SEM images of specimens showing the formation of ZSM-5 hollow spheres, (a) overview and (b) inside the spheres of parent mesoporous silica spheres, (c) overview, (d) enlarged image of the surface of ZSM-5 spheres, (e) hollow structure after crushing, (f) a profile view of the sphere shell[34]. Reproduced by permission of The Royal Society of Chemistry.…”