Racing Crystallization Mechanism for Economical Design of Single-Crystal Hollow ZSM-5 with the Broken Limit of Si/Al Ratio and Improved Mass Transfer

Abstract

Development of economic strategy to synthesize hollow zeolite with widely tunable Si/Al ratios providing variable acidity is of great significance in industry. Here, a one-step and low-cost strategy without mesoporogen was successfully developed to synthesize single-crystal hollow ZSM-5 containing mesopores/ macropores, with variable Si/Al ratios of about 14−∞ and 114−∞ at critical TPA + /SiO 2 ratios of 0.05−0.1 and 0.05, respectively. This is the first time the usage of a large amount of TPAOH was avoided while breaking the traditional limitation of Si/Al ratio (25−50). The component of synthesis system and crystallization temperature acting as the vital roles in hollow structure has been confirmed by a series of characterization. Moreover, according to the investigation of the evolution process, a novel racing crystallization mechanism based on the competition relationship between surface crystallization and the internal dissolution rate was proposed for the first time. The racing crystallization mechanism and internal nonprotective aluminum become the crucial factors for synthesis. The prepared hollow ZSM-5 zeolites exhibit superior catalytic performance in the different acidity-catalyzed condensation involving large molecules between benzaldehyde and n-butyl alcohol as well as 2-hydroxyacetophenone, which is mainly attributed to the property acidity, more accessible active Al sites on the surface, and shorter diffusion path. By calculating, the effectiveness factor (η) of hollow zeolite is close to 1, further confirming its better mass transfer ability. The strategy has also been successfully extended to the synthesis of high-amount Fe-doped, Ga-doped, and B-doped hollow silicate-1.

Effect of acid distribution and pore structure of ZSM-5 on catalytic performance

“…The 1100 cm −1 peak is the antisymmetric stretching vibration peak of the T–O–T bond, the 800 cm −1 peak is the symmetric stretching vibration peak of the T–O bond, the 450 cm −1 peak is the bending vibration peak of the T–O bond, and the 550 cm −1 peak is caused by the double ring vibration in the zeolite skeleton. 25–28 This shows that the three samples have typical MFI structure. Fig.…”

Controllable Orientation Growth of ZSM-5 for Methanol to Hydrocarbon Conversion: Cooperative Effects of Seed Induction and Medium pH Control

“…Apparently, a highly acidic environment was not favorable for the crystallization of ZSM-5, and sample 1-1 exhibited only an amorphous phase (Figure S2). As acidity decreased, the adverse effect of crystallization weakened and weak diffraction peaks attributed to the MFI structure appeared in 1-6 with the relative crystallinity reaching 34.5% (Figure ). Interestingly, in the near-neutral solution, crystallization was greatly promoted, and the relative crystallinity increased to 83.6% in 1-7 and 100% in 1-8.…”

Preparation of MFI Nanosheets with Distinctive Microstructures via Facile Alkaline Etching

“…To gain more insights into the structural properties of synthesized MFI NSs, all etched samples were further characterized by TGA. As shown in Figure 2l, the TG curves of all uncalcined samples exhibited significant weight loss peaks in the temperature range of 250− 500 °C, indicating that the corresponding tetraalkylammonium (TAA) species, 34,35 which served as templates, were incorporated in MFI channels during the NS formation process. Investigation of MFI NS Evolution Process.…”