Tetrapropylammonium Hydroxide Treatment of Aged Dry Gel to Make Hierarchical TS-1 Zeolites for Catalysis

Abstract

This work presents the development and systematic study of a method to prepare hierarchical titanium silicalite-1 (TS-1) zeolites with high tetra-coordinated framework Ti species content. The new method involves (i) the synthesis of the aged dry gel by treating the zeolite precursor at 90 °C for 24 h; and (ii) the synthesis of hierarchical TS-1 by treating the aged dry gel using tetrapropylammonium hydroxide (TPAOH) solution under hydrothermal conditions. Systematic studies were conducted to understand the effect of the synthesis conditions (including the TPAOH concentration, liquid-to-solid ratio, and treatment time) on the physiochemical properties of the resulting TS-1 zeolites, and the results showed that the condition of a TPAOH concentration of 0.1 M, liquid-tosolid ratio of 1.0, and treatment time of 9 h was ideal to enable the synthesis of hierarchical TS-1 with a Si/Ti ratio of 44. Importantly, the aged dry gel was beneficial to the quick crystallization of zeolite and assembly of nanosized TS-1 crystals with a hierarchical structure (S ext = 315 m 2 g −1 and V meso = 0.70 cm 3 g −1 , respectively) and high framework Ti Species content, making the accessible active sites ready for promoting oxidation catalysis.

Zeolite Crystal Engineering

“…architectures. − Soft templating techniques have been used as bottom-up approaches, whereas postsynthesis modification offers a top-down approach to enhance diffusion properties of zeolitic materials. Methods that combine heteroatom (e.g., Ti) incorporation in the design of hierarchical materials is also discussed in this virtual special issue. , …”

Kinetics of phenol hydroxylation reaction of open mesoporous TS-1 with high backbone titanium content

“…The TS-1 catalyst was synthesized according to the aging dry gel limited domain conversion method proposed by the group [16], the molar composition of the precursor was 1.0SiO2: 0.025TiO2: 0.33TPAOH:0.83IPA: 30H2O. After clarification and transparency, the solution was stirred and added dropwise to the mixture of TBOT and IPA for 30 min and then aged at 90 °C under condensation and reflux for 24 h. After aging, the solution was transferred to an oven at 100 °C and dried for 48 h until the solution became dry and the quality of the solution did not change.…”

“…Recently, we [16] proposed a synthetic method for the domain-limited conversion of aged dry gels to synthesise open mesoporous TS-1 with high skeletal titanium content, which gives open mesoporous TS-1 without anatase TiO2 in one step by treating aged dry gels with a TPAOH solution, obtaining the highest phenol conversion per titanium active site reported in the literature so far in the phenol hydroxylation reaction rate (TOF of 414) in the phenol hydroxylation reaction. Compared to the process based on the TPAOH treatment of the fully crystalline TS-1 powder, which is currently commonly used in the domestic industry, this method omits the process of synthesizing the molecular sieve powder and has the advantage of simplicity of operation and better catalytic performance of the resulting product, which is promising for industrial application.…”

Sheet-like silicalite-1 single crystals with embedded macropores displaying superior catalytic performance

“…[2][3][4] Diffusional transport constraints can be overcome by introducing meso-and macro-porosity into the zeolite crystals either during or after their synthesis, and various methods have been considered for introducing meso-and macro-porosity into zeolites. 2,[5][6][7] These include post-synthetic desilication/ dealumination, 8,9 as well as the nano-sized crystals assembly synthetic method, 10,11 and the hard/soft-template method via the hydrothermal or dry-gel conversion (DGC) strategy. 12,13 Of particular note is the DGC synthetic method which enables the synthesis of zeolites with hierarchical structures.…”