The ts-1 zeolite is an important catalyst for propylene epoxidation with high toluene-free performance due to the hierarchical structure and reduced diffusion barrier.ts-1 zeolite However, the synthesis of this catalyst requires expensive precursors, including high-purity tetraethyl titanate (TET) and calcined seeds. Therefore, the development of a green process is necessary to minimize the use of these materials and reduce costs. In this study, we report a simple and cost-effective preparation of ts-1 using recycled mother liquid. The zeolite obtained by adding NH4HCO3 to the calcined seeds in the hydrothermal crystallization of the mother liquid was characterized as having small particle size, high-content framework Ti and good catalytic activity in propylene epoxidation. The synthesis with the recycled mother liquid could be repeated to obtain ts-1 zeolite with similar morphology and textural properties.
To achieve a high-content framework Ti in ts-1, it is crucial to control the amount of modifier added in the hydrothermal crystallization process.ts-1 zeolite The molar ratio of the titanium source to silicon in the template plays a critical role in determining the quantity of Ti inserted into the crystal. Here, the synthesis of TS-1 was conducted with different amounts of modifier in the template to investigate the effect on the size and morphology of the obtained zeolite particles.
In order to avoid excessive modification of the tetrahedral Ti species in the zeolite, the amount of TBOT added was kept low. As a result, the size of the TS-1 crystals increased with increasing modifier addition. However, when the molar ratio of the Ti source to silicon in the template exceeded 0.1, the surface area and SBET of the resulting zeolite decreased significantly.
We also studied the influence of the crystallization time on the morphology and textural characteristics of the TS-1 zeolite. The XRD diffractograms of the samples synthesized with varying crystallization times are shown in Figure 4. All the samples exhibited characteristic diffraction peaks typical of the MFI topology, and the RC was relatively low for the sample with a crystallization time of 6 h. As the crystallization time was extended, the diffraction peak intensity increased and the RC continuously increased up to 91.2% for the sample with a crystallization duration of 12 h.
The SEM images of the TS-1 samples with various crystallization times are presented in Figure 5. All the samples exhibited a boat-shaped morphology. For the sample TS-1-6 h, a large number of amorphous phases were observed on the surface of the zeolite. The morphology of the zeolite became spherical for the sample TS-1-12 h.
Nitrogen sorption measurements showed that the porous structure of the TS-1 zeolite was pore-diameter modulated by the morphology and crystallization conditions.
The TS-1 samples with a spherical morphology exhibited a higher permeability than the TS-1 samples with a bridging-angle-controlled texture, which was associated with an increase in lateral interconnectivity between pores. This explains the excellent catalytic performance of these TS-1 samples in propylene epoxidation. In the future, we will continue to investigate the effects of other factors such as the morphology and textural characteristics on the catalytic performance of ts-1.
Tags:hy zeolite | h-y zeolite catalyst
