(NH4)2SO4-assisted synthesis of thin-walled Ti-rich hollow titanium silicalite-1 zeolite for 1-hexene epoxidation

The preparation of hollow zeolite with a large cavity structure to improve the accessibility to the active sites of catalyst is of great significance. A thin-walled Ti-rich hollow Titanium silicalite-1 (TS-1) Nanobox was synthesized by dissolution-recrystallization using Silicalite-1 (S-1) as the parent zeolite and (NH4)2SO4 as the dual-function crystallization-mediating agent. The wall thickness of the zeolite is about 30 nm, the hollow percentage (the ratio of the cavity area in the middle of the zeolite to the overall area of the zeolite) can reach 0.57, and the Si/Ti ratio is 39.63. The formation mechanism of hollow TS-1 was studied. As the parent zeolite, S-1 is easier to dissolve than TS-1, making it easier for the hollow zeolite to get a complete cavity. When the molar ratio of (NH4)2SO4/TEOS reaches 0.25, the dissolution rate matches the crystallization rate best, and a perfect hollow structure is obtained. The pH of the initial gel is the key factor for the hollow structure. The catalytic activity and stability were tested by 1-hexene epoxidation. The conversion of 1-hexene using HTS-1#S0.25 as the catalyst is much higher than that using hollow TS-1 prepared by the conventional method as the catalyst. HTS-1#S0.25 remains a high oxidation activity and high selectivity after five recycle experiments. In addition, the type of anion also has a great influence on the reactivity. This method can provide a new idea for the preparation of hollow TS-1.