In situ structural reconstruction triggers the hydrothermal synthesis of hierarchical Ti-Beta zeolites for oxidative desulfurization

Abstract

Fabricating hierarchical porosity in a metallosilicate zeolite crystal is a facile and efficient approach to increase the accessibility of active sites and to enhance the diffusion performance in the process of catalytic reactions, particularly those involving bulky guest organics. The straightforward and efficient synthesis of hierarchical metallosilicate zeolites was intensively limited by the high-cost mesoporogen, complicated and tedious synthesis procedures, broad mesoporous size distribution, restricted zeolite topologies, and low solid yield. Herein, an innovative hydrothermal synthesis methodology of a hierarchical heteroatom-containing zeolite, in this case of Ti-Beta, via in situ structural reconstruction was proposed. Tetraethylammonium hydroxide (TEAOH) played significant roles of not only as base source, functioning etching effect, but also as structure directing agent (SDA), reconstructing the framework structure in this hydrothermal synthesis. The mesoporosity and Ti⁴⁺ species coordinate state could be regulated by varying the TEAOH content, which was closely related to the catalytic activity in oxidative desulfurization. The optimal hierarchical Ti-Beta zeolite with a mesopore size of 7.8 nm and a high solid yield of more than 96% exhibited outstanding catalytic oxidation performance, far outperforming the hydrothermally synthesized Ti-Beta zeolite and postsynthesized Ti-Beta zeolite. This work provides a straightforward and facile methodology for rationally constructing the hierarchical Ti-Beta zeolite, which is promising to be an extension to synthesize other hierarchical heteroatom-containing zeolites without the assistance of a mesoporogen in a short time.