Regulating the Morphology and Catalytic Performance of Titanium Silicalite-2 Zeolite

Abstract

The morphology of zeolites plays a crucial role in determining their catalytic performance by influencing the effective access to active sites of the zeolites. In this study, the morphology of a titanium silicalite-2 (TS-2) zeolite (molar Si/Ti = 40) is regulated by adding ammonium carbonate into the synthesis system. This effectively alters the morphology of TS-2 particles, from the large 5–10 μm spherical aggregates made of self-assembled small crystals of ∼300 nm to monodispersed grain-shaped submicron-sized particles or monodispersed thin ribbon crystals of ∼25 nm thickness along the crystallographic b-axis. Concurrently, the content of octahedrally coordinated Ti increases in TS-2 samples synthesized in the presence of ammonium carbonate. When tested as catalysts in phenol hydroxylation, it reveals that this transformation from large spherical aggregates to grain-like smaller particles and then to thin ribbon crystals leads to a significant increase in the catechol selectivity and a small but steady increase in phenol conversion. The noticeable increase in catechol selectivity highlights the important effect of particle morphology on the effectiveness of TS-2 zeolites.