A one-step rapid synthesis of TS-1 zeolites with highly catalytically active mononuclear TiO₆species

Abstract

The modulation and determination of the coordination environments of Ti active sites in titanosilicate zeolites are key challenges in the rational design of high-performance heterogeneous catalysts.

Nanosponge TS‐1: A Fully Crystalline Hierarchical Epoxidation Catalyst

“…The band centered at 205 nm is typical of a 4‐coordinated Ti(OSi) 4 framework species (sometimes denoted as “closed sites”), while the band at 330 nm indicates the presence of anatase‐like TiO 2 domains, with bands of “open sites”(Ti(OSi) 3 (OH), 230 nm) and 5‐ and 6‐coordinated isolated framework‐attached titanium species (e.g., Ti(OH)(H 2 O)(OSi) 3 or Ti(OH) 2 (H 2 O) 2 (OSi) 2 ; [ 4c,34 ] bands at 260–290 nm) between those two border bands. [ 4c ] Excluding anatase‐like species, all others can contribute to the catalytic activity in epoxidation [ 13a,34,35 ] and other selective oxidation reactions, [ 21b ] although their mechanism remains controversial. [ 36 ] In addition, neighboring silanol groups may, in specific cases, such as phenol hydroxylation, contribute to transition state stabilization and thus further promote selective oxidation.…”

Titanosilicate zeolite precursors for highly efficient oxidation reactions

“…Very recently, Xu et al constructed a mononuclear TiO 6 species in TS-1 zeolite via seed-assisted microwave irradiation. 42 The octahedrally coordinated titanium species was identied with UV-Raman (excited at the 266 nm laser line) and X-ray absorption spectroscopy. The obtained TS-1 zeolite catalyst with mononuclear TiO 6 species displayed outstanding catalytic performance and stability in the epoxidation of 1-hexene.…”

Creation of Hierarchical Titanosilicate TS‐1 Zeolites

“…Recently, Yu and co‐workers studied the coordination environment and local structure of Ti species of a nanosized TS‐1 zeolite sample (TS‐1‐AM). [ 116 ] In comparison to the pure tetrahedrally coordinated TS‐1 zeolite, the intensity of the XANES pre‐edge peak of TS‐1‐AM sample decreases, indicating the existence of distorted Ti structure, with higher coordination states. Combined with the UV‐Raman spectroscopy excited at 266 nm, the authors verified that the distorted Ti species are octahedrally coordinated.…”

“…[ 130 ] TS‐1 zeolites have proven to be effective heterogeneous catalysts for the epoxidation reactions and extensive research effort has been extended toward the effective control of product selectivity. [ 73,89,116,130–132 ]…”