Quantitative Localisation of Titanium in the Framework of Titanium Silicalite-1 Using Anomalous X-ray Powder Diffraction

Overview

Journal Nat Commun

Specialty Biology

Date 2024 Sep 5

PMID 39237487

Authors

Przemyslaw Rzepka

Matteo Signorile

Thomas Huthwelker

Stefano Checchia

Francesca Rosso

Silvia Bordiga

Jeroen A van Bokhoven

Affiliations

Soon will be listed here.

Abstract

One of the biggest obstacles to developing better zeolite-based catalysts is the lack of methods for quantitatively locating light heteroatoms on the T-sites in zeolites. Titanium silicalite-1 (TS-1) is a Ti-bearing zeolite-type catalyst commonly used in partial oxidation reactions with HO, such as aromatic hydroxylation and olefin epoxidation. The reaction mechanism is controlled by the configuration of titanium sites replacing silicon in the zeolite framework, but these sites remain unknown, hindering a fundamental understanding of the reaction. This study quantitatively determines heteroatoms within the zeolite-type framework using anomalous X-ray powder diffraction (AXRD) and the changes in the titanium X-ray scattering factor near the Ti K-edge (4.96 keV). Two TS-1 samples, each with approximately 2 Ti atoms per unit cell, were examined. Half of the titanium atoms are primarily split between sites T3 and T9, with the remainder dispersed among various T-sites within both MFI-type frameworks. One structure showed significant non-framework titanium in the micropores of a more distorted lattice. In both samples, isolated titanium atoms were more prevalent than dinuclear species, which could only potentially arise at site T9, but with a significant energy penalty and were not detected.

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