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 H2O2, 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.

Beamline ID15A European Synchrotron Radiation Facility 71 Avenue des Martyrs 38000 Grenoble France

Department of Chemistry NIS and INSTM Reference Centre Università di Torino Via G Quarello 15 1 10135 and Via P Giuria 7 1 10125 Torino Italy

Institute for Chemical and Bioengineering ETH Zurich 8093 Zurich Switzerland

J Heyrovsky Institute of Physical Chemistry Dolejškova 2155 3 182 23 Prague 8 Czech Republic

Paul Scherrer Institute Center for Energy and Environmental Sciences PSI 5232 Villigen Switzerland

Swiss Light Source PSI 5232 Villigen Switzerland

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