Oxygen vacancy defects (VO) in Ti-based oxides play important roles in catalytic processes despite limited knowledge regarding their formation and characterization. Here, we demonstrate the use of X-ray absorption spectroscopy (XAS) measurements to compare the relative proportion of VO defects in as-grown alkali hexatitanate A2Ti6O13 (A = Li, Na, K). Both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) regions were studied. The similarity of measured XANES spectra of Ti K-edge in all samples indicates the presence of (Ti4+)O6 units in good agreement with reported X-ray diffraction results. The small influence of cations A at the tunnel was observed and can be well reproduced in the simulated spectra. In addition, we present a semi-quantitative approach to intuitively determine the content of VO defects in oxygen-deficient K2Ti6O13-x by in situ time-resolved XAS measurements under reducing conditions (10%H2/Ar, 50-650 °C). The in situ XANES measurements indicate that the oxidation state of bulk Ti remains the same as the as-grown sample, i.e., 4+, at elevated temperatures. By in situ EXAFS measurements, the relative number of VO defects is highest at a reduction temperature of ∼550 °C and slightly decreases after that. To confirm the formation of VO defects, first-principles calculations were independently carried out using a 126-atom K2Ti6O13 supercell with VO at various positions. Based on calculated EXAFS, the removal of the oxygen atom nearest to the tunnel, which is the lowest energy structure, provides a good match to the experimental spectra.
1,6-Hexanediol (1,6-HD) oxidation to ɛ-caprolactone (ɛ-CL) was investigated using (p-Cymene)RuCl2(L) complexes with phosphine (LP1-P5) and pyridine (LN1-N5) ligands as catalysts. Despite similar Ru electron density, the activity of (p-cymene)RuCl2(LP) increases...
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