Multifrequency and orientation-selective ESEEM spectroscopy of ammonia adsorbed on a silica-supported vanadium oxide catalyst
- Harvard Univ., Cambridge, MA (United States)
Multifrequency and orientation-selective ESEEM (electron spin echo envelope modulation) spectroscopies were utilized to probe the structural environment of a V{sup 4+} center on silica-supported vanadium oxide with adsorbed ammonia. Spectra were recorded at microwave frequencies ranging from 4.5 to 17.8 GHz. Modulations assigned to a proton bound to an atom coordinated to the vanadium were observed, together with a rich {sup 14}N ESEEM spectrum. Nitrogen hyperfine and quadrupole parameters were obtained by frequency-tracking techniques and detailed simulation of the spectra. A principally isotropic hyperfine coupling of {approximately}4.7 MHz was observed, and the quadrupole coupling was found to be axially symmetric with a coupling constant (e{sup 2}qQ/4) of {approximately}0.7 MHz. The unique axis of the {sup 14}N quadrupole interaction matrix lies approximately normal to the unique axis of the V{sup 4+} Zeeman and hyperfine interaction matrices. EPR and ESEEM results are consistent with a structural model of the oxo-vanadium (vanadyl) species with coordination of ammonia cis with respect to the oxo-vanadium bond. 44 refs., 8 figs.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 458829
- Journal Information:
- Journal of Physical Chemistry, Journal Name: Journal of Physical Chemistry Journal Issue: 22 Vol. 96; ISSN JPCHAX; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
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