NMR studies of catalysts: phosphorous-31 and vanadium-51 in vanadium-phosphorous-oxygen selective oxidation catalysts and the selective averaging of the second order quadrupolar interaction in aluminosilicates
Date of Award
Doctor of Philosophy
The results of EPR and ('31)P and ('51)V NMR experiments on vanadium-phosphorous-oxygen catalysts revealed the presence of V(III) as well as the expected V(IV) and V(V). Preparations known to be highly oxidized, such as (beta)-VOPO(,4) and B phase catalyst with P/V = 0.9, yielded NMR spectra showing only small effects of unpaired electron spin, and the EPR spin count indicated a correspondingly low concentration of V(IV). On the other hand, catalysts known to be highly reduced, such as butane-treated (VO)(,2)P(,2)O(,7) and B phase catalysts with P/V = 1.0, 1.1, gave NMR spectra with strong effects of unpaired electron spin but low EPR spin counts. Since EPR will routinely detect V(IV) but not V(III) (and no unpaired electron spins are associated with V(V)), the strong paramagnetic effects observed in the reduced catalysts must result from V(III). The catalysts examined included the model compounds (beta)-VOPO(,4) and (VO)(,2)P(,2)O(,7) before and after butane and butane treatment, precatalysts (P/V = 0.9, 1.0, 1.1) and B phase catalysts (P/V = 0.9, 1.0, 1.1) before and after butane treatment;The line broadening effects of the second order quadrupolar interaction cause loss of resolution in the NMR spectra of interesting systems, such as ('27)Al in zeolites. A multiple pulse sequence proposed to selectively average the effects of the second order quadrupolar interaction was investigated. The negative results obtained, including an echo of problematic origin, are described.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Russell Don Walker
Walker, Russell Don, "NMR studies of catalysts: phosphorous-31 and vanadium-51 in vanadium-phosphorous-oxygen selective oxidation catalysts and the selective averaging of the second order quadrupolar interaction in aluminosilicates " (1986). Retrospective Theses and Dissertations. 8123.