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

摘要

Results of EPR and sup 31 P and sup 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,l such as beta -VOPO sub 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) sub 2 P sub 2 O sub 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 sub 4 and (VO) sub 2 P sub 2 O sub 7 before and after butane and butene 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 sup 27 Al in zeolites. A multiple pulse sequence proposed to selectively average the effects of the second-order quadrupolar interaction was investigated. (ERA citation 12:035318)