BUTANE OXIDATION OVER MODEL-SUPPORTED VPO CATALYSTS
87
and is consistent with the conclusion that the bridging ported vanadia catalysts represent a suitable model sys-
– –
V O support bond is involved in the critical kinetic steps. tem capable of providing insights into the mechanism of
However, the range of TOFs is ꢁ104 for methanol oxidation n-butane oxidation on bulk VPO catalysts. The results of
and ꢁ102 for butane oxidation and DeNOx. The lower vari- this work also demonstrate that the goal of preparing the
ation of the TOFs for butane oxidation and DeNOx may active and selective supported catalysts for n-butane oxi-
reflect the additionalrole ofacidityin the controllingkinetic dation to maleic anhydride can be achieved by varying the
steps of these reactions. In summary, the oxidation of bu- properties of the metal oxide support.
tane to maleic anhydride depends on both the redox prop-
–
erties and acidic character of the bridging V O–support
ACKNOWLEDGMENTS
bond.
The work at Lehigh University was supported by the Division of
Basic Energy Sciences, Department of Energy under Grant DEFG02-
93ER14350. V.V.G., J.B.B., and S.S. wish to thank the AMOCO Chemi-
cal Corporation and National Science Foundation (Grant CTS-9100130)
for support. B.M.W. acknowledges the “Belgisch Nationaal Fonds voor
Wetenschappelijk Onderzoek” for a travel grant.
CONCLUSION
In the present study the supported vanadia catalysts
possessing the molecular structures reliably established by
Raman spectroscopy were employed in selective oxidation
of n-butane. The results of the present study demonstrate
that the nature of the metal oxide support plays a crucial
role in defining catalytic properties of vanadia monolayers
in n-butane oxidation to maleic anhydride. The butane ox-
idation TOF varied by ꢁ100 on changing the specific oxide
support. No evidence to suggest that the reducibility and
the average oxidation state of vanadium affect the catalytic
behavior has been found. The in situ Raman experiments
also demonstrated that the characteristics of the terminal
vanadyl oxygen do not correlate with the n-butane oxida-
tion TOFs and suggest the critical involvement of the bridg-
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