Degree Type

Dissertation

Date of Award

1989

Degree Name

Doctor of Philosophy

Department

Chemical and Biological Engineering

First Advisor

Glenn L. Schrader

Abstract

The role of lattice oxygens in two model catalysts, [beta]-VOPO[subscript]4 and (VO)[subscript]2P[subscript]2O[subscript]7, was investigated for the selective and nonselective oxidation of C[subscript]4 hydrocarbons to maleic anhydride and combustion products. Specific catalytic oxygen sites in each model catalyst were labeled with specific amounts of [superscript]18O. Labeled sites were identified by laser Raman spectroscopy and Fourier transform infrared spectroscopy. The level of [superscript]18O enrichment in each site was estimated from the laser Raman spectra and the stoichiometry of reactions involved in the synthesis of the labeled catalysts. Products of the anaerobic C[subscript]4 hydrocarbon oxidation and, in the case of (VO)[subscript]2P[subscript]2O[subscript]7, alternating pulses of oxygen with pulses of hydrocarbon, over labeled catalysts were monitored by quadrupole mass spectrometry. These studies reveal that, on both catalysts, more than one path to CO[subscript]2 exists involving lattice oxygens. The consecutive combustion of maleic anhydride involves mainly V=O oxygen, while all other oxygen sites are utilized to form small amounts of CO[subscript]2. In both catalyst systems, P-O-V sites are the source for selective oxygens. Additionally, specific selective oxygen sites could be related to mechanistic steps in the conversion of n-butane to maleic anhydride for both model catalysts. The results of this work indicate that the initial selective interaction of n-butane with the surface of the catalyst results in an intermediate which is very different than that of the other C[subscript]4's studied, and that this strongly adsorbed intermediate is constrained to react with specific P-O sites. Additional evidence suggests that [beta]-VOPO[subscript]4 is not the V(V) species formed in the oxidation-reduction couple on the surface of (VO)[subscript]2P[subscript]2O[subscript]7.

DOI

https://doi.org/10.31274/rtd-180813-11846

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Mark Edward Lashier

Language

en

Proquest ID

AAI9014920

File Format

application/pdf

File Size

166 pages

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