Date of Award

1990

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

First Advisor

Geoffrey L. Price

Abstract

Mixed oxides of iron-tellurium and iron-tellurium-selenium have been prepared by hydrothermal crystallization, solid state thermal reaction and coprecipitation from aqueous solution. The oxides were tested as catalysts in oxidative dehydrogenation of 1-butene to 1,3-butadiene and selective oxidation of propylene to acrolein in the temperature range 340-400$\sp\circ$C and 270-310$\sp\circ$C, respectively. Optical and scanning electron microscopy, BET, mercury porosimetry, electron dispersive X-ray analysis, atomic absorption spectroscopy, X-ray powder diffraction, infrared spectroscopy and isotopic tracer techniques have been used to characterize these catalysts. The mixed oxides synthesized by hydrothermal crystallization were highly crystalline. Both activity and selectivity for 1-butene reaction were dependent on the presence of gaseous oxygen and water. Sodium, incorporated in the catalyst during preparation, was also found to affect the catalytic properties. Grinding the catalysts in a ball mill has altered both the bulk structure and catalytic properties, while not significantly affecting the surface area. The catalytic behavior has been correlated mainly with the presence of Te-O groups, associated with an IR band at 769.3 cm$\sp{-1}$. $\sp{18}$O$\sb2$ and $\sp{16}$O$\sb2$ exchange reactions have partly explained the catalytic behavior. The grinding operation was the key to modifying the selectivity of the hydrothermal catalysts. The coprecipitated Fe-Te-Se oxide catalysts was active and selective for propylene oxidation to acrolein. The selenium has been found to be the hydrocarbon activating site. The activation energies for the acrolein and carbon dioxide formation are 17 Kcal/mol and 13 Kcal/mol, respectively. Reactions carried out with isotopic tracers, $\sp{18}$O$\sb2$ and C$\sb3$D$\sb6$, have shown lattice oxygen to be primarily responsible for the formation of both acrolein and carbon dioxide. The initial and rate determining step for the acrolein formation is hydrogen abstraction as determined by the isotope effects associated with the C$\sb3$D$\sb6$ reaction. No isotope effect is observed for carbon dioxide formation from C$\sb3$D$\sb6$. The mixed oxides synthesized by solid state thermal reaction, containing Fe$\sb2$Te$\sb3$O$\sb9$ and Fe$\sb2$TeO$\sb6$ phases, were found to be poor allylic oxidation catalysts.

Pages

228

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