Studies on the Selective Oxidation Activity of Iron-Tellurium-Oxide Catalysts.

Abstract

The selective oxidation of 1-butene to 1,3-butadiene and propylene to acrolein are important industrial processes. One of the critical factors which determines the feasibility of these processes is selectivity. Since iron oxide has shown potential as a component of a selective mixed oxide catalyst, and tellurium has been used as a promoter for selective oxidation catalysts, this study focusing on the development and investigation of an iron-tellurium mixed oxide catalyst for the selective oxidation of propylene and 1-butene has been undertaken. The study includes kinetic and mechanistic investigations, and simultaneous activity/selectivity and spectroscopic measurements for iron-tellurium catalysts have been developed. The purpose of this work is to characterize the role of tellurium in iron-tellurium mixed oxide selective oxidation catalysts, and to gain insight into other tellurium containing catalysts. Catalysts containing only iron and tellurium have been prepared and the active phase identified by X-ray powder diffraction as Fe(,2)TeO(,6). The catalysts show very good yields for the oxidation of 1-butene to butadiene and propylene to acrolein. The reaction orders and activation energies for the oxidation of propylene and 1-butene to both selective and extensive oxidation products have been determined. Selective oxidations of propylene and 1-butene are both first- and zero-order in hydrocarbon and oxygen partial pressures, and with activation energies of 35 and 33 kcal/mole, respectively. Extensive oxidation of propylene and 1-butene are first-order and half-order, respectively, in both hydrocarbon and oxygen partial pressures, and with activation energies of 41 and 29 kcal/mole, respectively. Pulse experiments have shown that the catalyst has different sites for the oxidation and isomerization reactions. However, the active sites for the selective and extensive oxidation reactions appear to be identical at first and rate-determining step. From Mossbauer and IR spectroscopies we infer that iron does not undergo oxidation state shifts during the selective oxidation process. Tellurium (VI) is thought to be the active species while iron simply provides a suitable environment for tellurium (VI) to exist.