Date of Award

Summer 1971

Document Type

Dissertation

Degree Name

Doctor of Engineering Science in Chemical Engineering

Department

Chemical Engineering and Chemistry

First Advisor

Ching-Rong Huang

Second Advisor

Saul I. Kreps

Third Advisor

Richard Clyde Parker

Fourth Advisor

Deran Hanesian

Fifth Advisor

John E. McCormick

Abstract

In this research the catalytic oxidation of carbon monoxide was investigated on magnesium aluminate catalysts, MgO:xAl2O3, with five different compositions, x, ranging from 1.0 to 3.0. The reaction was run at temperatures ranging from 500 to 600 °C. with radioactive carbon monoxide as the tracer. An experimental technique has been devised for the analysis of unreacted CO which takes into account a correction for the solubility of CO in CO2.

Four mathematical models were postulated to explain the mechanism of reaction. The models were examined against experimental data by means of non-linear least squares analysis. One model was found to fit the experimental data substantially better than the other models. This model is considered to represent a plausible explanation for the results of this study.

From the mathematical modeling it was found that the oxidation reaction proceeds by the reaction of gaseous CO with chemisorbed oxygen. The chemisorption involved in the process is of the "weak" type; oxygen is chemisorbed as a boundary layer and not by transfer of electrons. The importance of the electronic properties of a catalyst are called into question in this work because of the fact that magnesium aluminate is an insulator.

It is found that the activation energy and the number of active sites reaches a maximum at an Al2O3/MgO ratio equal to 1.667.

The catalytic activity is not directly related to the number of cation vacancies. The active sites for "weak" oxygen adsorption are the normal aluminum lattice cations, located in octahedral positions of the spinel structure.

The composition of crystal mixture in a single crystal structure is one of the factors which will greatly affect catalytic activity. The observed compensation effect of catalytic activity is related to the catalyst composition; the catalyst composition affects the strength of adsorption bond between the catalyst and adsorbed oxygen and also the number of pre-precipitation nuclei. The former affects the activation energy; the latter affects the number of active sites.

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