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Studies of the surface of titanium dioxide II. The effect of reduction by hydrogen on the weight and the magnetic susceptibility

1975; Elsevier BV; Volume: 39; Issue: 3 Linguagem: Inglês

10.1016/0021-9517(75)90298-5

1090-2694

T. Iwaki,

Catalytic Processes in Materials Science

Simultaneous measurements of weight and magnetic susceptibility of several kinds of titanium dioxide have been carried out after an introduction of hydrogen at temperatures between 400 and 550 °C and at pressures between 0.01 and 0.5 atm. The weight of titanium dioxide decreased gradually, while the magnetic susceptibility increased, when hydrogen was introduced above 400 °C. It was found that the rate of reduction obeys partly the Elovich equation and that the weight decrease per unit weight of the sample tends to increase with an increase in the specific surface area. It could not be revealed definitely whether the crystal structure of titanium dioxide, rutile or anatase, affects the behavior of the reduction. The activation energy increased gradually with the reduced amount. The magnetic susceptibility increased linearly with a decrease in the weight. These results support the previous findings of the hydrogen reduction of titanium dioxide in connection with the anatase-rutile transformation performed by Shannon. On the basis of these results, the reduction mechanism was discussed and the rate-determining step in the initial stage was presumed to be formation of the surface hydroxyl groups followed by rapid removal of water molecules from the surface.