Jean-Pierre Beaufils

Surface phases of Co and Mo oxides on alumina

Abstract Various amounts of cobalt and molybdenum were dispersed on a support of alumina of 104 m 2 g −1 of specific area by a method of simultaneous impregnation from a solution of cobalt nitrate and ammonium paramolybdate. The samples were decomposed and reduced by H 2 at 600 °C. The amount of oxygen absorbed at 300 °C by these reduced samples was measured gravimetrically. Plotting of these amounts against concentrations of molybdenum for series of samples of the same cobalt concentration gives several straight lines. The discontinuities in the slopes are interpreted as separations between domains of existence of several surface phases. In that way a phase diagram is drawn. Among the phases obtained, one corresponds to a definite value of the ratio Mo/Co, equal to 4. Such a surface phase could not be detected by diffraction experiments. The origin of this phase lies probably in the method of preparation.

A study of the sites involved in the chemisorption of hydrogen on Co3O4 by magnetic and nuclear neutron diffraction

D2 dissociates on Co3O4 at room temperature but not at 40 K, and donates electrons to Co3+ defects in tetrahedral sites.