摘要：

XAS, XPS, AEM, and temperature-programmed reduction were used to characterize the hydrogen reduction of bulk Co3O4 and Co3O4 supported on small (Co/SiO2-62) and large (Co/SiO2-923) pore size silica. The reduction process proceeded as Co3O4 → CoO → Co, with the CoO intermediate species spectroscopically identified on all three samples. The first step of the reduction, Co3O4 → CoO, occurred near 300°C for all three catalysts. The second step of the reduction, CoO → Co, showed significant differences among the samples, with the ease of reduction decreasing in the order Co3O4 > Co/SiO2-62 > Co/SiO2-923. The ease of reduction appeared to be correlated to the ease of removing the H2O produced during the CoO → Co step. The small pores (ca. 30 Å) of the Co/SiO2-923 sample made H2O removal and reduction for that sample the most difficult. Upon reduction of the Co3O4 supported particles to metallic Co the particle size decreased by 30-50% due to removal of oxygen from the Co3O4 particles. For the reduced Co/SiO2-62 sample, the Co particles were 90 Å in size and grouped together in 0.1-1-μm aggregates. The crystallographic orientation of the individual particles in each aggregate became radomized upon reduction and reoxidation. For the reduced Co/SiO2-923 sample the Co particles were 35 Å in size.

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