Distribution of molybdenum oxidation states in reduced molybdenum/alumina catalysts: correlation with benzene hydrogenation activity

Abstract

The distribution of Mo oxidation states in reduced Mo/Al{sub 2}/Al{sub 2}O{sub 3} catalysts (8 wt % MO) has been determined by ESCA. The results show that Mo oxidation states ranging from +6 to 0 produced on reduction in the range 500-900{degrees}C. The Mo 3d binding energy values obtained for various Mo oxidation states were the same as those reported in an earlier study of Mo/TiO{sub 2} catalysts. The full widths at half-maxima for all Mo 3d peaks were larger than those for the corresponding Mo/TiO{sub 2} system. The average Mo oxidation state estimated from ESCA for a reduced catalyst agrees with that obtained by measuring the O{sub 2} consumption on reoxidation. The benzene hydrogenation activity was measured for all reduced catalysts. Significant conversion occurs only for reduction temperatures {ge} 600C. The onset of catalytic activity coincides with Mo{sup 2+} formation. However, the comparison of the distribution of Mo oxidation states determined by ESCA with the catalytic activity indicates that Mo metal is the most active species.