DISTRIBUTION OF MOLYBDENUM OXIDATION-STATES IN REDUCED MO/AL2O3 CATALYSTS - CORRELATION WITH BENZENE HYDROGENATION ACTIVITY

The distribution of Mo oxidation states in reduced Mo/Al2O3 catalysts (8 wt % Mo) has been determined by ESCA. The results show that Mo oxidation states ranging from +6 to 0 are 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/TiO2 catalysts. The full widths at half-maxima for all Mo 3d peaks were larger than those for the corresponding Mo/TiO2 system. The average Mo oxidation state estimated from ESCA for a reduced catalyst agrees with that obtained by measuring the O2 consumption on reoxidation. The benzene hydrogenation activity was measured for all reduced catalysts. Significant conversion occurs only for reduction temperature greater-than-or-equal-to 600-degrees-C. The onset of catalytic activity coincides with Mo2+ 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.