Is there a relationship between the Mdouble bond; length as m-dashO bond length (strength) of bulk mixed metal oxides and their catalytic activity?

It is widely accepted in the catalysis literature that the bulk Mdouble bond; length as m-dashO bond of bulk mixed metal oxides controls catalytic activity. In the present study, for the first time, the bulk Mdouble bond; length as m-dashO bond lengths (strengths) and the surface catalytic activity of bulk metal vanadates and molybdates were quantitatively compared to allow examination of this long-standing hypothesis. The bulk Mdouble bond; length as m-dashO bond lengths were obtained from crystallographic studies and also determined by Raman spectroscopy. The surface catalytic activity was determined by CH3OH-temperature programmed surface reaction (TPSR) spectroscopy and steady-state methanol oxidation. The CH3OH-TPSR experiments provided the first-order rate constants for breaking of the Csingle bondH bond for the decomposition of the surface CH3O* intermediate to H2CO and the number of catalytic active sites (image). The corresponding steady-state methanol oxidation studies provided the equilibrium adsorption constant (image) for breaking the methanol Osingle bondH bond and the specific reaction rate (TOF). The findings clearly demonstrate the lack of correlations among image, image, TOF, and the bulk Mdouble bond; length as m-dashO bond length (strength). This finding is not so surprising when one considers that the adsorption step involves breaking the methanol Osingle bondH bond and the rate-determining step involves breaking the surface methoxy Csingle bondH bond on surface MOx sites, not bulk Mdouble bond; length as m-dashO bond-breaking.