(297c) Is There a Relationship between the M=O Bond Length in Bulk Mixed Metal Oxides and Catalytic Activity?

It's widely believed in the catalysis literature that the bulk M=O bond of bulk mixed metal oxides controls catalytic activity. In the present study, for the first time, the bulk Mo=O bond lengths and catalytic activity of bulk metal vanadates and molybdates are compared to allow examination of this long standing hypothesis. The bulk M=O bond lengths were measured with Raman spectroscopy and the corresponding catalytic activity was determined with CH₃OH-temperature programmed surface reaction (TPSR) spectroscopy. The CH₃OH-TPSR experiments provide the first-order rate constants for breaking of the C-H bond of the decomposition of the surface CH₃O* intermediate to H₂CO. The findings clearly show that there is no correlation between the rate constant, k_rds, and the bulk M=O bond length. This finding is not so surprising when one considers that the rds (rate determining step) involves C-H bond breaking, surface MOx sites and doesn't involve bulk M=O bond breaking.