Methanol Oxidation bulk metal vanadates towards

TOF and Selectivity of Bulk Metal Vanadates Toward Methanol Oxidation at Low Methanol Conversion... 

The significant difference between the TOP and selectivity of bulk metal molybdates and vanadates compared with pure metal oxides was a key factor in uncovering the true surface composition of those bulk catalysts. Table 11.3 and Table 11.4 show the number of surface active sites, redox TOP, and selectivity toward methanol selective oxidation products of bulk metal vanadates and the corresponding metal oxide, respectively. Similar results were obtained for bulk metal molybdates. Bulk metal vanadates possess a high selectivity to formaldehyde with some selectivity to dimethoxy methane (nickel vanadate), dimethyl ether (niobium, chromium, and aluminum vanadates), methyl formate (magnesium, chromium, and copper vanadates), and CO2 (niobium and silver vanadates). 

The observation that bulk metal vanadates posses a high selectivity toward formaldehyde strongly suggests that the surface of bulk metal vanadates is composed of vanadium oxide sites with redox properties that cover the counter-cation sites (Mg, Ni, Mn, Cr, Co, Zn, Al, Nb, Fe, Cu, and Ag) thus, inhibit methanol total oxidation. The TOF values of the bulk metal vanadates are similar indicating that there is no significant influence of the specific nature of the metal oxide counter-cation on the catalytic behavior. Moreover, there are significant differences between the TOF values of bulk metal vanadates and pure metal oxides. 

Figure 11.10 Comparison of the TOFs towards methanol selective oxidation products of monolayer supported vanadium (A symbols) and bulk metal vanadate catalysts ( ) at 300°C (From Briand, L.E., Jehng, J.-M., ComagUa, L.M., Hirt, A.M., and Wachs, l.E. Catal. Today 2003, 78, 257-268. With permission.)...

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