Abstract The equilibrium properties of bulk MgMoO 4 , Zr(MoO 4 ) 2 , Al 2 (MoO 4 ) 3 , SrMoO 4 , and Cr 2 (MoO 4 ) 3 have been characterized by coulometric titration at 873 K in order to understand the effect of the mixed-cation environment on the Mo 6+ –Mo 4+ redox properties and how this in turn affects reactivity for methanol oxidation. The structures of the oxidized and reduced phases were also characterized by XRD. With SrMoO 4 , reduction resulted in the formation of SrMoO 3 ; however, each of the other oxides underwent a reversible decomposition. MgMoO 4 formed a mixture of crystalline MgO and Mg 2 Mo 3 O 8 ; Zr(MoO 4 ) 2 reduced to MoO 2 and a mixture of monoclinic and tetragonal ZrO 2 ; and Cr 2 (MoO 4 ) 3 formed a new crystalline phase. For MgMoO 4 , Zr(MoO 4 ) 2 , Al 2 (MoO 4 ) 3 , and Cr 2 (MoO 4 ) 3 , removal of one O/Mo occurred at a P (O 2 ) of 10 −6 atm, corresponding to a Δ G of oxidation of −100 kJ/mol-O 2 ; however, the equilibrium between SrMoO 4 and SrMoO 3 occurred at 10 −26 atm O 2 , corresponding to a Δ G of oxidation equal to −375 kJ/mol-O 2 . These thermodynamic properties differ significantly from oxidation of MoO 2 to MoO 3 , for which Δ G is −220 kJ/mol-O 2 at 873 K. All of the mixed oxides were essentially inactive for the selective oxidation of methanol, with specific rates that were much lower than that observed for MoO 3 .