With an objective to elucidate the influence of structural changes on catalytic properties, the oxygen content, reducibility and chemical stability of substituted metavanadates of thorium, viz., Th(MnxVl-x03-)4 with 0 x 1, were monitored using temperature programmed reduction / oxidation (TPR/TPO), powder XRD and FTIR techniques in conjunction with thermogravimetry. Catalytic activity was evaluated for oxidation of CO as a function of Mn content. The formation of new phases ThMn2(V04)202 and ThMn408 was established and indexed on the basis of tetragonal unit cell with a0 = 7.124 A and CO = 6.348 A and the hexagonal unit cell with a0 = 6.468 A and CO = 11.188 A, respectively. The mixed oxide compositions generally exhibited better stability towards the repeated cycles of reduction and reoxidation compared to Mn02 or un-substituted vanadates or manganates. The reduction of an individual component in a mixed oxide depended on the extent of substitution and the catalytic activity of the mixed oxides was found to be very sensitive to resultant structural changes and to the oxygen non-stoichiometry.
The compositions with the oxygen rich V04 groups in general showed poorer activity for CO oxidation reaction compared to those comprising of V03 groups.