The Formation of Mn-Ce Oxide Catalysts for CO Oxidation by Oxalate Route: The Role of Annealing Conditions

A series of Mn-Ce oxide catalysts with Mn:Ce = 1 was synthesized by oxalate route under different annealing conditions. The physicochemical properties were characterized by means of XRD, HRTEM, N-2 adsorption, TPR, XPS and DD technique. All the catalysts were investigated in the CO oxidation reaction. The annealing conditions exhibited a great impact on the structural properties, which resulted in different catalytic performance. The activity of the samples calcined in air exceeds the activity of the samples prepared in argon at a similar temperature. In the inert at 300-400 degrees C, the oxalate precursor does not completely decompose to oxide; at 500-600 degrees C, MnO and ceria are formed. For the Mn-Ce oxide catalyst obtained in air, the combination of XRD, DD and TPR showed that the catalyst consists of a MnxCe1-xO2-delta (x similar to 0.2) solid solution, amorphous and crystalline manganese oxides (Mn3O4, Mn2O3, Mn5O8). XPS analysis indicates that the catalyst surface contains Mn cations in the form of Mn2+, Mn3+ and Mn4+. An increase in the calcination temperature results in the oxide sintering. During the variation of the calcination time at 300 degrees C, the composition of the MnxCe1-xO2-delta solid solution does not change, while transformations occur in Mn oxides. The most active Mn-Ce catalyst was obtained by annealing at 300 degrees C for 10 h in air and consists of a MnxCe1-xO2-delta solid solution and Mn5O8. [GRAPHICS]