SURFACE AND CATALYTIC PROPERTIES OF MANGANESE OXIDES SUPPORTED ON ACTIVE ALUMINA

A series of manganese oxides loaded on an active alumina support was prepared by mechanical mixing of a known amount of manganese carbonate with calculated amounts of a finely powdered alumina preheated in air at 450-degrees-C. The solids were heated in air at temperatures ranging between 400 and 1000-degrees-C. The amount of manganese, expressed as Mn2O3, was varied between 1.9 and 38 wt\%. The surface properties namely specific surface area (S(BET)), total pore volume (V(p)) and mean pore radius (rBAR) were computed for the various supported solids from nitrogen adsorption isotherms conducted at 77 K. The catalytic properties were studied via following the kinetics of CO oxidation by O2 at various temperatures between 100 and 300-degrees-C. The catalytic activities of the various solids expressed as reaction rate constant (k) and the reaction rate constant per unit area (kBAR), for Co oxidation reaction by O2 were found to increase progressively by increasing the amount of manganese present reaching maximum values at 15.2 wt\% Mn2O3 then remained unchanged by increasing the amount of manganese above this limit. The apparent activation energies of CO oxidation reaction conducted over the various solids were found to be not much affected by the amount of manganese present, especially for the solids calcined at temperatures greater-than-or-equal-to 500-degrees-C.