SURFACE AND CATALYTIC PROPERTIES OF MANGANESE OXIDES SUPPORTED ON ACTIVE ALUMINA

A series of manganese oxides loaded on an active alumina support was p repared 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 rangin g between 400 and 1000-degrees-C. The amount of manganese, expressed a s Mn2O3, was varied between 1.9 and 38 wt%. The surface properties nam ely 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 proper ties were studied via following the kinetics of CO oxidation by O2 at various temperatures between 100 and 300-degrees-C. The catalytic acti vities of the various solids expressed as reaction rate constant (k) a nd the reaction rate constant per unit area (kBAR), for Co oxidation r eaction by O2 were found to increase progressively by increasing the a mount of manganese present reaching maximum values at 15.2 wt% Mn2O3 t hen remained unchanged by increasing the amount of manganese above thi s limit. The apparent activation energies of CO oxidation reaction con ducted over the various solids were found to be not much affected by t he amount of manganese present, especially for the solids calcined at temperatures greater-than-or-equal-to 500-degrees-C.