Effects of ZnO and MoO3 Doping on Surface and Catalytic Properties of Manganese Oxide Supported on Alumina System

ABSTRACT

0.2Mn2O3/Al2O3 system was prepared by the impregnation method using finely powdered Al(OH)3 and a calculated amount of Mn(NO3)2 dissolved in the smallest amount of distilled water followed by drying and calcination at 400-600°C. Six doped solids were prepared by impregnating powdered Al(OH)3 Solids with different amounts of Zn(NO3)2 or (NH4)6Mo7O24.4H2O followed by drying, then impregnating with Mn(NO3)2. The doped solids were calcined at 400-600°C. The dopant concentrations were 0.75, 1.5, and 3 mol% ZnO or MoO3. The structural characteristics, surface and the catalytic properties of pure and variously doped solids were examined by using XRD, N2 adsorption at- 196°C and isopropanol conversion carried out at 140-280°C using a flow technique under atmospheric pressure. The obtained results revealed that the pure solids investigated and those doped with 0.75 and 1.5mol% ZnO or MoO3 calcined at 500°C, consisted of a mixture of nanosized MnO2 (Pyrolusite) and Mn2O3 (Partridgeite phase) together with κ-Al2O3. Increasing the calcination temperature of the variously doped solids to 600°C led to the complete conversion MnO2(Pyrolusite) to nanosized Mn2O3 (Partridgeite phase). The crystallite size of manganese oxide phases varied between 3 and 56 nm. All surface characteristics of the system investigated were much affected by calcination temperature and dopant concentration. Isopropanol conversion carried out over pure and doped system calcined at different temperatures proceeded via dehydration and dehydrogenation yielding propene and acetone, respectively. The activity and selectivity of the various solids were much affected by the reaction temperature, calcination temperature and dopant concentration.