Processing of Porous Metal Oxide Particles for Combustion Catalysis by Freeze-drying

Abstract

Porous particles of oxides of transitional metals, such as copper, nickel, cobalt, iron, manganese, and chromium, were prepared in single and binary mixtures by the freeze-drying process to serve as combustion catalysts. Aqueous metal sulfate solutions of the above metals were utilized as raw material for freeze-drying. Spherical drops of the solutions were instantly frozen in a cooled bath. The frozen particles were dried in a vacuum chamber. These were then calcined into particles of single and double oxides, as well as oxide mixtures. The open porosity within the freeze-dried particles induced by sublimation of ice crystals was retained during calcination and the subsequent firing. Methane/air was combusted in an adiabatic tubular reactor in the presence of the porous oxide particles to determine the particles' catalytic activity. The feed gas equivalence ratio and residence time were kept constant while methane conversions were measured as a function of gas temperature. The activity of the catalysts was assessed based on the temperature during the surface-kinetics-controlled regime. Among the catalysts examined, the strongest were binary oxides of cobalt and nickel.