N2O catalytic decomposition — effect of pelleting pressure on activity of Co-Mn-Al mixed oxide catalysts

Abstract

The effect of pelleting pressure (0–10 MPa) during the preparation of Co-Mn-Al mixed oxide catalyst on its texture and activity for N2O catalytic decomposition was examined for small grain sizes used in laboratory experiments, and for model industry catalyst particles. Adsorption/desorption measurements of nitrogen, mercury porosimetry and helium pycnometry were used for detail characterization of porous structure. A volume of micropores of about 20 mm3 g−1 was evaluated using modified BET equation. This value did practically not change with the increasing pelletization pressure except that of the sample formed at the pressure of 10 MPa. Although an increase of pelleting pressure caused an increase in bulk density and a decrease in pore size and pore volume of the prepared catalyst (resulting in lower values of N2O effective diffusion coefficient), no direct correlation between pelleting pressure used and catalyst activity has been found. In contrary, estimation of the internal diffusion limitation according to the Weisz-Prater criterion indicated that even laboratory experimental data obtained for catalyst grains with particle size lower than 0.315 mm pelletized at higher pressures could be influenced by internal diffusion. Estimation of the internal mass transfer limitation in industrial catalyst particles described by the effectiveness factor showed that effectiveness factor of about 0.07 and 0.2 can be obtained for spheres with the radius of 1.5 mm and 0.5 mm, respectively, if pelleting pressure of about 6 MPa was used for the catalyst preparation.