ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

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

Kateřina Galejová, Lucie Obalová, Květuše Jirátová, Kateřina Pacultová, and František Kovanda

Department of Physical Chemistry and Theory of Technological Processes, VSB — Technical University of Ostrava, 17. listopadu 15, 708 33 Ostrava, Czech Republic

E-mail: katerina.galejova.st@vsb.cz

Received: 18 April 2008  Revised: 6 October 2008  Accepted: 27 October 2008

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.

Keywords: pelleting pressure - nitrous oxide - catalytic decomposition - mixed oxides - layered double hydroxides

Full paper is available at www.springerlink.com.

DOI: 10.2478/s11696-008-0105-0

Chemical Papers 63 (2) 172–179 (2009)