Paper deals with design of pilot reactor for low temperature N2O decomposition in off-gases from HNO3 production. Pseudo-homogeneous one- dimensional model of an ideal plug flow reactor was used for modeling of N2O decomposition in a laboratory fixed bed reactor filled with grains or pellets of a Co-Mn-Al mixed oxide catalyst. Increase in inlet pressure up to 0.6 MPa did not influence the effective diffusion coefficient, but improved the achieved N2O conversion. Based on the laboratory data of N2O decomposition over Co-Mn-Al mixed oxide pellets, catalyst bed of 3400 kg was estimated for target 90% N2O conversion (30 000 m(3) h(-1) of exhaust gases from HNO3 plant containing 0.1 molar% N2O, 0.01 molar% NO, 0.01 molar% NO2, 3 molar% H2O, 5 molar% O-2) at 420 degrees C and 600 kPa inlet pressure. (c) 2012 Elsevier B.V. All rights reserved.