A two-dimensional reactor model based on reaction kinetics and heat and mass transfer for catalytic NH3 decomposition was constructed. A reactor design that minimizes the effect of endothermic reaction was investigated. It is difficult to design a single-tube reactor for NH3 treatment at a flow rate of 10 m(3)/h because heat transfer from the reactor wall cannot keep up with the fast consumption of heat by the reaction, even under low space velocity conditions. The target conversion was achieved by decreasing the NH3 supply rate. A reactor with a packed bed of suitable length was designed. Industrial-scale NH3 treatment can be achieved using a multi-tube reactor. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.