The aim of this work is to investigate the selective catalytic reduction (SCR) of NOx with NH3 in a loop reactor, which extends the flow-reversal concept to rotating port feeding in a loop-shape system made of N units. A simplified model is given and the predictions of this asymptotic model are compared with the results of numerical simulations of a finite-unit reactor model with various number of sections, thus proving the convergence to the asymptotic model. The influence of the main parameters, namely inlet temperature and flow rate, and of the catalyst kinetic parameters is addressed by means of bifurcational analysis. (c) 2006 Elsevier B.V. All rights reserved.