The effect of CuO-ZnO-Al2O3 (CuZnAl) metallic function composition on kinetic behaviour has been studied in the steam reforming of dimethyl ether (SAD), for bifunctional catalysts synthesized using this metallic function (with different formulations) and a HZSM-5 zeolite modified by treating it with NaOH in order to moderate acidity. The kinetic performance of the catalysts has been determined by experimentation in a fluidized bed reactor in the 225-325 degrees C range, and the reaction indices (dimethyl ether (DME) and methanol conversions and H-2 and CO yields) have been explained based on the physico-chemical properties of the metallic and acid functions and of the bifunctional catalyst. The catalyst prepared by wet physical mixing with a mass ratio of 1:1 between the metallic function (CuZnAl, with Cu/Zn/Al atomic ratio = 4.5:4.5:1.0) and the acid one, allows obtaining high values of DME conversion and H-2 yield in the 275-300 degrees C range by minimizing the CO formation rate and deactivation by coke, which is explained by the high dispersion of Cu on the metallic function and the moderate acid strength of the HZSM-5 zeolite modified by alkaline treatment. Although coke content in the catalyst is low, it is mainly deposited on the metallic function, causing a decrease in methanol conversion with time on stream. (c) 2013 Elsevier B.V. All rights reserved.