In this work, a synthetic mixture of natural gas is considered in a steam reforming process for generating hydrogen by using a membrane reactor housing a composite membrane constituted of a Pd-layer (13 mu m) supported on alumina. The Pd/Al2O3 membrane separates part of the produced hydrogen through its selective permeation, although it shows a relatively low H-2/N-2 ideal selectivity (>200 at 0.5 bar of trans-membrane pressure and T = 425 degrees C). The steam reforming reaction is performed at 420 degrees C, by varying the gas hourly space velocity between 4400 h(-1) and 6900 h(-1) and by using two different mixtures containing some common impurities found within natural gas pipeline. Specifically, the effect of N-2 and CO2 as impurities in the feed line is analyzed. The reaction pressure and steam-to carbon ratio (S/C) are kept constant at 3.0 bar (abs.) and 3.5/1, respectively. The best performance of the Pd-based membrane reactor is obtained at 420 degrees C, 3.0 bar and 100 mL/min of sweep-gas, yielding a methane conversion of 55% and hydrogen recovery >90%. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.