Bimetallic PdIn catalysts have been investigated for methanol steam reforming within a microstructured reactor. The catalytic activity and CO2 selectivity were found to be markedly dependent on the Pd: In ratio as well as on metal loading. The high CO2 selectivity of Pd-In/Al2O3 catalysts has been ascribed to the PdIn alloy formation, whereas the metallic Pd without contact with indium is responsible for CO selectivity. The initial start-up properties of the Pd-In/Al2O3 catalyst were significantly improved in comparison with Pd/ZnO catalyst, allowing for a rapid attainment of the steady state. These findings illustrate that the catalyst surface dynamically changes depending on the reaction environment and undergoes a self-optimization induced by the reactants, and consequently the pre-reduction at elevated temperature is not necessary to achieve high CO2 selectivity. (C) 2010 Elsevier B.V. All rights reserved.