Addition of Zn to Pd changes its catalytic behavior for steam reforming of methanol. Previous work shows that improved catalytic behavior (high selectivity to CO2) is achieved by the intermetallic, tetragonal L1(0) phase PdZn beta 1, where the Pd:Zn ratio is near 1:1. The Pd-Zn phase diagram shows a number of other phases, but their steady-state reactivity has not been determined due to the difficulty of precisely controlling composition and phase in supported catalysts. Hence, the role of Zn on Pd has generally been studied only on model single crystals where Zn was deposited on Pd(111) with techniques such as TPD and TPR of methanol or CO. The role of small amounts of Zn on the steady-state reactivity of Pd-Zn remains unknown. Therefore, in this work, we have synthesized unsupported powders of phase pure PdZn alpha, a solid solution of Zn in fcc Pd, using a spray pyrolysis technique. The surface composition and chemical state were studied using Ambient Pressure-XPS (AP-XPS) and were found to match the bulk composition and remain so during methanol steam reforming (MSR) (P-tot = 0.25 mbar). Unlike the PdZn beta 11 phase, we find that PdZn alpha is 100% selective to CO during methanol steam reforming with TOF at 250 degrees C of 0.12 s(-1). Steady-state ambient pressure micro-reactor experiments and vacuum TPD of methanol and CO show that the alpha phase behaves much like Pd, but Zn addition to Pd improves TOF since it weakens the Pd-CO bond, eliminating the poisoning of Pd by CO during MSR over Pd. The measured selectivity for fcc PdZn alpha therefore confirms that adding small amounts of Zn to Pd is not enough to modify the selectivity during MSR and that the PdZn beta 1 tetragonal structure is essential for CO2 formation during MSR. (C) 2012 Elsevier Inc. All rights reserved.