Structure-activity relationships of a nanostructured Cu/ZrO2 catalyst for the steam reforming of methanol (MSR) were investigated under reaction conditions by in Situ X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) combined with on-line mass spectrometry (MS). Ternperature-programmed activation by reduction in hydrogen or by reduction in a mixture of methanol and water (feed) was Studied by time-resolved Cu K edge XANES and TG/DSC/MS measurements. small and disordered CuO particles were identified as the main copper phase present in the precursors. After extended time on stream and treatment at 673 K in hydrogen, no significant sintering of the copper particles or deactivation of the reduced Cu/ZrO2 catalysts was detected, indicating a superior stability of the material. The initially low steam-reforming activity of the Cu/ZrO2 catalyst after reduction in hydrogen could be significantly increased by a temporary addition of oxygen to the feed. This increased activity after oxidative treatment is correlated with an increasing amount of oxygen in the copper particles. Cu-63 NMR Studies detected only a minor degree of microstrain in the active copper phase of the Cu/ZrO2 catalyst. The decreased reducibility of CuO/ZrO2. the low degree of microstrain, and the correlation between the amount of oxygen remaining in the copper particles and the catalytic activity indicate a different metal support interaction compared with Cu/ZnO catalysts. (c) 2005 Elsevier Inc. All rights reserved.