"Inverse" (ZrO2/ZrOxHy on Cu) and "real" (Cu nanoparticles on ZrO2) ultra-high-vacuum/ambient pressure model catalyst studies were performed using methanol steam reforming as a test reaction. The catalytic profile was correlated with structural and spectroscopic analysis using X-ray photoelectron and Auger electron spectroscopy and high-resolution electron-energy-loss spectroscopy. Access to water-activation-dependent pathways is achieved by special Cu/ZrOxHy phase boundary or interfacial sites formed during reaction, which were studied with respect to surface coverage, island size, and chemical state of Cu/Zr metal/oxide species. In the "real" model system, particle size effects increasing the amount of unwanted CO were observed beyond interfacial selectivity-steering effects. Oxidation of Zr-0 to Zr+4 during reaction forms the most efficient phase boundary with respect to redox-active sites. Ability for reversible hydroxylation of Zr and submonolayer Zr coverage for maximum ZrOxHy/Cu phase boundary dimensions are the most critical parameters in catalyst preparation. (c) 2014 Elsevier Inc. All rights reserved.