Previous research shows that bimetallic CuNi/SiO2 catalysts prepared by NaBH4 reduction perform well in ethanol steam reforming (ESR) compared to their monometallic counterparts. More importantly, these bimetallic catalysts yield simple products of only H-2, CQ(2), CO, and CH4, at high ethanol conversions. The as-prepared catalysts contain mainly alloy nanoparticles. This study shows that ESR performance can be further improved by catalyst pretreatment, i.e., calcination at 400 degrees C followed by reduction at 350 degrees C (coded hereafter as calc-CuNi-R350). Characterization using in situ X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) indicates that the calc-CuNi-R350 catalyst contains Cu-rich nanoparticles in close proximity to NiO nanocrystals. Compared to the uncalcined but reduced catalyst (asis-CuNi-R350), the calc-CuNi-R350 catalyst had higher turnover frequency for ethanol conversion and for acetaldehyde conversion and lower selectivity to CH4 formation. Increasing the steam/ethanol (S/E) ratio from 6 to 9 significantly suppresses CH4 formation from this calc-CuNi-R350 catalyst. The results of this study suggest that the interface between NiO and Cu-rich nanoparticles improves ASR/AD (acetaldehyde steam reforming/acetaldehyde decomposition) selectivity via stabilizing the methyl (or methylene) groups from the decomposition of acetaldehyde intermediate and consequently decreases the probability of CH4 evolution. If CH4 evolution is suppressed, the ESR reaction produces only H-2, CO, and CO2. This makes ESR an attractive sustainable route for H-2 production. (c) 2013 Elsevier B.V. All rights reserved.