The ethanol steam reforming (ESA) reaction was studied over a series of Ni-W-Ce oxide catalysts. The structures of the catalysts were characterized using in situ techniques including X-ray diffraction, pair distribution function, X-ray absorption fine structure, and transmission electron microscopy; while possible surface intermediates for the ESR reaction were investigated by diffuse reflectance infrared Fourier transform spectroscopy. In these materials, all the W and part of the Ni were incorporated into the CeO2 lattice, with the remaining Ni forming highly dispersed nano-NiO (<2 nm) outside the Ni-W-Ce oxide structure. The nano-NiO was reduced to Ni under ESR conditions. The Ni-W-Ce system exhibited a much larger lattice strain than those seen for Ni-Ce and W-Ce. Synergistic effects between Ni and W inside ceria produced a substantial amount of defects and O vacancies that led to high catalytic activity, selectivity, and stability (i.e., resistance to coke formation) during ethanol steam reforming. (c) 2014 Elsevier Inc. All rights reserved.