Yttria stabilized zirconia (YSZ) role as co-support in alumina (Al2O3) supported Al-Ni spinel (NiAl2O4) was investigated from three perspectives: (a) influence on catalyst morphology, (b) influence on catalyst crystalline phases, and (c) role during diesel steam reforming tests. For the first objective, YSZ surface properties were related to NiAl2O4/Al2O3 morphology. The interaction between these two species was examined using scanning electron microscopy (SEM); surface properties were determined using the multipoint Brunauer, Emmet, and Teller (BET) method for the specific surface area, and mass titration for the zero point charge (PZC) of the surface. The second objective demonstrated, mainly through X-ray diffraction (XRD) analysis, that YSZ enhanced the stabilization of a single Al2O3 phase and inhibited the formation of a metastable aluminates phase. Finally, for the third objective, Y2O3% used to stabilize ZrO2 was varied. Diesel steam reforming tests, using the various YSZ formulations were performed in a fixed-bed reactor setup, with a proprietary diesel-water emulsion mixture at 760 degrees C. It has been shown that there is a direct dependence of the catalytic activity on the support oxygen vacancies and a maximal Y2O3% was determined. (C) 2015 Elsevier B.V. All rights reserved.