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Two Co–Cr–O spinel catalysts with different stoichiometry were synthesized and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, N2 physisorption and temperature-programmed reduction in H2. Excess Co in Co1.5Cr1.5O4 existed as Co3+ that substituted for Cr3+ in the octahedral sites of the spinel lattice. High temperature treatment of the spinel catalysts in H2 resulted in stepwise reduction of Co3+ to Co2+ and eventually to Co metal. Both CoCr2O4 and Co1.5Cr1.5O4 catalysts were active and structurally stable in ethylene steam reforming under differential reaction conditions at 873 K, with the areal reforming rate over Co1.5Cr1.5O4 being one order-of-magnitude greater than that over CoCr2O4. The steady state reforming rate after oxidation was comparable to that over the fresh catalyst for both CoCr2O4 and Co1.5Cr1.5O4, indicating the stability of the spinel structure against reduction under steam reforming conditions. [ABSTRACT FROM AUTHOR]