Different Ni-based oxygen carriers were prepared by dry impregnation using gamma-Al2O3, as support. The reactivity, selectivity during methane combustion, attrition rate and agglomeration behavior of the oxygen carriers were measured and analyzed in a thermogravimetric analyzer and in a batch fluidized bed during multi-cycle reduction-oxidation tests. Ni-based oxygen carriers prepared on gamma-Al2O3 showed low reactivity and low methane combustion selectivity to CO, and H2O, because most of the impregnated NiO reacted to NiAl2O4. To avoid or to minimize the interaction of NiO with alumina some modifications of the support via thermal treatment or chemical deactivation with Mg or Ca oxides were analyzed. Thermal treatment of gamma-Al2O3 at 1150 degrees C produced the phase transformation to alpha-Al2O3. Ni-based oxygen carriers prepared on alpha-Al2O3, MgAl2O4, or CaAl2O4 as support showed very high reactivity and high methane combustion selectivity to CO2 and H2O because the interaction between the NiO and the support was decreased. In addition, these oxygen carriers had very low attrition rates and did not show any agglomeration problems during operation in fluidized beds, and so, they seem to be suitable for the chemical-looping combustion process. (c) 2008 Elsevier Ltd. All rights reserved.