Effect of support on reactivity and selectivity of Ni-based oxygen carriers for chemical-looping combustion

Abstract

Different Ni-based oxygen carriers were prepared by dry impregnation using γ-Al 2O 3 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 γ-Al 2O 3 showed low reactivity and low methane combustion selectivity to CO 2 and H 2O, because most of the impregnated NiO reacted to NiAl 2O 4. 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 γ-Al 2O 3 at 1150 °C produced the phase transformation to α-Al 2O 3. Ni-based oxygen carriers prepared on α-Al 2O 3, MgAl 2O 4, or CaAl 2O 4 as support showed very high reactivity and high methane combustion selectivity to CO 2 and H 2O 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.